Man-induced gradient adjustment of the South Fork Forked Deer River, west Tennessee

Journal Article · Thu Jan 01 04:00:00 EST 1987 · Environmental Geology and Water Sciences; (United States)

DOI:https://doi.org/10.1007/BF02449942· OSTI ID:5823764

Simon, A; Robbins, C H ^[1]

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1. Geological Survey, Nashville, TN (United States)

Channel modifications from 1968 to 1969 on the South Fork Forked Deer River in western Tennessee have caused upstream degradation, downstream aggradation, and bank failures along the altered channels, adjacent reaches, and tributaries. The result of these adjustments is a general decrease in gradient as the channel attempts to absorb the imposed increase in energy conditions created by channelization. Headward degradation at a rate of approximately 2.57 km/yr on the South Fork Forked Deer River caused from 1.52 m to about 3.14 m of incision over a 13.5 km reach from 1969 to 1981. As a consequence of substantially increased sediment supply, approximately 2.13 m of aggradation was induced downstream of this reach during the same period. This accumulation represents a 60% recovery of bed level at the downstream site since the completion of channel work in 1969. Gradient adjustment with time is described by exponential decay functions. The length of time required for adjustment to some new quasi-equilibrium conditions is computed by these decay functions and is about 20 years from the completion of channel work. Adjusted slopes are less than predisturbed values, probably because straightened channels dissipate less energy by friction, allowing more energy for sediment transport. An equivalent sediment load, therefore, can be transported at a considerably gentler slope. The predisturbed slope exceeds the adjusted slope by an order of magnitude on the downstream reach of the South Fork Forked Deer River.

• OSTI ID: 5823764
• Journal Information: Environmental Geology and Water Sciences; (United States), Journal Name: Environmental Geology and Water Sciences; (United States) Vol. 9:2; ISSN 0177-5146; ISSN EGWSE
• Country of Publication: United States
• Language: English

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