# GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 157-1
Presentation Time: 9:00 AM-6:30 PM

# STOCHASTIC NUMERICAL ANALYSIS OF UP-SCALED AQUIFER AND STREAMBED PROPERTIES FOR MODELING LAGGED RIVER DEPLETIONS DUE TO WELL PUMPING

MCCORD, James T., Amec Foster Wheeler, 104 West Anapamu Street, Santa Barbara, CA and GANGOPADHYAY, Subhrendu, U.S. Bureau of Reclamation, Technical Service Center, Denver Federal Center Bldg 67 5th Floor 25007, Denver, CO 80225, jim.mccord@amecfw.com

This paper describes a stochastic-deterministic approach for development of upscaled streambed properties to use in numerical simulation of streamâ€“aquifer interactions, specifically for analysis of delayed depletions to a partially penetrating stream due to pumping of a well close to a stream. Following a review of classical analytical methods used to compute lagged stream depletion, we develop a numerical model for a well pumping from an alluvial aquifer located near a partially penetrating stream. The model includes consideration of material heterogeneity such as one would expect in alluvial deposits. Using the model, we develop a method to estimate effective streambed conductance and aquifer conductivities for heterogeneous alluvial aquifers subjected to pumping by alluvial wells near streams. These effective properties can be used subsequently in coarse-grid numerical models to compute lagged river depletions due to the well pumping.Â Our stochastic-deterministic approach involves: (i) synthetically generating heterogeneous hydraulic conductivity fields based on field observations from alluvial / fluvial aquifer systems, (ii) Monte Carlo simulation of flow through 100 realizations of the random conductivity fields representing alluvial aquifer cross-sections in the vicinity of a stream influenced by well pumping, and (iii) inferring upscaled effective properties from the ensemble mean of the simulations. We apply this approach to results from large-scale aquifer pumping tests executed adjacent to the South Platte River in northeast Colorado.