In this chapter we'll describe the requirements for a distributed rainfall-runoff model to meet our needs:
Essential
Processes in the unsaturated zone
A proper description of the unsaturated zone is crucial in The Netherlands. As a result of evapotranspiration, the groundwater table may drop, causing the capillary rise and therefore the evapotranspiration to reduce. This means that the chosen model will have to have sufficiently flexible descriptions of soil types, convering pF-curves and layering.
Paved areas & sewage handling
Since The Netherlands is densely covered with paved surfaces, it plays a huge role in Rainfall-Runoff processes. The chosen Distributed Rainfall-Runoff model will therefore have to support rainfall on paved surfaces and preferrably also inflow into sewers and CSO's (Combined Sewer Overflows) and discharge towards Waste Water Treatment Plants.
Support of areas with controlled water levels
Since we're dealing with regions in The Netherlands, we'll encounter various areas where water levels are being controlled. This controlling is done through (adjustable) weirs, orifices or pumps. Probably the best way to deal with this in a model schematization would be to simulate these phenomena in 1D-hydrodynamics. However, the mere existence of such areas could have consequences for a Rainfall-Runoff schematization.
Important
Easy import of GIS-Files
Since we have GIS-files available for Soil Type, Landuse and Levels, it will be greatly appreciated if the simulation model is capable of importing these files and easily convert them into input parameter maps.
Less important
Spatial Rainfall vs Rainfall Gauge measurements
Building a distributed Rainfall-Runoff model also requires rainfall to be applied spatially. Sometimes however, rainfall is only available on point locations (Gauges). In that case, it will still need to be applied spatially, e.g. through Thiessen polygons. Additional tools by which this conversion can be carried out count as beneficial.
Overland flow
In The Netherlands, surface runoff is not a necessity as in most of the cases rainfall will be able to infiltrate.
Snow melt
Snow melt is rather rare and therefore not required for Rainfall-Runoff modeling in The Netherlands.
