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Accueil du site → Doctorat → États-Unis → 1999 → Urbanization and dryland fluvial systems : Modeling hydrogeomorphic change in ephemeral streams

University of California, Los Angeles (1999)

Urbanization and dryland fluvial systems : Modeling hydrogeomorphic change in ephemeral streams

Allen, Aaron O

Titre : Urbanization and dryland fluvial systems : Modeling hydrogeomorphic change in ephemeral streams

Auteur : Allen, Aaron O

Université de soutenance : University of California, Los Angeles

Grade : Doctor of Philosophy (PhD) 1999

Past studies have identified numerous hydrogeomorphic characteristics associated with urban river systems. Specifically, researchers have observed and documented substantial changes in the peak flow, velocity of storm flows and channel morphology in urbanized watersheds. In addition to bridges and concrete structures, urban channels also typically exhibit incised channels with increased bank erosion when compared to less developed reaches in the same basin. Past research, mostly focused on rivers in humid climates, indicates that stream channels in urban areas are subject to large-scale hydrogeomorphic changes with the transformation of the surrounding watershed To quantify hydrogeomorphic change associated with urbanization in an and river system, this study utilized a distributed model, linked to a GIS, and field surveys to examine changes in flow and channel morphology in Mint Canyon, a tributary to the Santa Clara River, California. The distributed watershed model combines a water balance methodology and the SCS direct runoff method to estimate the amount of direct overland flow and soil infiltration in the basin. The GIS is utilized to store all input parameters for the model and for spatial analysis of the model output. To examine the effect of urbanization, land use was altered during the study period to simulate the process of urbanization in the watershed. To assess the level of morphological channel change, twenty cross section were established prior to the 1997/98 El Nino storm season and monitored for six months until May of 1998 Model estimates indicate that the distributed model provides fairly accurate predictions for daily average flow in Mint Canyon. Analysis of the model errors shows that the distributed model tends to underestimate flow for very large storm events, overestimate flow with high soil moisture conditions and overestimate throughflow. Field survey data indicates that the lower portion of the Mint Canyon channel exhibits substantial channel incision. During the 1997/98 winter, cross sections in urban areas incised up to 1.3 meters and exhibited up to a 100% loss of riparian vegetation. Model estimates show that stream discharge and water yield has been augmented by 5% with approximately 10% of the basin occupied by urbanization and the percentage of flow from urban areas has substantially increased. Study results indicate that dryland basins have a reduced reaction to urbanization when compared to other studies in humid areas of urban-induced hydrogeomorphic change

Mots clés : Physical Geography Hydrology Environmental Sciences


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