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51 --- - referred to several good references (Simons and Senlurk, 1976, Criteria for Channels and Hydraulic Structures on Sandy Soils, 1981). Three geheral situations that can exist in the flood plain are considered in this section. The methqds used are conservative ancl apply toward an individual structure that is not affected b~ nearby structures, I n many flood plain situations the density of buildings and the diversion :of flow from other structures must be considered. Thus, in a flood plain where the derlSityof various structures is high, it is recom- mended that qualified engineers evaluate the situation. The three typical situations that apply to different flood proofed structures are waterproofed structures that are at ground level; structures elE~vatejd on piers, piles, posts or walls; and structures elevated on fill. Water proofed type struqures at ground level (see Figure 6.5) are subject to local scour as water is diverted around thf corner of the structure. Piers, piles, posts or walls that are used to elevate structure" are subject to local scour (Figu", 6.6) and require adequate burial depth or protection aga'nst scour. Compacted fill used to elevate structures is subject to erosion along the face of the fill and local scour as the fill impinges into the direction of flow (Figure 6.7). ~. -- .......-- ~~~-- '~~,' _....----~~~ .. DIRECTION OF FLOW ~!. ,~ [ DEPTH OF FLOW = d --~---.'.: ..:.~. ~:. .'~ ....,.~~-;: ._~~~-...' , .' --~ _ J -....,....--.-" ~A.REA OF GREATEST SCOUR DEPTH AT B0TH UPSTREAM CORNERS Figure 6.5, Scour action on a ground level building. \J ------- ~/""'I , DEPTH OF FLOW = d ~ --------- ~ ---------- DIRECTION OF FLOW.. ',." ~,'~'~"," DEPTH 0 -. . SCOUR = S '- ,,- '\ . ,; '" ~)) <,\ -7~~S7~'_t?, ~- ""f'il '- , U>~ ~';:t:r~~L~_:.: -;~- I I I "'-'--1 '-~./ Figure 6.6. Local scoure at piers, piles, posts, and walls.