THE OAK ORCHARD SOIL WATER ASSESSMENT TOOL A decision support system for watershed management Part 1: Calibration and Validation

Abstract

A hydrologic model (SWAT) was developed and calibrated for the Oak Orchard watershed to evaluate sources and sinks of sediment and nutrients. The model included the most important anthropogenic features that impacted water flow and nonpoint source pollution in the watershed. These features included reservoirs at the Iroquois National Wildlife Refuge, Waterport and Medina; point sources such as the Erie Canal, US Gypsum, Allen Canning, wastewater treatment plants at Medina, Oakfield and Elba, and tiledrains at the mucklands, an intensely farmed area that was drained to combat malaria in the 19th century. The model included point sources for every subbasin so that the effects of future point sources can be evaluated. The model was calibrated for waterflow and sediment using observed loading data collected by Makarewicz and Lewis (2000, 2009). To achieve the proper water balance observed at the watershed, seasonal inputs of water had to be added from the Erie Canal and the Onondaga escarpment. This water came from outside of the watershed. The resulting calibration had a Nash-Sutcliffe (NS) prediction efficiency of 0.81 for the calibration period (1997-1999). The total cumulative sediment loading was within 2%, of observed and the monthly sediment loads fell within the uncertainty of the observed data (NS=0.31). Cumulative total phosphorous loads were within 2% of observed and the NS prediction efficiency was 0.91. The model validated very poorly in the 2008 time period primarily because of inaccurate precipitation data and incorrect groundwater fluxes from the escarpment. Further research needs to evaluate the timing and amount of groundwater flow from the escarpment because it has a significant impact on monthly flows in this watershed. It is likely that other watersheds that are nestled against the Onondaga escarpment are impacted by spring flows from this geologic feature.