HYDRAULIC CONDUCTIVITY OF GLACIALLY DERIVED SEDIMENTS IN THE STONY CLOVE CREEK WATERSHED, CATSKILLS MOUNTAINS

The Ashokan Reservoir is experiencing an increase in turbidity due to slope failures in the Esopus Creek and its tributaries. The largest contributor of turbidity is the Stony Clove Creek watershed, which consists of glacially deposited sand, silt and clay-rich sediments. Hydraulic properties of the watershed’s sediments, such as hydraulic conductivity (K) of the stream bank materials, are vital to understanding the groundwater flow systems along stream banks, and are thus valuable in managing and mitigating slope failures.

The objective of this research is to develop a better way to determine the hydraulic conductivity of glacially derived sediments in the Catskills watersheds reliably and in a cost effective manner utilizing the grain size distribution method. This will aid in characterizing the groundwater flow systems along sites in the Catskills. Samples were collected from the Stony Clove Creek watershed and analyzed using the grain size distribution and constant head permeameter methods to determine the hydraulic conductivity of the sediments. It should be noted that constant head permeameter tests are more reliable than the grain size distribution method, but are also more expensive and time consuming. The hydraulic conductivity obtained from the grain size distribution using the Hazen Method has a wide range of potential values since the method is based on an empirical equation which can vary significantly depending on grain shape and sorting. The value of the Hazen coefficient (C) has a range of 40 for any given grain size category. Hydraulic conductivity values obtained from both methods were compared and analyzed. The coefficients chosen for the Hazen equation was then selected to match the values obtained from the constant head permeameter method for each sample. This new observational analysis approach reduces the range for the Hazen coefficient down to 10. More research and data analysis is needed to come up with a better way to determine the hydraulic conductivity of the glacially derived sediments in this watershed, however it is important to note that our approach would produce less uncertainty in the estimates.