RIVER BANK EROSION, FLOODPLAIN SEDIMENT DEPOSITION, AND A FLOODPLAIN SEDIMENT BUDGET OVER A 60 YEAR TIME PERIOD

Shifting hydrologic flow regimes in river systems and variability in climatic conditions are poised to alter sediment dynamics along river corridors. Changes in snowpack and the timing of snowmelt in mountainous systems, in particular, are likely to cause changes in the magnitude and timing of peak flow in snow-melt dominated mountain rivers. These changes can shift the balance between water and sediment in river systems, cascading to further challenges confronting water resources including increased frequency of extreme floods, loss of lateral connectivity of water across floodplains, and sedimentation of streams and reservoirs. We use an aerial lidar dataset, aerial photographs, field surveys and measurements of sediment depth, marker horizons, water and soil sampling, and spatial analysis to estimate floodplain overbank deposition, bank erosion, and a floodplain sediment budget along the East River, CO over 60 years. A combination of measured stream flow and historical flow analysis identify the mean recession limb of the hydrograph as the primary predictor of river bank erosion over six time intervals between seven aerial images. The duration of overbank flow is the strongest predictor for lateral accretion. Measurements of total suspended solids during peak flow as a first order estimate of the annual volume of water needed to close the sediment budget. We posit that more frequent, shorter duration peak flows expected to result from low snowpack and early snowmelt are likely to increase bank erosion and decrease overbank deposition along the East River.