In early 2009, the city of Oslo, Minnesota, was notified by FEMA that its existing levee system needed to be recertified within two years to continue to be included in FEMA’s flood insurance program. The city hired Barr to evaluate the levee system, design remedial measures, obtain USACE approvals, provide construction management services, and produce the documentation necessary to achieve FEMA accreditation of the levee system. Barr’s experienced geotechnical team provided recommendations for cost-effective solutions to upgrade more than 2,000 feet of existing unstable riverbank which was identified as an USACE system deficiency.
Barr’s evaluation included review of available data, field investigations and inspections, and engineering analysis. The results indicated additional deficiencies in the levee system. Ultimately, the USACE’s periodic inspection resulted in an unacceptable rating of the levee system; failure to resolve the levee deficiencies within the tight timeline would place the entire city in the 100-year floodplain and virtually eliminate all possibility of future residential or commercial development. The required improvements included property acquisitions, addressing USACE deficiencies, raising significant portions and realigning portions of the levee, raising gatewells, modifying the existing pump station, utility penetration rehabilitation, roadway modifications, potable water tank replacement, and earthen road closures as well as constructing new levees and a railroad closure structure.
To remedy the known riverbank instability deficiency, the geotechnical project team implemented a subsurface investigation which included borings, piezometer and inclinometer installation, and monitoring. We used the data to perform computer modeling, including seepage and stability analyses for the proposed levee improvements with the software programs GeoStudio SEEP/W and SLOPE/W, as well as specialty modeling with FLAC. The project implemented 2,800 feet of new levee construction, raising 13,500 feet of the existing levee, over 300 feet of floodwall, railroad closure structure across Canadian Pacific Railway tracks, existing pumping station improvements, new tractor driven pump station, seepage mitigation, property acquisitions, and public infrastructure improvements.
Barr provided engineering support, technical oversight, and on-site construction oversight during construction. We managed safety plans, progress reporting, progress monitoring, pre-inspections, and schedules. We developed and followed quality management procedures to support evaluation of levee, utility, street enhancements, pump station modifications, structural improvements, and other construction activities.
We ultimately developed a design documentation report, construction report, as-built and record drawings, and the FEMA 44 CFR 65.10 tabbed submittal needed for FEMA accreditation. Barr also developed a new operations and maintenance manual for the entire rehabilitated flood-risk management system in accordance with USACE criteria and as a requirement of the Section 408 approval. The plan was approved by the USACE and submitted to FEMA meeting the project end goal of levee system accreditation.