An Alternatives Analysis of Restoration Project Concepts across Farm, Fish and Flood Interests: Skagit Hydrodynamic Model Project - Phase 2 Report

The Farm, Fish, and Flood Initiative (3FI) aims to create and advance mutually beneficial strategies that support the long-term viability of agriculture and salmon while reducing the risk of destructive floods. As with many places throughout Puget Sound, the Skagit Delta land base is limited and population growth contributes additional pressures on the landscape. In the Skagit River, where salmon are a cornerstone of tribal culture and economy, it was estimated that an additional 1.35 million smolts, approximately 2,700 acres of estuary/delta habitat, are needed for a sustainable Chinook population. The delta also supports a strong agricultural economy and community that faces risks from floods due to aging flood/drainage infrastructure. Climate change is also anticipated to impact estuarine habitat, agriculture, and flooding.

Under the umbrella of 3FI, local representatives from salmon recovery, flood risk reduction, and agricultural groups have worked together on the Skagit Hydrodynamic Modeling (SHDM) Project led by National Oceanic and Atmospheric Administration Restoration Center (NOAA), The Nature Conservancy (TNC) and Washington Department of Fish and Wildlife (WDFW). The SHDM project contributes to 3FI work and is a landscape-scale alternatives analysis with the goal of developing well-supported actions to achieve long-term viability of Chinook salmon and community flood risk reduction in a manner that protects and enhances agriculture and drainage. The geographic focus of the SHDM study is within the tidally-influenced portion of the Skagit Watershed including the Swinomish Channel and southern portion of Padilla Bay.

The SHDM Team was comprised of individuals from 14 organizations representing farm, fish and flood interests, guided the project. The SHDM Team identified twenty-three restoration concepts for evaluation in the alternative analysis. Three types of projects were assessed:

1. Dike setbacks or removals that restore tidal and riverine inundation and construction of new dikes to protect adjacent lands;
2. Hydraulic projects that change the flow pattern by excavating new channels to distribute flow; and
3. Backwater channels where an existing channel waterward of the dikes is altered to increase backwater flow.

Most of these projects were identified and described in the Skagit River Chinook Recovery Plan, some of which include further refinements from later planning processes such as the Puget Sound Nearshore Estuary Restoration Project or individual project sponsor actions. A few projects were pulled from the Skagit River Flood General Investigation or developed by the SHDM Team.

The SHDM Team used a logic framework as the foundation for the alternatives analysis. Representatives from each interest group developed objectives with measurable indicators against which restoration concepts could be assessed. These objectives included benefits to be maximized as well as impacts to be minimized (Figure E-1). Each interest group received 100 points that could be divided between the different objectives allowing for weighting of any high priority objectives. The scores for each interest were then summed for a multiple-interest benefit and multiple-interest impact score. The objectives, indicators, and their weighting assignments were shared with other stakeholders and organizations from the respective interest groups for review and comment. The SHDM Team worked with scientists and technical experts to quantify the indicators hydrodynamic modeling, estimates of habitat connectivity and smolt production, predictions of sediment transport processes, GIS calculations, and local tidal and river flood and drainage knowledge. This work was an iterative process that allowed for input from each interest group to ensure the results are meaningful.

Using the outputs of the technical analyses, each project concept was assessed to determine how it contributed to each objective. For each indicator, the projects were normalized on a scale of 0-1 and then multiplied by the assigned points for that objective. Project objective scores were summed for a total benefit and impact score at the interest and multiple-interest level. The multiple-interest project scores were graphed in order to identify groupings of projects based on how they provided benefits or minimized impacts (Figure E-2). Five management groups (Figure E-3) were identified with different timelines and recommendations for each group as described below. It is assumed that some project concepts within these groups may move forward faster or slower than the processes described below and that some may never advance due to impacts or other limitations and constraints.

Additional hydrodynamic modeling examined cumulative effects if all project concepts except the red group were implemented, and provided an initial assessment of how climate change may affect projects and their benefits. Cumulative effects analyses found no major impacts to flow distribution between the North Fork and South Fork Skagit RIver nor the performance of individual projects. Climate change results can be used to better understand or evaluate how the benefits of projects may change over time. Additional analysis of climate changes, and sediment transport processes should be conducted to address future needs for drainage and diking infrastructure.

This SHDM project report covers the development and application of the technical analyses used to calculate scores and evaluate project concepts. It also describes how project concepts with similar benefits and impacts were grouped and the management recommendations and timelines for each group. Finally, the report summarizes the results from the climate change analysis and how potential future impacts to habitat, coastal flood resiliency, drainage, and irrigation may be impacted.