Described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris. This method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand. In these types of environments, buoyancy forces are typically more important factors in woody debris stability than fluid drag. Buoyant forces are counteracted by the weight of the structure, earth anchors, and sediment deposits. Design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37-km 2 watershed. Large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention. Construction costs per unit channel length were 23-58% of costs for recent stone bank stabilization projects within the same region. During the second year following construction, 31% of the structures failed during high flows, probably due to inadequate anchoring.
Large woody debris structures hold promise as cost-effective stream corridor rehabilitation measures. Effectiveness of these structures placed in incised, rapidly eroding, sand-bed channels is governed by the effects of the structures on the velocity field at the toe of eroding banks. Effects of recently placed large woody debris structures were examined using depth and depthaveraged velocity data collected using self-contained acoustic Doppler/pressure transducer data loggers. Six of these instruments were placed along two cross-sectional transects at the apex of a sharp meander bend in Little Topashaw Creek, Mississippi. Simultaneous records of runoff events before and after placement of large woody debris structures along the outside of the bend showed that the debris structures were effective in reducing mean storm event velocities from about 150% of channel centerline velocities to levels between 3% and 45% of centerline velocities. The region protected by the structure experienced moderate deposition (<0.4 m) during the first high flow season following construction. A series of laboratory flume tests were run to assess accuracy of the acoustic Doppler/pressure transducer instruments, which were found to produce depth records within 5% of manual measurements and velocity measurements within 5% of depth-averaged velocities determined by numerically integrating point velocities measured using a laboratory acoustic Doppler velocimeter.
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