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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #145983
Title: ESTIMATING BEST MANAGEMENT PRACTICE EFFECTS ON WATER QUALITY IN THE TOWN BROOK WATERSHED, NEW YORK

Author
item GITAU, M - PENN STATE UNIV.
item Gburek, William
item JARRETT, A - PENN STATE UNIV.

Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Proceedings
Publication Acceptance Date: 7/28/2002
Publication Date: 8/1/2002
Citation: Gitau, M.W., Gburek, W.J., Jarrett, A.R. 2002. Estimating best management practice effects on water quality in the town brook watershed, New York. Federal Interagency Hydrologic Modeling Conference. 2:1-12.

Interpretive Summary: Best Management Practices (BMPs) for controlling phosphorus (P) loss from agriculture are being implemented within the 1969-sq-mi New York City water supply watersheds. It is intended that BMP implementation eventually extend to the entire area. To best plan this endeavor, we must quantify the effectiveness of the BMP program at the watershed scale. This study establishes a methodology to evaluate the effectiveness of the BMP effort by applying the Soil and Water Assessment Tool (SWAT) model and a related BMP tool to the 14-sq-mi Town Brook Watershed, part of the New York City Watersheds. SWAT is a distributed model that simulates runoff, stream flow, ground water, and sediment and nutrient loading. It provides detailed watershed description, and simulates associated P loss at that same level of resolution. The BMP tool provides estimates of BMP effectiveness based on site characteristics. Results show that targeting BMPs to high P-producing areas of the watershed is generally a very effective means of reducing overall P losses, suggesting that BMP placement need only be targeted to key contributing areas. The distributed nature of SWAT enables us to define those areas. It also enhances the use of the BMP tool by providing input data specific to the discrete units. The BMP assessment tool provides a simple means of estimating BMP effectiveness under a variety of site-specific conditions, thus serving as a valuable resource in BMP selection and placement.

Technical Abstract: The 3700-ha Town Brook Watershed (TBW), located in Delaware County, New York, is part of the watershed system that supplies drinking water to New York City. Agriculture in this watershed is mainly dairy, with cropland being confined to that supporting the dairy industry. Phosphorus (P) is the major water quality pollutant of concern in this area, with P pollution thought to be the result of runoff emanating from manured fields and barnyards. Ongoing efforts to control P loss have involved the implementation of on-farm best management practices (BMPs) applied on a farm-by-farm basis within the watershed. There is, however, a need to determine the effects of these BMPs in decreasing P losses at the watershed scale, particularly since it is intended that BMP implementation cover the TBW and, eventually, the entire New York City water supply watershed system (510,000 ha). This study is aimed at establishing a methodology to evaluate the effectiveness of the watershed-wide BMP effort by applying the Soil and Water Assessment Tool (SWAT) model and a related BMP assessment tool to the Town Brook Watershed. SWAT is a distributed model that simulates runoff, stream flow, ground water, sediment and nutrient loading on a daily time step. The BMP assessment tool provides a means of obtaining effectiveness estimates based on site characteristics. We first present model simulations of flows and P loads from selected hydrologic response units, as well as at the watershed outlet, representing current levels of BMPs installed. We then examine various post-BMP scenarios consistent with the current approach to BMP implementation on the watershed. Finally, we discuss model application in targeting critical source areas of P loss in context of BMPs.