Abstract
The soil and water assessment tool (SWAT) is used to assess the influence of small upland reservoirs (PL566) on watershed nutrient yield. SWAT simulates the impact of collectively increasing and decreasing PL566 magnitudes (size parameters) on the watershed. Totally removing PL566 reservoirs results in a 100%increase in total phosphorus and an 82%increase in total nitrogen, while a total maximum daily load (TMDL) calling for a 50%reduction in total phosphorus can be achieved with a 500%increase in the magnitude of PL566s in the watershed. PL566 reservoirs capture agriculture pollution in surface flow, providing long-term storage of these constituents when they settle to the reservoir beds. A potential strategy to reduce future downstream nutrient loading is to enhance or construct new PL566 reservoirs in the upper basin to better capture agricultural runoff.
Highlights
Public Law (PL) 566 dams are flood control structures built by the United States Soil Conservation Service to mitigate the effects of increased flooding from recent land use change
This study presents a comprehensive simulation of the Waco Lake catchment using the soil and water assessment tool (SWAT) [9]
Removing PL566 reservoirs from the calibrated simulation dramatically illustrates the importance of the small reservoirs for mitigating downstream nutrient and sediment pollution
Summary
Public Law (PL) 566 dams are flood control structures built by the United States Soil Conservation Service to mitigate the effects of increased flooding from recent land use change. Dams are generally assumed, regardless of size, to negatively affect downstream environments, Duke et al [1, 2] have shown that these reservoirs are a positive ecological influence, because they enhance downstream riparian growth. This downstream benefit will last only as long as the PL566s remain viable, and does not necessarily equate to the positive ecological health within the reservoirs themselves. The Waco Lake catchment (see Figure 1) in Central Texas, USA, has been identified as an impacted watershed due to nonpoint source pollution causing noticeable eutrophication [3]. The purpose of this study is to illustrate the relative impact of small upland reservoirs on simulated nutrient and sediment yields from the Waco Lake catchment
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