Impacts of Watershed Hydrology on Long-Term Landscape Evolution
Open Access
- Author:
- Huang, Xiangjiang
- Graduate Program:
- Civil Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- March 17, 2006
- Committee Members:
- Jeffrey D Niemann, Committee Chair/Co-Chair
Arthur Carl Miller, Committee Chair/Co-Chair
Peggy Ann Johnson, Committee Member
Christopher J Duffy, Committee Member
Rudy L Slingerland, Committee Member - Keywords:
- watershed hydrology
landscape evolution - Abstract:
- Numerous studies have examined the impacts of geomorphology on the hydrologic processes of river basins, but much less attention has been given to the complementary problem: the effects of hydrologic processes on the geomorphic changes of river basin topography. Fluvial erosion processes are driven by water discharge on the land surface, which depends on precipitation rates, soil moisture conditions, and groundwater discharge. Much evidence indicates that these hydrologic processes have influences on long-term landscape evolution. This dissertation focuses on obtaining a deeper understanding about how watershed hydrology affects the long-term evolution of a fluvial geomorphic system. In particular, the dissertation addresses the question from three different stages. First, the Geomorphic Effective Event (GEE) is often assumed to represent basin hydrology in most analysis and modeling of landscape evolution, the implications of the GEE in landscape evolution are explored through analytical and numerical approaches when the stream power erosion model with a threshold is used. It is found that the GEE is highly affected by the threshold and the exponent on discharge. Next, in order to account for the temporal and spatial variations of discharge rates at any location in a basin, a distributed hydrologic model was developed to consider the variability of precipitation, infiltration, evapotranspiration, and groundwater movement. The hydrologic model was calibrated using the hydrologic data of the WE-38 basin in Pennsylvania, and then coupled with a widely used geomorphic model. The combined hydrologic/geomorphic model was used to examine the geomorphic role of Horton runoff and groundwater discharge. Results show that groundwater processes produce three distinct zones, which have different relationships between annual streamflow and contributing area. Groundwater processes also produce the abrupt hillslope-valley transition in the future topography of the WE-38 basin. Finally, the conditions under which groundwater plays an important role in shaping the river basin topography are determined through exploring the sensitivity of watershed slope-area relationships and hypsometric curves to hydrologic and geomorphic parameters. It is found that groundwater produces an abrupt hillslope-valley transition only if the erosion threshold is close to zero and the exponent on discharge is below one.