Modeling spatial and temporal patterns in flow and sediment transport and storage in large, lowland rivers

Spatial and temporal patterns of sediment transport and storage control the distribution and condition of aquatic and riparian habitats in large, lowland rivers. These patterns in transport and storage are predicted by coupling hydrology with sediment transport data and models in the Sacramento basin. The predictions are used to assess river rehabilitation strategies that have been proposed to increase the distribution and improve the condition of habitats in the mainstem Sacramento. Empirical time series models of streamflow and suspended sediment concentration are developed to assess historical patterns in suspended sediment transport and storage since the construction of major dams. A model of stochastic hydrology is created to predict inflow to the mainstem from major tributaries based on basin-wide hydroclimatology. The model is applied to the Sacramento to simulate pre- and post-dam flow, detect bed level change, and assess the viability of riparian forest restoration. A method is devised for computing spatial and temporal patterns of bed-material transport and storage by combining stochastic hydrology with sediment transport equations calibrated to data from the Sacramento basin. This method is used to assess the impact of three major river rehabilitation strategies: gravel augmentation to benefit salmonid spawning habitat, levee setbacks to re-create floodplain corridors, and flow alteration to restore an array of disrupted geomorphic processes and environmental cues. The models of suspended sediment transport suggest the influence of humans and tectonics on spatial storage patterns. The stochastic hydrology model corroborates predicted erosion in one river reach that may be undergoing bed degradation, and it suggests that riparian forest restoration is not viable at one floodplain location without flow alteration. The method for computing bed-material transport predicts large divergences, or imbalances, in sediment storage throughout the Sacramento River. These imbalances in bed-material storage are generally reduced following the implementation of three river rehabilitation strategies. The models may be applied by agencies and managers to anticipate the first-order impacts of large-scale river rehabilitation over a period of decades.