Effects of Channel Stabilization in Tucson Stream Reaches on Infiltration and Ground-Water Recharge: Volume I Model Studies

Abstract

Volume I Executive Summary: The increase in extreme flood events in Tucson stream channels has led to the use of channel stabilization procedures to mitigate flood damage. These procedures include bank protection with soil cement, channel modification, and grade control structures. The channel stabilization and grade control structures are typically constructed to depths up to 20 ft below the channel bottom. Channel modification generally consists of widening and straightening channels in bank-protected reaches. There is concern that structural changes in the rivers will reduce infiltration and recharge during the periodic flow events. Ground-water recharge occurs when water that has infiltrated at the land surface and percolated through the vadose zone reaches the water table. The vadose zone is the partially saturated geological region between the land surface and the water table. Recognizing this concern, Pima County contracted with the Water Resources Research Center of the University of Arizona, to estimate the effect of channel modification on infiltration and recharge by undertaking computer simulations of subsurface flow during a representative runoff event in modified and unmodified channels. The purpose of a companion study, which is reported in Volume II of this report, was to estimate the effect of channel modification in localized reaches on the basin-wide recharge regimen.