The Major Rehabilitation Evaluation Report for Jetty System at the Mouth of the Columbia River supports the following actions:
- North Jetty – Scheduled repair with head stabilization at or near STA 101, (less extensive than the previously proposed capping). These repairs will be conducted after the base condition maintenance repairs to stations 86-99 and lagoon fill to stop erosion of the jetty root. It does not include spur groin construction.
- South Jetty – Base condition (interim repairs) allowing head recession. It does not include spur groin construction. Dune augmentation near the jetty root will be implemented in FY 13 as a separate action and not included in the cost estimate. Although the base condition is the NED plan, the interim repair, hold head alternative is very close in AAC, differing by 0.9 percent. When conditions are appropriate (i.e., repairs of the South Jetty allow for a haul road to be established to the end of the jetty approximately FY 2019), head stabilization could be re-evaluated—using parameters such as least cost, environmental acceptability and engineering feasibility.
- Jetty A – scheduled repair and head stabilization at approximately STA 89. It does not include spur groin construction. The modeling performed to assess the project alternatives assumes that Jetty A is in place and fully functioning. This is because Jetty A, as originally constructed, protects the North Jetty and helps to train the Columbia River main stem. In addition, Jetty A is believed to play an important function for the Columbia River plume. The plume is an important food source for the 13 Columbia River salmonid evolutionarily significant units (ESUs) listed under the Endangered Species Act (ESA).
The project has a combined Benefit-to-Cost Ratio of 1.1 for the system (all three jetties).
The initial construction schedule is projected to be from 2014 through 2020. Based on the 100% federally fully funded, feasibility level design in 2012 dollars, project first cost at an effective price level of 01 October 2012 is $238,547,000 and a total project cost fully funded of $257,201,000. Total project costs fully funded are estimated as follows per jetty: North Jetty at $79,797,000; South Jetty at $146,884,000; and Jetty A at $30,520,000.
The scheduled jetty repairs plan will reduce ongoing erosion to the surrounding shoals. Stabilizing the North Jetty and Jetty A lengths will have positive effects on the adjacent shorelines as well as the configuration and evolution of the ebb tidal shoal. Scheduled repairs will also help to stabilize both the above and below water morphology at the project.
Chapter 1 of this report provides a general introduction to the MCR jetties system and surrounding area, including:
· The purpose and importance of the jetty system;
· A detailed history of the construction, past repairs, and morphologic changes;
· The technical, as well as budget challenges; and
· A description of the current conditions.
Chapter 2 provides the economic rationale for the federal interest, a summary of how costs are calculated, and the benefit-to-cost ratios of the various repair/rehabilitation alternatives.
Chapter 3 provides the engineering basis for the development and analysis of the alternatives. This chapter includes:
· A characterization of the wave climate and morphologic processes at the MCR;
· The current issues/risks of deterioration or failure for each of the jetties and associated consequences;
· A characterization of the design of each jetty and the relevant performance modes;
· The description of the methodology and model used for assessing the reliability and life-cycle performance of the jetties, including alternatives;
· A summary of how the model was calibrated using historical and hindcast data; and
· A description of each of the repair/rehabilitation alternatives, including the model analysis results related to projected future long-term maintenance actions and reliability.
Chapter 4 builds upon the previous two chapters to provide a comparison of the alternatives based on initial and life-cycle costs, reliability, and environmental considerations. Based on these comparisons, a recommended plan for each jetty is given.
Chapter 5 summarizes the anticipated environmental effects of the proposed rehabilitation of the MCR jetty system, and the coordination undertaken related to environmental compliance issues. The associated EA provides a full evaluation of the project and associated environmental compliance considerations. Additional discussion and pertinent correspondence is included in Appendix D, Environmental Documentation. Any citations in this chapter can be found in the References section of the EA. The discussion is pulled directly from the EA which evaluates the effects of the Major Rehabilitation actions, the Major Maintenance Report actions, and South Jetty dune augmentation actions.
Chapter 6 provides an overview of the construction methods (both land-based and water-based) and estimated production rates and schedule for the recommended plan. The associated cost estimates are provided.
Chapter 7 is the recommendation signed by the USACE District Commander.
The first six appendices provide further technical details of the information summarized in Chapters 3 and 4 of the report. Appendices C, D, E, F, and G provide detailed information related to the economic, environmental, and programmatic discussions of Chapters 2, 5, and 6. Appendix D also includes the signed Finding of No Significant Impact (FONSI). Appendix H is a summary of key project events and provides an audit trail for all report reviews.