Turbidity and particle signatures imparted by runoff events in ashokan reservoir, Ny

Abstract

The occurrence, temporal and spatial patterns, and origins of turbidity events, and their linkage to runoff events, are documented for a water supply impoundment with two separated basins, Ashokan Reservoir, NY. The analysis is supported by a comprehensive 6-week study of the major inflow and the reservoir during the summer of 1996, that captured the effects of a single runoff event, and turbidity (Tn) measurements made in the reservoir and the water supply intakes for the entire year. Measurements supporting the short-term study include: temperature, specific conductance, beam attenuation coefficient, electronic particle counts, Secchi disc transparency, Tn, up- and downwelling cosine irradiance, chlorophyll, microscopy-based individual particle size and chemistry, and total suspended solids (TSS) on sediment trap collections. The external load of mostly quartz and clay particles delivered by die principal tributary, as an interflow, during the summer runoff event imparted distinct signatures in Tn and deposition within the epilimnion of the receiving basin; the other basin remained unaffected by comparison. The deposition rate of TSS and Tn increased in the receiving basin in response to die runoff-based loading; decreasing gradients in both parameters were observed within this basin downstream of the entry point of die tributary. More than 85% of Tn in die receiving basin during die 6-week study is attributed to inorganic tripton particles of terrigenous origins. Analysis of the longer-term data indicates elevated Tn values (maximum of 150 NTU) occur routinely in die receiving basin following runoff events, and diat diis effect extends to die other basin, including the water supply intake(s), during intervals other than summer stratification. © 1998 Taylor & Francis Group, LLC.