Watershed Scale Modeling of Critical Source Areas of Runoff Generation and Phosphorus Transport

Abstract

A curve number based model, Soil and 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 streamflows over the four‐year simulation period (Nash‐Sutcliffe coefficient: SWAT, 0.62; SMDR, 0.33). Both models varied streamflow 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 overpredicted annual flow volumes, while SWAT underpredicted the same. Neither model routes runoff over the landscape to water bodies, which is critical to surface transport of phosphorus. SMDR representation of the watershed as grids may allow targeted management of phosphorus sources. SWAT representation of fields as hydrologic response units (HRUs) does not allow such targeted management.

Flow and nutrient transport in intermittent rivers: a modelling case-study on the Vène River using SWAT 2005

“…Although its use for nutrient and pesticide modelling is less documented in the literature than that for flow modelling (Tolson & Shoemaker, 2007), more material is becoming available (Santhi et al, 2001;Muleta & Nicklow, 2005;Srinivasan et al, 2005;Tolson & Shoemaker, 2007;Gevaert et al, 2008).…”

Distributed hydrological modelling of total dissolved phosphorus transport in an agricultural landscape, part I: distributed runoff generation

“…where K s =K(θ s ) and K m =K(θ m ) are the hydraulic conductivity at saturation and at macroporous drainage limit, respectively, and α is an universal constant equal to 13 for a large range of soils (Bresler et al, 1978;Steenhuis and van der Molen, 1986). Lateral outflows from each cell are then distributed according to local aspect between one cardinal and one diagonal downslope neighboring cells, following the D ∞ algorithm (Tarboton, 1997).…”

“…The SMDR model is based on a soil moisture balance calculation initially developed by Steenhuis and van der Molen (1986), later modified and integrated into the Geographic Resources Analysis Support System (GRASS) Geographic Information System (GIS) (US Army C.E.R. L., 1991;Neteler and Mitasova, 2002) by Zollweg et al (1996), Frankenberger et al (1999) and Kuo et al (1999).…”

Distributed hydrological modeling of total dissolved phosphorus transport in an agricultural landscape, part II: dissolved phosphorus transport

“…Details of the water balance components are presented in a companion to this paper (Gérard-Marchant et al, 2006). The model has been successfully applied to several New York and Pennsylvania watersheds (Frankenberger et al, 1999;Kuo et al, 1999;Johnson et al, 2003;Mehta et al, 2004;Srinivasan et al, 2005). The model is designed to simulate sloping areas, and does not work in flatter areas such as alluvial floodplains, nor does it account for infiltration excess runoff that can be produced on dry soils by brief, intense summer rainstorms.…”