Advancing the state of stream restoration design using sediment transport modeling and risk assessment

Due to imposed constraints and potentially altered hydrologic and sediment discharge regimes, the design of stream restoration projects is rather unclear. The first objective of this study was to examine relationships between form and processes, the strengths and weaknesses of existing relationships, and the current lack of understanding in applying the relationships in the urban environment. A primary goal was to identify relationships that are critical to urban stream restoration and provide recommendations for future research into how this information can be used to improve the design effort.; The second objective of this study was to use a combination of field investigations and long-term alluvial channel modeling to evaluate the effect of rigid in-stream structures on channel processes and verify the current and future stream channel stability of a relocated stream reach. The model was calibrated and verified using field data. The model was used to simulate long-term adjustments within the study reach under two scenarios, one scenario that included rigid structures and a second scenario that did not contain rigid structures. With respect to a case study reach, instances where rigid in-stream structures have a significant impact on channel form and adjustment were identified. In addition, the long-term simulations indicated that changes to initial design characteristics would have resulted in a more stable, sustainable project.; The use of stability verification methods, such as a check of sediment transport capacity/supply and alluvial channel modeling, can involve considerable time and effort; however, application can result in design modifications that reduce project uncertainty, and risk. The final objective of this study was to present a risk-based design approach using Design Failure Modes and Effects Analysis (DFMEA) and risk quantification to incorporate uncertainty and decision-making. The DFMEA identifies risk in terms of the consequence of failure, the likelihood of occurrence of a failure, and the ability to detect a failure. DFMEA consequence and occurrence ratings were used to calculate the risk associated with different design alternatives. The estimates of risk for each alternative were compared to provide justification for selecting the most cost effective restoration design alternative.