Effects of Instream Boulders On Bed Load Transport

Boulder arrangements, as a measure of stream restoration, have been known to significantly impact the local sediment transport around the elements as well as the reach-averaged sediment transport in the channel. The present experimental study explores how the boulder concentration and bed slope affect bed load transport in a channel. Boulders with 4 concentrations of 0 (no boulder), 3.4%, 5.4%, and 8.3% were partially submerged into a mobile gravel bed in a flume. Each boulder concentration was repeated at 3 different bed slopes: 0.5%, 1.0%, and 1.5%. Flow discharge varied from 55 to 80 L/s. Bed load transport was recorded with a sediment trap at the flume exit and the water depth was recorded to calculate the bed shear stress. A formula is developed to predict the bed load transport rate in the channel with boulders.