REQUESTER: In compliance with 33 USC 408 (Section 14 of the Rivers and Harbors Act of 1899; hereinafter Section 408), Economic Development Administration and Klingner & Associates PC request permission on behalf of Muscatine Island Levee District to modify the Muscatine Island Levee, an existing federally authorized FRMP.
LOCATION: The proposed project is located along the Muscatine Island Levee District, in Muscatine, Iowa.
LOCATION MAP(S)/DRAWING(S): See Figures 1, 2, and 3.
REQUESTER’S PROPOSED ACTION: The existing Muscatine Island Levee District FRMP consists of approximately fourteen miles of earthen embankment, mainstem, and tie-back levees. Muscatine Island Levee District proposes a Levee Improvement Project on a three-mile reach of the mainstem levee (Feature 1, Figure 1), to be funded by the Economic Development Administration, and a Hardened Controlled Overtopping Structure at the downstream end of the levee (Feature 2, Figure 1).
Feature 1 includes raising and strengthening the mainstem levee from STA. 165+00 (Maple Grove Road) to STA. 332+00 (Muscatine-Louisa County Line). This feature would provide a more resilient flood protection system and move the incipient point, the most likely overtopping location, of the sand levee downstream (Feature 2) to reduce flood risk due to an overtopping event. The proposed improved section of levee is near critical infrastructure and industrial development, as well as multiple communities. If levee overtopping were to occur in this reach, there is potential for catastrophic damages, loss of life, and environmental catastrophe due to the rapid inundation of the levee district. By improving the levee in this reach and moving the incipient point further downstream, the district is increasing the time for preparation, reaction, and, if necessary, evacuation during a potential major levee overtopping event.
Feature 1 involves placing sand on the levee crown and landside levee slope to widen and raise the proposed reach to the 100 year + 4.5 feet of freeboard level (Figure 2). The borrow sand for the project would be excavated from a historic sand stockpile located at Muscatine County Deep Lakes Park. Feature 1 is being funded with a 50% match from EDA.
Feature 2 includes the construction of a hardened controlled overtopping reach near STA. 700+00 (Figure 3). This one thousand lineal foot (1000 LF) structure would provide resilience at the new downstream incipient point. The levee slope and toe would be hardened with a specialized geosynthetic turf surface that is resistant to high velocity water flow. This would provide protection against erosion and scour in the event the levee is overtopped at this location. Providing a resilient levee overflow structure allows for controlled inflows of flood water during extreme events while allowing for a quick recovery once the river flood waters have receded. During a potential overtopping event, the structure would direct the flow into the downstream end of Muscatine Slough which feeds into the drainage network for the Muscatine-Louisa Drainage District 13 Pump Station. Feature 2 would be fully funded by the local Muscatine Island Levee Stakeholders and local government entities.