Assessment Approach for Identifying Compatibility of Restoration Projects with Geomorphic and Flooding Processes in Gravel Bed Rivers

Abstract

A critical requirement for a successful river restoration project in a dynamic gravel bed river is that it be compatible with natural hydraulic and sediment transport processes operating at the reach scale. The potential for failure is greater at locations where the influence of natural processes is inconsistent with intended project function and performance. We present an approach using practical GIS, hydrologic, hydraulic, and sediment transport analyses to identify locations where specific restoration project types have the greatest likelihood of working as intended because their function and design are matched with flooding and morphologic processes. The key premise is to identify whether a specific river analysis segment (length ~1-10 bankfull widths) within a longer reach is geomorphically active or inactive in the context of vertical and lateral stabilities, and hydrologically active for floodplain connectivity. Analyses involve empirical channel geometry relations, aerial photographic time series, LiDAR data, HEC-RAS hydraulic modeling, and a time-integrated sediment transport budget to evaluate trapping efficiency within each segment. The analysis segments are defined by HEC-RAS model cross sections. The results have been used effectively to identify feasible projects in a variety of alluvial gravel bed river reaches with lengths between 11 and 80 km and 2-year flood magnitudes between ~350 and 1330 m(3)/s. Projects constructed based on the results have all performed as planned. In addition, the results provide key criteria for formulating erosion and flood management plans.

Detailed assessment of spatial and temporal variations in river channel changes and meander evolution as a preliminary work for effective floodplain management. The example of Sajó River, Hungary

“…next 30-50 years). There is still a demand for detailed geomorphological inputs for management strategies; however, many policy-makers argue with a necessary preservation of the previous channel development trajectories (Thorne et al, 1998;DeVries and Aldrich 2015;James 2015). The next step for managers would be to decide which strategy to adopt: protecting the floodplain (Piégay 1998;Morandi et al, 2014;Alber and Piégay 2017) or defining an erodible corridor where lateral shifting will not be hindered (Piégay et al, 2005;Habersack and Piégay 2007)?…”

Streambed scour of salmon (Oncorhynchus spp.) redds in the Sauk River, Northwestern Washington

“…Measured scour suggests that imbalances in sediment transport rates within the study reaches may have led to maximum scour depths that exceeded 2D 90 , the maximum scour depth associated with equilibrium transport. Although scour depths suggestive of this imbalance occurred in both study reaches, deep scour exceeding a depth of 2D 90 occurred at each ASM location within the downstream reach, which occupied a braided, largely unvegetated channel that is susceptible to large-scale geomorphic changes including channel avulsions (DeVries and Aldrich, 2015). During sediment transporting peak-flow events, the quantity of water and sediment conveyed by different channels within the braided section of the Sauk River may change, resulting in local erosion and deposition of sediment and planform channel changes.…”