Sediment deposition and transport patterns following a reservoir sediment release

A reservoir sediment release on the North Fork Poudre River supplied simila r to 7000 m(3) of silt- to pebble-sized sediment to an originally boulder b ed channel. Deposition along the 12 km of channel downstream from the reser voir occurred primarily in pools. During the subsequent snowmelt hydrograph , sediment was progressively scoured from the upstream and then the downstr eam pools. Initial sediment reworking in the pools created a deep, narrow t halweg scoured to the original pool bed, with additional sediment depositio n in lateral eddies. Continued reworking reduced but did not completely rem ove these eddy deposits. The channel became supply-limited with respect to finer grain-sized fractions (clay to medium sand) first at upstream and the n at downstream sites and eventually became supply-limited with respect to coarser grain-sized fractions (coarse sand to pebbles). Bedload transport r ates at a site were strongly linked to the depletion of sediment stored in upstream pools. Magnitude, duration, and sequence of flows were all importa nt controls on bedload transport and return of the channel to its prereleas e state.