Sediment Yield and Transport on a Mountainous Small Watershed

Abstract

Observations on the runoff of rain, sediment yield and transport on a small mountainous watershed, called Hirudani, were carried out. Main sediment production sites were three landslide slopes and by use of particle size distribution analysis and petrographical classification of run off sediments the sources of sediments were identified. The majority of sediment was transported as contact load and sometimes the sediment reached the outlet of the watershed long after the arrival of the flood. The lag time varied case by case, depending on the antecedent sediment storage in the stream channel. A conceptual model of the sediment runoff was proposed and the channel process was analyzed using the bed load formula. A stair like channel configuration with many falls and pools could consume a great part of the energy by rollers at the bottom of the falls and the effective slope for transportation of sediment should much flatter than actual topographical inclination.