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SECTION 5 . Mod.ifvin~ the Building and/or Relo~ating Contents to Minimize Damage. Potential building modificatiOns may be clasSified mto "dry" and "wet" floodproofing measures. Dry floodproofing measures are designed to prevent floodwaters from enterin<> the interior of a bu~ld~ng but do n?t prevent their encroachment on the exterior. Dry measu;es include sealing bUlldmg walls with waterproofing compounds ,or impermeable sheetin<>; shields used over building openings and sewer check valves. Dry measures are generally n~t recommended for buildings constructed on crawl spaces or basements due to a susceptibility to uplift pressures. Wet floodproofing measures permit a building to flood inside but attempt to insure that there is minimal damage to the structure and its contents. Appliances and utilities might be permanently or temporarily moved to a higher floor. For shallow floodina these items might instead be elevated in place or water proofed with plastic bags and shebeting. Another ;et floodproofing concept is to construct a small addition with an elevated floor. The addition would serve as dry storage during flood events. Wet floodproofing is generally not an accepted practice by FEMA. ALTERNATIVE FUTURE FLOOD HAZARD MITIGATION ACTIVITIES 5.1 INTRODUCTION Before developing a preferred Flood Hazard Mitigation Plan for the Town of Georgetown, a very broad range of possible mitigation alternatives was investigated at a conceptual level. Alternative mitigation concepts given consideration consisted of the following: . Floodproofing . Upstream Storage . Channel Dredging . Channel Floodwall/Levee System . Permanent Bypass Conveyance . Temporary Bypass Conveyance Because of small lot sizes, the lack of high ground on most effected properties, and the historic character of many of the affected structures, relocation of buildings is not a viable option for structures affected by flooding in Georgetown. Pros and cons were developed for each concept and, where warranted, conceptual level analysis ~as carried out and cost estimates were developed. The information developed by this process was presented to the Town on September 3, 1998 in a public workshop. Information describing each alternative concept given consideration is presented in the following sections. 5.2 ALTERNATIVES Construction of levees or floodwalls around structures was also not considered a viable larae- scale solution for flooding. Space limitations around many structures in the historic town and ;he severe aesthetic impacts of such protective measures limit the potential applicability of this concept to a very small number of structures in the flood-prone area. 5.2.1 Floodproofing Building modification and relocation of contents are certainly measures which individual homeowners should consider for minimizing damage incurred during flood events. However, because such measures do not reduce the actual extent or severity of flooding, they were not considered for inclusion in the overall Flood Hazard Mitigation Plan for the town. Floodproofing is defined as "any combination of structural or non-structural changes or adjustments incorporated in the design, construction or alteration of individual buildings or properties that will reduce flood damages" (USACE, 1993). More simply, floodproofing refers to any effort by property owners to reduce potential flood damage to buildings or their contents. There are three general approaches to flood proofing: . Raising or Moving the Building. Almost any structurally sound building can be elevated. Typically the least expensive type of structure to elevate is a one-story frame building constructed over a crawl space (foundation walls). Brick buildings or slab on grade construction is generally the most expensive to elevate. Relocation of a building is of course the most reliable means of floodproofing but often it is also the most expensive and disruptive measure for owners. . Construction of Floodwalls or Levees around the Building. Floodwalls and levees are freestanding structures located away from the building that prevent encroachment of floodwaters. They may completely surround the building or protect only the low side of the property. A sump and pump system may be required to concentrate and remove water, which infiltrates either through, or beneath the levee or floodwall. The only floodproofing concept given serious consideration was the raising of structures subject to flooding. Based on current FEMA Flood Insurance Rate Maps (FIRMs) for Georgetown, there are as many as 88 buildings subject to some level of inundation during the lOa-year flood. A ~ummary of the types of structures subject to flooding and their total square footage is presented m Table 5-1. Not all structures in the floodplain would have to be elevated. Some already have a lowest finished floor elevation significantly above the adjacent ground, and others such as multi- family residences use the lowest floor only for parking and storage. For purposes of evaluatin<> this alternative, it was assumed that half of the buildings in the floodplain would have to b~ elevated. The total estimated cost for elevating 44 structures is $2.1 million, assuming that affected structures will be raised above the lOa-year flood level and that the typical structure is fr~e construction on a foundation wall. It is estimated that buildings would typically have to be raised 2 feet above existing grade. A unit cost of $25/sf to raise frame and foundation wall structures was derived from typical costs recommended by the Army Corps of Engineers. 5-1 5-2