A Holistic Approach To River Restoration Design And Conservation Planning On The Reach And Basin Scales Using Hydraulic Modeling And Multi-Objective Optimization Tools

Flooding events around the world cost billions (USD) in damages each year. For decades, engineers have combated flood related damages by implementing flood mitigation controls such as channelization, levees or berms, and armoring. Recent advances in the study of river dynamics, however, have challenged the efficacy of these traditional flood mitigation techniques and pose that these structures are disconnecting channels from their floodplains, increasing flow rates, and contributing to more erosion. The effects of climate change combined with future predictions of increased storm frequency and intensity make it necessary to revise flood hazard mitigation strategies. A more nature-based alternative to building structural defenses, is to reconnect disconnected floodplains and conserve those floodplains that are already well-connected. A well-connected floodplain allows floodwaters to overtop the channel banks more frequently to dissipate flood energies and slow stream flow thereby decreasing downstream damages. Additional benefits include provision of habitat and improved water quality.When choosing techniques and locations for floodplain conservation and reconnection, planners have a multitude of concerns to consider (e.g., water quality, flood resiliency, habitat improvement, project effectiveness, existing land use, budget, and lost opportunity costs). Considering all stakeholder objectives within budgetary constraints is a difficult and complex process, made even more challenging because these objectives often compete. Consequently, there is a need for computational tools that can optimize restoration locations and conservation strategies to help planners synthesize, justify, and visualize design choices. To help alleviate the uncertainty in planning for improvement projects, multi-objective optimization was performed to optimize both the locations and techniques for conservation and restoration while considering the tradeoffs between multiple stakeholder objectives. Three case studies in Vermont are used for illustration. In the first, a tool is developed that semi-automates the extraction and analysis of five evaluation parameters from a 2D hydraulic model (2D Hydrologic Engineering Center’s River Analysis System, 2D HEC-RAS) to compare hydraulic effectiveness of four floodplain reconnection scenarios on the Black Creek. This same tool is leveraged in the second case study along a section of the Mad River to develop an n-dimensional objective function to rank floodplain reconnection techniques while considering multiple stakeholder objectives (i.e., enhanced flood resiliency, improved water quality, and minimized socioeconomic impacts). The third case study in the Winooski River watershed, applies an evolutionary algorithm to a geospatial database of river network connectivity data on the basin scale to provide planners with a suite of optimal conservation locations that balance the tradeoffs between stakeholder goals including flood resiliency, water quality, and cost effectiveness. The tools developed aided in the advancement of a more holistic approach to floodplain conservation and reconnection design creating a more efficient method to narrow in on optimal sites at the watershed and reach scales considering multiple stakeholder objectives/concerns.