Hydraulics and sediment transport processes in a pool-riffle rocky mountain stream

Sediment transport processes related to varying channel-bed morphology were investigated from April to November, 1993 along a 1 km pool-riffle and step-pool reach of North Saint Vrain Creek, a small mountain stream in the Northern Colorado Rocky Mountains. Three hundred sixteen 16-256 mm tracer particles placed in two separate pool-riffle-pool sequences, forty-three direct bedload measurements at three separate cross-sections in discharges ranging between 0.27-8.8 m3/s, and indirect velocity measurements at thirteen cross-sections in 23 discharges ranging between 0.23-9.2 m3/s are used to assess sediment sorting patterns and sediment transport capacity variations. An investigation of secondary flow features and wave patterns provides preliminary evidence of turbulent controls on sediment entrainment and transport, and was used to develop a conceptual model of bedload transport and channel-bed maintenance on North Saint Vrain Creek. Recirculating eddy systems provide a means to constrict flow in pools, leading to modeled velocity-reversals at high flows. Tracer particle depositional evidence also indicates higher sediment transport capacities in pools versus riffles at high flow. Modeled hydraulic conditions and depositional evidence of tracers indicates that high-flow recirculating-eddy-influenced velocity-reversals and associated turbulence may provide the primary pool maintenance processes in this channel.