Does the Birkbeck type bedload sediment trap effect local flow velocity?

A series of experiments was conducted to determine to what extent a trap for bedload sediment effects local flow velocity. The Birkbeck type bedload pit sampler consists of a metal box with internal load cell for continuous weighing of trapped bedload sediment. It is installed in streams and flumes in order to capture and weigh the amount of bedload sediment being transported in the flow. Sediment enters the trap through an aperture in the top surface. A model of the bedload sediment trap was tested in a flume in the Mountain StreamLab located in the Center for Ecohydraulics Research at the University of Idaho in Boise. Two variations of the trap were built: a standard aperture opening and a full width opening. Each variation was tested with two conditions: trap empty and trap half-full of sediment. Velocity was measured by Particle Imaging Velocimetry (PIV) for three flow rates. It was determined that trap entrance treatment and the volume of trapped sediment cause a measureable difference in the velocity of the approaching flow.