T328 Using Natural and Anthropogenic Tracers to Determine Recharge and Residence Times within Arid to Semi-Arid Inter-Montane Aquifer Systems

Wednesday, 25 October 2017
1:30 PM - 5:30 PM
Room 618/619/620

BASEFLOW RECESSION FROM UNSATURATED-SATURATED FLOW

Paper number: T328-10
Program: Technical Sessions
Time: 3:55 PM – 4:10 PM

Authors

Abstract

Water flow in Unsaturated zones is an important process in subsurface flow cycles. A mathematical model for a coupled unsaturated-saturated flow in an unconfined aquifer is presented. Semi-analytical solutions for hydraulic heads and discharges are derived using Laplace transform and Cosine transform. The effects of the lateral discharge of the unsaturated zone and aquifer compressibility are specifically taken into consideration. The lateral discharge of the unsaturated zone is significant when dimensionless constitutive exponent κD of the unsaturated zone less than 1, and becomes negligible when κD larger than 100. The compressibility of the aquifer has a non-negligible impact on the discharge at early times. For late times, the power index b of the recession curve -dQ/dt~aQb , is 1 and independent of κD, where Q is the baseflow discharge, t is time, and a is a constant lumped aquifer parameter. For early times, b is approximately equal to 3 but it approaches infinity when t→0. The present solution is applied to synthetic data and field data. The present solution matches the synthetic data better than both the linearized Laplace equation and linearized Boussinesq equation solutions, with a minimum relative error of 16% for estimate of hydraulic conductivity. The present solution is well applied to the observed streamflow discharge in Iowa, and estimated values of the aquifer parameters are reasonable.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302315

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