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Iowa: Nonstructural and Natural Storage Approaches after Levee Damaged

Recurring significant flood events and resultant physical damages to levees throughout the Midwest region have increased interest in implementing nonstructural alternatives to levee repairs. Public Law 84-99 (P.L. 84-99) provides USACE with the authority and responsibility to either repair flood-damaged levees enrolled in its levee Rehabilitation and Inspection Program or to implement nonstructural alternatives to those structural repairs.

Following the Midwest floods of June 2008, the Iowa Interagency Levee Work Group (now Iowa Flood Risk Management Team [Iowa Silver Jackets]) identified and coordinated a precedent-setting nonstructural alternative to full repair of the Louisa County, Iowa, #11 Levee District's levee system. The alternative is a combination of over 300 acres of Natural Resources Conservation Service flood plain easements with significantly reduced structural repairs to protect a state highway. The alternative required the cooperation of the levee's public sponsor, the county and state mitigation agencies, USACE and Natural Resources Conservation Service (NRCS) to implement. This nonstructural alternative consisted of leaving five breaches in the lower end of the levee system open while repairing two breaches in the upper end of the system. The remaining increment of repaired levee will continue to provide flood deflection benefits for a major county road and approximately 400 acres of agricultural lands within the levee district.

This alternative reconnects nearly 3,200 acres of previously isolated floodplain with the Iowa River as well as increased flood storage benefits to downstream interests. As a result of collaboration, over 1200 acres of formerly protected area was returned to the floodway, gaining not only improved environmental habitat but increase flood storage capacity while continuing to protect an important state road. The NRCS (Emergency Watershed Protection) easements were crucial in the sense that protection of those lands no longer provided benefits to support full structural repair. As implemented, the cost to PL 84-99 was estimated to be $187,000 less than the full structural repair.

The Iowa team was encouraged by this success and is currently working to implement another nonstructural alternative with the Green Island Levee and Drainage District at the confluence of the Maquoketa and Mississippi Rivers (downstream of the [former] Lake Delhi Dam). USACE is providing assistance to NRCS in the development of a Wetland Reserve Enhancement Program project proposal request to acquire easements on nearly 1,400 acres of cropland previously protected by the Green Island levee.