Improving the Urban Stream Restoration Effort: Identifying Critical Form and Processes Relationships

Stream restoration projects are often based on morphological form or stream type and, as a result, there needs to be a clear tie established between form and function of the stream. An examination of the literature identifies numerous relationships in naturally forming streams that link morphologic form and stream processes. Urban stream restoration designs often work around infrastructure and incorporate bank stabilization and grade control structures. Because of these imposed constraints and highly altered hydrologic and sediment discharge regimens, the design of urban channel projects is rather unclear. In this paper, we examine the state of the art in relationships between form and processes, the strengths and weaknesses of these existing relationships, and the current lack of understanding in applying these relationships in the urban environment. In particular, we identify relationships that are critical to urban stream restoration projects and provide recommendations for future research into how this information can be used to improve urban stream restoration design. It is also suggested that improving the success of urban restoration projects requires further investigation into incorporating process-based methodologies, which can potentially reduce ambiguity in the design and the necessity of using an abundant amount of in-stream structures.     

MODELING THE LONG TERM IMPACTS OF USING RIGID STRUCTURES IN STREAM CHANNEL RESTORATION1

Abstract: Natural channel designs often incorporate rigid instream structures to protect channel banks, provide grade control, promote flow deflection, or otherwise improve channel stability. The long term impact of rigid structures on natural stream processes is relatively unknown. The objective of this study was to use long term alluvial channel modeling to evaluate the effect of rigid structures on channel processes and assess current and future stream channel stability. The study was conducted on Oliver Run, a small stream in Pennsylvania relocated due to highway construction. Field data were collected for one year along the 107 m reach to characterize the stream and provide model input, calibration, and verification data. FLUVIAL-12 was used to evaluate the long term impacts of rigid structures on natural channel adjustment, overall channel stability, and changing form and processes. Based on a consideration of model limitations and results, it was concluded that the presence of rigid structures reduced channel width-to-depth ratios, minimized bed elevation changes due to long term aggradation and degradation, limited lateral channel migration, and increased the mean bed material particle size throughout the reach. Results also showed how alluvial channel modeling can be used to improve the stream restoration design effort.