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Water Quality Division


Paired Watersheds Method

The Paired Watersheds Method is used to document best management practice (BMP) effects on water quality. The method allows us to observe and document the impact pollutants have on two similar watersheds. After BMPs are installed in one of the two watersheds, data from both watersheds are compared to predict what the water quality would have been if the BMPs had not been installed.

How it works:

  1. Choose two watersheds.
    For the method to work, both watersheds must be similar in size, slope, location, soils, geology, population, and land cover.
  2. Collect water quality data from both watersheds.
    Data is used to determine if there is a statistically significant relationship between the two streams (are they enough alike?); if so, proceed with BMPs.
  3. Install BMPs in only one of the watersheds.
  4. Continue collecting water quality data from both watersheds.
  5. Analyze the data.
    Differences between predicted and observed water quality responses to BMPs are illustrated with a regression graph. The graph can show if, when exposed to the same pollutant load, the watershed with BMPs had less impairment than the other watershed where BMPs weren't installed. Assuming that the only major change that occurred in either watershed was the installation of BMPs, any differences in water quality can be attributed to BMPs.
  6. Realize the results of best management practices.
Last Modified on 06/20/2007