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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #147121
Title: WATERSHED-SCALE MODELING OF CRITICAL SOURCE AREAS OF RUNOFF GENERATION AND PHOSPHORUS TRANSPORT

Author
item SRINIVASAS, M - PENN STATE UNIV.
item GERARD-MARCHANT, PIERRE - CORNELL UNIV.
item Gburek, William
item STEENHUIS, T - CORNELL UNIV.

Submitted to: American Water Resources Association Summer Specialty Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/12/2003
Publication Date: 5/14/2003
Citation: Srinivasas, M.S., Gerard-Marchant, P., Gburek, W.J., Steenhuis, T.S. 2003. Watershed-scale modeling of critical source areas of runoff generation and phosphorus transport. American Water Resources Association Summer Specialty Conference. p. 1-4.

Interpretive Summary: Hydrologic studies have shown that only certain areas of a watershed contribute surface runoff to streamflow during rainfall events. Several methods have been posed to identify and map these contributing areas since their identification is critical for managing nutrient loss from the watershed. However, very limited field data are available by which to quantify the occurrence and dynamics of these critical source areas. Watershed-scale data collection is severely limited by spatial scale issues. Consequently, computer models based on the known physical processes of runoff generation offer simple approaches to address spatial scale issues. A computer model, Soil Moisture Distribution and Routing (SMDR), was used to simulate the critical source areas within a 39.5-ha watershed in east-central Pennsylvania. Using spatial data (soils, topography, slope) and temporal data (hydrology and weather) from 1996 to 2001, the model identified areas adjacent to the stream as source areas of streamflow. The areas identified correspond to soils with restricting layers that limit infiltration. The model results are very much in agreement with the observations from a runoff generation study conducted within this watershed. The model was able to simulate the variable participation of watershed in runoff generation, which is the crux of the variable-source-area hydrology. Surface transport of phosphorus and other pollutant have been shown to be highly dependent on their spatial occurrence within a watershed. Thus, the model's ability to describe areas of surface runoff generation areas is critical for P transport. Additional refinement of the SMDR model is essential to account for shallow soils, which, currently, the model identifies as critical runoff areas.

Technical Abstract: According to the variable-source-area (VSA) concept, only a small part of a watershed directly contributes to storm flow 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 critical, as a combination of potential runoff generation and high phosphorus (P) available areas can lead to polluted water bodies. Based on the knowledge gained at a hillslope scale, watershed-scale prediction of runoff generation areas can effectively be carried out through modeling. Earlier data from hillslope scale studies within two headwater watersheds in Pennsylvania have shown that near-stream areas and soils with restricting layers have higher potentials of runoff generation and P transport in runoff. These studies showed that these potential source areas are characterized by relatively higher soil moisture conditions, which could have resulted from shallow water table and/or poor soil drainage conditions. Based on these results, 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 moisture content changes in a watershed between rainfall events, and the potential of these areas to generate runoff based on soil moisture storage availability. Successful model simulation would allow transfer of hillslope scale results to watershed scale, and selection and implementation of better P management strategies for improved water quality.