WATERSHED CONFIGURATION AND GEOGRAPHIC INFORMATION-SYSTEM PARAMETERIZATION FOR SPUR MODEL HYDROLOGIC SIMULATIONS

A grid cell geographic information system (GIS) is used to parameterize SPUR, a quasi-physically based surface runoff model in which a watershed is configured as a set of stream segments and contributing areas. GIS analysis techniques produce various watershed configurations by progressive simplification of a stream network delineated from digital elevation models (DEM). We used three watershed configurations: greater-than-or-equal-to 2nd, greater-than-or-equal-to 4th, and greater-than-or-equal-to 13th Shreve order networks, where the watershed contains 28, 15, and 1 channel segments with 66, 37, and 3 contributing areas, respectively. Watershed configuration controls simulated daily and monthly sums of runoff volumes. For the climatic and topographic setting in southeastern Arizona the greater-than-or-equal-to 4th order configuration of the stream network and contributing areas produces results that are typically as good as the greater-than-or-equal-to 2nd order network. However both are consistently better than the greater-than-or-equal-to 13th order configuration. Due to the degree of parameterization in SPUR, model simulations cannot be significantly improved by increasing watershed configuration beyond the greater-than-or-equal-to 4th order network. However, a range of Soil Conservation Service curve numbers derived from rainfall/runoff data can affect model simulations. Higher curve numbers yield better results for the greater-than-or-equal-to 2nd order network while lower curve numbers yield better results for the greater-than-or-equal-to 4th order network.