Streamflow requirements for habitat protection were determined at several critical riffle reaches in the Assabet River and Charles River Basins. The R2Cross and Wetted-Perimeter methods yielded median streamflow requirements of 0.75 cubic feet per second per square mile (ft3/s/mi2) and 0.13 ft3/s/mi2, respectively. Three study reaches are on tributaries to the Assabet River (Danforth Brook, Great Brook, and Elizabeth Brook), two are on the mainstem of the Charles River, and one is on a tributary to the Charles River (Mine Brook). The strength of the R2Cross and Wetted-Perimeter methods is that they may be applied at ungaged locations.
A Range of Variability Approach analysis was conducted on a common 30-year period of record from 1969 to 1998 for five mostly unaltered flow, streamgaging stations. The discharge range defined by the median R2Cross and Wetted-Perimeter streamflow requirements brackets the interquartile range for the median of monthly-mean flows during the summer low-flow period, as defined by the Range of Variability Approach analysis of five streamgaging stations. The median R2Cross streamflow requirement for the five riffles compares very closely to the median Tennant 40-percent of the mean annual flow requirement for good habitat condition. The median Wetted-Perimeter streamflow requirement compares closely to the median Tennant 10-percent of the mean annual-flow requirement for a poor habitat condition. Tennant and Range of Variability Approach methods require continuous discharge records for analysis.