Basic water model use case (Water Overlay)

For all effective uses of any variant of the water overlay, you must first set up a basic water model. This water model includes both your hydrological system, as well as the parameters used to perform any calculations. The behavior of any water, whether it's pre-existing, expected inflow, or due to natural event or calamity, is affected by the presence of features which can capture or steer water in other directions. The more real-world hydrological features and hydrological constructions are loaded in, the more accurately the water flow can be simulated.

Requirements

Before getting started, there are a few requirements which must be met first.

Determine what overlay you need

The first step is to determine which variant of the available Water Overlays best suits your needs. This depends largely on what primary calculation you wish to perform.

Create your project

The Water Overlay will be able to calculate most accurately if your project has been created with the following criteria in mind:

Your project has been loaded in with a high-resolution DEM. This can be configured during the new project wizard.
Your project is large enough to account for edge effects.

Additionally, consider the following:

When creating a new project in the new project wizard, consider using the 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 IMWA dataset for hydrological structures. Although this dataset is not complete, some information about constructions which serve as culverts or 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.

Prepare your data

The next step is preparing your data. Note that this step can be skipped if you do not have any data applicable to your project area.

The following data should be prepared as GeoJSONs. Click on any of the data types for more information.

Data	Description	Alternative/default
Water areas	Water areas set the water level of all open water within their boundaries.	In the configuration wizard, it is possible to generate a single water area for the entire project area.
Weirs	Weirs allow for water to flow between bodies of water, with the amount of water increasing as the water level increases.	There are no default weirs in a project.
Culverts	Culverts allow for water to flow between bodies of water, at a maximum rate determined by their size.	For project areas inside the Netherlands culverts may be imported automatically as part of the project creation process.
Pumps	Pumps move water from locations with lower towards higher water levels.	There are no default pumps in a project.
Inlets and outlets	Inlets are point locations where water can be added to the water system. Outlets are point locations where water can leave the water system.	There are no default inlets or outlets in a project.
Sewer areas	Sewer areas serve as controlled storage of water flowing on top of constructions located inside these sewer areas.	In the configuration wizard it is possible to generate sewer areas based on the neighborhoods in the project area.
Sewer overflows	Sewer overflows are a way for water to leave the sewers and flow back into the surface water system.	There are no default sewer overflows in a project, but these can be generated in the presence of both water level areas and sewers (either generated or imported).

Note that it is preferable to use the Tygron Platform's naming convention for attributes (such as CULVERT_THRESHOLD) when preparing GeoJSON files, to prevent multiple structures or features from having the same keys and conflicting with each other in the Water Overlay's setup.

The following data should be prepared as GeoTiffs. Click on any data type for more information.

Data	Description	Alternative/default
Groundwater	Only relevant for groundwater overlays. Will set the height of the saturated zone's water in the underground.	The groundwater overlay will assume the entire ground is saturated. Other overlays will not use the underground water model.

Verify your data

After preparing the data, it is important to undertake a few additional checks to make sure the model functions as much as expected as possible. These checks can best be performed directly after preparing the data.

Missing attributes: When your datasets have been created, take a moment to check how many features in your data have either missing attributes or placeholder values for attributes. Make sure that for each data type, you are aware of how the Tygron Platform will react when data is missing, or set to an unrealistic (or realistic) placeholder value.

Pumps and inlets/outlets: If you have pumps in your model, divide them into two groups: pumps and inlets. Pumps are the structures within your project area, which move water from one location in your hydrological model to another location in your hydrological model. Inlets (and outlets) are pumps at the edge of the hydrological model (in a topological sense), where water appears in your hydrological model, or is removed from your hydrological model. They form the "edges".

Construction shapes: Make sure that all constructions which should be line-shaped are actually line-shaped. Constructions such as weirs are commonly stored as points, while the Tygron Platform requires them to be lines, so that it can be determined exactly where the water flows to and from.

Constructions in unblocked waterways (can also be checked after loading in)

Also make sure that when a line-shaped construction exists in a waterway, the water which is ment to flow via the construction has no alternative way of flowing past the construction. In practice, this often means blocking the waterway in which the construction lies, in the location of the construction, such that flowing through the construction is the only way water can flow past the obstruction. Consider the following options:

You can manually create an obstruction in the DEM by adjusting the elevation model
You can draw a breach in the waterway with a BREACH_HEIGHT set to the height of the surrounding land.

Construction placement in waterways (can also be checked after loading in): Make sure all hydrological constructions are placed such that their relevant centers are well in the waterways they apply to. If the endpoint of a culvert or other line-based construction is on the edge or slope of a waterway, exact topography may cause the construction to be less well connected to the actual water, requiring water to rise to a higher level before it is affected by the construction. In general, topology matters more than exact topography, so moving construction endpoints should not cause considerable deviations from realism.

Overlapping constructions of the same type (can also be checked after loading in)

If there are multiple constructions in the same location, such as parallel culverts, make sure their endpoints do not overlap/end up in the same cell. If such culverts exist, consider the following options:

Move the culverts, so that their endpoints are no longer in the same cell
Merge the culverts, by creating a single one with appropriate attributes to mimic the combined function of the two separate culverts.

Overlapping constructions of different types (can also be checked after loading in)

If there are multiple constructions in the same location, such as a culvert with a weir directly on the end, they should be adjusted as well to prevent multiple endpoints ending up in the same cell. In these situations, consider the following options:

Move the constructions, such that water first passes through the first construction into an intermediate water basin, and then flows on through the other construction.
Merge the constructions, such that only as single construction exists but which constricts/facilitates the waterflow mimicking/approximating the combined effect of the two separate constructions.

Notes

Take note of the following while configuring the basic water model:

Calculations based on default data.: The rainfall and groundwater variants of the Water Overlay already form basic water models when they are added to a project without further configuration. However, all data and configurations explicitly performed will enhance the model greatly.

Pre-existing constructions: If you have prepared your own dataset of hydrological structures, make sure to delete any pre-existing structures of the same type before loading in your dataset. You can perform this action in the wizard. Otherwise, there may be constructions in locations where there shouldn't be.

Further corrections: After the calculation completes you may still see some odd results. This may indicate there might be an issue somewhere in the model still. Depending on the severity of the anomaly, consider investigating and correcting the cause of the issue, and rerun the calculation.

Creating the basic water model

How to create a basic water model:

Add the overlay, as described here: How to add and remove an Overlay.
Open the overlay's wizard, and perform each step if possible. When in doubt on what to configure exactly, a step can be skipped.

After creating a basic water model, a number of additional configurations may be relevant for your use-case:

Limit rain: If your use case involves rain and water level areas, it is possible and recommended to limit the rain to regions which are covered by water level areas. This can be done in the step of the configuration wizard related to simulation time and weather effects.

Maximum height of water bottom: If your use case involves detailed flow through waterways, and no detailed waterway information is available, it is highly recommended to set the MAX_WATER_BOTTOM_M attribute of the Water Overlay to a value such that all waterways are deep enough for water to flow through.

Ground water: If groundwater is not an important factor in your calculation, and you are using a groundwater overlay variant (or if groundwater is important and you are not using a groundwater overlay variant), make sure the GROUND_WATER attribute of the Water Overlay is used appropriately.

Cell size: The grid cell size should be set to a maximum value approximately equal to the width of a small waterway. Generally, a size in the range of 1-4 meters is proper. Note that a smaller grid size will lead to a longer calculation time.