Whitewater Watershed “Paired-Watershed” Monitoring Project

John Nieber, Professor
Bradley Hansen, Senior Scientist
Gregory Johnson, Minnesota Pollution Control Agency

Funding Source

Minnesota Pollution Control Agency

Objective

To assess the differences of runoff, sediment yield, and nutrient yield from two small watersheds located in southeast Minnesota and to evaluate the ability of the complex hydrologic simulation model, GSSHA, to simulate the hydrology of those two watersheds.

Need or Impact

With the need to develop Best Management Practices (BMPs) for land uses and Total Maximum Daily Loads (TMDLs) for streams in Minnesota, it is necessary to acquire hydrologic and water quality data from areas of critical interest. A TMDL for the Whitewater River Watershed is sediment. It is therefore necessary to quantify runoff and sediment concentrations/yield from different areas within the watershed. To extrapolate the experimental results from the small watershed sites, it is necessary to test and calibrate hydrologic/water quality models for the watersheds.

Project Status

This study involves the continuation of a monitoring program for acquisition of field data. We will continue to monitor the watersheds through 2006. We now have data from 1997. We have processed all precipitation, water flow, and water quality collected since the beginning of the project up through 2005, and these data have been summarized into the US-EPA STORET system. The GSSHA (Gridded Surface Subsurface Hydrologic Analysis) model has been set up for the two watersheds. This has consisted of generating the gridded surface from a digital elevation model and entering the grid cell dependent properties of soil characteristics and land cover types. The model is being used to simulate the storm runoff hydrographs measured for these watersheds and ground water contributions to sustained flows. The surface runoff portion of the model is being calibrated using a subset of stormflow hydrographs, and the ground water component is being calibrated using baseflow recession data. The calibrated model will be verified with an independent subset of stormflow hydrograph data. The calibrated model will be used to evaluate proposed changes in land use within the watershed and to simulate nitrate and phosphorus export from the watersheds. In addition to the modeling activity, the flow and water chemistry data are being used to characterize the source waters of the paired watersheds. Data used include nitrate and phosphorus concentrations, water temperature, and stable isotope (deuterium and oxygen-18) concentrations. Preliminary analysis has shown that the two watersheds, while they are side-by-side, behave differently in terms of their ratios of surface and subsurface contributions to runoff. One of the watersheds has runoff dominated by surface runoff, while the other watershed has runoff dominated by ground water.