Built in the mid-1990s by the U.S. Army Corps of Engineers, the existing levee flood control system protected the city of Alvarado in 1997, 2005, 2009, and 2010. Even though the levee system has performed adequately since its completion, has been well maintained, and has been shown on Federal Emergency Management Agency’s current flood insurance rate maps (FIRMs) as providing protection from the 100 year flood (base flood), FEMA requires documentation be submitted that demonstrates that the levee system, including operations and maintenance procedures, meet the requirements of Title 44 of the Code of Federal Regulations (CFR), Section 65.10 (44 CFR §65.10), titled “Mapping of Areas Protected by Levee Systems.” The compliance documentation must include design criteria (i.e., freeboard, closures, embankment protection and stability, foundation stability, settlement, interior drainage), operations, and maintenance.
The city hired Barr to perform a preliminary engineering assessment of the existing levee system relative to 44 CFR §65.10 and identify remedial measures for the city’s interior drainage concerns and needed improvements to correct other deficiencies discovered during the engineering assessment. Detailed hydrologic, hydraulic, and geotechnical analyses conducted during the preliminary engineering phase of the project revealed that modifications to the existing levee system are required in order for the flood protection system to obtain FEMA accreditation and to meet current USACE design criteria. The city also requested that Barr design, permit, and implement the needed levee system improvements. Since the improvements include modification to the existing federally built levee system, the improvements were designed in accordance with USACE standards and require 33 USC 408 approvals.
To address levee deficiencies and restore the city to the USACE levee safety program, Barr developed and received USACE approval of a System-Wide Improvement Framework (SWIF) Letter of Intent (LOI)
Upgrading the flood protection system consisted of the following major tasks:
Construct a rock buttress along 800 feet of the levee system
Remove material along a 400-foot reach of the levee system on the riverside of the existing floodwall (bank unloading) near West Bend
Grading to achieve adequate geotechnical factors of safety
Stabilization of the river bank adjacent to section of the levee
Realignment of the existing levee in the southwest corner of the city to achieve adequate geotechnical factors of safety and protect the area from erosion
Storm sewer for interior drainage near West Bend Lane and Gatewell B
The project was completed in summer 2014 and FEMA certification was completed in early 2015.