Impacts of Woody Debris on Fluvial Processes and Channel Morphology in Stable and Unstable Streams

Abstract

Abstract : This report documents the findings of a year long study to assess the impact of Large Woody Debris (LWD) upon channel evolution and morphology in unstable sand bed rivers in northern Mississippi. The aim of this research is to gain an improved understanding of the basin-wide impact of LWD dynamics in unstable and stable channel environments and to develop a set of coherent debris management strategies for erosion control, habitat enhancement, and maintenance/design considerations for run-of-river structures, based upon sound geomorphic and engineering analysis. Data from the US Army Corps of Engineers Demonstration Erosion Control (DEC) survey program, conducted in May 1995, has been used to locate significant debris jams with respect to planform and long profile data on 23 river reaches in northern Mississippi. The reaches surveyed are between 4000 and 12000 feet long and range in upstream basin area from 3.5 to 150 square miles. A comprehensive understanding of debris dynamics can be attained from surveying these channels because reaches fall into several categories including, stable/unstable reaches, straight/meandering reaches and reaches which have either a predominantly agricultural or wooded riparian zone. The debris jams in each reach have been surveyed in detail to determine the mechanisms and locations of debris input, jam impact upon channel morphology and sediment routing and jam stability over time. The final of these objectives has been assessed by comparing the survey results of the current study with those obtained in the 1994/1995 research effort.