Sediment sources near the extreme ends of the catchment continuum and the topographic dependence of denudation in a global context

Abstract

Sedimentation in reservoirs and pollution of harbours are serious problems throughout the world. Reservoirs are vital components of water supply including irrigation water and hydropower generation. Harbours are precious assets that maintain a rich array of values and uses. Sustainability of these reservoirs and harbours is severely threatened by sedimentation and pollutants attached to sediments. The two case studies of Mangla Reservoir and Darwin Harbour are no exception.

This thesis presents field-based research that focuses on two applied problems: sediment delivery to Mangla Reservoir and to Darwin Harbour and the search for topographic controls on denudation rates. Applied problems are examined by combining estimates of sediment yield/denudation rate, elements of sediment sources, and topographic analysis. The fundamental problem of topographic controls of denudation is approached by combining topographic analysis with denudation rate informed by top soil tracers.

This study provides accounts of sediment sources based upon top soil tracers, sediment yield, denudation rates, and estimates of the proportion of sheet and channel and/or landslide erosion in the Mangla Reservoir and Darwin Harbour catchments, presents mean slope, mean relief and denudation rate relationships for the two catchments, and compares the results with global denudation rate and relief data from previous published studies.

This research also provides an alternative global view of the relation between denudation rate and topography. Regression using the General Exponential Growth Model (GEGM), for the combined data set of eighty basins, yields a relation D = 0.0015e^{0.29 S} (r² = 0.97, p <0.0001) and indicates that catchment slope is a more meaningful correlate of denudation rate than relief. The relationship combined with a Geographic Information System (GIS) approach for the calculation of mean catchment slope from a Digital Elevation Model (DEM) provides a model for the estimation of denudation rate at catchment level.

Date of Award	2010
Original language	English
Supervisor	Diane Pearson (Supervisor), Robert Wasson (Supervisor), David Parry (Supervisor) & Waqar Ahmad (Supervisor)