Elevation (Water Overlay)

The elevation model defines the height of the terrain on and in which the hydrology is modeled. Elevation includes the relief on the surface of dry land, but also the height of the stream beds of water bodies.

By default the elevation 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 elevation model may be insufficient. For these situations it's possible to load in a(n additional) GeoTIFF defining elevations, load in a GeoJSON file with water depths, or manually modify the elevation model.

In addition to the elevation model, the height of buildings is also taken into account. Breaches are also embedded into the resulting Digital Surface Model the Water Module uses for its calculations.

During a session, a number of actions can directly affect the terrain height. Actions such as the creation of levees, or the creation of open water, both affect the topography. Placing or removing buildings also affects the terrain height, in terms of where water can flow.

Alternatively, the elevation can be supplied by an other grid overlay, and configured using the Terrain elevation prequel. This can be useful in case you do not want to change the elevation model of your project. However, the prequel overlay must be calculated in advance and must be set to inactive in order for it to be used by the water overlay.

Notes

Reconstruction: No matter which option is configured for the elevation of a water overlay, it still will be reconstructed according to the requirements of the algorithm. Building heights (to some extend) are also included in this reconstruction.

1D linear piecewise reconstruction.Source: Kurganov and Petrova (2007)^[1]
2D linear piecewise reconstruction. Source: Horváth et al. (2014)^[2]

How-to's

References

↑ 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)
↑ 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)