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. , . . '. . . I I . . . . I . I I I I I proposed conditions HEC-2 model were used to determine the crest elevations of the proposed levees along this reach. The top of levee elevations shown on plate 2 depict minimum elevations required for lOO-year and 500-year levels of protection, but these elevations do not account for any freeboard, The proposed levees should provide adequate flood protection for structures behind the levees, but would not be sufficient to remove the structures from the floodplain from a regulatory standpoint. Certain freeboard and construction requirements would need to be met in order for FEMA to consider removing levee-protected areas from the regulated floodplain. The constructed levees should adhere to Corps of Engineers criteria which includes, at minimum, a 10-foot top width and 3H to IV side slopes, A compaction of 95% for the embankment material should also be achieved, Typical levee cross-sections are shown on plates 3 and 4, however a more detailed investigation of Corps criteria should be made during final design of the levees. A short reach of the channel between the upstream study limit (County Road 69) and the abandoned railroad line (Chicago, Milwaukee, St. Paul & Pacific) is proposed to be relocated. Approximately 1,500 linear feet of channel would be excavated just to the west of the existing alignment so that levees could be constructed on both sides of the new channel. The old channel would be filled in with the excavated material, A typical cross-section for this reach is shown on plate 4. For the purpose of developing preliminary quantity and construction cost estimates, the levee heights were estimated by taking the difference between the computed water surface elevations and the approximate ground elevations along the levee alignments. Ground elevations along the final levee alignments should be surveyed and tied to MSL datum so that the actual levee heights can be appropriately designed. Hiawatha Avenue to 9th Street NE The portion of the Main Ditch along this reach was conceptually designed for 100-year capacity with an excavated channel section and a very minor levee (one foot high) along the west channel bank at the 90 degree bend, A trapezoidal channel having a 100-foot bottom width and 3H to I V side slopes was evaluated for the reach between 9th Street NE and the 90 degree bend downstream from there, The channel invert and alignment would essentially match those of the existing channel. A typical cross-section for the excavated lOO-year channel is shown on plate 3, The short reach of Main Ditch between Hiawatha Avenue and the 90 degree bend would remain 7