ESTIMATING WATERSHED AREA FOR PLAYAS IN THE SOUTHERN HIGH PLAINS, USA

Hydrologic budgets for depressional wetlands required estimates of runoff from watersheds. In the Southern High Plains, where there is little elevation relief. ground surveys Provide accurate watershed estimates but are time-consuming and costly. Estimates can be derived at lower cost from DEMs (Digital Elevation Models) and topographical maps. but data resolution and interpretation introduces errors. Other computational methods provide alternatives for estimating watershed area. Two computational methods based oil longitudinal distances and elevations are described: minimal distance method and weighted minimal distance method. Twenty playas were ground Surveyed to obtain baseline estimates of watershed area. Watershed areas for these 20 playas were also estimated using topographic maps, DEMs. and the two computational methods. The DEM method Was not subsequently included in analyses because they did not have sufficient resolution. There were small differences in bias among the other methods. However, comparing the three alternative methods to ground survey estimates revealed that errors for the minimal distance method were larger than topographic map and weighted minimal distance methods. For computational accuracy, topographic map and weighted minimal distance methods are preferred. For modeling and computational ease, the weighted minimal distance method provides a simple alternative for calculating watershed area of playas.