Spatial Variation of Alluvial and Bedrock Channel Type in the Upper Guadalupe River, Texas

Abstract

This dissertation investigates the spatial distribution of alluvial and bedrock channel types in the Upper Guadalupe River in central Texas. The objectives of this work are to investigate the controls on the spatial distribution of alluvial-tending and bedrock-tending reaches and gravel bars in the Guadalupe River. Through traditional field and statistical techniques, this research examines channel reach type and depositional landforms. The purpose of this research is to investigate watershed scale controls on the distribution of reach type in a mixed alluvial-bedrock channel in central Texas and to explain observed differences between alluvial and bedrock reaches. Observed differences between reach types include the distribution of depositional landforms, channel planform geometry, and channel width.

A comparison of reach characteristics between alluvial and bedrock reaches is presented including slope, reach length and transitions, sinuosity and floodplain width. An analysis of bar characteristics including their spacing, type, and grain size is also included. The spatial distribution of geologic and soil units in the study area are compared for the correlation to different channel reach types or transitions. Results that pertain to human effects on the fluvial geomorphology in the study reach are presented and separated from the natural processes. The distribution of forcing agents, including roads and dams, is included. The natural forcing effects of tributaries are also addressed. The combined processes of bedrock incision and sediment transport are active in creating the mixed alluvial-bedrock fluvial landscape of the Upper Guadalupe River. Rivers in the Balcones Escarpment region in central Texas are unique with respect to climate, hydrology, and sediment supply. This research aims to provide a foundation to build a conceptual model of mixed alluvial-bedrock fluvial landscape evolution in central Texas.