Degree Name

Master of Science (MS)

Semester of Degree Completion

1993

Thesis Director

William A. Weiler

Abstract

The Charleston Side-Channel Reservoir has been experiencing extensive shoreline erosion since its completion in 1982. A diagnostic/feasibility study of the reservoir in 1992 rated shoreline erosion as the second largest source of sedimentation. Sedimentation reduces the reservoir volume, increases nutrient loading, and increases water turbidity.

As a part of Clean Lakes Program Phase II, the use of willow cuttings for bank stabilization was proposed as a possible treatment for shoreline erosion. While the use of willows for streambank stabilization has been extensively reported, lake documentation is rare. This experiment determined the feasibility of such action for the Charleston Side-Channel Reservoir and the extent of bank stabilization success.

Four sites around the reservoir were designated as test areas. Each site consisted of 24 m (80 ft) of shoreline and contained an untreated control section (c), and erosion-control matting section (m), a section of willow treatment alone (w), and a section of willow and matting treatment in combination (mw). Planting material was taken from a nearby stand of sandbar willows (Salix interior), cut into 0.9 m (3 ft) lengths, and planted in four, staggered rows along the banks. Reinforcement bars were driven into the banks before treatment in order to monitor erosional rates.

Propagation success was very high after the cuttings broke dormancy in Spring of 1992. Out of 477 cuttings planted, 442 (92.7%) had produced shoots. By October 1992, 380 (79.7%) still remained viable. The number surviving plummeted to 141 (29.6%) in May 1993. After reservoir levels rose as a result of excessive precipitation in the spring, all sites except site 3 showed a drastic reduction in willow survival. Wave erosion caused the collapse of large amounts of sediment from the cliff face, thereby uprooting or burying cuttings. The erosion-control fabric was found to increase survival by about 20% on sites having mw survival ratios significantly greater than w ratios. Both site 3 (p=0.0317) and site 4 (p=0.0025) had mw values significantly larger than w values. The use of matting is not advised in future willow cutting projects, however, considering labor, material cost, and survival benefits.

This project has demonstrated some success in willow establishment but may fail in long-term bank protection under all conditions. Future planting on low erosion areas is more feasible than on high erosion areas. Combinations of shoreline stabilization techniques in order to reduce wave action will most likely be required.

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