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{{learned|what the Water Overlay is|what use-cases the Water Overlay can be applied to|what data is required to fully configure the Water Overlay|what options are available to configure the Water Overlay|how to analyse the results of the Water Overlay|how the Water Overlay's functionality has been implemented}}
A Water Overlay is a [[Grid Overlay|grid overlay]] for which results are calculated by the [[Water Module]]. The [[Water_Module_Basics|Basic theory of the Water Module]] in the {{software}} is an implementation of a 2D grid based shallow water model based on the 2D Saint Venant equations. The module is further enhanced with infiltration, evaporation, groundwater flow and hydraulic structures. Depending on the use case, the simulated period can be set to few seconds and up to a few months. The [[Water_Module_Theory|theory]] section describes in detail how calculations are performed.
==What is the Water overlay==
__NOTOC__
The water overlay is an implementation of a large number of hydrological formulas which together can simulate the flow of water across large areas with a high level of detail. Its calculations form a simulation of an arbitrary amount of time, during which water is allowed to move.
To perform the calculations, the project area is divided into a [[Grid overlay|grid of cells]]. Each cell has a specific quantity of water and specific hydrological parameters based on the data in the project. The total time which should be simulated is divided into discrete [[Timestep formula (Water Overlay)|timesteps]]. Per timestep, each cell communicates with its adjacent cells to exchange water, based on its water level, surface height, current flow direction and other factors. Accuracy and reliability is obtained by dividing the project area and simulation time into sufficiently small cells and steps, at the cost of more computation time.


Water flow is affected by properties of the surface across which it flows, including the [[terrain height]] and the properties of the underlying [[terrain]].
The final results of the calculation can be inspected, as well as intermediate snapshots of the hydrological situation during the simulation, known as [[Timeframes (Water Overlay)|timeframes]].


To perform the calculations, the project area is divided into a [[Grid overlay|grid of cells]]. Each cell has a specific quantity of water, and specific hydrological parameters based on the data in the project. The total time which should be simulated is divided into discrete {{inlink|Timestep formula|timesteps}}. Per timestep, every cell communicates with all adjacent cells to exchange water. By dividing the project area and simulation time into sufficiently small cells and steps the behavior becomes effective continuous.
==Variants==
 
A Water Module will be initialized by adding one of the following Overlays to a project. Each variant has a number of parameters tuned to best fit specific use-cases. This means that each of these overlays is based on the same theory and calculation method, however they are customized to conveniently provide insight in different aspects of the Water Module.  
The final results of the calculation can be inspected, as well as snapshots of the hydrological situation in the simulation, known as {{inlink|lcase=1|Timeframes}}.
 
===Variants===
The water overlay can be added to a project as one of a number of variants. Each variant has a number of parameters tuned to best fit certain use-cases. The following preconfigured variants exist:
* [[Rainfall_(Overlay)|Rainfall Overlay]], provides insight into the water stress caused by (excessive) rainfall.
* [[Flooding_(Overlay)|Flooding Overlay]], provides insight into water stress caused by breaches in levees or other sources causing excessive water inflow.
* [[Groundwater_(Overlay)|Groundwater Overlay]], provides insight into long-term processes of water flow both on the surface and underground.
 
===Use cases===
{{main|Use cases Water Overlay}}
{{stub|type=section}}
The water overlay is complex and versatile, and can configured for a large number of different detailed use cases.
Due to the complexity of the water overlay, if an exact understanding of the functioning of the water overlay is not required or desired, it may be preferable to follow the instructions to complete one or more specific use cases, as found on the [[Use cases Water Overlay|water overlay's use cases page]].
 
==How to use the Water overlay==
<onlyinclude>{{#if:{{{how to use|<noinclude>main</noinclude>}}}|<!--
 
-->In general, when a water overlay is added to a project it will immediately be capable of calculating results. However, these will be based on default settings and will at best give a broad sense of water stress.
 
To use any variant of the overlay properly, it is recommended that you ensure the project meets a number of {{inlink|lcase=1|Prerequisites}}. Next, it is recommended to prepare all {{inlink|Data|data related to the hydrological model}}, which defines the functioning and flow of the water. Included in this preparation is a clear idea of the {{inlink|{{#if:<noinclude>main</noinclude>|Model connections|Calculation properties}}|climate conditions}} and what kind of {{inlink|{{#if:<noinclude>main</noinclude>|Result type|Result types}}|output}} is desired. After these preparations have been made, {{inlink|{{#if:<noinclude>main</noinclude>|Configuration|Adding and configuring the overlay}}|creation and configuration}} of the overlay can begin. When the configuration is completed, a [[Grid overlay#Grid recalculation|recalculation]] of the overlay will yield more accurate and appropriate results.
 
After the overlay has calculated results, a number of means exist to {{inlink|{{#if:<noinclude>main</noinclude>|Results|Data analysis}}|analyse the results}} of the calculation performed.<!--
 
-->|}}</onlyinclude>
 
===Prerequisites===
<onlyinclude>{{#if:{{{prerequisites|<noinclude>main</noinclude>}}}|<!--
 
-->When creating your [[project]], make sure it meets the following criteria:
* Your project has been loaded in with a high-resolution DEM. This can be configured during the [[Terrain_height#Terrain_height_in_the_Tygron_Platform|new project wizard]].
* Your project is large enough to account for {{#if:<noinclude>main</noinclude>|{{inlink|lcase=1|Edge effects}}|[[Water_Overlays#Edge effects|edge effects]]}}.<!--
--><includeonly>
For more tips for preparation and use, see the [[Water Overlay#Additional tips for preparation and use|Water Overlay]] page.</includeonly><!--
 
-->|}}</onlyinclude>
 
===Additional tips for preparation and use===
<onlyinclude>{{#if:{{{tips|<noinclude>main</noinclude>}}}|<!--
 
-->There are a number of additional points of attention when creating a project with the intent of using this overlay:
* When creating a new project in the [[Wizard|new project wizard]], consider using the [[GEO_Data#AHN3|AHN3]] dataset rather than the default AHN2. Where coverage is available, the AHN3 dataset will be more accurate. Where coverage is not available, the default AHN2 should be used.
* Additionally, when creating a new project, consider whether you want to use the [[GEO_Data#IMWA|IMWA]] dataset for {{#if:<noinclude>main</noinclude>|{{inlink|lcase=1|Hydrological constructions}}|[[Water_Overlays#Hydrological constructions|hydrological constructions]]}}. Although this dataset is not complete, some information about constructions which serve as {{#if:<noinclude>main</noinclude>|{{inlink|lcase=1|Culvert}}|[[Water Overlay#Culvert|culvert]]}}s other relevant objects can be loaded in from this datasource. If more complete or accurate data is available to be loaded in into the project after it is created, it may be desirable to disregard this source so that hydrological constructions are not doubly included.
* Water flow can often be dictated by small features in an area, such as small openings between buildings, and thin [[levee]]s. To have these small features included properly in the calculations, the {{#if:<noinclude>main</noinclude>|{{inlink|Grid cell size configuration|grid cell size}}|[[Water Overlay#Grid cell size configuration|grid cell size]]}} will need to be set to an appropriate size. The default setting offered by the {{software}} will often need to be adjusted to allow for smaller features to be recognized without having their presence averaged out with their surroundings.
* The water overlay performs a complete simulation, which is a series of complex calculations across multiple layers. Depending on the configuration of the overlay, the {{#if:<noinclude>main</noinclude>|{{inlink|Calculation time impacts|calculation time}}|[[Water Overlay#Calculation time impacts|calculation time]]}} can range from seconds to hours. If the overlay is to be used in a setting where response times need to be short, it may be preferable to configure the overlay for greater speed rather than excessive precision.<!--
 
-->|}}</onlyinclude>
 
==Configuration==
When first added to the project, each variant of the water overlay will be created with a default configuration which will allow for an initial calculation to take place and results to display. For most use-cases, it is desirable to add additional data and tweak the settings and parameters of the overlay. This will improve the accuracy and relevancy of the overlay. It is possible to configure the parameters manually, or by using the configuration wizard.
 
===Configuration wizard===
<!--[[File:Config_wizard.JPG|900px]]-->The configuration wizard is a special interface which helps to guide the configuration of the overlay. Across multiple steps, it progresses through each type of {{inlink|lcase=1|Data}} which can be configured, along with the most important {{inlink|lcase=1|Attributes}} of the overlay.
 
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Configuration wizard}}
 
Each of the water overlay variants has a configuration wizard which helps the user with configuring the overlay. The general structure of the wizard is the same for all variants, with the exception that for [[Flooding_(Overlay)|flooding overlays]] a step for configuring a {{inlink|lcase=1|Breach}} area is included as well.
 
When the wizard has been completed once, it can be reopened at any time, and any step can be accessed anew.
 
====Step 1: Weather====
The {{inlink|Weather|weather event}} defines the total simulation time and the weather and climate effects during the simulation. Specifically, the amount of rain and when it falls during the simulation, as well as the evaporation which takes place.
====Step 2: Water system====
The water system is the most complex step of the configuration, and contains a multitude of substeps to configure all geographical data. In order, the following data can be configured:
: '''Breach''' ([[Flooding_(Overlay)|flooding overlays]] only): A {{inlink|lcase=1|Breach}}, a location where an (uncontrolled) inflow of water takes places, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
: '''Water areas''': {{inlink|Water level area}}s, defined regions in which a specific water level is maintained, can be [[Geo Data Wizard|imported]] or connected to the hydrological model. It is also possible to have the wizard generate a single water level area for the entire project area.
: '''Ground water''': {{inlink|Ground water}}, the height of the underground saturated by water, relative to {{datum}}. A [[GeoTIFF]] can be [[Geo Data Wizard|imported]].
: '''Sewers''': {{inlink|Sewer area}}s, the broad definitions for where what kind of sewers exist, can be [[Geo Data Wizard|imported]] or connected to the hydrological model. It is also possible to have the wizard generate sewer areas based on the [[neighborhood]]s in the project area.
: '''Inundation areas''': {{inlink|Inundation|Inundation area}}s, definitions of water on the surface, in the forum of inundated land, can be [[Geo Data Wizard|imported]] or connected to the hydrological model. It is also possible to have the wizard generate a single inundation area covering the entire project area.
: '''Aquifer areas''': {{inlink|Aquifer|Aquifer area}}s, definitions for transmissivity or hydraulic conductivity of the underground layer.
 
: '''Weirs''': {{inlink|Weir}}s, minor barriers in the water flow, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
: '''Culverts''': {{inlink|Culvert}}s, tunnels which form direct connections between two locations, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
: '''Pumps''': {{inlink|Pump}}s, structures which move water from a lower to a higher location, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
: '''Inlets''': {{inlink|Inlet}}s, structures which add or remove water, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
: '''Sewer overflows''': {{inlink|Sewer overflow}}s, points where water from sewers can flow back onto the surface, can be [[Geo Data Wizard|imported]] or connected to the hydrological model.
 
====Step 3: Hydrological coefficients====
Hydrological coefficients are values of existing elements of the world, specifically {{inlink|lcase=1|Terrain}} and {{inlink|Miscellaneous hydrological properties of constructions|constructions}}. The coefficients dictate the ability of water to flow between cells and layers. The following data can be configured:
: '''Surface terrain''': For the surface {{inlink|lcase=1|Terrain}}s, attributes can be adjusted directly.
: '''Underground terrain''': For the underground {{inlink|lcase=1|Terrain}}s, attributes can be adjusted directly as well.
: '''Constructions''': For {{inlink|Miscellaneous hydrological properties of constructions|constructions}}, the wizard links to the [[function values]] editing screen, and will open it the "WATER" filter for the values to display.
 
====Step 4: Interaction====
The wizard provides a few options to automatically generate methods of interaction with the hydrological model. The {{inlink|lcase=1|System visualization}} can be activated or deactivated. Additionally, for some hydrological constructions and features panels can be generated which allow for their most important attributes during a [[session]].<!--
: '''System visualisation''':
: '''Interaction panels''':
-->
 
====Step 5: Output overlays====
Multiple {{inlink|lcase=1|Result type}}s are available. In the wizard multiple result types can be selected. One result type (indicated with the "First" checkbox) will be the main overlay's result type. The other selections will become {{inlink|lcase=1|Result child overlays}}. Relevant attributes can be modified as well, if they are related to selected result types.
 
Finally, the {{inlink|TIMEFRAMES}} attribute can be configured here as well, defining the amount of result snapshots which should be made during the calculation.
 
====Step 6: Input overlays====
To gain more insight into the data used by the model, you may opt to add one or more {{inlink|lcase=1|Input overlay}}s as well. These add [[Average Overlay]]s configured for the geographical display of attribute values relevant for the calculation of the water model.
 
===Manual configuration===
Besides using the configuration wizard, it is also possible to configure a number of settings manually. A few settings can only be changed manually. Besides the [[Data|data]] of geographical features, which have their own means of loading in depending on their type, all manual configuration options are listed here.
 
====Grid cell size configuration====
{{main|Grid overlay#Shared settings|Grid overlay}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Change grid}}
Like all grid overlays, the water overlays have a number of configuration options related to their general method of calculation. Most notably, it is possible to configure the cell size on which the calculations occur.
 
The grid cell size can be changed by selecting "Change Grid". The minimum and maximum grid cell size depend on the project size. A larger cell size will allow for faster calculations. A smaller cell size will produce more detailed results.
 
====Calculation preference configuration====
{{main|section=section|Calculation preference formula}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Calculation preference}}
The calculation preference indicates the level of accuracy the calculations should be performed with. Depending on the configuration timesteps will be calculated more conservatively. This affects the time it takes to perform the full calculation, and the exact quantities of water moving between cells.
 
The calculation preference can be changed by selecting a different setting.
 
====Weather configuration (simulation time, rainfall, evaporation)====
{{main|section=section|Weather}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Keys tab|"Edit", next to weather}}
The weather configuration, which dictates the {{inlink|Rain and simulation time|duration of the simulation, the amount of rain}} and the {{inlink|lcase=1|Evaporation rate}}, is modeled as a separate weather object which is connected to the water overlay. The weather object can be replaced with another, changing the main simulation and weather properties. The weather itself can be changed as well.
 
By selecting the weather object and then switching to the "Simulation" tab, it's possible to change the settings of the weather either for a simple linear setup or with a more complex sequence of values for the duration of the simulation. The complex setup can be created by loading in a [[comma-separated values]] file. By switching to the attributes tab of the weather object, the same properties can be adjusted by directly modifying the attributes.
 
====Ground water configuration====
{{main|section=section|Ground water data model|Ground water}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Keys tab|Include ground water tiff}}
A ground water [[GeoTIFF]] can be loaded in to prepopulate the underground with water in the form of a saturated zone. This is only a relevant configuration when the {{inlink|lcase=1|Underground model}} is active. A ground water GeoTIFF is optional. If no ground water tiff is selected, the assumed ground water level is equal to the {{inlink|WATER_LEVEL}} of the {{inlink|lcase=1|Water level area}}.
 
The presence of a ground water GeoTIFF can be toggled by checking or unchecking the "Include ground water tiff" checkbox. When checked, a number of GeoTIFFs are available for ground water levels by default. Other GeoTIFFs for groundwater levels can also be loaded in by clicking on "Select GeoTiff".
 
====Subsidence configuration====
{{main|section=section|Subsidence data model|Subsidence}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Keys tab|Include subsidence}}
It's possible to connect the water overlay to a [[Subsidence (Overlay)|subsidence overlay]], if one exists in the project. The result of the subsidence calculation, specifically the amount the terrain has lowered, are applied to the terrain height at the start of the water model's simulation. A connection to a subsidence overlay is optional. If no subsidence overlay is connected, the terrain height is not adjusted in this fashion.
 
The connection to a subsidence overlay can be made by changing the value selected in the "Subsidence" dropdown to the appropriate subsidence overlay.
 
====Showing system visualization setting====
{{main|section=section|System visualization|System visualization}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Show system visualization}}
The water overlay performs a simulation in which much detailed flow takes place, but in which a number of features perform special functions related to water flow. These features include the sewers and the {{inlink|lcase=1|Hydrological constructions}}. The flow of these sections of the hydrological model can be visualized as an explicit graph overlayed on the overlay.
 
The system visualization can be toggled by checking or unchecking the "Show System Visualization" checkbox.
 
====Active in simulation setting====
{{main|Grid overlay#Active|Grid overlay}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Active in simulation}}
Like all grid overlays, the water overlays can be configured to either an active or inactive state. This is especially useful when the results of a calculation should be available for insight without the computational overhead of always recalculating the overlay when changes in the project take place.
 
An overlay can be toggled between active and inactive by checking or unchecking the "Active in simulation" checkbox.
 
====Result type configuration====
{{main|section=section|Result type}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Result type}}
The water model performs a complete simulation in which water flows through the project area. For many use-cases only a specific type of output resulting from the simulation is relevant. The result type of the water overlay indicates exactly what kind of data is recorded and outputted.
 
The result type can be changed by selecting the desired result type in the "Result type" dropdown.
 
Note that via the {{inlink|lcase=1|Configuration wizard}} multiple result types can be added in parallel in the form of {{inlink|lcase=1|Result child overlays}}.
 
====Legend configuration====
{{main|Grid overlay#Legend|Grid overlay}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Legend tab}}
Depending on the selected {{inlink|lcase=1|Result type|}}, the output created by the water overlay can or should be interpreted in different ways. The raw data calculated is assigned colors based on the configured legend. Each result type has an assigned default legend which helps with interpreting the output. The default legends will often be sufficient, but can be modified to fit specific meanings or result ranges.
 
The legend can be modified in the "Legend" tab by checking the "Has custom legend" checkbox. Entries for the legend can then be added, modified, and removed. Any changes in the legend are applied to the visualization immediately, without recalculation of the overlay's output values.
 
====Keys configuration====
{{main|section=section|Keys}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Keys tab}}
The water model's calculations rely on a number of [[area]]s and [[construction]]s for their input data. {{inlink|Hydrological features}} and {{inlink|lcase=1|Hydrological constructions}} have special meanings in terms of policy or scenario. To allow for both compatibility with external data as well as parallel calculations for different scenario's, it is possible to (re)define the exact attributes the overlay uses for those inputs. This would allow two instances of a water overlay to work with the same dataset but with different configurations for hydrological features or constructions.
 
The exact attributes the overlay uses as input from hydrological features and constructions can be changed on the "Keys" tab, by using the relevant dropdown to change the attribute name to the desired attribute.
 
====Attributes configuration====
{{main|section=section|Attributes}}
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=Attributes tab}}
The water model's calculations make use of a number of centralized parameters, which are configured as [[attribute]]s of the overlay. Depending on the exact {{inlink|lcase=1|Variants}} of the water overlay, some of the parameters will have different defaults to better suit the exact type of calculation. The parameters can be tweaked further to better fit specific use-cases, but in general the defaults are appropriate for most calculations.
 
Any of the attributes of the overlay can be changed on the "Attributes" tab, by changing the value in the input box for the attribute which is to be changed.
 
==Results==
When the calculation completes, the results are stored as numerical values in a grid spanning the entire [[3D world]]. The exact values and their meanings depend on the selected {{inlink|lcase=1|Result type}}. Each {{inlink|Timeframes|timeframe}} and each {{inlink|lcase=1|Result child overlays}} has it's own grid of data. There are multiple ways to interact with this data. In addition, there are a few additional outputs provided by the water overlay specifically to gain further insight, verification, and visualization of the results.
 
===Geographical overview===
The most common method of analyzing the results of the calculation is by performing a simple visual inspection of the values of the grid. A basic visual overview along with the ability to select a specific location for further information can suffice for most initial result analysis.
 
====Visualization====
The results of the calculation are visualized when the overlay is selected, based on the colors configured for the overlay's [[Grid overlay#Legend|legend]]. Each location in the [[3D world]] is displayed using a color either matching a value as configured in the legend, or an interpolation of colors between the colors of two values. This means a grid of numerical values, which would be difficult to inspect at a glance, can instead be viewed intuitively.
 
====System visualization====
Depending on whether the option is selected, the hydrological system can be visualized when when the overlay is activated. Each {{inlink|lcase=1|Water level area}} will be visualized by a blue floating sphere and a striped border along the surface of the terrain. {{inlink|Sewer area}}s are visualized by an orange floating sphere. If the sewer has a {{inlink|lcase=1|Sewer overflow}}, the overflow is connected to the sewer's sphere via an orange line. {{inlink|Hydrological constructions|Culverts, weirs, and pumps}} are visualized by green, orange, and red spheres respectively for their endpoints, connected by blue lines.
 
If water has flowed through any of the {{inlink|lcase=1|Hydrological constructions}}, animated arrows in the connecting lines will indicate that movement.
 
====Hover panel====
When the overlay is selected, it's possible to click anywhere in the 3D world to open the [[hover panel]]. This panel shows some information about the clicked location. The following information is displayed by the hover panel:
* The ground height, which is the {{inlink|Terrain height|terrain height}} relative to {{datum}}.
* The output value of the overlay, which is dependent on the selected {{inlink|Result type|result type}}.
* The hydrological properties of the terrain (if applicable), such as {{inlink|WATER_MANNING|manning value}} and {{inlink|GROUND_INFILTRATION_MD_surface|infiltration speed}}.
* The hydrological properties of features (if applicable), such as {{inlink|WATER_LEVEL|water level}}, {{inlink|INUNDATION_LEVEL|inundation level}}, and {{inlink|BREACH_HEIGHT|altered terrain height}}.
* The hydrological properties of constructions (if applicable), such as {{inlink|WATER_STORAGE|building storage}}, and {{inlink|SEWER_STORAGE|sewer storage}} of {{inlink|SEWERED|sewered buildings}}.
 
===Detailed results===
After a first visual inspection of the output, there are several means of gaining a more detailed insight into the results. Several built-in tools allow for a more intuitive way of reading and comparing results, while there are also means available to use the results for further programmatic analyses.
 
====Timeframes====
The water overlay can be configured to store multiple {{inlink|TIMEFRAMES|timeframes}} of results. Each timeframe is a complete snapshot of results of the entire project area. These results can be viewed in sequence for an intuitive overview of the progression of the simulation. By clicking on the "play" button in the [[session interface#Legend|legend in the session interface]], an animation is started which displays the timeframes in sequence.
 
Note that the simulation time is divided into a {{inlink|TIMEFRAMES}} amount of periods, and at the end of each period a timeframe is recorded. This means the first timeframe is not a snapshot of the initial state of the simulation, but a snapshow of the state of the simulation after the first period of time has passed already.
 
====TQL====
{{main|TQL}}
The overlay's data can be computationally retrieved using TQL. This allows the results of the overlay to be summarized, and to be used in the calculations of [[excel]]s for the use in [[indicator]]s or [[panel]]s.
 
====Measuring tool====
{{main|Measuring tool}}
While viewing the overlay, a general impression of the values can be seen at a glance. However, depending on the configuration of the overlay's [[Grid overlay#Legend|legend]] the exact values may be difficult to view exactly. Using the measuring tool it's possible to retrieve the values of the overlay on exact locations. Additionally, cross-sections can be defined and easily have their values inspected.
 
====Exporting Geotiff====
{{main|Grid overlay#Export|Grid overlay}}
The [[3D client]] offers sufficient ways to visually inspect the water overlay's results for general overview, but use-cases exist in which post-calculation analysis in external tools is desirable. For these situations it is possible to export the results of the calculation in the form of a [[GeoTIFF]]. The resulting file can be opened in other GIS software.
 
===Additional forms of output===
A number of output forms don't fit in the analysis structure described above, but can provide additional information or insight into the calculation. These can provide different ways of looking at both the input and output of the simulation. They are offered as a means to further visualize but also verify the performed calculations.
 
====Weather visualization====
When a water overlay exists in a project, and the animation of a [[weather]] is triggered (either manually or automatically), the animation of the weather will include a visualization of the water as it progresses during the simulation.
 
During the weather animation, panels which make use of the [[Panel#VISIBLE_TIMEFRAME|VISIBLE_TIMEFRAME]] attribute will appear only from the specified {{inlink|Timeframes|timeframe}}.
 
In a setup where only a single water overlay refers to a weather effect, when that weather effect is triggered that water overlay's simulation is animated. When multiple water overlays or no water overlay refer to a weather effect, the behavior for visualization is not consistently defined, and a water overlay will be semi-randomly selected for visualization.
 
====Saving overlay result====
{{main|Grid overlay#Save|Grid overlay}}
When a water overlay has completed a complex calculation, it may be interesting to save the results as an inactive copy. This will create a duplicate overlay configured exactly the same way as the original, but set to be [[Grid overlay#Active|inactive]]. This will allow the current results to be kept available as a separate overlay without additional computational overhead, and for the original overlay to be used for further calculations of other scenario's.
 
====Water balance====
[[File:water_balance.jpg|thumb|250px|A water balance with multiple input and output entries.]]
 
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Show water balance}}
 
During the simulation, a tally is kept of the total amount of water which the hydrological model is initialized with, how much flows in and out, and how much is left in various layers when the simulation completes. The overview of these tallies is known as the water balance, and can be accessed after the calculation has completed. It will display water categorized into input (where it was initialized and/or how it entered the hydrological system) and output (where in the hydrological system it ended up, or through which path or process it left the hydrological system).
 
The following entries are displayed:
{|class='wikitable'
! Input
! Output
|-
| style="vertical-align:top"|
* Breach
* Inlet
* Rain
* Water surface
* Inundated land
| style="vertical-align:top"|
* Breach out
* Outlet
* Land surface
* Water surface
* Building surface
* Sewer storage
* Underground unsaturated storage
* Underground saturated storage
* Evaporated
|}
For completeness, a total for both water input and output is displayed, as well as a check on any eventual water loss in the system. Depending on the size of the project area and the amount of water flowing through various cells, there may be a minor difference between the input and output due to numerical rounding. In these cases the difference should amount to less than a tenth of a millimeter of water per cell in the calculation.
{{clear}}
 
====Debug info====
[[File:debug_info.jpg|thumb|250px|Debug information as generated by a calculation of the Water Overlay.]]
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab|Debug info}}
 
After the calculation completes, some additional information is tallied and output for debugging purposes. This is intended for verification that the model has computed as expected, and may provide some basic information at a glance. It is not meant as a primary tool for in-depth analysis of the results.
 
The following information is displayed:
{|class='wikitable'
! Debug info
|-
| style="vertical-align:top"|
* Total rainfall
* Simulation time (and amount of timeframes)
* Map size
* Amount of cells and amount of {{inlink|Timestep formula|computational timesteps}}
* Amount of special hydrological areas
* Amount of flow over weirs
* Amount of overflow from sewers
* Total calculation time, and the amount of [[GPU]]'s used to perform the calculation
* Total volume of water processed
|}
 
====Input overlay====
{{main|Average Overlay}}
The water overlay's calculations rely on multiple geographical parameters, such as {{inlink|WATER_MANING|manning value}}s and {{inlink|WATER_EVAPORATION_FACTOR_surface|evaporation factors}}. To help with both understanding the outcome of the calculation as well as verifying the results, the {{inlink|Configuration wizard|configuration wizard}} offers the option to add input overlays to the project, which are [[Average Overlay]]s configured to display the input parameters geographically.
 
Overlays such as these can also be created manually, by creating an Average Overlay and configuring it such that it functions on the desired [[attribute]], and with an as small an averaging distance as possible. Optionally, a specific layer (such as [[construction]]s or [[terrain]]s) can be configured which the overlay should inspect.
 
==Model connections==
The hydrological model can be linked to other models, which adds and defines more data for the simulation. Some models are automatically connected, and are required for the calculations to take place. Others are optional, and can apply additional detail to the calculations. When the optional models are absent, default behavior is defined.
 
===Terrain height===
{{main|Terrain height}}
Terrain height in the {{software}} is modeled in the form of an underlying grid, potentially amended by a [[GeoTIFF]].
 
The terrain height defines the height of the terrain on and in which the hydrology is modeled. Terrain height includes the relief on the surface of dry land, but also the height of the stream beds of water bodies.
 
Terrain height is a required and automatic connection. Each [[project]] has a terrain height model. By default the terrain height model will be derived from data sources relevant to the geographical location of the project area. However, especially in water bodies the level of detail of the terrain height may be insufficient. For these situations it's possible to load in an additional GeoTIFF of terrain heights.
 
{{GeoTIFFSpec
|title=Terrain height
|description=The height of the terrain's surface across the project area.
|nodata=Data is unchanged from the base terrain height.
|value=Terrain height
|unit={{mdatum}}
}}
 
===Weather===
Weather in the {{software}} is modeled in the form of a [[weather|weather definition]].
 
[[Weather]] defines a number of environmental circumstances the hydrological model is subject to. It also defines the (total) simulation time.
 
Weather is a required connection. There is always exactly one weather connected to a water overlay, and by default if no weather exists an appropriate weather effect is created and connected automatically.
 
====Rain and simulation time====
Rain is a consistent addition of water to the hydrological model over a specified period of time. At the end of the rainfall's duration, the specified amount of rain will have fallen in each location in the project. The simulation can calculate both periods of rain as well as dry periods.
 
The total simulation time is composed of both the periods of rain, and the dry periods. It is possible to set up a simple, linear rainfall situation, in which a period of consistent rain is followed by a dry period. More complicated, custom configurations can be loaded in as well.
 
During a period of rain, the rainfall is constant. In each timestep an equal amount of water will fall, such that by the end of the period of rain that exact of rain will have fallen.
 
'''Linear configuration'''<br>{{RequestImage|description=Graph showing one period of rain, and one dry period. A second line showing the total amount of rain fallen up to that point. The total amount of time marked as simulation time.}}
When configuring a simple rainfall situation, it is possible to enter the properties for rain and simulation time by adjusting the linear properties. When using this method, the simulation will be composed of one period of rain, followed by one dry period.
{| class="wikitable"
{| class="wikitable"
! Property
|[[File:Overlay_rainfall.png]]
! Unit
|[[Rainfall_(Overlay)|Rainfall Overlay]]
! Description
|provides insight into the water stress and impact caused by (excessive) rainfall
|-
|Rain for
|minutes
|How long rain should last at the start of the simulation.
|-
|-
|Total rainfall
|[[File:Overlay_flooding.png]]
|mm
|[[Flooding_(Overlay)|Flooding Overlay]]
|How much rain should fall in the specified period.
|provides insight into water stress and impact caused by breaches in levees or other sources causing excessive water inflow
|-
|-
|Dry after rain (days, hours, minutes)
||[[File:Overlay_groundwater.png]]
|days, hours, minutes
|[[Groundwater_(Overlay)|Groundwater Overlay]]
|How long the simulation continues after the rain has fallen.
|provides insight into long-term processes of water flow both on the surface and underground
|}
|}
<!--==Input Data and Settings==
The calculations performed by the Water Overlay are influenced by many kinds of geographical information present in the project area. For any given location, [[terrain]], [[construction]]s and other features can influence either the initial state of the simulation or how water flows in a given area.


'''Custom configuration'''<br>{{RequestImage|description=Graph showing multiple periods of varying duration and varying rain intensities. A second line showing the total amount of rain fallen up to that point. The total amount of time marked as simulation time.}}
Furthermore, the Water Overlay features a number of overall settings which can be configured for the hydrological calculations and its results. These settings do not have a geographical or temporal element to them, and are fixed values relevant for the simulation as a whole.
If a use-case requires a more complex sequence of rain than a single period of rain followed by a single dry period, it is possible to prepare a [[comma-separated values]] file with a sequence of periods and values.
{{CSVSpec
|title=Rain and simulation
|line=Additional rainfall until specified moment
|criteria=<!--
-->Time should always be greater than or equal to previous time<!--
--><br>Rain should never be negative<!--
-->
|attribute=RAIN_M
|header1=Time|unit1=s
|header2=Rain|unit2=m
|l1e1=Time when first period ends|l1e2=Total rain during first period
|l2e1=Time when second period ends|l2e2=Total rain during second period
}}
The last time value also indicates the end of the simulation.


====Evaporation rate====
;[[Hydrologic_features_(Water_Overlay)|Hydrological features]]
Evaporation is the consistent removal of water from the hydrological model over a specified period of time. As long as evaporation takes places at a certain rate, water both on the surface and underground can be subject to removal from the hydrological model. The evaporation rate defined by the weather is the base amount of evaporation for the {{inlink|Evaporation model|evaporation model}}.
:The water system can be enhanced with a number of hydrological features, which can be loaded in as [[area]]s. These hydrological features form special properties or modifications on the hydrological system. See [[Hydrologic_features_(Water_Overlay)|Hydological features]] for a list of supported features.
;[[Hydraulic structures (Water Overlay)|Hydraulic structures]]
:See [[Hydraulic structures (Water Overlay)|Hydraulic structures]] for the list of supported structures.
;[[Additional_hydrological_attributes_of_buildings_(Water Overlay)|Hydrological attributes of buildings]]
:Besides the [[building]]s which directly influence the hydrologic model as a [[Hydraulic structures (Water Overlay)|hydraulic structure]], each building may also have attributes which can contribute to the hydrological model in some way. These attributes are stored and used on a grid cell level. This is different from the hydraulic structure attributes, which are stored and used on an object level. For a full list, see [[Additional_hydrological_attributes_of_buildings_(Water Overlay)|Additional hydrological attributes of buildings]].
;[[Terrain_attributes_(Water_Overlay)| Hydrological attributes of terrain]]
:[[Terrain]]s in a project have a number of hydrological attributes which can influence the flow of water in a project. Because there is always both surface and underground terrain defined for the entirety of the project area, all cells are affected by all attributes of terrains, unless a building is present with overwriting values. For a full list, see [[Terrain_attributes_(Water_Overlay)| Terrain attributes for the water overlay]].
;[[Model_attributes_(Water_Overlay)|Model settings]]
:For a full list, see: [[Model_attributes_(Water_Overlay)|Water Model attributes]]


'''Linear configuration'''<br>{{RequestImage|description=Graph showing constant amount of evaporation, and a fictive water amount decreasing consistently over time.}}
==Troubleshoot, warnings and recommendations==
When configuring a simple evaporation situation, it is possible to enter this property directly by adjusting the linear property. When using this method, the simulation will use a single rate of evaporation for the duration of the simulation.
When the Water Overlay is used and calculations take place, there are some problems or points of attention the calculation can run into. Where possible, the Water Overlay will show appropriate warnings when running into any issues.
{| class="wikitable"
See [[Warning_and_recommendations_(Water_Overlay)|Troubleshoot, warnings and recommendations]];
! Property
! Unit
! Description
|-
|Surface evaporation
|mm/day
|The speed at which water evaporates during the simulation
|}
 
'''Custom configuration'''<br>{{RequestImage|description=Graph showing varying amounts of evaporation in multiple periods, and a fictive water amount decreasing consistently over time with the speed of the evaporation.}}
If a use-case requires a more complex pattern of evaporation than a single evaporation rate, it is possible to prepare a [[comma-separated values]] file with a sequence of periods and values.
{{CSVSpec
|title=Evaporation
|line=Rate of evaporation until specified moment
|criteria=<!--
-->Time should always be greater than or equal to previous time<!--
--><br>Evaporation should never be negative<!--
-->
-->
|attribute=RAIN_M
|header1=Time|unit1=s
|header2=Evaporation|unit2=m
|l1e1=Time when first period ends|l1e2=Amount of evaporation during first period
|l2e1=Time when second period ends|l2e2=Amount of evaporation during second period
}}
===Ground water===
Ground water in the {{software}} is modeled in the form of a [[GeoTIFF]].
The hydrological model can simulate the {{inlink|Underground model|underground}} environment as well. To enhance the level of detail of the underground environment, it is possible to connect a groundwater [[GeoTIFF]] to the water model. The ground water GeoTIFF will dictate the underground water levels relative to {{datum}} at the start of the simulation, influencing how much more water can be stored underground and how much water can flow from the underground.
Ground water is only a relevant connection when the {{inlink|lcase=1|Underground model}} is active. If the ground water model is not active, a connection with a ground water model is not relevant, regardless of whether it's present or not.
Ground water is an optional connection. If no ground water is connected to the water model, the ground water level relative to {{datum}} is equal to the water level as defined by the {{inlink|lcase=1|Water level area}}s.
{{GeoTIFFSpec
|title=Groundwater
|description=The height of the ground water level across the project area.
|value=Groundwater level
|unit={{mdatum}}
}}
===Subsidence===
{{main|Subsidence (Overlay)}}
Subsidence in the {{software}} is modeled in the form of a [[Subsidence_(Overlay)|subsidence overlay]].
The hydrological model is greatly influenced by the [[terrain height|height of the terrain]]. In virtually all cases water flows from higher places to lower places. The water model can be connected to a [[Subsidence_(Overlay)|subsidence]] calculation which affects the terrain height. This allows the model to take into account a period of subsidence which changes the terrain, and calculate the impact, effects, and flow in the future.
When a subsidence calculation is connected to the hydrological calculation, the outcome of the subsidence calculation affects the terrain height used by the hydrological calculations. The effect does not apply the other way around; output from the water model is not used as input or effect for the subsidence model.
Subsidence is an optional connection. If no subsidence model is connected to the water model, no subsidence is applied to the model prior to the calculations. Other effects on the terrain height, such as {{inlink|lcase=1|Breach}}es, still apply.
==Data==
The calculations performed by the water overlay are influenced by many kinds of geographical information present in the project area. For any given location, [[terrain]], [[construction]]s and other features can influence either the initial state of the simulation or how water flows in a given area.
===Hydrological features===
The water system can be enhanced with a number of hydrological features, which can be loaded in as [[area]]s. These hydrological features form special properties or modifications on the hydrological system.
====Water level area====
A water level area represents real-world water level areas. Within a water level area, the heights of all water [[terrain]]s are set to a specified level. {{RequestImage|description=An image (before)showing a terrain with part of it marked as water terrain. A second image (after) showing the same terrain, with the water terrain no longer specially marked but with a quantity of water on top. Both images have one valley marked as water terrain and another one which is regular terrain.}}
{| class="wikitable"
! Attribute
! Unit
! Description
! Default (when attribute is not present)
|-
|{{anchor|WATER_LEVEL|WATER_LEVEL}}
|{{mdatum}}
|The water level for all water terrains in this water level area
|n/a
|}
If no water level area is present in the project, the water level on water terrains is assumed to be extremely low. This allows water to flow into the open water areas at all times.
====Sewer area====
A sewer area is part of the definition of a system of sewers in the specified area. Sewer storage is present in the hydrological model wherever the sewer area intersects with a {{inlink|Sewered constructions|sewered construction}}.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default (when attribute is not present)
|-
|{{anchor|SEWER_STORAGE|SEWER_STORAGE}}
|m
|The maximum height the water can reach in this sewer. This value, multiplied by the surface area of the sewered constructions the sewer area intersects with, forms the total amount of water this sewer can store.
|n/a
|-
|{{anchor|SEWER_PUMP_SPEED|SEWER_PUMP_SPEED}}
|m3/s
|The amount of water removed from the sewer by removing it from the hydrological model entirely.
|0
|}
Sewers don't have default storage amount, but when generating them automatically in the {{inlink|lcase=1|Configuration wizard}}, suggested values are 0,007m for older sewers and 0,04 for newer sewers.
====Breach====
A breach is a modification to the [[terrain height]], with an optional in- or outflow of water for the hydrological model. This can be used to represent calamitous situations, such as a breach in a levee. Breaches can also be used to easily simulate a terrain height increase, effectively creating a levee.
A breach can either be defined solely as a terrain height modification using its {{inlink|BREACH_HEIGHT}} attribute, or as a connection to a water body outside of the hydrological model by adding attributes related to the external water body. If the breach is only defined as a terrain height change, only water that is already created or defined in some other way in the hydrological model can flow through and from it.
If the breach is given the attributes required for the external water body, water will automatically be created or removed uniformly on the breach, depending on the simulated water body "behind" the breach.
The breach can grow over time, based on its initial width and the critical speed at which water may flow. If a {{inlink|BREACH_WIDTH}} is defined, the breach's polygon is intersected with a circle emanating from the centerpoint of the polygon. It is only in that intersection, dubbed the "active breach", that water will flow in from the simulated external water body.. The radius of the circle defining the intersection will expand when the water flowing in from the external water body exceeds the {{inlink|BREACH_SPEED}}. Water flowing in the hydrological model across the breach's surface without explicitly entering or leaving the hydrological model through the breach and its simulated water body does not "count" for the critical speed. All cells in the active breach are considered directly adjacent to the external water body.
The entire breach area is considered lowered to the height defined by its {{inlink|BREACH_HEIGHT}} attribute, even if the active breach does not extend across the entirety of the breach area.
If no critical speed is defined, the active breach will never grow. If no width is defined, the width is assumed to be very large, creating an intersection exactly the size of the polygon.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default (when attribute is not present)
|-
|{{anchor|BREACH_HEIGHT|BREACH_HEIGHT}}
|{{mdatum}}
|The new [[terrain height]] at the location of the breach.
|n/a
|-
|{{anchor|BREACH_WIDTH|BREACH_WIDTH}}
|m
|The radius of the breach as drawn on the polygon defining the breach, emanating from the center point.
|10000
|-
|{{anchor|BREACH_SPEED|BREACH_SPEED}}
|m/s
|The speed at which water should flow through the breach before the width begins to increase.
|n/a
|-
|{{anchor|EXTERNAL_SURFACE_LEVEL|EXTERNAL_SURFACE_LEVEL}}
|{{mdatum}}
|The height of the bottom of the external water body behind the breach. The lowest level the external water level can lower to.
|0
|-
|{{anchor|EXTERNAL_WATER_LEVEL|EXTERNAL_WATER_LEVEL}}
|{{mdatum}}
|The water level of the external water body behind the breach. The initial level the water level is set to.
|0
|-
|{{anchor|EXTERNAL_AREA|EXTERNAL_AREA}}
|m²
|The surface area of the external water body behind the breach. The larger the external water body, the more water can flow from it, and the smaller the effect of the inflow or outflow of water on the external water level.
|n/a
|}
====Inundation====
An inundation is an initial placement of a quantity of water. This differs from the {{inlink|lcase=1|Water level area}}s in that an inundation level allows you to place water anywhere on the surface.{{RequestImage|description=Same image as for water area, but in which the water terrain is already filled and the other valley isn't, but in the second image is filled with water.}}
{| class="wikitable"
! Attribute
! Unit
! Description
! Default (when attribute is not present)
|-
|{{anchor|INUNDATION_LEVEL|INUNDATION_LEVEL}}
|{{mdatum}}
|The height of the water.
|n/a
|}
====Aquifer====
{{stub|type=section}}
The aquifer is an additional definition for the underground, allowing for {{inlink|Underground model|underground horizontal flow}} different from the underground terrain's {{inlink|GROUND_INFILTRATION_MD_underground}}.{{RequestImage|description=Wide Depiction of underground terrain. Part of the underground has 1 or 2 arrows to depict flowing right. A part further right is highlighted (the aquifer) and has 3 or 4 arrows depicting flow to the right.}}
{| class="wikitable"
! Attribute
! Unit
! Description
! Default (when attribute is not present)
|-
|{{anchor|AQUIFER_KD|AQUIFER_KD}}
|m²/day
|The hydraulic diffusivity of the aquifer, which dictates the speed at which water can flow through the underground.
|n/a
|}
===Hydrological constructions===
The water system can be enhanced with a number of hydrological [[construction]]s. These are constructions which effect water flow in specific cells, according to the parameters and rules of the constructions used. The effects of these constructions can be adjusted by setting the appropriate attributes.
In general, hydrological constructions are loaded in as underground constructions.
Hydrological constructions can be either line-based or point-based:
* {{Anchor|Line-based constructions}}'''Line-based constructions'''<br>{{RequestImage|description=A simple polygon shape (rectangle), then the visualization of the skeleton lines, then the highlighting of the relevant endpoints.}}Line-based constructions form a direct connection between two exact cells, allowing water to flow from one point to another. The flow is dictated by the construction's formula. The endpoints of a line-based construction, the exact cells which are connected by the construction, are computed based on the orientation and size of their polygon. Essentially, the furthest ends of the polygon are used as end-points. Because the cells are considered adjacent, any calculated flow through line-based hydrological constructions is instantaneous.
* {{Anchor|Point-based constructions}}'''Point-based constructions'''<br>{{RequestImage|description=A simple polygon shape (square), then the visualization of the calculation of the centerpoint, and finally the highlighting of the endpoint.}}Point-based constructions add or remove water in one or more computational layers, based on their formula's. The centerpoint of a point-based construction, the exact cell where the effect takes place, is is the geometric center of the construction's polygon.
Note that the more complex the polygon is, the more difficult it is for the {{software}} to resolve it to a simple line or center point.
When the calculation of the water overlay completes, the total amount of water which has flowed through a specific construction is stored in an attribute in that construction. By default, this attribute is {{inlink|OBJECT_OUTPUT_FLOW}}, and the flow is expressed in m3. If multiple water overlays exist in the project simultaneously, the attribute name is appended with a number so that each overlay (as they are added to the project) has a unique attribute it writes its results to.
Hydrological constructions can only function as a single hydrological construction. If a single construction has attributes related to multiple hydrological constructions, the resulting behavior is undefined.
====Culvert====
Culverts are effectively tunnels or pipes directly connecting two bodies of water, and allow water to flow in either direction. Culverts can also be used to model tunnels on land, creating a hole which water can flow through when it is flowing over land. The throughput of a culvert is limited by its dimensions.
A culvert is a {{inlink|lcase=1|Line-based constructions}}.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|CULVERT_DIAMETER|CULVERT_DIAMETER}}
|m
|The diameter of the culvert. For throughput calculations, the culvert is assumed to have a spherical cross-section.
|1
|-
|{{anchor|CULVERT_THRESHOLD|CULVERT_THRESHOLD}}
|{{mdatum}}
|The height of the culvert. (When set to a level lower than the terrain for either endpoint of it, the culvert's height is equal to the height of the (highest) {{inlink|Terrain height|terrain}} under either endpoint.)
|0
|-
|{{anchor|CULVERT_N|CULVERT_N}}
|manning value
|The manning value of the culvert's material, which influences the flow speed.
|0,014
|}
====Weir====
Weirs are effectively small dams in the water, and allow water to flow from a water body with a higher water level to a lower water level. Any water exceeding the height of the weir can flow over it, increasing the throughput as the water level increases. Strictly, water can flow over the weir in either direction.
A weir is a {{inlink|lcase=1|Line-based constructions}}.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|WEIR_HEIGHT|WEIR_HEIGHT}}
|{{mdatum}}
|The height of the weir.
|n/a
|-
|{{anchor|WEIR_WIDTH|WEIR_WIDTH}}
|m
|The width of the weir.
|5
|-
|{{anchor|WEIR_COEFFICIENT|WEIR_COEFFICIENT}}
|coefficient
|The flow coefficient related to the shape of the weir
|1,1
|}
====Pump====
Pumps are constructions which can move water against its natural flow. Specifically, it moves water from the lower end of the pump to the higher end of the pump. The terrain height is used to determine the low end and the high end of the pump.
A pump is a {{inlink|lcase=1|Line-based constructions}}.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|PUMP_SPEED|PUMP_SPEED}}
|m3/s
|The speed at which water is pumped from the lower end-point to the higher end-point.
|n/a
|}
If a pump is placed such that both end-points are at locations with equal terrain height, the pump will be inactive and no water will flow through it.
====Sewer overflow====
Sewer overflows are points where water is moved from the sewer area to the above-ground water system. A sewer overflow will allow water to flow through if the water in the sewer exceeds the {{inlink|SEWER_OVERFLOW_THRESHOLD}}, and the water in the connected sewer exceeds the height of the terrain at the location of the sewer overflow. It will then function for all sewers part of that sewer area.
A sewer overflow is a {{inlink|lcase=1|Point-based constructions}}. It must intersect with a {{inlink|lcase=1|Sewer area}}, but does not need to intersect with a an actual sewer.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|SEWER_OVERFLOW|SEWER_OVERFLOW}}
|{{mdatum}}
|The height of the bottom of the sewer, relative to the average terrain height of the connected sewer. Starting from this height, the water height in the sewer must exceed the height of the terrain at the location of the overflow in order for water to flow out.
|n/a
|-
|{{anchor|SEWER_OVERFLOW_SPEED|SEWER_OVERFLOW_SPEED}}
|m3/s
|The maximum speed at which water can flow out from the sewer through this overflow.
|10
|}
Note that at most one overflow can exist per sewer area.
====Inlet====
Inlets are points where water is either added to or removed from the hydrological model. It will add or remove water at a defined maximum rate, with optional thresholds for the amount of water to add or remove.
An inlet is a {{inlink|lcase=1|Point-based constructions}}.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|INLET_Q|INLET_Q}}
|m3/sec
|The maximum amount of water flowing into the model through this inlet. A negative value means the construction functions as an outlet, and water is removed from the hydrological model.
|n/a
|-
|{{anchor|INLET_CAPACITY|INLET_CAPACITY}}
|m3
|The maximum amount of water which can flow in or out through this construction. Water flowing back in the other direction replenishes the capacity.
|Infinite
|-
|{{anchor|LOWER_THRESHOLD|LOWER_THRESHOLD}}
|{{mdatum}}
|If a lower threshold is set, water will only flow into the model through this inlet until the water level at the point of this inlet is equal to or greater than the threshold. If the threshold is not set, the amount of water flowing in is not limited in this fashion.
|None
|-
|{{anchor|UPPER_THRESHOLD|UPPER_THRESHOLD}}
|{{mdatum}}
|If an upper threshold is set, water will only flow out the model through this outlet until the water level at the point of this inlet is equal to or lower than the threshold. If the threshold is not set, the amount of water flowing out is not limited in this fashion.
|None
|}
Note that all inlet attributes function as flow limits. If multiple are defined, water can flow in or out up until any of those limits are reached. If none are defined, no water flows in or out.
Also note that an inlet shares attribute names with the {{inlink|lcase=1|Breach}}es, and that changing the attribute keys for inlets also affects the keys for breaches.
===Miscellaneous hydrological properties of constructions===
Besides the [[construction]]s which directly influence the main water flow in the hydrological model, all constructions have properties which may interact with the hydrological model in some way.
The effects of these constructions can be adjusted by setting the appropriate attributes. In some cases, these are attributes which relate to [[function values]]. For these attributes, either can be adjusted to the same effect. Note that attributes which are connected to a function can not be redefined, like the attribute names for {{inlink|lcase=1|Hydrological constructions}} and {{inlink|lcase=1|Hydrological features}} can be redefined.
In contrast with {{inlink|lcase=1|Hydrological constructions}} and their properties, all constructions can have any or all of the following miscellaneous effects on the hydrological model.
====Sewered constructions====
Sewered constructions are constructions under which a sewer exists, and through which water can flow into the sewer. When a sewered connection overlaps with a {{inlink|lcase=1|Sewer area}}, that overlap forms an actual sewer, with the storage capacity of the {{inlink|SEWER_STORAGE}} attribute of the sewer area. Any surface water entering the cell of a sewered construction is directly moved to the sewer (unless the sewer is filled to capacity).
{| class="wikitable"
! Attribute
! Unit
! Function value
! Description
|-
|{{anchor|SEWERED|SEWERED}}
|boolean
|Connected to sewer
|Whether this construction is connected to the sewer.
|}
====Water storage constructions====
Constructions capable of water storage can store some surface water without allowing it to flow back into the rest of the model. Water stored in constructions can not flow out or evaporate away.
{| class="wikitable"
! Attribute
! Unit
! Function value
! Description
|-
|{{anchor|WATER_STORAGE|WATER_STORAGE}}
|m³/m²
|Water storage (m³/m²)
|How much water this construction can store.
|}
====Porous constructions====
Some constructions are porous or open, and can allow water to infiltrate into the {{inlink|Underground model|underground unsaturated zone}}.
The speed at which water can infiltrate is dependent on both the infiltration properties of the constructions as well as on the underlying {{inlink|Hydrological properties of terrain|surface terrain}}. Of the infiltration values of the construction and the surface terrain, the lowest value is used. If either has an infiltration value of 0, water cannot infiltrate into the underground unsaturated zone.
{| class="wikitable"
! Attribute
! Unit
! Function value
! Description
|-
|{{anchor|GROUND_INFILTRATION_MD_constructions|GROUND_INFILTRATION_MD}}
|m/day
|Ground infiltration per day (m)
|The speed at which water can flow vertically from the surface to the underground unsaturated zone.
|}
====Crops and foliage====
Constructions representing crops and foliage can draw water from the {{inlink|Underground model|underground}}, allowing it to evaporate. This behaves in the same way as terrain which is configured as {{inlink|lcase=1|Plants}}.
{| class="wikitable"
! Attribute
! Unit
! Function value
! Description
|-
|{{anchor|ROOT_DEPTH_M_constructions|ROOT_DEPTH_M}}
|m
|Depth of plant roots (m)
|The depth of the roots of this construction, relative to the terrain height at the location of this construction. Water can be drawn from the underground and evaporated if the roots can reach it.
|-
|{{anchor|WATER_EVAPORATION_FACTOR_constructions|WATER_EVAPORATION_FACTOR}}
|factor
|Water evaporation
|How fast this construction can evaporate water from the underground. The {{inlink|lcase=1|Weather}}'s evaporation speed is multiplied by this factor to determine the rate of evaporation.
|}
Note that when a construction is present in any given location, the values for evaporation will overrule any values set by {{inlink|Hydrological properties of terrain|terrain}} in the same location. To model underground evaporation without a construction, set these attributes on the applicable terrain type instead.
====Critical structures====
Some constructions may be considered critical, meaning the consequences of water stress are greater for these structures than for others. Examples include hospitals and (elementary) schools. Critical constructions will receive additional highlighting by the {{inlink|IMPACTED_BUILDINGS}} result type when the building is impacted by the amount of water defined by {{inlink|IMPACT_FLOOD_THRESHOLD_M}}.
By using different values for differing (kinds of) constructions, it is possible to have impacted structures highlight with different values as well. This makes it possible to differentiate in greater detail between the kinds of impacted structures.
{| class="wikitable"
! Attribute
! Unit
! Function value
! Description
|-
|{{anchor|CRITICAL_INFRASTRUCTURE|CRITICAL_INFRASTRUCTURE}}
|nominal integer
|Critical infrastructure
|Whether this construction is deemed a critical construction. 0 means the construction is never deemed impacted.
|}
====Chemical emitters/decomposers====
Chemical emitters are constructions which produce specific chemicals. The net amount of chemicals a single construction creates is spread out across it's surface. After the chemicals are created, any water flowing through the same location will carry a part of the chemicals with it.
Chemicals have generic definitions, in terms of name and magnitude, to allow for the modeling of arbitrary substances.
Structures which are defined to create a negative amount of chemicals function as a scrubber or decomposer, removing the specified quantity of chemicals from the hydrological model.
In situations where water is absent, chemicals cannot move between cells.
{| class="wikitable"
! Attribute
! Unit
! Description
! Default
|-
|{{anchor|SUBSTANCE_A_constructions|SUBSTANCE_A}}
|x/m²
|The amount of substance A created per second per m² in this location.
|0
|-
|{{anchor|SUBSTANCE_B_constructions|SUBSTANCE_B}}
|x/m²
|The amount of substance B created per second per m² in this location.
|0
|-
|{{anchor|SUBSTANCE_C_constructions|SUBSTANCE_C}}
|x/m²
|The amount of substance C created per second per m² in this location.
|0
|-
|{{anchor|SUBSTANCE_D_constructions|SUBSTANCE_D}}
|x/m²
|The amount of substance d created per second per m² in this location.
|0
|}
Chemical emitters's attributes do not take the form of function values, and must be added manually<!--[[constructions#Adding_attributes]]--> or as part of [[Geo_Data_Wizard|loading in geodata]].
====Manning value (construction)====
Constructions have an inherent "roughness", which influences how fast water can flow across the surface. This is known as the Manning coefficient or Manning value.
{| class="wikitable"
! Attribute
! Unit
! Terrain type
! Description
|-
|{{anchor|WATER_MANNING_constructions|WATER_MANNING}}
|s/(m<sup>1/3</sup>)
|Surface
|The Gauckler–Manning coefficient of the terrain.
|}
Note that if no construction is present in any location, the {{inlink|WATER_MANNING_surface|WATER_MANNING}} value of the surface terrain present is used instead.
====Construction height====
Though not an explicit attribute or function value in and of itself, the height of constructions is taken into account when computing the flow of water above ground. Constructions are computed to have at most a height of {{inlink|DESIGN_FLOOD_ELEVATION_M}}. Lower constructions retain their own construction height. Taller constructions have their height capped at the attribute's value.
===Hydrological properties of terrain===
[[Terrain]]s in a project have a number of hydrological properties which can influence the flow of water in a project. Because there is always both surface and underground terrain defined for the entirety of the project area, all cells are affected by all properties of terrains, unless a construction is present with overwriting values.
====Water====
Water terrains are processed by the water model in a specific manner before the simulation is started. For each water terrain in the 3D world, the bottom of the water body is treated as a land surface in the same fashion as dry land. Water is then placed on it on the {{inlink|Surface model|surface layer}}, up to the level defined by the overlapping {{inlink|lcase=1|Water level area}}'s {{inlink|WATER_LEVEL}} attribute. Terrains not marked as water terrain are not initiated with water.
Terrains marked as water are subject to an additional check for the {{inlink|WATER_STRESS}} result type. If the amount of water on a water terrain has not increased by more than {{inlink|ALLOWED_WATER_INCREASE_M}} relative to the {{inlink|lcase=1|Water level area}}'s water level, that terrain will not count as stressed for that result type. The amount of water on that location must be at least {{inlink|ALLOWED_WATER_INCREASE_M}} more than the {{inlink|lcase=1|Water level area}}'s water level.
{| class="wikitable"
! Attribute
! Unit
! Terrain type
! Description
|-
|{{anchor|WATER|WATER}}
|boolean
|Surface
|Whether the specified terrain is a water terrain.
|}
====Plants====
Terrains can be configured with plant-related attributes, similar to {{inlink|lcase=1|Crops and foliage}} constructions, allowing it to draw water from the underground and {{inlink|Underground evaporation model|evaporate}} it.
{| class="wikitable"
! Attribute
! Unit
! Terrain type
! Description
|-
|{{anchor|ROOT_DEPTH_M_surface|ROOT_DEPTH_M}}
|m
|Surface
|The depth of the roots of this surface terrain, relative to the surface. Water can be drawn from the underground and evaporated if the roots can reach it.
|-
|{{anchor|WATER_EVAPORATION_FACTOR_surface|WATER_EVAPORATION_FACTOR}}
|factor
|Surface
|How fast this terrain can evaporate water from the underground. The {{inlink|weather}}'s evaporation speed is multiplied by this factor to determine the rate of evaporation.
|}
Note that when a construction is present in any given location, the values for evaporation of the construction will overrule any values set by terrain in the same location. This is also true if the construction has its evaporation values set to 0; they will overrule the terrain's values and thus not allow evaporation of underground water to occur.
Also note that the groundwater level reduction is inversely proportional to the {{inlink|WATER_STORAGE_PERCENTAGE}}, as the contribution of a given volume of water to the groundwater level increases when the capacity for water storage in the underground layer decreases.
====Infiltration and storage====
Based on the properties of the terrain, water may infiltrate into the {{inlink|Underground model|underground water system}}.
The speed at which water can infiltrate from the surface to the underground unsaturated zone is dependent on both the infiltration properties of the surface terrain, as well as any construction in that location, if present. Of the infiltration values of the construction and the surface terrain, the lowest value is used. If either has an infiltration value of 0, water cannot infiltrate into the underground unsaturated zone.
{| class="wikitable"
! Attribute
! Unit
! Terrain type
! Description
|-
|{{anchor|GROUND_INFILTRATION_MD_surface|GROUND_INFILTRATION_MD}}
|m/day
|Surface
|The speed at which water can flow vertically from the surface to the underground unsaturated zone.
|-
|{{anchor|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}}
|m/day
|Underground
|The speed at which water can flow vertically from the underground unsaturated zone to the underground saturated zone, and horizontally through across the saturated zone.
|-
|{{anchor|WATER_STORAGE_PERCENTAGE|WATER_STORAGE_PERCENTAGE}}
|fraction
|Underground
|The percentage of the underground volume which can be filled with water. A lower percentage means the underground will be able to store less water, and the saturated zone will rise higher with the same amount of water in the underground layer.
|}
====Manning value (terrain)====
Terrains have an inherent "roughness", which influences how fast water can flow across the surface. This is known as the Manning coefficient or Manning value.
{| class="wikitable"
! Attribute
! Unit
! Terrain type
! Description
|-
|{{anchor|WATER_MANNING_surface|WATER_MANNING}}
|s/(m<sup>1/3</sup>)
|Surface
|The Gauckler–Manning coefficient of the terrain.
|}
Note that if a construction is present in the same location, that construction's {{inlink|WATER_MANNING_constructions|WATER_MANNING}} value is used instead.
==Settings==
The water overlay features a number of overall settings which can be configured for the hydrological calculations and its results. These settings do not have a geographical or temporal element to them, and are fixed values relevant for the complete simulation.
===Result type===
{{Editor ribbon|header=Current situation|bar=Overlays|left panel=The overlay|right panel=General tab}}
The water model performs complex calculations, and multiple types of results can be provided. In principle, each overlay can be configured to display a single result type.
Result types can differ in the kind of data they display, the layer (surface or underground) of which they display that information, and how that data is recorded. Different result types can monitor data in the following ways:
* {{Anchor|Start_resulttype}}'''Start''': The data is determined at the start of the simulation, and does not change afterwards.
* {{Anchor|Last_resulttype}}'''Last''': The data is the latest value determined at the timestep the data is recorded. The values can increase and decrease between different timesteps. This mode is primarily used for monitoring progression.
* {{Anchor|Maximum_resulttype}}'''Maximum''': The data is the highest value determined up until the timestep the data is recorded. The values can only increase or stay the same, but will never decrease. This mode is primarily used to gain insight into impact; the most severe situation any point had to endure.
* {{Anchor|Total_resulttype}}'''Total''': The result of a running tally, counting the relevant data up until the timestep the data is recorded. The value can only increase or stay the same, but will never decrease. This mode is primarily used to gain insight into quantities rather than duration.
The following results types are available:
{| class="wikitable"
! Result type
! Unit
! Display mode
! Description
|-
|{{anchor|BASE_TYPES|BASE_TYPES}}
|Nominal value
|{{inlink|Start_resulttype|Start}}
|Categorization of the individual cells based on how they are processed by the water model, displaying which cells are considered to be specific features.<br>
0: Cell on the edge of the project area<br>
1: Water area<br>
2: Land<br>
3: Sewer<br>
4: Water object<br>
5: Breach Area<br>
6: Active Breach
|- <!--


==Results==
With a Water Overlay, a user can generate multiple [[Results_(Water_Overlay)|results]] for a single water simulation. For further information about these outcomes, see also [[Results_(Water_Overlay)|results]] and [[Result type (Water Overlay)|result types]].


|{{anchor|CHLORIDE|CHLORIDE}}
==How-to's==
|x/m²
* [[How to add and remove an Overlay]]
|{{inlink|Last_resulttype|Last}}
* [[How to manually configure a Water Overlay|Configure a Water Overlay]]
|The amount of chloride present. The value is the sum of the quantities on the surface, and the underground.
* [[How to edit an overlay legend|Edit an overlay legend]]
|- -->
* [[How to add Subsidence (Water Overlay)|Combine with Subsidence Overlay]]
* [[Water Model Limits]] (some basic rules)


 
===Features and components===
|{{anchor|DIRECTION|DIRECTION}}
* [[Hydrological features (Water Overlay)|Hydrological features]]
|Degrees
* [[Hydraulic structures (Water Overlay)|Hydraulic structures]]
|{{inlink|Last_resulttype|Last}}
* [[How to_manually_configure_a_Water_Overlay|Manual configuration Options]]
|The direction in which water is flowing.
* [[Simulation data (Water Overlay)|Simulation data]]
|-
|{{anchor|EVAPORATED|EVAPORATED}}
|m (mm)&sup1;
|{{inlink|Total_resulttype|Total}}
|The amount of water that has evaporated. The value is the sum of the quantities evaporated from the surface and the underground.
|-
|{{anchor|GPU OVERVIEW|GPU OVERVIEW}}
|nominal integer
|{{inlink|Maximum_resulttype|Maximum}}
|Shows which GPU cluster calculated which part of the overlay.
|-
|{{anchor|IMPACTED_BUILDINGS|IMPACTED_BUILDINGS}}
|nominal integer
|{{inlink|Maximum_resulttype|Maximum}}
|Constructions impacted by excess water. Constructions are considered impacted when the construction itself or an adjacent cell contains more water on the surface than configured in {{inlink|IMPACT_FLOOD_THRESHOLD_M}}.<br>
0: Construction is not impacted<br>
1...N: The {{inlink|Critical structures|(critical) construction}} is impacted, and has a critical [[function values]] set to this value.
|-
|{{anchor|LAST SPEED|LAST SPEED}}
|m/s
|{{inlink|Last_resulttype|Last}}
|The speed of water flow in any given location.
|-
|{{anchor|MAX SPEED|MAX SPEED}}
|m/s
|{{inlink|Maximum_resulttype|Maximum}}
|The speed of water flow in any given location.
|- <!--
 
 
|{{anchor|NITROGEN|NITROGEN}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of nitrogen present. The value is the sum of the quantities on the surface, and the underground.
|-
|{{anchor|PHOSPHORUS|PHOSPHORUS}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of phosphorus present. The value is the sum of the quantities on the surface, and the underground.
|- -->
 
 
|{{anchor|SEWER_LAST_VALUE|SEWER_LAST_VALUE}}
|m (mm)&sup1;
|{{inlink|Last_resulttype|Last}}
|The amount of water stored in the sewer.
|-
|{{anchor|SEWER_MAX_VALUE|SEWER_MAX_VALUE}}
|m (mm)&sup1;
|{{inlink|Maximum_resulttype|Maximum}}
|The amount of water stored in the sewer.
 
|-
|{{anchor|SUBSTANCE_A|SUBSTANCE_A}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of {{inlink|SUBSTANCE_A_constructions|substance A}} present. The value is the sum of the quantities on the surface, and in the underground.
 
|-
|{{anchor|SUBSTANCE_B|SUBSTANCE_B}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of {{inlink|SUBSTANCE_B_constructions|substance B}} present. The value is the sum of the quantities on the surface, and in the underground.
 
|-
|{{anchor|SUBSTANCE_C|SUBSTANCE_C}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of {{inlink|SUBSTANCE_C_constructions|substance C}} present. The value is the sum of the quantities on the surface, and in the underground.
 
|-
|{{anchor|SUBSTANCE_D|SUBSTANCE_D}}
|x/m²
|{{inlink|Last_resulttype|Last}}
|The amount of {{inlink|SUBSTANCE_D_constructions|substance D}} present. The value is the sum of the quantities on the surface, and in the underground.
 
|-
|{{anchor|SURFACE_DURATION|SURFACE_DURATION}}
|s (min)&sup1;
|{{inlink|Total_resulttype|Total}}
|The amount of time the water depth on the surface exceeds {{inlink|SHOW_DURATION_FLOOD_LEVEL_M}}.
|-
|{{anchor|SURFACE_DURATION|SURFACE_ELEVATION}}
|
|
|''Description wil be added''
|-
|{{anchor|SURFACE_FLOW|SURFACE_FLOW}}
|m&sup3;/m&sup2;
|
|''Description wil be added'' <!--Total volume of water passed a grid-cell, scaled by the cell surface (grid cell-size^2)-->
|-
|{{anchor|SURFACE_LAST_VALUE|SURFACE_LAST_VALUE}}
|m (mm)&sup1;
|{{inlink|Last_resulttype|Last}}
|The amount of water on the surface.
|-
|{{anchor|SURFACE_MAX_VALUE|SURFACE_MAX_VALUE}}
|m (mm)&sup1;
|{{inlink|Maximum_resulttype|Maximum}}
|The amount of water on the surface.
|-
|{{anchor|UNDERGROUND_FLOW|UNDERGROUND_FLOW}}
|m&sup3;/m&sup2;
|
|''Description wil be added'' <!--Amount of water which has infiltrated from the surface to the underground-->
|-
|{{anchor|UNDERGROUND_LAST_STORAGE|UNDERGROUND_LAST_STORAGE}}
|m (mm)&sup1;
|{{inlink|Last_resulttype|Last}}
|The (effective) amount of water in the underground unsaturated zone.
|-
|{{anchor|UNDERGROUND_LAST_VALUE|UNDERGROUND_LAST_VALUE}}
|m (mm)&sup1;
|{{inlink|Last_resulttype|Last}}
|The distance between the surface and the groundwater level.
|-
|{{anchor|UNDERGROUND_MAX_STORAGE|UNDERGROUND_MAX_STORAGE}}
|m (mm)&sup1;
|{{inlink|Maximum_resulttype|Maximum}}
|The (effective) amount of water in the underground unsaturated zone.
|-
|{{anchor|UNDERGROUND_MAX_VALUE|UNDERGROUND_MAX_VALUE}}
|m (mm)&sup1;
|{{inlink|Maximum_resulttype|Maximum}}
|The distance between the surface and the groundwater level.
|-
|{{anchor|UNDERGROUND WATERTABLE|UNDERGROUND WATERTABLE}}
|{{mdatum}}
|{{inlink|Last_resulttype|Last}}
|The groundwater level, relative to [[datum]].
|-
|{{anchor|WATER_STRESS|WATER_STRESS}}
|m (mm)&sup1;
|{{inlink|Maximum_resulttype|Maximum}}
|The amount of water on the surface, similar to {{inlink|SURFACE_MAX_VALUE}}. However, for {{inlink|Water|water terrains}}, the water level must rise by at least {{inlink|ALLOWED_WATER_INCREASE_M}}. Otherwise, the reported value in those locations is 0.
|}
 
&sup1; the units between () are as displayed in the 3D client. If exported to GeoTiff the SI-convention is used: meters (m) and seconds (s).
 
Each result type would consist of a unique output of data after a calculation, and is accompanied by its own {{inlink|Legend configuration|legend}}. When the result type of the overlay is changed, the legend is updated automatically, but the data may not be recalculated automatically. This may result in the visual output of the overlay changing, because the unchanged data is displayed with a new legend. When changing the result type, it is recommended to force a recalculation of the overlay before {{inlink|Results|interpreting the output}}.
 
====Result child overlays====
Each overlay can only display a single result type. When using a water overlay, it is conceivable that multiple result types are relevant to a project's use case. It's possible to duplicate the overlay, and set the copy of the overlay to a different result type, but this is not recommended. Downsides of this approach are that the simulation has to run in full multiple times, causing a severe increase in calculation time, and that when changes to the overlay's configuration have to be made those changes need to be made to all water overlays.
 
It is possible to add result child overlays overlays to a water overlay, which can display different results coming forth from the same calculation. The advantages of using result child overlays are that for any given water overlay, the calculation of the overlay only occurs once, rather than multiple times equal to the amount of desired result types. Additionally, the configuration for the calculation is only defined in a single overlay, which makes it easier to make sure all results come forth from the exact same simulation.
 
Result child overlays do not recalculate if either they or their parent is set to {{inlink|Active in simulation setting|inactive}}.
 
If a calculation overlay is removed, all result child overlays which are children of that overlay are removed as well. Separate overlays set as child overlays (such as {{inlink|lcase=1|Input overlay}}) of the overlay will not be removed.
 
It is only possible to add result child overlays via the {{inlink|lcase=1|Configuration wizard}}, in the {{inlink|Step 5: Output overlays|output overlays step}}.
 
===Keys===


===Attributes===
===Attributes===
The water model calculations rely on a number of calculation-wide parameters. These parameters are available as attributes of the water overlay and can be modified as such.
* [[Model attributes (Water Overlay)|Water Module Attributes]]
 
* [[Hydrological attributes of buildings (Water Overlay)|Hydrological Attributes of Buildings]]
{| class="wikitable"
* [[Hydrological attributes of terrains (Water Overlay)|Hydrological Attributes of Terrains]]
! Attribute
! Unit
! Description
|-
|{{anchor|ALLOWED_WATER_INCREASE_M|ALLOWED_WATER_INCREASE_M}}
|m
|The amount by which the water level on a water terrain must increase before it is considered stressed by water. This is used to compute the {{inlink|WATER_STRESS}} result type.
|-
|{{anchor|DESIGN_FLOOD_ELEVATION_M|DESIGN_FLOOD_ELEVATION_M}}
|m
|Constructions in the 3D world are assumed to have at most this height compared to the surface of the terrain. Greater values can create a more accurate model but will impact performance.
|-
|{{anchor|GROUND_BOTTOM_DISTANCE_M|GROUND_BOTTOM_DISTANCE_M}}
|m
|Assumed distance under the terrain surface where the soil becomes impenetrable for water. The groundwater level cannot go below this depth, relative to the surface. The maximum amount of water that can be stored underground is equal to this attribute multiplied by the local terrain's {{inlink|WATER_STORAGE_PERCENTAGE}}.
|-
|{{anchor|GROUND_WATER|GROUND_WATER}}
|boolean
|Whether {{inlink|Underground model|underground water flow}} is simulated during the calculation. If this is deactivated, surface infiltration, underground infiltration, and {{inlink|Underground evaporation model|underground evaporation}} do not occur. Water flowing {{inlink|Sewer model|in- and out of the sewer}} are still simulated when sewers are present.
|-
|{{anchor|IMPACT_FLOOD_THRESHOLD_M|IMPACT_FLOOD_THRESHOLD_M}}
|m
|The amount of water a construction must experience before it is considered impacted by water. Water must reach this height either on one of the cells the construction is on, or on one of the cells adjacent to it. This is used to compute the {{inlink|IMPACTED BUILDINGS}} result type.
|-
|{{anchor|MAX_SPEED_MS|MAX_SPEED_MS}}
|m/s
|Maximum speed at which water is allowed to flow. This effects the preservation of impulse in water, and as a result the length of {{inlink|Timestep formula|computational timesteps}}. Impulse is more accurately preserved as the maximum speed increases, but will reduce the time per step of the calculation, increasing the total time for the calculation to complete.
|-
|{{anchor|MIN_SLOPE|MIN_SLOPE}}
|ratio
|The minimum slope required to account for the effect of gravity on the speed of the water. If the slope of the terrain is less than the minimum slope, the effect of gravity on the speed of the water is assumed to be 0. The ratio is the height over distance.
|-
|{{anchor|QUAD_CELL|QUAD_CELL}}
|boolean
|This attribute name is reserved for future functionality. Currently, this marks an experimental feature which is currently under development and may result in unexpected behavior when activated.
|-
|{{anchor|SEWER_OVERFLOW_THRESHOLD|SEWER_OVERFLOW_THRESHOLD}}
|fraction
|How much of a sewer's storage must be filled with water before the {{inlink|Sewer overflow|sewer's overflows}} are allowed to overflow water.
|-
|{{anchor|SHOW_DURATION_FLOOD_LEVEL_M|SHOW_DURATION_FLOOD_LEVEL_M}}
|m
|The amount of water which must be present in a specific location before the duration of surface water can be recorded. This is used to compute the {{inlink|SURFACE_DURATION}} result type.
|-
|{{anchor|SUPERGRID|SUPERGRID}}
|boolean
|This attribute name is reserved for future functionality. Currently, this marks an experimental feature which is currently under development and may result in unexpected behavior when activated.
|-
|{{anchor|SURFACE_WATER_EVAPORATION_FACTOR|SURFACE_WATER_EVAPORATION_FACTOR}}
|factor
|The factor by which the {{inlink|lcase=1|Weather}}'s evaporation factor is multiplied to compute the amount of {{inlink|Evaporation model|evaporation}} which takes place on the surface.
|-
|{{anchor|TIMEFRAMES|TIMEFRAMES}}
|integer
|The number of intermediate results recorded during the calculation. Each {{inlink|Timeframes|timeframe}} becomes a snapshot of data which can be viewed and analysed. The total simulation time is divided by this value, and at each interval of that period of time a snapshot of the results so far is made. Note that the first timeframe does not contain the starting conditions of the simulation, but the state of the simulation after the first period of time has passed.
|}
 
==Calculations==
The water overlay performs a large number of calculations to form a complete hydrological simulation. Depending on the desired viewpoint, both the overarching concepts as well as the implemented formulas can be reviewed for detailed insight into how the water overlay works.
 
===Models===
Multiple models are implemented which in conjuction form the water model in its entirety.
 
====Surface model====
The water model's primary function is the simulation of the flow of water on the surface of the terrain. The surface model includes the flow of water across the surface of the terrain, including over {{inlink|Water|water terrains}}, including the flow through {{inlink|lcase=1|Hydrological constructions}} and water that is created or removed by hydrological constructions.
 
The surface is defined by the {{inlink|Terrain height|terrain height}} in the project. The terrain height is further influenced by the height of constructions present in the project (bounded by {{inlink|DESIGN_FLOOD_ELEVATION_M}}) and by the {{inlink|BREACH_HEIGHT}} of {{inlink|lcase=1|Breach}}es.
 
The surface water level is initialized based on hydrological features present in the project. For all {{inlink|Water|water terrains}}, water is placed on the surface of the world. The amount of water placed is such that the resulting water level in that location is equal to the {{inlink|WATER_LEVEL}} attribute of the {{inlink|lcase=1|Water level area}} in that location. If there is no water level area in that location, the water level is assumed to be so low that no water is created. Besides the water level areas, {{inlink|Inundation}} is added to the model. Water is placed in all locations where inundation is defined (regardless of the terrain type in that location, in contrast to the water level areas), such that the resulting height of the water inundating the land is equal to the inundation area's {{inlink|INUNDATION_LEVEL}} attribute.
 
After the surface is initialized with water, all water on the surface will flow in accordance with the same rules. It does not matter whether the water was created when the model was initialized, and whether that water was due to a water terrain or due to inundation, or whether the water came in from another source.
 
On the surface, water can flow from one cell to an adjacent cell based on the relative heights of the water, the slope of the terrain, and the manning value of the terrain or construction in that location.
 
In addition to water flowing between geographically adjacent cells, water can also flow through {{inlink|Hydrological constructions|hydrological constructions}}. When a {{inlink|Line-based_constructions|line-based hydrological construction}} exists in the project area, the 2 cells indicated by the endpoints of the line are considered adjacent as well. Flow between those cells is not dictated by the same parameters as the regular surface flow. Instead, water can flow between the 2 indicated cells based on the construction's underlying formula.
 
Water can also be added to or removed from the water model by {{inlink|Point-based_constructions|point-based hydrological constructions}}. Based on the construction's underlying formula water can be added or removed to the cell indicated by the construction. Only that single cell will receive or lose the calculated amount of water.
 
Water can also be removed from the surface by {{inlink|Miscellaneous hydrological properties of constructions|other properties}} of constructions, based on the construction's polygons (either moving it to another part of the hydrological model, or removing it completely from the hydorlogical model). When water is removed from the surface via a polygon-based construction, the removal of water is calculated per individual cell.
 
====Underground model====
The water model includes an underground model which dictates the movement of water in the soil. The underground model includes the flow of water from the surface into the underground via infiltration, the flow of water from one underground location to another, and the exfiltration of water from the soil back onto the surface layer.
 
The underground model can be explicitly activated or deactivated by setting the {{inlink|GROUND_WATER}} attribute of the water overlay to the appropriate value. If the underground model is deactivated, no water can move from or to the underground in any form, including {{inlink|Underground_evaporation_model|underground evaporation}}.
 
The underground is bounded vertically by the {{inlink|Terrain height|surface of the terrain}} at the top, and an assumed impenetrable layer at the bottom. The distance between the surface and the impenetrable layer, and thus the effective height of the underground, is equal to {{inlink|GROUND_BOTTOM_DISTANCE_M}}. In other words, the impenetrable underground layer is assumed to be a set distance below the surface. The distance is uniform across the entire project area, and follows the profile of the surface.
 
The underground is composed of 2 layers: the unsaturated zone and the saturated zone. The saturated zone is the region of the underground where the soil is saturated with water. This water is assumed to work as a continuous volume of water able to flow horizontally. The unsaturated zone is the region of the underground above the saturated zone. The edge between the unsaturated and saturated zone can be considered the groundwater level.
 
The groundwater level, and thus the height of the saturated zone, is determined both by the amount of water in the saturated zone, and the underground terrain's {{inlink|WATER_STORAGE_PERCENTAGE|WATER_STORAGE_PERCENTAGE}}. The lower the water storage percentage of the soil, the greater the volume of soil that is saturated by the same amount of water, and thus the higher the the groundwater level will become.
 
The underground water level is initialized with the values of the {{inlink|Ground water|ground water GeoTIFF}} connected to the water model. If no ground water data is connected, the ground water level relative to {{datum}} is equal to the surface water level relative to {{datum}}, as defined by the {{inlink|WATER_LEVEL}} attribute of the {{inlink|lcase=1|Water level area}} in that location.
 
When water infiltrates from the surface, it infiltrates at a speed dictated by the surface terrain's {{inlink|GROUND_INFILTRATION_MD_surface|GROUND_INFILTRATION_MD}} attribute, the underground terrain's {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}} attribute, or (if present) by the construction's {{inlink|GROUND_INFILTRATION_MD_constructions|GROUND_INFILTRATION_MD}}, whichever value is lowest. The least porous material present will always serve as a bottleneck for the water to flow through, even if the other layers allow for a high rate of infiltration.
 
Surface water infiltrates into the underground unsaturated layer. Water in the unsaturated layer is assumed to be spread equally across the entire unsaturated volume. Water then flows from the unsaturated zone into the saturated zone at the speed dictated by the underground terrain's {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}}. For a given timestep, the distance the water travels is determined. The amount of water that flows from the unsaturated zone to the saturated zone is equal to the amount of water in a section of the unsaturated zone the height of which is equal to that distance. After water has been added to the saturated zone, the groundwater level (and thus the height of the saturated zone) is redetermined. The water in the unsaturated zone is redistributed uniformly across the (remaining) unsaturated zone.
 
Water stored in the underground saturated zone can flow horizontally from one underground cell to another, if the groundwater level relative to {{datum}} is higher than the neighboring cell's ground water level, relative to {{datum}}. The amount of water which can flow from one cell to another is dictated by the underground terrain's {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}}.
 
Water stored in the underground saturated zone can also exfiltrate out of the underground and back onto the surface, if the groundwater level relative to {{datum}} exceeds the neighboring cell's surface water level relative to {{datum}}. The amount of water which can flow from the underground of one cell onto the surface of an adjacent cell is dictated by the underground terrain's {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}}.
 
====Rain model====
Rain is implemented in the water model.
 
Rain can be implicitly activated and deactivated by defining an appropriate period of {{inlink|Rain and simulation time|rainfall}} in the {{inlink|lcase=1|Weather}}. If a period with no rainfall is defined, that period is simulated but no rain is simulated.
 
Currently, during a period in the simulation where {{inlink|Rain and simulation time|rainfall}} is defined, water is uniformly added to the {{inlink|Surface model|surface}} of all cells in the project area. During any single defined period of rain, the amount of rain is consistent over time. At the end of the defined period of rain, exactly the defined amount of rain will have fallen on each cell.
 
====Evaporation model====
Water can evaporate from the hydrological model over time. Multiple forms of evaporation are implemented.
 
All forms of evaporation can be implicitly activated and deactivated by setting the {{inlink|Weather|weather}}'s {{inlink|Evaporation|evaporation rate}}. If the evaporation factor is set to 0, no evaporation will take place in any form.
 
The weather's evaporation rate is defined as a period during which a certain rate of evaporation will take place. Multiple periods of evaporation can be defined, and at any specific moment during the simulation an exact evaporation rate is defined by the weather.
 
For all forms of evaporation, the weather's evaporation rate is used as a base for determining the exact rate of evaporation for that form of evaporation.
 
=====Surface evaporation model=====
Water can evaporate from the {{inlink|Surface_model|surface}}, based on the {{inlink|Weather|weather}}'s {{inlink|Evaporation|evaporation factor}} and the overlay's {{inlink|SURFACE_WATER_EVAPORATION_FACTOR}}. These values compute to a net rate of evaporation which is applied to the surface of all cells. Only water on the surface of cells is affected by this evaporation.
 
Cells without water on the surface are not affected by evaporation.
 
=====Underground evaporation model=====
Water can evaporate from the {{inlink|Underground model|underground}} if the cell has either a {{inlink|Crops and foliage|construction which allows for underground evaporation}}, or a {{inlink|Plants|surface terrain type}} which allows for underground evaporation and is unobstructed by a construction. In other words: if a construction is present the construction's properties are used, otherwise the terrain's properties are used.
 
Underground evaporation can be implicitly activated or deactivated by setting the relevant properties of all terrain types and constructions to appropriate evaporation values. If the relevant properties are set to 0, no underground evaporation will take place. Underground evaporation is also explicitly deactivated when the {{inlink|lcase=1|Underground model}} is deactivated.
 
Water can evaporate from the underground via crops and foliage. It can draw water from the underground unsaturated and saturated zones, if their roots reach deep enough and the terrain or construction have a configured evaporation factor. Water is drawn directly from the underground and evaporated, removing it from the hydrological model entirely.
 
The rate of evaporation is determined by the {{inlink|Weather|weather}}'s {{inlink|lcase=1|Evaporation rate}}, and either the construction's {{inlink|WATER_EVAPORATION_FACTOR_constructions|WATER_EVAPORATION_FACTOR}} or the surface terrain's {{inlink|WATER_EVAPORATION_FACTOR_surface|WATER_EVAPORATION_FACTOR}}.
 
Evaporation can only take place if the roots of the terrain or construction can reach underground water. The depth the roots can reach is defined by either the construction's {{inlink|ROOT_DEPTH_M_constructions|ROOT_DEPTH_M}} or the surface terrain's {{inlink|ROOT_DEPTH_M_surface|ROOT_DEPTH_M}}.
 
Water can be evaporated both from the saturated and the unsaturated zones of the underground. The amount of water that can be taken from the saturated and the unsaturated zones is limited by the amount of water in either zone in reach of the roots.
 
====Sewer model====
Sewers are available in the water model, allowing for the retention of excess water which would otherwise stay and flow on the surface.
 
Sewers can be implicitly activated and deactivated by adding or removing {{inlink|lcase=1|Sewer area|}}s. If no sewer areas exist, no sewers are available in the water model and no water can flow to and from there.
 
Sewer areas define the areas in which sewers exist. The capacity of those sewers is based on the sewer area's {{inlink|SEWER_STORAGE}} attribute. The actual locations where the sewer exists is the intersection between the sewer areas and the {{inlink|lcase=1|Sewered constructions}} in the project area. The total surface area of the actual sewer is equal to that intersection.
 
If there is water on the {{inlink|Surface model|surface}}, in a cell with a sewered construction, and there is a sewer present in the same location, the water flows directly into the sewer. Water can flow in until the sewer is filled to capacity. Water can only flow into a sewer a via sewered construction. It is not possible for water to flow from a sewer back to the surface via a sewered construction, unless that construction is is explicitly a sewer overflow.
 
Water can flow from a sewer overflow back onto the surface via a {{inlink|lcase=1|Sewer overflow}}. A sewer overflow removes water from the sewer and places it on the surface of the cell where the overflow is located. The speed at which this water flows is determined by the {{inlink|SEWER_OVERFLOW_SPEED}}.
 
To overflow from the sewer to the surface, two criteria need to be met. Firstly, the amount of water in the sewer relative to the sewer's total capacity must exceed the {{inlink|SEWER_OVERFLOW_THRESHOLD}}. Secondly, the water level in the sewer must exceed the terrain height at the location of the sewer overflow.
 
Water can be removed from a sewer based on the sewer area's {{inlink|SEWER_PUMP_SPEED}}. Water removed from the sewer in this way is removed entirely from the hydrological model.
 
====Storage model====
Water on the {{inlink|Surface model|surface}} can be stored in {{inlink|lcase=1|Water storage constructions}}.
 
Water storage in constructions can be implicitly activated or deactivated by ensuring that all constructions in the project area have appropriate water storage properties. If there are no constructions in the project area with water storage capacity, no water storage will take place.
 
When water flows onto a cell with a {{inlink|Water storage constructions|construction capable of storing water}}, that water will be stored in the construction until the construction's water storage capacity has been reached. Water cannot leave that storage, either through flow back into the hydrological model or by being removed from it altogether. When the storage is filled, no additional water cannot flow into that storage for the remainder of the simulation.
 
====Chemical flow model====
Chemicals can be modeled in the hydrological model, as quantities picked up and carried along with the water.
 
The chemical model can be implicitly activated and deactivated by having construction in the project area have the appropriate attributes configured. If no constructions have attributes configured to interact with the quantities of chemicals, then no chemicals are computed.
 
Chemicals are tracked as an exact amount on a given location. The substances are generically defined and do not have a set unit or magnitude.
 
Chemicals are added to the hydrological model and removed from the hydrological model by {{inlink|Chemical emitters/decomposers|chemical emitters and decomposers}}. The chemicals created are then placed on the {{inlink|Surface model|surface}} of the cells where they are created. Chemicals can also be removed by chemical constructions, if their attributes are configured appropriately. When chemicals enter the cell which contains a chemical decomposer, the chemicals are removed from the hydrological model.
 
When water moves from a cell which also contains chemicals, the chemicals are carried along with the water. The chemicals are uniformly distributed between the water which remains in the cell, which flows to other cells, and which infiltrates. Water which flows into the sewer explicitly cannot carry chemicals along with it.
 
====Model border====
The outer edge of cells of the water model are excluded from calculations. No water can flow from or to there.
 
===Formulas===
The precise calculations which govern the water overlay's simulation are many and varied, and based as much as possible on available expert knowledge.
 
====Timestep formula====
An adaptive timestep is implemented according to Kurganov and Petrova (2007)<ref name="Kurganov1" />. At every timestep, the courant-number is kept smaller than 0.25 for every active computation cell.
 
[[File:Inundation_overlay_03.PNG|400px]]
 
Especially at low depths, choosing the appropriate timestep is critical to avoid numerical instability. Therefore the following principles are used to determine the right time step:
* the timestep is choosen so that all computation cells follow one of the following criteria.
* if a cells waterdepth is below the flooding threshold, 5 * 10<sup>-3</sup> (m) there is no flow assumed between that cell and it neigboring cell.
* if the cells waterdepth is above above the flooding threshold, the maximum timestep is assumed to be 100 * the waterdepth at the cell.
* if the waterdepth increases, the timestep is assumed to be not larger than the formula above.
 
If the numerical flux decreases, larger timesteps are allowed than set by Kurganov and Petrova<ref name="Kurganov1" />, depending on the {{inlink|Calculation preference formula|configured calculation}}.
 
====Calculation preference formula====
The calculation preference influences the calculation of individual timesteps.
: ''Δt  = Δx /u<sub>max</sub>''
 
Where:
* Δt = computational timestep
 
* Δx = grid cell size
* u<sub>max</sub> = max velocity, assumed 2.5 (SPEED), 5 (AVERAGE) and 10 (ACCURACY) m/s respectively
 
====Surface water level formula====
Surface water level is calculated per cell.
: ''WL<sub>surface</sub> = W<sub>surface</sub> + H<sub>surface</sub>''
 
Where:
* WL<sub>surface</sub> = The water level, relative to {{datum}}.
 
* W<sub>surface</sub> = The amount of water (the water column) on the surface.
* H<sub>surface</sub> = The terrain height in the cell, relative to {{datum}}.
 
====Surface flow formula====
Surface flow is calculated using the 2D Saint Venant equations.
 
=====2D Saint Venant=====
The base equations describe the conservation of mass and momentum in both the x and y direction.
 
[[File:Inundation_overlay_01.PNG|350px]]
 
The following processes are described in these equations:
* friction
* bed slope
* water pressure
* convection (changes in bathemetry over space)
* inertia (increase or decrease of velocity over time)
 
=====Numerical scheme for the 2D Saint Venant equations=====
[[File:Inundation overlay 04 HWP(1).PNG|thumb|250px|Source: Horváth et al. (2014)<ref name="Horvath"/>]]
 
[[File:Inundation overlay 04 HWP(2).PNG|thumb|250px|Source: Horváth et al. (2014)<ref name="Horvath"/>]]
 
The explicit second-order semi-discrete central-upwind scheme for the 2D Saint Venant Equations is implemented. A reconstruction of cell bottom, water level and velocity at the interfaces between computational cells as proposed by Lax and Wendroff (Rezzolla, 2011)<ref name="Rezolla"/>. The {{software}}'s water model relies on the scheme described in Kurganov and Petrova (2007)<ref name="Kurganov2"/>. The reconstruction method is taken from Bolderman et all (2014) and ensures numerical stability at the wetting and drying front of a flood wave<ref name="Bollerman" />.
 
A clear explanation on the numerical approach can be found at Horváth et al. (2014)<ref name="Horvath"/>, but in general it follows these steps:
# The elevation value of the cell (denoted as B in included figures) is equal to the elevation value at the center of the cell. At the same time, it is equal to the average value of the elevation values at the cell interface midpoints.
# The slopes of the conserved variables (denoted as U in included figures), continuity and momentum in x and y direction, are reconstructed.
# Values of conserved variables at the cell interface midpoints are compared with the left-sided and right sided values at cell centers.
# At partially dry cells, the slope is modified to both avoid negative depths and numerical instability.
# (Numerical) fluxes are computed at each cell interface to determine the values of the conserved variable at the cell centers for the next time-step.
{{clear}}
 
====Groundwater level formula====
Groundwater level is calculated per cell.
: ''WH<sub>underground</sub> = W<sub>sat</sub> / WSP''
: ''WL<sub>underground</sub> = WH<sub>underground</sub> + H<sub>surface</sub> - GBDM''
 
Where:
* WL<sub>underground</sub> = The groundwater level, relative to {{datum}}.
* WH<sub>underground</sub> = The height (column) of the saturated zone.
 
* W<sub>sat</sub> = The amount of water in the saturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
* H<sub>surface</sub> = The terrain height in the cell, relative to {{datum}}.
* GBDM = The {{inlink|GROUND_BOTTOM_DISTANCE_M}} (effectively available height in the underground model).
* WSP = The {{inlink|WATER_STORAGE_PERCENTAGE}} of the underground terrain type.
 
====Surface infiltration formula====
Surface infiltration is calculated per cell.
 
Infiltration capacities:
: ''C<sub>water</sub> = W<sub>surface</sub>''
: ''C<sub>top</sub>'' = max( I<sub>con</sub>, I<sub>surf</sub> )
:: I<sub>surf</sub> = 0 if a construction is present
:: I<sub>con</sub> = 0 if no construction is present
 
Actual infiltration:
: ''Δw =  min( C<sub>water</sub> , Δt * C<sub>top</sub>)''
 
Where:
* Δw = The surface infiltration which takes place.
* Δt = Computational timestep.
 
* C<sub>water</sub> = The amount of infiltration that can take place based on the amount of water on the surface.
* C<sub>top</sub> = The amount of evaporation that can take place based on the infiltration values present.
 
* W<sub>surface</sub> = The amount of water (the water column) on the surface.
* I<sub>con</sub> = The {{inlink|GROUND_INFILTRATION_MD_constructions|GROUND_INFILTRATION_MD}} of a construction on a specific cell (if present).
* I<sub>surf</sub> = The {{inlink|GROUND_INFILTRATION_MD_surface|GROUND_INFILTRATION_MD}} of the surface terrain type. This value should be interpreted as the vertical conductivity (Kv) of the sub-soil.
 
====Underground infiltration formula====
Underground infiltration (from the unsaturated zone to the saturated zone) is calculated per cell.
 
First the height of the unsaturated zone is calculated.
: ''H<sub>unsat</sub> = H<sub>surface</sub> - WL<sub>underground</sub>''
 
Then the ratio of water amount to unsaturated height is calculated.
: ''S = W<sub>unsat</sub>/H<sub>unsat</sub>''
 
Then calculate the distance of the unsaturated zone which can infiltrate.
: ''C<sub>inf</sub> = min( H<sub>unsat</sub> , Δt * I<sub>und</sub> )''
 
Finally, calculate the amount of actual amount of water infiltrating.
: ''Δw = C<sub>inf</sub> * S''
 
Where:
* Δw = The underground infiltration which takes place.
* Δt = Computational timestep.
 
* H<sub>unsat</sub> = The height of the unsaturated zone.
* S = Ratio of water to height in the unsaturated zone.
* C<sub>inf</sub> = The height in the unsaturated zone which can be subject to infiltration to the saturated zone.
 
* W<sub>unset</sub> = The amount of water in the unsaturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
* WL<sub>underground</sub> = The groundwater level, relative to {{datum}}.
* H<sub>surface</sub> = The terrain height in the cell, relative to {{datum}}.
* I<sub>und</sub> = The {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}} of the underground terrain type.
 
====Underground flow formula====
Underground flow between cells is calculated using Darcy's law<ref name="Modflow"/>.
 
: ''C<sub>d</sub> = Δt * I<sub>und</sub> * width * A * ( (WL<sub>source</sub> - WL<sub>target</sub>) / distance )
 
Since both ''width'' and ''distance'' are directly related to the cell size, and the result should be in water height rather than volume, the formula can be rewritten as follows:
 
: ''C<sub>d</sub> = Δt * I<sub>und</sub> * A * (W<sub>source</sub> - W<sub>target</sub>) / cell
 
Because the underground may have a different porousness, the maximum amount of water that can flow to another cell has to take into account the relative water storage capacities of the underground.
 
: ''C<sub>wsp</sub> = (WL<sub>source</sub> - WL<sub>target</sub>) * (WSP<sub>source</sub> / (WSP<sub>source</sub> + WSP<sub>target</sub>) )
 
The amount of water which flows from the source to the target cell is calculated as follows:
 
: ''Δw = max( 0 , min( C<sub>d</sub> , C<sub>wsp</sub> ) )
 
Where:
* Δw = The underground flow which takes place.
* Δt = Computational timestep.
* cell = Cell size.
 
* C<sub>d</sub> = The capacity for water flow possible based on the relative water heights.
* C<sub>wsp</sub> = The capacity for water flow possible based on the relative water storage percentages.
 
* WL<sub>source</sub> = The amount of water in the saturated zone of the source cell. The height of the water column if the equivalent amount of water was placed on the surface.
* WL<sub>target</sub> = The amount of water in the saturated zone of the target cell. The height of the water column if the equivalent amount of water was placed on the surface.
* A = Contact area of the underground cells
* I<sub>und</sub> = The {{inlink|GROUND_INFILTRATION_MD_underground|GROUND_INFILTRATION_MD}} of the underground terrain type of the origin cell.
* WSP<sub>source</sub> = The {{inlink|WATER_STORAGE_PERCENTAGE|WATER_STORAGE_PERCENTAGE}} of the underground terrain type of the origin cell.
* WSP<sub>target</sub> = The {{inlink|WATER_STORAGE_PERCENTAGE|WATER_STORAGE_PERCENTAGE}} of the underground terrain type of the target cell.
 
====Culvert formula====
<!--Culvert flow is calculated based on the 2 end-point cells.-->
Flow through culverts is based on an open channel flow calculation <ref name="hydradius" />.
 
The actual height of the culvert is at least the height of the terrain on either end of the culvert:
: ''CH<sub>real</sub> = max( CH<sub>attr</sub> , T<sub>left</sub> , T<sub>right</sub> )''
 
The height of the water column at either end of the culvert, relative to the culvert, is calculated:
: ''WH<sub>left</sub> = max(0, WL<sub>left</sub>-CH<sub>real</sub>)''
: ''WH<sub>right</sub> = max(0, WL<sub>right</sub>-CH<sub>real</sub>)''
 
The potential flow through the culvert is then calculated, both for a fully filled culvert and a partially filled culvert:
: ''C = 0.9 * A * sqrt( 2 * G * abs(WH<sub>left</sub> - WH<sub>right</sub>) )''
 
Finally the actual amount of water flow is calculated:
: ''Δw = ''Δt * C / cell''
 
Where:
* Δw = The water flow which takes place.
* Δt = Computational timestep.
* cell = Cell size.
 
* C = The potential rate of water flow through the culvert.
* WH<sub>left</sub> = The height of the water column relative to the bottom of the culvert on the left side of the culvert.
* WH<sub>right</sub> = The height of the water column relative to the bottom of the culvert on the right side of the culvert.
* CH<sub>real</sub> = The {{inlink|CULVERT_THRESHOLD}} of the culvert, recalculated so the culvert is not below ground on either side.
 
* U<sub>partial</sub> = Loss coefficient for partially submerged culverts (0,9). <!--What is the exact value?-->
* A = Flow area, based on the highest water level.
* G = Acceleration factor of gravity
* CW = The {{inlink|CULVERT_DIAMETER}} attribute of the culvert. <!--Unused-->
* CH<sub>attr</sub> = The {{inlink|CULVERT_THRESHOLD}} attribute of the culvert.
* WL<sub>left</sub> = The water level on the left side of the culvert, relative to {{datum}}.
* WL<sub>right</sub> = The water level on the right side of the culvert, relative to {{datum}}.
 
====Weir formula====
<!--Q = 1.7 * C * B * H ^ N-->
Flow across weirs is calculated differently for free flow and submerged flow.
 
The height of the water at each end of the weir, relative to the weir, is calculated:
: ''WH<sub>source</sub> = max(0, max( WL<sub>left</sub>, WL<sub>right</sub> ) - WH<sub>weir</sub>)''
: ''WH<sub>dest</sub> = max(0, min( WL<sub>left</sub>, WL<sub>right</sub> ) - WH<sub>weir</sub>)''
 
For free flow, capacity is calculated directly:
: ''C<sub>free</sub> = 1.7 * WC * WW * ( WH<sub>source</sub> - WH<sub>dest</sub> )<sup>3/2</sup>''
 
For submerged flow, a culvert-like calculation is used:
: ''C<sub>submerged</sub> = U * A * sqrt( 2 * G * (WH<sub>source</sub> - WH<sub>dest</sub>) )''
 
Based on the relative water heights, the weir is judged to have either a submerged flow or a free flow, based on the following ratio:
: ''WH<sub>relative</sub> = WH<sub>dest</sub> : WH<sub>source</sub>''
:: C = min( C<sub>submerged</sub> , C<sub>free</sub>) if WH<sub>relative</sub> &gt; 0,5
:: C = C<sub>free</sub> otherwise
 
Finally the actual amount of water flow is calculated:
: ''Δw = ''Δt * C / cell''
 
Where:
* Δw = The water flow which takes place.
* Δt = Computational timestep.
* cell = Cell size.
 
* C = The potential rate of water flow across the weir.
* WH<sub>relative</sub> = The ratio of water heights on either side of the culvert.
* C<sub>free</sub> = The potential rate of water flow across the weir, based on a free flow calculation.
* C<sub>submerged</sub> = The potential rate of water flow across the weir, based on a submerged calculation.
* WH<sub>source</sub> = The height of the water column relative to the top of the weir, on the side with the highest water level.
* WH<sub>dest</sub> = The height of the water column relative to the top of the weir, on the side with the lowest water level.
 
* U = Loss coefficient for submerged weirs (0,9).
* A = Flow area, based on the highest water column height relative to the top of the weir, and the weir width
* G = Acceleration factor of gravity
* WC = The {{inlink|WEIR_COEFFICIENT}} attribute of the weir.
* WW = The {{inlink|WEIR_WIDTH}} attribute of the weir.
* WH<sub>weir</sub> = The {{inlink|WEIR_HEIGHT}} attribute of the weir.
* WL<sub>left</sub> = The water level on the left side of the weir, relative to {{datum}}.
* WL<sub>right</sub> = The water level on the right side of the weir, relative to {{datum}}.
 
====Pump formula====
The flow created by a pump is calculated based on the lowest end point of the pump.
 
: ''Δw = min( WH<sub>lower</sub> , Δt * PS )''
 
Where:
* Δw = The amount water water pumped from the lower to the higher endpoint.
* Δt = Computational timestep.
 
* WH<sub>lower</sub> = The height of the water column at the lower end of the pump, relative to the terrain.
* PS = The {{inlink|PUMP_SPEED}} of the pump.
<!--* H<sub>lower</sub> = The terrain height at the lower end point, relative to {{datum}}.-->
 
====Overflow formula====
<!--Needs the sewer overflow threshold-->
Overflow from the sewer is calculated for the entirety of the sewer, and the single attached sewer overflow.
 
The amount that can overflow relies on both the sewer overflow itself as well as the sewer overflow threshold:
: ''C<sub>threshold</sub> = max( 0 , WH<sub>sewer</sub> - SS * SOT )''
: ''C<sub>height</sub> = max( 0, T<sub>sewer</sub> + SO + WH<sub>sewer</sub> - T<sub>overflow</sub> )''
: ''C = min ( C<sub>threshold</sub>, C<sub>height</sub> )''
 
Actual overflow is then calculated:
: ''Δw = min( 0 , C * Σ<sub>sewer</sub> , Δt * SOS )''
 
where:
* Δw = The amount of sewer overflow which takes place.
* Δt = Computational timestep.
 
* C = The amount of water that can overflow out of the sewer
* C<sub>threshold</sub> = The amount of water that could overflow, based on the sewer overflow threshold.
* C<sub>height</sub> = The amount of water that could overflow, based on the properties of the sewer overflow.
 
* Σ<sub>sewer</sub> = The surface area of the sewer.
* WH<sub>sewer</sub> = The height of the water column in the sewer.
* T<sub>sewer</sub> = The average height of the terrain where the sewer is present, relative to {{datum}}.
* T<sub>overflow</sub> = The height of the terrain at the centerpoint of the sewer overflow, relative to {{datum}}.
* SO = The {{inlink|SEWER_OVERFLOW}} attribute of the sewer overflow.
* SOS = The {{inlink|SEWER_OVERFLOW_SPEED}} attribute of the sewer overflow.
* SS = The {{inlink|SEWER_STORAGE}} attribute of the sewer area.
* SOT = The {{inlink|SEWER_OVERFLOW_THRESHOLD}}.
 
====Inlet formula====
The amount flowing in or out of inlets is calculated for the cell the inlet resides on.
 
When calculating '''inlets''', first the capacities are calculated.
 
If a T<sub>lower</sub> is defined:
: ''C<sub>inthres</sub> = max( 0 , T<sub>lower</sub> - WL<sub>surface</sub> )''
 
If a I<sub>Q</sub> is defined:
: ''C<sub>speed</sub> = Δt * I<sub>Q</sub>''
 
If a C<sub>total</sub> is defined:
: ''C<sub>incap</sub> = C<sub>used</sub> - C<sub>total</sub>''
 
After calculating the capacities, the actual water inflow is calculated.
: ''Δw = max( 0 , min( C<sub>inthres</sub> , C<sub>speed</sub> , C<sub>incap</sub> ) ) / cell''
: If any of the terms are undefined, they are not included.
 
 
When calculating '''outlets''', first the capacities are calculated.
 
If a T<sub>lower</sub> is defined:
: ''C<sub>outthres</sub> = min( 0 , T<sub>upper</sub> - WL<sub>surface</sub> )''
 
If a I<sub>Q</sub> is defined:
: ''C<sub>speed</sub> = Δt * I<sub>Q</sub>''
 
If a C<sub>total</sub> is defined:
: ''C<sub>outcap</sub> = -C<sub>total</sub> - C<sub>used</sub>''
 
After calculating the capacities, the actual water ouflow is calculated.
: ''Δw = min( 0 , max( C<sub>outthres</sub> , C<sub>speed</sub> , C<sub>outcap</sub>) ) / cell''
: If any of the terms are undefined, they are not included.
 
 
 
After the water flow (either inflow or outflow) is computed, the capacity is updated.
: ''C<sub>used</sub> (new) = C<sub>used</sub> (old) + (Δw * cell)''
 
 
Where:
 
* Δw = The amount of water flow which takes place.
* Δt = Computational timestep.
* cell = Cell size.
 
* C<sub>speed</sub> = The amount of water inflow (or outflow when negative) possible based on the inlet's {{inlink|INLET_Q}} attribute.
* C<sub>incap</sub> = The amount of water inflow possible based on the total {{inlink|INLET_CAPACITY|capacity}} of the inlet.
* C<sub>outcap</sub> = The amount of water outflow possible based on the total {{inlink|INLET_CAPACITY|capacity}} of the outlet.
* C<sub>inthres</sub> = The amount of water inflow desired based on the inlet's {{inlink|LOWER_THRESHOLD}} attribute.
* C<sub>outthres</sub> = The amount of water outflow desired based on the outlet's {{inlink|UPPER_THRESHOLD}} attribute.
 
* WL<sub>surface</sub> The water level on the surface, relative to {{datum}}.
* C<sub>total</sub> = The {{inlink|INLET_CAPACITY}} attribute of the inlet.
* I<sub>Q</sub> = The {{inlink|INLET_Q}} attribute of the inlet.
* T<sub>lower</sub> = The {{inlink|LOWER_THRESHOLD}} attribute of the inlet.
* T<sub>upper</sub> = The {{inlink|UPPER_THRESHOLD}} attribute of the inlet.
 
====Surface evaporation formula====
Surface evaporation is calculated per cell.
: ''Δw = min( WL<sub>surface</sub> , Δt * E<sub>weather</sub> * E<sub>overlay</sub> )''
 
where:
* Δw = The amount of evaporation which takes place.
* Δt = Computational timestep.
 
* W<sub>surface</sub> = The amount of water (the water column) on the surface.
* E<sub>weather</sub> = The {{inlink|lcase=1|Evaporation rate}} of the weather.
* E<sub>overlay</sub> = The {{inlink|SURFACE_WATER_EVAPORATION_FACTOR}}.
 
====Underground evaporation formula====
Underground evaporation is calculated per cell.
 
Evaporation capacities:
 
For all underground evaporation, the height of the unsaturated zone is used.
: ''H<sub>unsat</sub> = H<sub>surface</sub> - WL<sub>underground</sub>''
 
First the capacity for saturated evaporation is calculated, based on how much of the saturated area is in contact with the roots.
: ''C<sub>sat</sub> = max( 0 , min( RD , GBDM ) - H<sub>unsat</sub> ) * WSP''
 
Next the height of the unsaturated zone, and based on that the capacity for unsaturated evaporation is calculated.
: ''C<sub>unsat</sub> = max( 0 , min( RD , H<sub>unsat</sub> ) ) * ( W<sub>unsat</sub> / H<sub>unsat</sub> )''
 
Finally, the actual evaporation is calculated:
: ''Δw<sub>unsat</sub> = min( C<sub>unsat</sub> , Δt * E<sub>weather</sub> * E<sub>top</sub> )''
: ''Δw<sub>sat</sub> = min( C<sub>sat</sub> , (Δt * E<sub>weather</sub> * E<sub>top</sub>) - Δw<sub>unsat</sub> )''
: ''Δw = Δw<sub>unsat</sub> + Δw<sub>sat</sub>''
 
Where:
* Δw = The total amount of evaporation which takes place.
* Δt = Computational timestep.
 
* Δw<sub>unsat</sub> = The amount of evaporation which takes place from the unsaturated zone.
* Δw<sub>sat</sub> = The amount of evaporation which takes place from the saturated zone.
* C<sub>sat</sub> = The amount of evaporation that can take place from the saturated zone.
* C<sub>unsat</sub> = The amount of evaporation that can take place from the unsaturated zone.
* H<sub>unsat</sub> = The height (column) of the unsaturated zone.
 
* W<sub>unsat</sub> = The amount of water in the saturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
* WL<sub>underground</sub> = The groundwater level, relative to {{datum}}.
* H<sub>surface</sub> = The terrain height in the cell, relative to {{datum}}.
* RD = The {{inlink|ROOT_DEPTH_M_constructions|ROOT_DEPTH_M}} of the construction if present, the {{inlink|ROOT_DEPTH_M_surface|ROOT_DEPTH_M}} of the surface terrain otherwise.
* GBDM = The {{inlink|GROUND_BOTTOM_DISTANCE_M}} (effectively available height in the underground model).
* E<sub>weather</sub> = The {{inlink|lcase=1|Evaporation rate}} of the weather.
* E<sub>top</sub> = The {{inlink|WATER_EVAPORATION_FACTOR_constructions|WATER_EVAPORATION_FACTOR}} of the construction if present, the {{inlink|WATER_EVAPORATION_FACTOR_surface|WATER_EVAPORATION_FACTOR}} of the surface terrain otherwise.
 
===Computational structure===
{{stub|type=section}}
The formulas and concepts come together in a single computational structure which is repeated a large number of times until the total simulation duration has been reached.
 
====Order of operations====
Calculations are performed in the following order:
* Horizontal surface flow and horizontal underground flow
* Rain
* Building storage
* Sewer inflow
* Surface evaporation
* Groundwater evaporation (saturated zone)
* Groundwater evaporation (unsaturated zone)
* Underground infiltration
* Surface infiltration
* Exfiltration
 
====Calculation time impacts====
 
==Warnings==
When the water overlay is used and calculations take place, there are some problems or points of attention the calculation can run into. Where possible, the water overlay will show appropriate warnings when running into any issues.
 
===Configuration wizard warnings===
While configuring the water overlay using the {{inlink|lcase=1|Configuration wizard}}, each type of {{inlink|lcase=1|Data}} loaded in or found in the project must meet certain requirements to be functional. For example, configured {{inlink|WATER_LEVEL|water levels}} may deviate greatly from the mean terrain height in the project, or certain {{inlink|lcase=1|Hydrological constructions}} may not be shaped appropriately or intersect with required features. In these cases, the configuration wizard will show the warnings in the steps related to the specific type of data.
 
===Inaccurate terrain===
When the [[Terrain_height#Terrain_height_in_the_Tygron_Platform|project is created]], the advanced options allow for selecting a high-resolution height map to be loaded in. The default, low resolution height map can introduce artifacts in the calculation due to inaccuracy. This issue can currently only be resolved by reloading the project area.
 
===Calculation halted===
If the overlay is recalculated, but the [[Recalculate indicators|(re)calculation is halted]], the water overlay will not contain meaningful results. A warning will be displayed indicating that the calculation did not complete.
 
===Large cell size===
The water overlay performs its calculations based on a discretization of the project area. This means both that areas of water are considered a single block, and that obstacles and hydrological properties are averaged out over the extent of a cell. To best approach a realistic, continuous water flow and a realistic model of obstacles and values, it is sufficient to reduce the size of the cells the calculation uses.
 
==References==
<references>
<ref name="Kurganov1">Kurganov A, Petrova G (2007) ∙ A Second-Order Well-Balanced Positivity Preserving Central-Upwind Scheme for the Saint-Venant System ∙ p 15 ∙ found at: http://www.math.tamu.edu/~gpetrova/KPSV.pdf (last visited 2018-06-29)</ref>
 
<ref name="Horvath">Zsolt Horváth, Jürgen Waser, Rui A. P. Perdigão, Artem Konev and Günter Blöschl (2014) ∙ A two-dimensional numerical scheme of dry/wet fronts for the Saint-Venant system of shallow water equations ∙ found at: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.700.7977&rep=rep1&type=pdf ∙ http://visdom.at/media/pdf/publications/Poster.pdf ∙ (last visited 2018-06-29)</ref>
 
<ref name="Rezolla">Rezzolla  L (2011) ∙ Numerical Methods for the Solution of Partial Differential Equations ∙ found at: http://www.scirp.org/(S(lz5mqp453edsnp55rrgjct55))/reference/ReferencesPapers.aspx?ReferenceID=1886006 (last visited 2018-06-29)</ref>
 
<ref name="Kurganov2">Kurganov A, Petrova G (2007) ∙ A Second-Order Well-Balanced Positivity Preserving Central-Upwind Scheme for the Saint-Venant System ∙ found at: http://www.math.tamu.edu/~gpetrova/KPSV.pdf (last visited 2018-06-29)</ref>
 
<ref name="Bollerman">Bollermann A, Chen G, Kurganov A and Noelle S (2014) ∙ A Well-Balanced Reconstruction For Wetting/Drying Fronts ∙ found at: https://www.researchgate.net/publication/269417532_A_Well-balanced_Reconstruction_for_Wetting_Drying_Fronts (last visited 2018-06-29)</ref>
 
<ref name="Modflow">Langevin, C.D., Hughes, J.D., Banta, E.R., Niswonger, R.G., Panday, Sorab, and Provost, A.M. (2017) ∙ Documentation
for the MODFLOW 6 Groundwater Flow Model: U.S. Geological Survey Techniques and Methods, book 6, chap. A55 ∙ p 31 ∙ found at:  https://doi.org/10.3133/tm6A55 (last visited 2019-02-04)</ref>


<ref name="hydradius">Hydraulic Radius Equations Formulas Calculator ∙ found at: https://www.ajdesigner.com/phphydraulicradius/hydraulic_radius_equation_pipe.php ∙ (last visited 2019-02-11)</ref>
{{WaterOverlay output nav}}
{{Overlay nav}}


</references>
[[Category:Water Module]][[Category:Overlays with result types]]

Latest revision as of 13:40, 17 January 2023

A Water Overlay is a grid overlay for which results are calculated by the Water Module. The Basic theory of the Water Module in the Tygron Platform is an implementation of a 2D grid based shallow water model based on the 2D Saint Venant equations. The module is further enhanced with infiltration, evaporation, groundwater flow and hydraulic structures. Depending on the use case, the simulated period can be set to few seconds and up to a few months. The theory section describes in detail how calculations are performed.

To perform the calculations, the project area is divided into a grid of cells. Each cell has a specific quantity of water and specific hydrological parameters based on the data in the project. The total time which should be simulated is divided into discrete timesteps. Per timestep, each cell communicates with its adjacent cells to exchange water, based on its water level, surface height, current flow direction and other factors. Accuracy and reliability is obtained by dividing the project area and simulation time into sufficiently small cells and steps, at the cost of more computation time.

The final results of the calculation can be inspected, as well as intermediate snapshots of the hydrological situation during the simulation, known as timeframes.

Variants

A Water Module will be initialized by adding one of the following Overlays to a project. Each variant has a number of parameters tuned to best fit specific use-cases. This means that each of these overlays is based on the same theory and calculation method, however they are customized to conveniently provide insight in different aspects of the Water Module.

Overlay rainfall.png Rainfall Overlay provides insight into the water stress and impact caused by (excessive) rainfall
Overlay flooding.png Flooding Overlay provides insight into water stress and impact caused by breaches in levees or other sources causing excessive water inflow
Overlay groundwater.png Groundwater Overlay provides insight into long-term processes of water flow both on the surface and underground

Results

With a Water Overlay, a user can generate multiple results for a single water simulation. For further information about these outcomes, see also results and result types.

How-to's

Features and components

Attributes

Water Module
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Water Module
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Tutorials
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Overview button.png
Overview
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Theory button.png
Theory
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Benchmarks
Group
Output keys
Object flow output • Object height output • Object datum output a • Object datum output b • Object width output
Output other
Result type • Water balance • System visualization • Weather visualization • Debug info
Related
Building attributes • Hydraulic structures • Hydrological features •  Terrain attributes • Model attributes • Simulation data
Overlays
Categorization
Grid • Parent • Result Child • Result Parent • Result type
Default
City
Administrative
Ownership • Ownership Grid • Zipcodes • Zoning • Neighborhoods • Municipalities • Vacancy
Environmental
Heat Stress • Traffic Density • Traffic Noise • Traffic NO2 • Livability
Water
Rainfall • Flooding • Groundwater • Subsidence • Watershed
Grid Calculation
Average • Combo • Distance • Sight Distance • Travel Distance • Inference • Iteration
Geo Data
GeoTIFF • WCS • WMS • Image • Area • Attribute • Function
Topography
Satellite • Digital Surface Model • Digital Terrain Model • Underground • Source
Network
Network Distance • Network Overview • Network Ownership
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