The effects of urbanization on the streambed sediment characteristics in a ridge and valley watershed /

by 1979- Thames, Brantley Allison

Urbanization causes flow and sediment regime changes, which leads to alterations in the bed sediment characteristics and degradation of the ecological habitat. Evidence shows that changes in the characteristics of streambed sediment occur in urbanized watersheds; however a link between urbanization and changes in streambed sediment is not well established in the literature. Limited support in the literature does suggest that urbanization is linked to a decline in the diversity of algae, invertebrate, and fish populations. Relationships between urbanization and bed sediment characteristics were explored by three studies using the AnnAGNPS and CONCEPTS models. AnnAGNPS is a GIS-based sediment delivery model with land erosion rates determined by the revised Universal Soil Loss Equation (RUSLE) and sediment yield rates determined by the Hydrogeomorphic USLE (HUSLE) for watersheds primarily dominated by agricultural land use. CONCEPTS is a sediment transport and channel adjustment model that routes sediment input from AnnAGNPS and sediment inputs from channel bed and bank erosion. Both models were developed by the United States Department of Agriculture – Agricultural Research Service (USDA ARS). The research objectives for this project included: 1) conducting a sensitivity analysis of the AnnAGNPS and CONCEPTS models to evaluate the significance of various model inputs that incorporate the mosaic of urban land use and require field measurements for the non-urbanized and urbanized subwatersheds, 2) producing and executing several combinations of model run simulations with altered runoff and erosion from the hillslope using the entire AnnAGNPS-CONCEPTS modeling couple to simulate varying levels of urbanization, and 3) evaluating AnnAGNPS model results of 15 urban and non-urban subwatersheds iii across Beaver Creek watershed to gain insight to dominant sediment delivery dynamics resulting from urbanization using a multivariate cluster analysis between the model output, field measurements, stream power, subwatershed area, and percent urbanization. The studies addressing the first and second research objectives were conducted using the geographic data in two subwatersheds of the Beaver Creek watershed in Knox County, Tennessee, whereas the third study used data across the entire Beaver Creek watershed. The two subwatersheds include Hines Branch, which is a highly disturbed urban subwatershed, and Cox Creek, which is a subwatershed with minimal urban development. The results from the three studies included the following main conclusions: 1) the AnnAGNPS and CONCEPTS models were fairly insensitive to the model input parameters tested in the sensitivity analysis on an individual basis; however, when comparing the sensitivities between the urban and non-urbanized subwatersheds for the AnnAGNPS analysis, the percent difference between the sensitivity slopes for each model input parameter ranged from 150 to 300 percent; 2) simulations with altered runoff and erosion from the hillslope showed that altered runoff had a greater impact on the bed sediment characteristics and sediment yield; and 3) the cluster analysis of the five watershed characteristics illustrated that percent urbanization of each subwatershed and suspended sediment from AnnAGNPS model output over subwatershed stream power and total subwatershed area were the most related to the bed sediment size distributions collected at each site. Assuming the AnnAGNPS-CONCEPTS modeling couple represents the physical watershed and channel processes, then this thesis shows that urbanization does impact bed sediment characteristics, and it appears hydrology is more of a controlling factor to bed sediment characteristics than hillslope erosion. iv