Abstract:
The GIS-based distributed
hydrological model, WetSpa, whose flow
routing method is described in this paper is
suitable for flood prediction and watershed
management on catchment scale. The model
predicts outflow hydrographs at the basin
outlet or at any converging point in the
watershed, and it does so at a user-specified
time step. The model is physically based,
spatially distributed and timecontinuous.
This paper focuses on the GISbased
diffusive transport approach for the
determination of rainfall runoff response
and flood routing through a catchment. The
watershed is represented as a grid cell mesh,
and routing of runoff from each cell to the
basin outlet is accomplished using the first
passage time response function based on the
mean and variance of the flow time
distribution, which is derived from the
advection–dispersion transport equation.The
flow velocity is location dependent and
calculated in each cell by the Manning
equation based on the local slope, roughness
coefficient and hydraulic radius. The
hydraulic radius is determined according to
the geophysical properties of the catchment
and the flood frequency. The total direct
runoff at the basin outlet is obtained by
superimposing all contributions from every
grid cell. The model is tested on the Ziarat
_Gorgan watershed with 4years of observed
hourly rainfall and discharge data, and the
results are in excellent agreement with the
measured hydrograph at the basin outlet.
