Exercise: A spatial model of a catchment
Note 1: this exercise is designed to be used with libral and Gtk2::Ex::Geo tools. Note 2: the tools have to be currently the CVS versions.
Required data: a land cover raster and a DEM. Results: the hydrological structure (lakes, subcatchments, stream sections, and their topological structure) of a catchment as a vector layer.
Students should follow the outline below and do the same procedure for a catchment of their own selection. Each step may involve explanations by the teacher.
Steps of the exercise:
- open land cover raster
- zoom to probable catchment area (rather too large than too small!)
- clip a piece of the land cover, name it "lc" (*)
- make a 'lakes' raster by saying $lakes = $lc == 43 (or whatever the land cover code for water is) [TODO: add instructions for removing streams from the lakes raster]
- give unique id's for all lakes: $lakes->number_areas
- open a DEM raster
- clip a similar piece(***) of the dem, name it 'dem'
- compute pitless flow direction grid: say(**) $fdg = $dem->filldepressions (*4)
- fix the FDG so that each lake has one and only one outlet, say: $fdg->kill_extra_outlets($lakes)
- compute upslope area grid, say: $uag = $fdg->uag
- search for the catchment (lake) outlet cell and compute a catchment raster: $c = $fdg->catchment(Fatal error: The format of the coordinate could not be determined. Parsing failed.