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DEVELOPMENT OF FLOODPROOFING CONCEPTS AND STRATEGY The next step was to develop a floodproofing strategy. A 100-year flood was chosen as a standard in evaluat- ing floodproofing techniques. The IOO-year flood or base flood is tbe regulatory standard used by FHH in defining flood risks Vlithin the community. For each structure, the estimated interior I OO-year flood depth was determined, using the lowest floor elevation provided on each structure's elevation certificate. To provide a safety factor in the evaluation of flood proofing techniques, a freehoard of one foot was added to the IOO-year flood depth to define tlle design beight on any floodproofing measures. In evaluating different techniques, a flood depth of three feet (four feet with freeboard) defined the breakpoint between the recommended adoption of simpler less costly measures, such as using exterior sealants, and the mure expensive floodproofing techniques, such as constructing floodwalls nr dikes. Generally, use of exterior sealants is not recommended for flooding depth greater than three-feet, since the bydrostatic force at higher depths frequently result in structural failure or damage to the exterior wall.' The engineering team developed floodproofing techniques that are tailored to the unique structural charac- teristics of eacb of the 23 commercial and industrial facilities in the demonstration project, and the antici- pated 100-year flood depth. Dry floodproofing techniques include waterpruof coatings on exterior surfaces, flood shields to span IVindows and doors, and permanently sealed windows and door openings. Finally, the floodproofing strategy estimated costs for each floodproufing technique, including the cunstruc- tion and operations and maintenance costs. Sources for unit costs included FE~H, the U.S. Anny Corps of Engineers, and data from manufacturers of materials used in the floodproofing, Empbasis was given to estimating costs associated IVith inspection and maintenance of the floodproofing. Utilizing Benefit-Cost Analysis to Evaluate Feasible Projects A Benefit-Cost (BC) Analysis was performed for e-.ich of the 23 structures, using the FEMA Riverine Flood, Full Data Module, Version 5.2.3. The following sections describe in more detail the methods that were used to calculate the BC Analysis. Methods, Tbe Full Data Module derives a BC Analysis by using flood discharges and flood elevations from FEMA Flood Insurance Studies (FlSs) and Flood Insurance Rate Maps (FIRMS). To detennine whether a flood mitigation project is cost-effective, the Module translates the annual benefits produced by the mitigation practices into a single present-day dollar value. This dollar value is compared to the cost of the lnitigation project, and the Benefit-Cost Ratio is calculated. If tbe BC Ratio is equal or greater tban 1.0, the project is cost-effective, since the benefits are equal to or greater tban the cost.][) The FE~H BC Analysis Module calculates the benefits of flood hazard lnitigation by comparing the projected annual flood losses from before and after mitigation. The flood losses can account for physical damages to structures and their contents and loss of revenue during business closure. In the ~Iecklenhurg County Flood Audit project, each structure was initially evaluated for cost-effectiveness considering only the physical damage to the structure and contents. If the project was shown not to be cost-effective, then loss of revenue was estimated in an attempt to make tbe project cost-effective. II Structure Replacement Value. The strucnll-a! damage incurred during a flood event is estimated using the structure replacement value and a function that describes the percent of structure damage incurred for a given flood depth. To develop the structure replacement value, the procedures outlined in Marshall Valua- tion Service (~lVS 1999, Marshall & Swift, LP, Los Angeles, CA) were used. Tbe V.\IS Calculator ~Iethod estimates replacement cost based on average square foot for tjpical buildings depending on their class and l}pe. Items considered in this method include the tjpe of occupancy, number and heigbt of stories in tbe building, square footage of the building, building paJ".uneter, type of heating and/or cooling systems, and 46