Unit 16 - Flooding simulation

Beside DEM (see Unit 15 - Data reprojection) also river streams are required. Such data can be downloaded from OSM database similarly as done in Unit 02 - First steps in the case of Jena city region. See Map Features for details.

Note

Rivers and lakes has been downloaded from OSM using Overpass API.

[bbox:50.85374080,11.50084754,50.98991003,11.67463202];
(
way["waterway"];
);
/*added by auto repair*/
(._;>;);
/*end of auto repair*/
out;

Exported GeoJSON file has been converted to GeoPackage by GDAL ogr2ogr utility:

ogr2ogr -f GPKG -dialect SQLite \
-sql "select * from export where st_geometrytype(geometry) IN ('LINESTRING', 'MULTILINESTRING')" \
-nln jena_rivers jena_rivers.gpkg export.geojson

For simplification pre-processed river streams are included in sample dataset as osm/jena-rivers.gpkg file.

../_images/jena-rivers.png

Fig. 88 DEM, Jena boundary and rivers provided by OSM.

Flooding can be easily simulated by r.lake module which fills a lake to a target water level from a given start point or seed raster. The resulting raster map contains cells with values representing lake depth (NULL for all other cells beyond the lake).

The r.lake requires seeds coordinates and water level to be defined. The coordinates can be set also interactively as Fig. 89 shows.

../_images/r-lake-coords.png

Fig. 89 Set seed coordinates interactively from map display.

Height of seed point can be determined by querying DEM map layer grass-info Query raster/vector map(s) from Map Display toolbar (see Fig. 90) or directly using r.what module:

r.what map=dem coordinates=681734,5644423
../_images/goto-coordinates.png

Fig. 90 Select Go to coordinates.

../_images/dem-what.png

Fig. 91 Query DEM layer for an elevation value.

Note

Before running r.lake let’s start organizing our work. Till now we used PERMANENT mapsets only. There is input data like DEM, Jena city region, cloud mask vector map, Sentinel bands, results of NDVI computation and so on. Data organization can be improved by using multiple mapsets. Let’s create a new mapset flooding in the current location jena-region. New mapset from Data tab or by g.mapset module.

../_images/create_mapset.png

Fig. 92 Create a new mapset in Data tab.

Before starting computation the computation region have to be set based on dem raster map.

g.region raster=dem

r.lake elevation=dem water_level=146.4 lake=lake coordinates=681734,5644423
../_images/r-lake-150.png

Fig. 93 Flooding simulation on water level 150m, OSM WMS as basemap.

../_images/r-lake-150-3d.png

Fig. 94 Flooding similation in 3D view.