Estimating Minimum Instream Flow Requirements for Minnesota Streams from Hydrologic Data and Watershed Characteristics

Minimum instream flow recommendations, identified as the inflection point on the curve describing the relation between stream discharge and wetted perimeter, were developed for 27 Minnesota streams with mean annual discharges ranging from 41 to 568 ft3/s. The relation of instream flow recommendations to hydrologic and watershed variables was examined to develop models for rapid assessment. Instream flow recommendations were most strongly correlated with mean annual discharge (r = 0.97) and drainage area (r = 0.85). Two linear regression models were developed for estimating the instream flow recommendations. The first model used only mean annual discharge as a predictor. Because gauging stations are not located on all streams, the second model used drainage area and soil type as predictors. The instream flow recommendation, expressed as a percentage of the mean annual discharge, decreased as stream size increased. Hydrologic and watershed characteristics can be used to rapidly assess the minimum instream flow needs of streams.