Morphological Changes Associated with Gravel Mining along the Colorado River, Texas
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There are countless bridges, buildings, parking lots, miles of highway, and numerous other structures throughout the United States. All of these structures require aggregate in their construction. Regions such as Austin, Texas, have expanded at an exceptionally rapid rate, and the demand for abundant sources of nearby gravels is being partially accommodated by floodplain mines along the Colorado River. While there is no doubt that gravel is necessary for the development, growth, and improvement of infrastructure, an assessment of how the excavation process and subsequent evolution of a mining site over time affects its surroundings, particularly the river system, should be addressed.
Many breaches into floodplain gravel mines are observed along the Colorado River. Streambed incision, bank erosion, channel widening, and channel straightening (through meander cutoffs) are documented results of gravel mining in fluvial environments. A concurrent loss of riparian vegetation is common, which can increase runoff into the river. An increase in turbidity and change in average grain size can negatively affect aquatic life.
The natural rates of sediment transport through a river are influenced by many factors, including breaches in the bank between the channel and flooded gravel pit (leading to channel widening) and the increase in sand supply to the channel that occurs downstream of gravel pits. An analysis of the trends in sediment moving through areas affected by gravel mining provides data necessary to describe past morphological changes and help predict future changes associated with floodplain gravel mining. Three sites of past and present floodplain gravel mining on the Colorado River are studied, and the sediment transport rates through the river upstream and downstream of each site measured. A surface based transport model allows for the comparison of transport rates, particularly increased mobility associated with higher sand content downstream of the mines. Collection of material along gravel bars and on the channel bed was used to compare actual rates of sediment transport to calculated rates of movement. The model is used to predict rates of sediment transport over a range of possible flow events.
CitationSimmang, C. M. (2007). Morphological changes associated with gravel mining along the Colorado River, Texas (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.
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