The project team performed an assessment of the existing levees to evaluate whether the levee system meets the requirements of 44 CFR §65.10 — Mapping of Areas Protected by Levee Systems and to document any deficiencies that exist. Deficiencies in Freeboard, Closures, Embankment Protection and Stability, Interior Drainage, Vegetation Management and Right-of-Way Encroachment were identified for both the riverside and lakeside levees that render the levees not certifiable in their current state. Since the levees are not certifiable in their present condition, a rehabilitation project would be necessary to change the FEMA floodplain mapping and insurance requirements for the west part of the city. Many levee embankment options were considered, including sheet piles, secant piles, cutoff walls, inverted T-walls, box culverts, reconstruction in place and setback levees. Due to cost considerations, environmental and community impacts as well as construction risks, the preferred alternative for levee certification would be a traditional earthen embankment, constructed either in situ or relocated behind the existing levee. An inverted T-wall may also be a viable alternative in areas where it is desirable to reduce the width of the levee cross section and settlement risk are low such as along segments of the riverside levees. A proposed certifiable embankment cross section was developed with landside side-slopes of 2:1 and waterside sideslopes of 3:1. The height would be set at three feet above the 1% annual-chance water surface elevation (WSE) with a crest that is 12 feet wide. A Benefit-Cost Analysis (BCA) was created to compare the various reconstruction alternatives. It compared the cost of flood insurance and potential flood damages against the cost of constructing and rehabilitating the levees. The results of the conceptlevel BCA is a Benefit-Cost Ratio (BCR) greater than 1.0 for all three alternatives. The benefits of avoiding private flood insurance costs and gaining property protection outweigh the public cost amount for levee improvements based on the preliminary analysis and engineering performed. Three levee rehabilitation alternatives were compared with respect to the major criteria important to Provo City: Affordability, Flood risk protection/ FEMA certifiability, Environmental, Recreational Quality and Minimization of private property acquisition. Ultimately, the alternative that balanced setback distances from the river and property acquisition was recommended over options that held extremes for those mentioned criteria. However, it may be discovered later that environmental permitting constraints could cause larger setbacks to be more feasible. The full report and study were presented to the Provo City Council, who directed the team to gather more information and possibly reevaluate the hydraulic analysis that determined the flood discharges that led to the proposed FEMA FIRMs. References Bowen Collins & Associates. Provo City Storm Drain Master Plan. January 2019. Gerhart Cole. Technical Memorandum: Provo City West Side Levees Geotechnical Engineering Evaluation, Job No. 20-1278. December 11, 2020. Provo City, 2009. Utah Lake Dike, Brief History. January 29. 4 pp. United States Army Corps of Engineers (USACE)], 1983. News Release. Sacramento District. April 18. 3 pp. United States Army Corps of Engineers (USACE). Levee Owner’s Manual for Non-Federal Flood Control Works: The Rehabilitation and Inspection Program, Public Law 84-99. March 2006. United States Army Corps of Engineers (USACE). EP 1110-2-18: Guidelines for Landscape Planting and Vegetation Management at Levees, Floodwalls, Embankment Dams, and Appurtenant Structures. May 1, 2019. State Stream Alteration Program Fact Sheet SA-1, Second Edition. Utah Division of Water Rights. Provo River LAMP Study, Utah County, UT by AECOM for FEMA, July 11, 2019. 45
RkJQdWJsaXNoZXIy MTg3NDExNQ==