Estimating Streambed and Aquifer Parameters from a Stream/Aquifer Analysis Test

The Tamarack State Wildlife Area in eastern Colorado is being investigated as a possible managed recharge project to redirect flows in the South Platte River for water quantity management. Two primary surface water/groundwater interactions exist at Tamarack: (1) between the South Platte River and alluvial aquifer and (2) between backwater sloughs, or secondary river channels, and the alluvial aquifer. Knowledge of river/slough/groundwater interaction could play a vital role in the design and operation of the recharge system. Quantifying the magnitude of stream/aquifer interaction requires estimates of the streambed hydraulic conductivity. Silt, clay, and organic materials are often deposited in streams resulting in the streambed having a lower hydraulic conductivity than the underlying alluvial aquifer. A stream/aquifer analysis test is performed at the site to investigate the surface water/groundwater interaction during alluvial well depletions. Water levels are measured in the alluvial aquifer, slough, and South Platte River to determine the depletive effects of pumping. The stream/aquifer analysis test is also used to investigate the use of recently proposed analytical solutions for inversely estimating streambed conductivity and aquifer parameters from observed aquifer drawdown. Estimates of aquifer parameters are compared to data from recent aquifer tests and estimates from published reports. Estimated streambed conductivity is compared to in-situ measurements using falling-head permeameter tests. 1 Department of Civil Engineering, Colorado State University, Fort Collins, CO 80523-1372, Email: [email protected]