Diffusivity of Glacial‐Outwash Aquifer by the Floodwave‐Response Technique

Abstract

ABSTRACTAquifer diffusivity (transmissivity divided by storage coefficient) was calculated for three sites in a glacial‐autwash valley aquifer near Cortland, New York from water‐level fluctuations induced by rises in stream stage. The observed response data were analyzed through use of a one‐dimensional floodwave‐response model to calculate the theoretical head response in the aquifer generated by a floodwave in the stream, and then matched to the observed head response. Diffusivity values computed from sharply peaked flood rises ranged from 6.08 to 8.68 ft2. The closest match between observed and calculated heads was obtained from a site where the aquifer is confined and the saturated thickness (and thus the diffusivity) remains constant with the passage of a floodwave. Arrival time of the observed flood‐peak seems to be the most useful criterion for curve matching, especially under unconfined conditions, where a match to the rising limb and floodpeak is difficult because of changes in the saturated thickness.A transmissivity value of 14,700 ft2/d for the glacial‐outwash aquifer, calculated from specific capacity data from a nearby industrial well, combined with diffusivity calculated by the floodwave‐response method, indicates a storage coefficient between the normal ranges for unconfined and confined aquifers. Calculated storage coefficients were 0.015, 0.027, and 0.034 at the three sites.The floodwave‐response method of calculating aquifer diffusivity is relatively inexpensive compared to standard aquifer tests and is effective in glacial‐valley fill aquifers that are hydraulically connected to a major stream or river.