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57 --~ VII. DESIGN CRITERIA FOR STRUCTilURES 7.1 General This chapter identifies general types of floodproofi~g construction and critical areas of con- cern for each, Floodproofing methods can be as vari!ed as the hundreds of sites subject to flooding in Colorado; therefore design criteria for typical flood proofing methods are presented here, This will give a better underslandin~ of what can and should be done III flood-prone areas. ' Elevated structures, waterproofed structures, levees, and floodwalls are all frequently used ,n flood hazard areas, They are defined in the following, sections, A freeboard requirement (in feet above the BFE) has been established for all of t!hese methods, Table 7,1 presents the freeboard for each method. For a discussion of condrete and block masonry walls, the reader is referred to Chapter XI. Table 7,1, Freeboard ReRuil'ements. Freeboard Type of Floodproofing Ht above BFEl 4 3 1 1 1 1 1 Dike or levee system 100 ft. upstrf'ar~l of a roadway embankment or bridge. Dike and levee system for cornmLlnit~ protection. Flood plain regulations. Building site fill. Closure of ofwnings. Floodproofing design of individual ~t~LJctures. Retaining walb and/or floodwalls for ;individual strlJctures. 7,2 Elevated Structures The starting point for design of d structure in a flood-t)rone area is the consideration of site con- ditions. So it is with deciding on a technique to be ,bed for elevating a structure. In many cases, the most important site factor will be! flood elevation. This will influence or may even dictate the landscaping measures as discussed i~ Chapter III and foundation design as dis- cussed in basement design, Chapter XI. Direction of f1q,od flow is also important and the surface area of walls exposed to flowing flood waters "hould be minimized when orientating a new building. Methods available for elevating structures are many.lbey include raising on fill or raising on stilts such as posts, piles, piers, and walls. 7,2.1 On Fill Elevating a structure on fill so that construction is abqve the design flood can be a good method for protection from flood damage. However, the fill m~lterial cannot generally be placed within a designated floodway for compliance with state and f~d('ral regulations. If a structure on fill contains a basement and soil saruration is probable, hydrostatic pressures must be considered as explained in Chapter XI. For olher structures, with all construction above the water level and saturation point, the critical component in this kind of design is the earth fill.