Publication Date

2010

Document Type

Honors Thesis

Department

Engineering

Keywords

Colorado River (Tex.), Streamflow-Texas-Austin, Hyporheic zones-Texas-Austin, Hydrology, Dams-Environmental aspects, River regulation, Stream-aquifer interactions, Surface water-ground water interactions, Heat transport

Abstract

This study investigates how large, regular stage fluctuations alter surface water-groundwater exchanges in time and space. The Lower Colorado River, which runs through Austin, TX is heavily regulated for hydropower generation. The study site at Hornsby Bend is affected daily by releases from the Tom Miller Dam located 23 km upstream, causing the stage to fluctuate by more than 1.5 m with a mean depth of 1.3 m. At the site, the river is altered from a regionally gaining river to a river that both gains and loses on a daily basis due to the 1.5 m stage fluctuations. I used temperature and pressure measurements to map the vertical extent of the hyporheic zone and to determine how it varies spatially and temporally. This work provides unique insight with detailed field observations highly resolved in space and time over two separate campaigns of three days each. Temperature and head monitoring was conducted in the river, riverbed, and adjacent bank along a transect perpendicular to the river. River-groundwater exchange flux is largest close to the bank and decreases away from the bank. Correspondingly, both the depth of the hyporheic zone and the exchange time are largest close to the bank. Adjacent to the bank, the riverbed hyporheic zone head response is hysteretic, indicating that transient bank storage affects the magnitude and direction of vertical exchange close to the bank. Further field studies supplemented by fluid flow and heat transport simulations are needed to fully understand the impacts of dam regulation on the hydrologic, thermal, and ecologic dynamics of rivers and their hyporheic and riparian zones.

Language

English

Comments

vii, 48 p. : ill. (some col.), maps Honors Project-Smith College, Northampton, Mass., 2010. Includes bibliographical references (p. 45-48)

Share

COinS