WATERSHED-SCALE MODELING OF CRITICAL SOURCE AREAS OF RUNOFF GENERATION ANDPHOSPHORUS TRANSPORT

摘要

According to variable source area (VSA) concept, only a small part of a watershed directly contributes to stormflow during rainfall events. Numerous studies have established this concept at field and hillslope scales, though watershed-scale experimental studies are limited. However, identification of storm flow source areas at a watershed scale is morecritical as a combination of potential runoff generation and high phosphorus (P) available areas can lead to polluted waterbodies. Based on the knowledge gained at hillslope scale, watershed-scale prediction of runoff generation areas caneffectively be carried out through modeling. Earlier data from hillslope scale studies within two headwater watersheds inPennsylvania have shown that near-stream areas and soils with restricting layers have higher potentials of runoff generationand P transport in runoff. These studies showed that these potential source areas are characterized by relatively higher soilmoisture conditions, which could have resulted from shallow water table and/or poor soil drainage conditions. Based of theseresults, we evaluated the potential of a distributed parameter, grid based model, the Soil Moisture Distribution and Routing(SMDR) Model, in simulating runoff generation and P transport at a watershed scale. SMDR simulates trends of moisturecontent changes in a watershed between rainfall events, and the areas potential of generating runoff based on soil moisturestorage availability. Successful model simulation would allow transfer of hillslope scale results to watershed scale, andselection and implementation of better P management strategies for improved water quality.