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| ==What is the Inundation overlay==
| | [[File:FloodingOverlay2.png|right|thumb|200px|Flooding overlay]] |
| The inundation is developed for the computation of surface (water) flow in a wide range of applications. These applications include large scale inundations due to dike breaches and inundations at the bottom of hill-slopes. Therefore the commonly applied 2D Saint Venant Equations are implemented on a highly parallel applicable explicit numerical scheme suitable for Tygron GPU clusters. | | The Flooding Overlay is a variant of the [[Water Overlay]], which in turn is a [[Grid overlay|grid overlay]]. Water overlays are connected to the [[Water Module]], a complex hydrological calculation module within the {{software}}. |
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| ==Adding and removing==
| | The Flooding Overlay calculates and visualizes the movement of water over land, due to a [[Breach_(Water_Overlay)|breach]] or other [[Inlet_(Water_Overlay)|inflow]] of water in the project area. |
| To add an inundation overlay go to the Overlays menu in the GEO DATA ribbon and select Add Inundation. To remove the overlay, press Remove below the overlays list.
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| [[File:Rainfall_overlay_01.PNG|600px]] [[File:Rainfall_overlay_02.PNG|600px]] | | In order to get more familiar with the different components of the Flooding Overlay check out Quadrant 1 of the [[Testbed_water_module|Water Module Testbed]]. This Testbed is available to you as a project in the {{software}}. |
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| ==Result types== | | ==Flooding overlay results== |
| The rainfall overlay is a [[grid overlay]] showing results of heavy rainfall on the surface (flooding), sub-surface (groundwater), open water and sewer system. The following results are produced: | | The Flooding Overlay is a Water Overlay that is connected to the Water Module. This Water Module performs two dimensional grid based water simulations for a large set of input data and parameters, configured mostly through a related [[Water_Overlay_Wizard|Water Overlay Wizard]]. When a simulation finishes, the module stores the result in the Flooding overlay based on the selected result type. Only one result type can be stored per Flooding overlay. |
| {| class="wikitable"
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| ! Result type
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| ! Unit
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| ! Description
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| |-
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| |BASE_GROUNDWATER_DISTANCE
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| |m (below surface)
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| |Initial groundwater level relative to the surface level (NL: ontwateringsdiepte).
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| |-
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| |BASE_TYPES
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| |nominal value
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| |Division of gridcells in water, land or sewer areas that are connected to the sewer.
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| |-f
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| |EVAPORATED
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| |m (mm)¹
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| |Total evaporation over the simulation period
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| |-
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| |IMPACTED_BUILDINGS
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| |nominal value
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| |Constructions impacted by flood: the value from the function value indicator is assigned to a building if the water depth at a grid-cell surrounding the building exceeds the overlay attribute value IMPACT_FLOOD_TRESHOLD_M
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| |-
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| |SEWER_LAST_VALUE
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| |m (mm)¹
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| |The amount of water in the sewer storage at the end of simulation
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| |-
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| |SEWER_MAX_VALUE
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| |m (mm)¹
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| |Maximum amount of water in the sewer storage during the simulation
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| |-
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| |SURFACE_DURATION
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| |s (min)¹
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| |The amount of time the water depth in a cell exceeds the value set in the overlay attribute value SHOW_DURATION_FLOOD_LEVEL_M
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| |-
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| |SURFACE_FLOW
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| |m3/m2
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| |Total volume of water passed a grid-cell, scaled by the cell surface (grid cell-size^2)
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| |-
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| |SURFACE_LAST_VALUE
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| |m (min)¹
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| |Water depth at the end of simulation | |
| |-
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| |SURFACE_MAX_VALUE
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| |m (min)¹
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| |Maximum water depth during the simulation
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| |-
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| |UNDERGROUND_FLOW
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| |m³/m²
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| |Totall infiltration amount from the surface to groundwater
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| |-
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| |UNDERGROUND_LAST_VALUE
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| |m (mm)
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| |The amount by which the groundwater table has risen above the initial groundwater level at the end of simulation
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| |-
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| |UNDERGROUND_MAX_VALUE
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| |m (mm)
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| |The maximum amount by which the groundwater table has risen above the initial groundwater during the simulation
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| |-
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| |WATER_STRESS
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| |m (mm)
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| |The Maximum water depth during the simulation. At water cells only a water depth is shown if the depth exceeds the overlay attribute value ALLOWED_WATER_INCREASE_M
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| |}
| | The Water Module however, is not restricted to generating only one type of result. Instead it can produce multiple unique result types for one single simulation. |
| | Fortunately it is possible to add additional result type overlays which relate to a particular Rainfall overlay. These are known as [[Result Child Overlay]]s. Again, each child overlay only stores one particular result type. |
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| ¹ the units between () are as displayed in the 3D client. If exported to GTiff the SI-convention is used: meters (m) and seconds (s).
| | Apart from multiple result types, the Flooding overlay can also store result data of multiple, intermediate simulation results, instead of just a single end result. These intermediate simulation results are known as [[Timeframes_(Water_Overlay)|timeframes]]. |
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| ==Inundation Model==
| | For the full list of result types, see [[Result type (Water Overlay)#List of Result Types|List of Result Types]]. |
| | For other results, which are not overlay results, but still related to the simulation of a Flooding overlay, see [[Results (Water Overlay)|water overlay results]] |
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| ===2D Saint Venant equations=== | | ==Module== |
| The 2D Saint Venant equations describe the conservation of mass in a gridcell and the conservation of momentum in both x and y, direction:
| | A Flooding Overlay can be configured by opening the Flooding Overlay Wizard. More in-depth information can be found under each of the categories below. |
| | {{Water Module buttons}} |
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| [[File:Inundation_overlay_01.PNG]]
| | {{WaterOverlay output nav}} |
| | | {{Overlay nav}} |
| The Saint Venant equations describe the following processes:
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| * friction
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| * bed slope
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| * water pressure
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| * convection (changes in bathemetry over space)
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| * inertia (increase or decrease of velocity over time)
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| ===Numerical scheme===
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| 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). The Tygron Engine Inundation module relies on the scheme described in Kurganov and Petrova (2007). The reconstruction method is taken from Bolderman et all (2014) and ensures numerical stability at the wetting and drying front of a flood wave.
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| A clear explanation on the numerical approach can be found at Horváth et al. (2014), but in general it follows these steps:
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| # The elevation value of the cell (B in figures below) is equal to the elevation value at the centre of the cell. At the same time, it is equal to the average value of the elevation values at the cell interface mitpoints
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| # The slopes of the conserved variables (U in figures below), continuity and momentum in x and y direction, are reconstructed
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| # Values of conserved variables at the cell interface midpoints are compared with the left-sided and right sided values at cell centres
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| # At partially dry cells, the slope is modified to both avoid negative depths and numerical instability
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| # (Numerical) fluxes are computed at each cell interface to determine the values of the conserved variable at the cell centres for the next time-step
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| [[File:Inundation overlay 04 HWP(1).PNG|450px]][[File:Inundation overlay 04 HWP(2).PNG|450px]]
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| The numerical scheme as been tested on the [[Inundation(Benchmarks)|benchmark]] of the UK Environmental Agency
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| ===Computation time step===
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| An adaptive timestep is implemented according to Kurganov and Petrova (2007). At every timestep, the courant-number is kept smaller than 0.25 for every active computation cell:
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| [[File:Inundation_overlay_03.PNG|400px]]
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| 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:
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| * the timestep is choosen so that all computation cells follow one of the following criteria
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| * if a cells waterdepth is below the flooding threshold, 5 * 10&sup-3; (m) there is no flow assumed between that cell and it neigboring cell
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| * if the cells waterdepth is above above the flooding threshold, the maximum timestep is assumed to be 100 * the waterdepth at the cell
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| * if the waterdepth increases, the timestep is assumed to be not larger than the formula above
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| If he numerical flux decreases, the larger timesteps are allowed than set by Kurganov and Petrova, depending on the calculation preference set in the general tab of the inundation overlay (speed, average or accuracy).
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| ===Calculation Preferences (General Tab)===
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| ===Overlay Keys===
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| ==References==
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| # 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)
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| # Environmetal Agency (2013). Benchmarking the latest generation of 2D hydraulic modelling packages ∙ report Report – SC120002 ∙ found at: https://consult.environment-agency.gov.uk/engagement/bostonbarriertwao/results/appendix-6---neelz--s.---pender--g.--2013--benchmarking-the-latest-generation-of-2d-hydraulic-modelling-packages.-bristol_environment-agency.pdf (last visited 2018-08-03)
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| # Kurganov A, Petrova G (2007) ∙ A Second-Order Well-Balanced Positivy Preserving Central-Upwind Scheme for the Saint-Venant System ∙ found at: http://www.math.tamu.edu/~gpetrova/KPSV.pdf (last visited 2018-06-29)
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| # 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)
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| # 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)
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The Flooding Overlay is a variant of the Water Overlay, which in turn is a grid overlay. Water overlays are connected to the Water Module, a complex hydrological calculation module within the Tygron Platform.
The Flooding Overlay calculates and visualizes the movement of water over land, due to a breach or other inflow of water in the project area.
In order to get more familiar with the different components of the Flooding Overlay check out Quadrant 1 of the Water Module Testbed. This Testbed is available to you as a project in the Tygron Platform.
Flooding overlay results
The Flooding Overlay is a Water Overlay that is connected to the Water Module. This Water Module performs two dimensional grid based water simulations for a large set of input data and parameters, configured mostly through a related Water Overlay Wizard. When a simulation finishes, the module stores the result in the Flooding overlay based on the selected result type. Only one result type can be stored per Flooding overlay.
The Water Module however, is not restricted to generating only one type of result. Instead it can produce multiple unique result types for one single simulation.
Fortunately it is possible to add additional result type overlays which relate to a particular Rainfall overlay. These are known as Result Child Overlays. Again, each child overlay only stores one particular result type.
Apart from multiple result types, the Flooding overlay can also store result data of multiple, intermediate simulation results, instead of just a single end result. These intermediate simulation results are known as timeframes.
For the full list of result types, see List of Result Types.
For other results, which are not overlay results, but still related to the simulation of a Flooding overlay, see water overlay results
Module
A Flooding Overlay can be configured by opening the Flooding Overlay Wizard. More in-depth information can be found under each of the categories below.
