Assessment of a Rapid Approach for Estimating Catchment Areas for Surface Drainage Lines U.S. Geological Survey Center of Excellence for Geospatial Information Science 1400 Independence Road, Rolla Missouri, 65401

The catchment, or catchment area, is the area associated with a segment of a drainage network. Surface runoff in a catchment flows into the associated network segment. Catchment area is commonly used for estimating watershed parameters, such as upstream drainage area, flood frequency, or surface-water flow. Hydrologic analyses require relatively accurate catchment area estimates to furnish substantive conclusions. Conversely, alternative uses for catchment area may not require such precise estimates. Estimation of catchment areas using Thiessen polygons around evenly spaced points along network features is a rapid and computationally simple approach when compared to the alternative of deriving catchments from an elevation model; however, Thiessen-estimated catchments do not precisely follow the ridgelines of surface models and only provide approximate subdivisions of the watershed. This paper assesses the accuracy of Thiessen-derived catchment area estimates for several drainage networks having various drainage densities and landscape types. Thiessen-derived catchment area estimates are compared to those derived from surface-elevation models.