6.1 INTRODUCTION

Since the beginning of mankind, sedimentation processes have affected water supplies, irrigation, agricultural practices, flood control, river migration, hydroelectric projects, navigation, fisheries, and aquatic habitat. In the last few years, sediment also has been found to play an important role in the transport and fate of pollutants; thus, sedimentation control has become an important issue in water quality management. Toxic chemicals can become attached to, or adsorbed by, sediment particles and then be transported to and deposited in other areas. By studying the quantity, quality, and characteristics of sediment in rivers and streams, scientists and engineers can determine the sources of the sediment and evaluate the impact of pollutants on the aquatic environment. In the United States, sedimentation control is a multibillion-dollar issue. For example, approximately $500 million are spent every year to dredge waterways and harbors for navigation purposes. Most of the dredged sediment is the result of substantial soil erosion in watersheds. Estimates by the U.S. Department of Agriculture indicate that annual offside costs of sediment derived from copland erosion are on the order of $2 billion to $6 billion, with an additional $1 billion arising from loss in compared productivity.

The sediment cycle starts with the process of erosion, where by particles or fragments are weathered from rock material. Action by water, wind, glaciers, and plant and animal activities all contribute to the erosion of the earth s surface. Fluvial...