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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #162477
Title: WATERSHED-SCALE MODELING OF CRITICAL-SOURCE-AREAS OF RUNOFF GENERATION AND PHOSPHORUS TRANSPORT

Author
item SRINIVASAN, M - PENN STATE UNIV
item GERARD-MARCHANT, P - CORNELL UNIV
item Veith, Tameria - Tamie
item Gburek, William
item STEENHUIS, T - CORNELL UNIV

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2004
Publication Date: 4/1/2005
Citation: Srinivasan, M.S., Gerard-Marchant, P., Veith, T.L., Gburek, W.J., Steenhuis, T.S. 2005. Watershed scale modeling of critical source-areas of runoff generation and phosphorus transport. Journal of the American Water Resources Association. 41:361-375.

Interpretive Summary: Runoff generation processes within a small watershed in Pennsylvania were studied using the Soil & Water Assessment Tool (SWAT), an empirically-based model and the Soil Moisture Distribution and Routing (SMDR), a physically-based model. The SMDR model structure allowed representation and study of watershed processes at small (5-m x 5-m) spatial scales. On a daily-basis, the SWAT simulations matched the observed stream flows better than the SMDR simulations did. Both models were able to represent the seasonal changes in stream flows, though the degrees of agreement with observed stream flows varied with seasons. The SMDR model identified shallow soils with vertical-flow limiting layers as 'critical areas' for runoff generation. This was in agreement with the observations made in this watershed. Both SMDR and SWAT lacked the routines to describe the flow of surface runoff across landscape, which can be a major handicap in depicting phosphorus transport processes at watershed scale.

Technical Abstract: A curve-number based model, Soil & Water Assessment Tool (SWAT) and a physically-based model, Soil Moisture Distribution and Routing (SMDR), were applied in a headwater watershed in Pennsylvania to identify runoff generation areas, as runoff areas have been shown to be critical for phosphorus management. SWAT performed better than SMDR in simulating daily stream flows over the 4-year simulation period (Nash-Sutcliffe coefficient, SWAT, 0.62; SMDR, 0.33). Both models varied stream flow simulations seasonally as precipitation and watershed conditions varied. However, levels of agreement between simulated and observed flows were not consistent over seasons. SMDR, a variable-source-area based model, needs further improvement in model formulations to simulate large peak flows as observed. SWAT simulations matched the majority of observed peak flow events. SMDR over-predicted annual flow volumes, while SWAT under-predicted the same. Neither models route runoff over landscape to water bodies, which is critical to surface transport of phosphorus. SMDR representation of watershed as grids may allow targeted management phosphorus sources within field and transport from fields to streams. SWAT representation of fields as HRUs does not allow such targeted management.