THE DISCHARGE OF SEDIMENT IN CHANNELIZED ALLUVIAL STREAMS

Abstract

ABSTRACT: Approximately 400 million cubic feet of channel sediments have been delivered to the Mississippi River from the Obion‐Forked Deer River system in the last 20 years. The discharge of sediment from these channelized networks in West Tennessee varies systematically with the stage of channel evolution. Variations in yields over time reflect the shifting dominance of fluvial and mass‐wasting processes as the networks adjust to lower energy conditions. Maximum bed‐material discharges occur during the initial phases of degradation (Stage III). In contrast, yields of suspended‐sediment peak during the threshold stage (Stage 1V: large‐scale mass wasting) as sediments are delivered from main‐channel banks and tributary beds. Suspended‐sediment yields then decrease as aggradation (Stage V) becomes the dominant trend in the main channels, but remains relatively high through restabiliza‐tion (Stage VI) because of continued degradation and widening in the tributaries. Bed‐material discharges decrease from the degradation stage (III) to Stage V, and increase again during restabiliza‐tion (Stage VI) because secondary aggradation increases gradients and incipient meandering serves to rework bed sediments. This secondary maxima in bed‐material discharge is analogous to those described previously as complex, or oscillatory, response. The trends of sediment production and transport described from these rejuvenated networks are in agreement with experimental and theoretical results of earlier investigations. Copyright © 1989, Wiley Blackwell. All rights reserved