|Shields jr, Fletcher|
Submitted to: Hydrobiologia
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2002
Publication Date: 9/23/2003
Citation: SHIELDS JR, F.D., KNIGHT, S.S., MORIN, N., BLANK, J. RESPONSE OF FISHES AND AQUATIC HABITATS TO SAND-BED STREAM RESTORATION USING LARGE WOODY DEBRIS. HYDROBIOLOGIA. 2003. 494:251-257. Interpretive Summary: Many stream corridors in agricultural watersheds suffer from accelerated erosion and sedimentation. Traditional measures for controlling bank erosion require costly stone and concrete structures. Fallen trees are an essential component of stream aquatic habitat, providing substrate, cover, and velocity shelter for fish and insects. Damaged streams often have relatively low levels of woody debris density. Although woody materials have long been used to control stream erosion, scientifically-based guidelines for their use are scarce. Samples of fish and their habitats taken before and after treatment of a damaged stream with structures made from felled trees. The number and size of fish increased in following treatment, as did the quality of fish habitat. High flow water velocities along eroding banks were reduced by the presence of debris structures, leading to sediment deposition instead of erosion. Results from this experiment could provide technical bases for future woody debris structure applications that cost only about one-third as much as orthodox approaches featuring rock riprap measures.
Technical Abstract: Large woody debris structures hold promise as cost-effective stream corridor rehabilitation measures. Pre- and post construction data are presented that describe effects of habitat rehabilitation of Little Topashaw Creek, a sinuous, fourth-order sand-bed stream draining 37 km2 in northwest Mississippi. The rehabilitation project, constructed in 2000, consisted of placing 72 large woody debris structures along eroding concave banks and planting 4000 willow cuttings in sandbars. Response was measured by monitoring flow, channel geometry, physical aquatic habitat, and fish populations. Initially, debris structures reduced high flow velocities at concave bank toes, preventing further erosion and inducing deposition. Physical response during the first year following construction included creation of sand berms along eroding banks and slight increases in base flow water width and depth. Flow velocities at moderate discharge levels, measured using slug injection of a tracer dye, were about 40% lower in the treated reach than in a similar untreated reach. Fish collections showed assemblages typical of incising streams within the region, but minor initial failure of the structures and renewed erosion were observed during the second year after construction.