The Effect of GIS Database Grid Size on Hydrologic Simulation Results

Abstract

The use of geographic information systems (GIS) for assessing the hydrologic effects of management is increasing. In the near future most of our spatial or "mapped" information will come from GIS. The direct linkage of hydrologic simulation models to GIS should make the assessment process more efficient and powerful, allowing managers to quickly evaluate different landscape designs. This study investigates the effect the resolution of GIS databases have on hydrological simulation results from an urban watershed. The hydrologic model used in the study was the Soil Conservation Service Curve Number Model which computes the volume of runoff from rainfall events. A GIS database was created for High School Wash, a urban watershed in Tucson, Arizona. Fifteen rainfall-runoff events were used to test the simulation results. Five different grid sizes, ranging from 25x25 square feet to 300x300 square feet were evaluated. The results indicate that the higher the resolution the better the simulation results. The average ratio of simulated over observed runoff volumes ranged from 0.98 for the 25x25 square feet case to 0.43 for the 300x300 square feet case.