Impact of Urbanization in Watersheds on Stream Stability and Flooding

To meet the demands of growing populations, there has been increasing urbanization and associated developments in the watersheds of a number of streams. Urbanization in watersheds involves denudation by removal of trees and vegetation, alterations in land use due to construction of buildings, streets, and associated infrastructure, and rerouting of surface runoff by storm sewers and detention/retention basins. Most of the impacts of these developments occur on the hydrologic regimes of relatively small streams where the resulting increases in flooding and stream erosion may be significant. In general, there is reduction in infiltration and soil erosion and increase in volumes and peaks of surface runoff of the stream. This paper presents a comparative evaluation of the surface runoff hydrographs, sediment yield of the watershed, and patterns of degradation/aggradation of the stream before and after a portion of the contributing watershed has been urbanized with and without detention basins.