Board of Adjustment Agenda and Packet 2014 09 17

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III1rr1 `J`1 `III Louisville Mill Site Floodplain Development Letter August 22, 2014 Page 2/3 areas of ponding where average depths are between 1 to 3 feet and that Base Flood Elevations (BFE) have been determined. The warehouse building and its proposed addition are located outside the mapped 100 -yr floodplain and is located within Zone X. Zone X is definite as the areas between the limits of the base flood and the 0.2- percent - annual- chance (or 500 -year) flood. Per the FEMA mapping, the site does not lie within the 100 -year floodway. The 100 -yr BFE for the site is noted on the FIRM map is 5333. Two structures are proposed within the floodplain. The first structure is the minor additions to the existing Grain Elevator. The lowest surveyed first floor elevation is 5334.7. The Grain Elevator has an existing basement with an approximate floor elevation of 5327.1. The basement is an unoccupied space with a dirt floor housing the historic elevator equipment. As part of the rehabilitation project, the basement walls are being replaced with new concrete walls where required. Two minor additions will be added to the structure. The finished floor elevation (FFE) of the proposed eastern addition to the Grain Elevator will match the existing FFE at 5334.7. This will place this addition 1.7 -ft above the BFE. The western addition will be built over the historic porte cochere foundation and will step down from the main level FFE to match the top of the existing footers on the north side. The elevation of this addition will be 5332.7 on the low side and 5334.3 on the high side. The western addition will be below the BFE, and therefore a floodplain development permit variance is required. The second structure is a new multi -story commercial building to be built near the demolished commercial building site. The new structure will be built with a first floor elevation of 5334. The foundation will be either a crawl space or a finished basement depending on tenant and owner preferences at the time of building permit application. The first floor elevation will be 1.0 feet above the BFE. If a basement is proposed, the floor elevation will be approximately 5322. The basement will be dry floodproofed according to FEMA regulations with concrete foundation walls, impermeable membranres or other flood proofing measures. The attached calculations demonstrate the hydraulic loadings the structure will experience when inundated up to the flood protection elevation. The building's structural design will accommodate these loads, and will be provided to the City for review upon Building Permit app lication. We do not anticipate the project will adversely impact the water surface elevation of the base flood elevation in this area based on the following: the proposed project is not located within the 100 -yr floodway; Zone AH is an area of shallow flooding and ponding not directly connected to the major drainageway; and the project adds a net increase of 5140 square feet of building footprint inside the floodplain. The commercial building has an estimated footprint of 7100 square feet, and the demolished building has an approximate footprint of 3360 square feet for a net addition of 3740 square feet. The grain elevator additions will total approximately 1400 square feet in ground level footprint, and will be primarily built on existing foundation/basement of the historic structure further reducing the impact to the floodplain.