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<br />38 <br /> <br />5.3 Natural features <br /> <br />Natural features that can be incorporated as flood proofing include various naturally occur- <br />ring structures in the flood plain. One very obvious feature is islands that occur within a <br />flood plain which are not submerged during the regulatory flood. Two examples of this fea- <br />ture are shown in Figures 5.2 and 5.3, The figures show two different areas along the Gun- <br />nison River. Figure 5,3 shows the actual flood pl'lin boundary around the island. As shown in <br />the figures, it is important that access to such areas be designed and elevated above the <br />regulatory flood. <br /> <br />A second type of natural flood proofing feature is rock outcrops and stone building materials, <br />Large rock outcrops can be used as part of an anchoring system by securing the structure to <br />the outcrop. Large stones are good building materials for both buildings and flood walls. <br />Figure 5.4 shows 'l picture of the highway maintenance building, constructed partly of rock, <br />which survived the Big Thompson Flood, Other Structures that add weight and thus stability <br />include rock chimneys, walls, and stairways. Placed on the downstream side of the structure, <br />they can add significant stability. <br /> <br />Along with rock type structures, large trees and dense vegetation can be used on the <br />upstream side of a building structure to divert flood flows and reduce velocities. <br /> <br /> <br />ISLAND DEVELOPMENT <br /> <br />{/ <br /> <br />r <br /> <br /> <br />[] <br /> <br />Figure 5.2, Island development <br />