Watershed Management Tools
As part of an USDA funded project focusing on the improvement of the New York State Phosphorus Index I developed a web-based tool that predicts areas in the landscape that are susceptible to generating runoff during storm events. These areas are called variable source areas, a term that was first introduced by Dunne and Black (1970). Variable source areas are hydrologic hot spots in the landscape that generate saturation excess overland flow or shallow subsurface storm flow during rainfall events. Where VSA intersect with agricultural fields there exists the risk of rapid nutrient, pollutant, or pathogen transport with storm runoff to streams. Thus, prediction of VSA locations and storm runoff amounts is important to improve non-point source pollution mitigation. The web-based VSA prediction tool has a watershed hydrology model implemented that predicts on a daily basis where, when, and how much runoff is generated and even predicts storm runoff generating areas for the near-future 24-48 hours. This VSA prediction tool can be coupled with different methods for predicting nutrient loads (i.e. phosphorus, nitrogen). Tools like this will hopefully assist farmers and stakeholders in the near future in their daily decision of nutrient applications. The tool was originally developed for the Salmon Creek watershed north of Ithaca, NY (see figure below). Current real-time application of the VSA prediction tool is the Owasco Lake watershed southeast of Auburn, NY.
- Field testing of the web-based VSA prediction tool with farmers and stakeholders of the Owasco Watershed Lake Assoc. (OWLA). (Key-collaborators: Dr. M. Todd Walter, Dr. Zachary Easton)
- Development of the VSA prediction tool for smart phones and tablet computers.
- The VSA prediction tool unites a water balance model optimized for hydrologic predictions of saturated areas in watersheds dominated by saturation-excess overland flow, with 24-48 hour projections of weather conditions in an online-based, real-time tool.
The tool enables users to utilize the system without an in-depth knowledge of the individual components and the expertise required to calibrate the water balance
model or to integrate meteorological forecasts into the model.
- The tool identifies locations of areas prone to saturation or surface runoff and determines the risk of NPS pollution by estimating the relative risk of saturation or storm runoff.
- The VSA prediction tool provides basic annual and monthly statistics on the probability that a certain part of the watershed is contributing runoff and potentially pollutants during storm events.
- The extent of VSA is modeled based on antecedent moisture conditions and daily meteorological data within a water balance model.
The tool can be used to locate fields with low saturation potential that could, potentially receive more liberal manure applications without increasing the risk of NPS pollution.
The tool has the potential to improve transport-factor estimates in the NYS P-Index, which is used for longer-term nutrient management planning.
Figure above: Wet Areas in Dutch Hollow sub-watershed for the month November. Wet areas in Owasco Lake Watershed were modeled using weather data from the past ten years. The wet areas highlighted in red are expected to generate the most runoff – so they are most sensitive to contaminants that travel in surface water.
- Dahlke, H.E., Easton, Z.M., Fuka, D.R., Walter, M.T., Steenhuis, T.S. Real-Time Forecast of Hydrologically Sensitive Areas in the Salmon Creek Watershed, New York State, using an Online Prediction Tool. Water 5(3): 917-944.