Extreme case of sedimentation of a weir pool upstream of a v-notch weir.  The high sediment load at this site makes the choice of a flume a better option than a weir.  By design, flumes pass sediments and solids better than weirs.  This is accomplished by their lack of a need for an upstream weir pool and their flat (usually) floors.

While simple devices, weirs require more maintenance than flumes in order to produce accurate flow data.