THE EFFECTS OF URBANIZATION ON CHANNEL MORPHOLOGY OF RIVERS IN TEXAS

The response of river morphology to channel and watershed alteration is an important body of research in which Coastal Plains Rivers have historically been underrepresented. Coastal Plains Rivers in North America flow through multiple, terraced floodplains resulting from cyclic transgression/regression episodes typically dating to the Oligocene. The rivers flow through self-formed, sand or silt bed channels valleys in passive-margin, tectonically stable areas. In North America, strong seasonal variations in evapotranspiration and rainfall produce drastically different hydrologic seasons which create order of magnitude differences in wetted perimeter, width-depth ratios, and roughness values on the same reach from season to season. Within this setting, Texas has experienced population growth at rates surpassing the United States national average 15-fold (1997-2012), mostly in urban settings built on riverbanks. To understand and potentially predict the response of rivers in the Coastal Plains to the effects of increasing human population coupled with effects of associated climate change and variability, this study selects three rivers from the region which are heavily impacted by growing urbanization and assesses hydraulic and morphological characteristics upstream and downstream of urbanization. The Brazos River near Waco, Texas, the Colorado River near Austin, Texas, and the Trinity River near Dallas, Texas, are investigated in this study. Beginning approximately six miles upstream of each respective urban center and continuing six miles downstream, stability is assessed using qualitative morphological indicators, stream power and unit stream power calculations, and sediment size comparison. Potential effects of alterations to sediment size on geomorphology and biogeomorphology are considered. A comprehensive review of the impact of land-cover alteration in watersheds and its direct effects on channel morphology, indirect effects on morphology through climate alteration, and varying impacts based on modification type is presented, with a discussion of land-cover types in each HUC-12 watershed studied. Finally, current methods of classifying Coastal Plains Rivers and assessing their stability are discussed, and modified methods proposed