Local Scour in the Vicinity of Spur Dikes

Principal Investigator: Dr. Roger Kuhnle

Problem:

A spur dike can be defined as an elongated structure having one end on the bank of a stream and the other end projecting into the current. Spur dikes have been widely used to protect eroding stream banks. They have also been used to enhance aquatic habitats by causing stable pools in unstable, disturbed streams. In general, spurs are more beneficial to aquatic habitat resources than other types of bank protection, primarily because their presence causes pool habitat to be created and maintained. The depth and volume of local scour caused by a spur dike is difficult to estimate accurately. The complex physics of the 3-D unsteady flow associated with the scouring process are poorly understood and difficult to characterize. As a result, most scour prediction algorithms are empirically based and only predict the maximum depth of scour.

Objective:

The goal of this research is to provide information toward optimizing the design of spur dikes for aquatic habitat as well as for bank stabilization. This is being accomplished by relating upstream flow conditions to the maximum depth of scour, geometry, planar area, and volume of the local scour associated with spur dikes of different length and angle.

Description of Work:

A laboratory investigation is underway to measure the volume of the scour hole for a range of spur dike lengths and approach flows. Future experiments will determine the effect of the angle of the spur dike to the bank on the volume and geometry of the scour hole. Characterization of the flow in the scour hole will lead to an improved understanding of the processes involved in the scour hole formation.

Benefit:

These findings are important for designing spur dikes for the maximum benefit to aquatic habitats as well as providing adequate bank protection. The goal of designers should be to select spur dike geometry which stabilizes the bank and provides the largest scour volume subject to cost constraints. These results will lead to improved spur dike designs which will yield improvements to aquatic habitats as well as protect valuable lands adjacent to streams.