EFFICACY OF ARC/INFO GIS APPLICATION TO HYDROLOGIC MODELING

A hypothetical water shed was constructed to test the efficacy of using the ARC/INFO geographic information system to provide spatially related input for the U.S. Army Corps of Engineers HEC-1 hydrologic model. The ARC/INFO system performed the tedious and time-consuming tasks of spatial averaging (basin areas, average runoff curve numbers. etc.) quite well. Difficulties, however, were encountered in using the TIN (triangulated irregular network) module to accurately assess average rainfall intensities. The inaccuracies associated with the computation of average basin rainfall intensities were quantified by using a defined rainfall pattern imposed upon a simple geometric shape (equilateral triangle) and were found to be directly related to the number of prescribed contouring intervals. The highest density of contouring intervals (0.010 nm) resulted in only a 0.55% overestimation. The number and location of rain gages relative to watershed boundaries imparted a significant error (approximately +/- 10%) to average rainfall estimation.