Man-induced channel adjustment in Tennessee streams

Abstract

Ihis report is an attempt to relate the effects of channel modifications to the resulting instabilities in the fluvial system. The primary objective is to provide the Tennessee Department of Transportation with information concerning channel stability in relation to river crossing structures. Several new analytical techniques are presented that can aid in the understanding of channel adjustment to natural ana man-induced stress. The methods of analyses presented herein should be applicable to other areas with alluvial, sand-bed channels, especially in the Gulf Coastal Plain States.

A model of channel response in disturbed alluvial channels

“…1969 1969 1970 1978 1970 1970 1972 1974-77 1974-76 1973-78 1976-78 1973-77 14 A. SIMON 142 u 1 uo 139 are best described mathematically by nonlinear functions which asymptotically approach a condition of minimum variance. The description of channel adjustment and evolution by nonlinear decay functions is well documented (Schumm and Lichty, 1965;Graf, 1977;Bull, 1979;Hey, 1979;Robbins and Simon, 1983). However, there seems to be considerable disagreement as to the mathematical form of the function.…”

“…Where available, gauging station records were used to record annual changes in the water-surface elevation at a given discharge. Changes in the stage-discharge relation imply similar changes on the channel bed and can be used to document bed-level trends (Blench, 1973;Wilson, 1979;Robbins and Simon, 1983;Williams and Wolman, 1984).…”

CHANNEL INSTABILITY IN THE LOESS AREA OF THE MIDWESTERN UNITED STATES1

“…In coiitrast, the processes of aggradation and degradation, which represent systematic changes in bed elevation over a period of years (Mackin, 1948), can affect long stream reaches, entire stream lengths, or whole stream systems. In fact, longer-termed adjustment processes can, by themselves, instigate or exacerbate local scour problems (Robbins and Simon, 1983).…”

“…A survey of 15 counties in northwestern Missouri identified 957 highway structures as damaged by channel degradation. Degradation and channel widening in the bess area led to the collapse of several bridges in West Tennessee (Robbins and Simon, 1983), southwest Mississippi (Wilson, 1979), Missouri (Emerson, the midwestern United States focused additional attention on channel-stability problems in the bess area because scores of bridges were either closed or failed during and immediately after the floods.…”

Indications and potential sources of change in sand transport in the Brazos River, Texas

“…These changes can occur rather suddenly, as in response to abrupt disturbances such as channel shortening or straightening (Robbins and Simon, 1983); but often the changes will occur over long periods of time in response to more subtle disturbances such as land-use changes. Observed changes in channel characteristics might be remnant responses to disturbances that occurred decades earlier.…”