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<br />\ <br /> <br />__1 <br />~ <br />( <br />f <br />( <br />i <br />t <br />( <br />\ <br />\ <br />( <br />\ <br />\ <br />I <br />i <br />t <br />i <br />\ <br />( <br />( <br />. <br />t <br />, <br />, <br />\ <br />; <br /> <br />CHAPTER 9 <br />ELEVATING NEW STRUCTURES <br /> <br />i <br />, <br />I <br />( <br />, <br />( <br />, <br />" <br />( <br />I, <br />( <br />I <br />" <br />~ <br />f <br />" <br />i <br />( <br />( <br />I <br />l <br />i <br />i <br />t <br />I <br />i <br />i <br />( <br />( <br />( <br />~ <br />i <br />t <br />, <br />i <br />I <br />, <br />, <br />, <br />, <br />i <br />" <br />, <br />I <br />~ <br />, <br />i <br />i <br />f <br />i <br />i <br />,. <br />( <br /> <br />Description <br />New residential structures or substantial additions to existing structures to be built on flood <br />hazard sites are required, under the National Flood Insurance Program, to have their lowest <br />floor elevated to or above the base flood level. I n coastal zones it is the lowest portion of the <br />structural members of the lowest floor which must be elevated to this elevation. Nonresidential <br />structures have the option of making a structure watertight or elevating. The idea of elevating a <br />structure is not new, however. Numerous residential and commercial structures built in flood <br />hazard areas have been elevated for years (1). The means used varies depending principally <br />upon aesthetics, the type and use of structure, availability of materials, and upon the nature of <br />the flood hazard. Commonly used methods include: earth fill, concrete walls, and wood, steel, <br />concrete or masonry posts, piles or piers. Figure 9-1 shows several structures elevated in this <br />manner and Reference 1 describes the methods in detail. <br /> <br />Physical Feasibility <br />Earth fill is commonly used in residential subdivisions, shopping centers, industrial parks, as <br />well as for individual structures. It is especially suited for use over large areas because not only <br />can the structures be elevated, but utilities, roads and storage areas are elevated as well. It has <br />the added advantage of being placed and contoured in a manner which makes it harmonize <br />with natural terrain. It is applicable to individual structures although the landscaping has to be <br />unique for each structure. <br /> <br />The principal factors which govern the use and height of earth fill are: <br /> <br />. Availability - adequate amounts and quality of fill material must be available locally. <br /> <br />. Settlement - foundation material upon which fill is placed and the fili itseif must be <br />capable of supporting both fill and structure within acceptable limits of settlement. <br /> <br />. Erosion - slopes exposed to erosive flow must be protected. <br /> <br />. Compensatory Storage and Flow Cross-Section - when extensive areas of the flood plain <br />fringe are filled it may be necessary to provide compensatory storage or flow cross section <br />to prevent increased peak flows downstream and higher flood stages upstream. Both must <br />be maintained and kept free from sediment encroachment. <br /> <br />. Aesthetics - the height and location of earthfill should be compatible with the natural <br />landscape. Often this is a limiting factor regarding height of fill. placement (location and <br />height) can also influence the market value of adjacent land. <br /> <br />Columns, piers, posts and piles are structural members commonly used as foundation <br />supports for residential, commerciai and industrial buildings. The selection of the appropriate <br />type is influenced by the following factors: <br /> <br />. Settlement - foundation material upon which the support rests and the support itself must <br />be capable of carrying the load of the structure and any other design loads. <br /> <br />. Scour - foundations must be capable of being designed to be protected against scour. <br /> <br />62 <br />