Chapter 5 - Fluvial Geomorphic Processes

Abstract

Transport of sediment by moving water is a fundamental feature of earth processes. One of the primary interdisciplinary aspects of stream ecosystem structure and function is the relationship between flow dynamics and the movement of the substratum of stream and river channels. Stream flow variance plays a central role in the structure and function of stream ecosystems. Near-bed flow velocity, streambed instability, and scour induce a subsequent ecosystem response that often exerts density-independent effects on stream, as well as riparian, organisms. These changes in stream discharge, flow velocity, and shear stress cause spatial variability in fluid forces and thus differential entrainment, transport, and deposition of sediment. There is a need in stream ecology for a condensed derivation of basic equations used to describe shear stress and incipient motion, coupled with an analysis of streambed stability and the utility of deriving stability indices. This chapter introduces the concepts of flow-competence, shear stress, and the fundamental processes in threshold entrainment of bed material in river systems.