|Shields jr, Fletcher|
Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/29/2003
Publication Date: 3/1/2004
Citation: Shields Jr., F.D., Morin, N., Cooper, C.M. 2004. Large woody debris structures for sand-bed channel. Journal of Hydraulic Engineering. p. 208-217. Interpretive Summary: Many stream corridors in agricultural watersheds suffer from accelerated erosion. Traditional erosion control measures require costly stone and concrete structures. This project tested the use of interlocking piles of trees anchored to the stream bed and banks to stabilize caving banks and restore riparian habitats. These tree structures are designed to be stable until they are buried by sediments. Data and observations indicate that the structures are creating water flow conditions favorable to habitat restoration and causing sediment deposition in areas formerly subject to erosion. Results from this experiment could provide technical bases for future applications that cost only about one-third as much as orthodox approaches featuring rock riprap measures.
Technical Abstract: Described is an experimental project featuring intermittent placement of structures made of large woody debris to control bank erosion and accelerate deposition in a deeply incised sand-bed channel draining a 37 km2 watershed. Construction costs per unit channel length were 23% to 58% of recorded costs for recent stone bank stabilization projects in this region. A force balance for a typical structure indicated that buoyancy forces are more important than fluid drag. A simple model was derived to compute net buoyant forces as a function of flow depth given structural dimensions and wood density. Application of the model indicated that recently completed structures should be stable in flows up to the five-year event. Older structures should be stable in even higher flows as they become anchored by sediment deposits and eventually by woody vegetation that colonizes these deposits as structures decay.