Assessing sediment dynamics and channel bar repsonse in the Brazos River near Glen Rose, Texas

Abstract

Over the past century the Brazos River, the third largest river in Texas, has become a highly managed system due to the construction of dams and reservoirs. Currently the river provides seven billion gallons of water each year to surrounding cities, agriculture and industry. Impoundments along the river and increased water allocation have changed the magnitude and frequency of the flow, and thereby disrupted the natural hydrologic cycle. To date, numerous studies have reported on the fragmentation of major fluvial systems within the United States and the subsequent impact on sediment discharge. Similar studies along the Brazos River are scarce. This paper discusses the results of a one-year study examining sediment transport rates and channel bar morphology in the Brazos River near Glen Rose, Texas. All observations were made along a study site located below De Cordova Bend Dam at Lake Granbury. The project aimed at understanding the historic migration patterns of channel bars pre- and post-dam construction. This was achieved through the analysis of aerial photography and GIS. Additionally, the project monitored present sediment flux and channel bar response to understand short term changes within the system. Suspended load and bedload were measured over a range of flow conditions, and channel bars surveyed continuously to capture seasonal variability. Channel bar development is largely controlled by stream capacity and the availability of sediment, and therefore channel bars within our study area represent key observational features for understanding the current dynamics of the fluvial system. Results from this study indicate how this reach of the Brazos River has responded to the construction of a major impoundment, and how current conditions are shaping the channel morphology.