Spatial Pattern of Turbulence Kinetic Energy and Shear Stress in a Meander Bend with Large Woody Debris

This paper explores the effect of a partial LWD dam on the spatial pattern of turbulence kinetic energy (TKE) and shear stress within a meander bend of a small stream in East Central Illinois, USA. Field data on three-dimensional velocity components were collected using an acoustic doppler velocimeter (ADV). Results show that upstream of the bend apex the highest values of TKE occur near the base of the outer bank. As flow approaches the LWD obstruction, which is located along the outer bank downstream of the bend apex, a zone of stagnant fluid develops along the outer bank, shifting the region of maximum TKE toward the center of the channel. Shearing of fluid between the stagnation zone and the adjacent streaming flow produces near-bed maximum values of TKE that are more than two times greater than those along the outer bank upstream of the bend apex. Downstream of the LWD obstruction, the zone of maximum TKE is located near the inner bank along a shear layer extending downstream from the margin of the obstruction. The net effect of the LWD obstruction is to locally increase maximum TKE values, but to shift the zone of maximum TKE away from the toe of the outer bank downstream of the bend apex-a location where rates of bank erosion usually are greatest in meander bends.