Country Specific – Switzerland

The elevation model for Switzerland in SCALGO Live is based on swissALTI3D from Bundesamt für Landestopografie swisstopo.

The analyses are done in 0.5 m resolution for the whole country in LV95. The heights are in LN02. Workspaces constructed from this model also have a resolution of 0.5 m. We strive to keep the model up to date with the latest sources.

In order to use an elevation model for hydrological analysis of surface water, such as watershed and flow accumulation computations, three conditions need to be met:

• The upstream area of any river should be covered by the elevation model.
• Structures on top of the terrain should only be present in case they actually block water from flowing under or through them.
• Structures transferring water below the terrain surface should be taken into account.

Below, we discuss how we process the model to fulfil these conditions as well as possible.

Extensions

In order to cover the upstream areas of all rivers crossing the country, we have extended the model in the following areas:

• France, we use data from RGE ALTI®.
• Austria, we use the 10 m Digitales Geländemodell Österreich.
• Germany and Italy, we included data from the 30-meter EU-DEM data set, which in turn is based on SRTM and ASTER GDEM data.

Buildings

Buildings are not included in the terrain models, since they represent the "bare earth" elevations. When computing water flow paths, more realistic results are generally obtained when the elevation model does include buildings so water can be simulated to flow around them. In SCALGO Live, we accomplish this by adding buildings back into the model using a data set of building footprints, where we raise all grid cells covered by a building to a height 10 meters above the highest terrain point within the building footprint. This model is called "Terrain/Buildings" and is the basis for all nationwide hydrological computations.

The building footprints are taken from the swissTLM3D dataset.

Bridges, underpasses and hydrological corrections

Major bridges have generally been removed from the models, but for many smaller bridges and underpasses additional hydrological corrections that allow water to flow through such structures are necessary. SCALGO Live Switzerland includes a nationwide hydrological correction set based primarily on the swissTLM3D. Corrections have been generated at road underpasses and intersections of roads, railroads and buildings with rivers. Each correction thus follows a line in the river network or a road underpass, with end points adjusted to match the elevation model as well as possible.

The set of corrections is available under the Hydrological Corrections category in the Library.

The national analyses use these corrections, and workspaces created using the predefined "Flash Flood Map" button also include them by default. If you create a workspace through any other means than the predefined button (e.g. if you upload your own model), you can include corrections in that workspace through the workspace Actions tab by clicking Import corrections; they will not be included automatically.