Summer Streamflow

Lack of adequate water flowing in the rivers—particularly in the summertime—is one of the primary constraints on maintaining the health of aquatic habitat and aquatic life. The summer streamflow measure is a composite that considers: average flow during August and once-in-ten-year low flows (7Q10) for these rivers; the minimum level of water for fish to pass (R2Cross and Wetted Perimeter); and analysis of recommended flows based on long-term flow at unaltered gages (Tennant method). Daily streamflow measured by the U.S. Geological Survey at established stream gaging stations on the Sudbury River (Framingham), Assabet River (Maynard), and Concord River (Lowell) is used to compute daily scores from May through September. These daily scores are then averaged to compute a seasonal (summer) score. Flows in cubic feet per second (cfs) per square mile are also averaged. Because the scoring function is nonlinear, seasonal average streamflow and seasonal average score do not necessarily correlate.