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<br />:37 <br /> <br />---- <br /> <br />v. NATURAL AND INHERENT METHODS OF FLOODPROOflNG <br /> <br />5.1 General <br /> <br />Inherent flood proofing characteristics refer to natural and developed features of a flood <br />plain that in some way provide a degree of flood protection, Natural features include large <br />islands, rock outcrops, shallow areas and thick vegetation. Developed features are structures <br />that already exist in the flood plain from previous development, including embankments that <br />are parallel to or cross the drainage channel and actual streets themselves acting as channels <br />during flooding, <br /> <br />The main purpose in identifying these areas is that they can be incorporated into a flood- <br />proofing scheme and used to help minimize the overall costs of floodproofing and the <br />damage that will occur during flooding. Every flood plain has its own characteristics and dif- <br />ferent features, The features discussed in subsequent sections are typical to many flood <br />plains. However, they are not the only features that could help mitigate flood damage. The <br />main characteristics of all features is that in some manner the velocity and depth of flooding <br />are being reduced. <br /> <br />5,2 The Flood Plain <br /> <br />In evaluating the flood plain for development, it is important to know the different <br />regulatory areas within the flood plain. The 1 DO-year flood plain is also referred to as the <br />designated flood plain within the state of Colorado. This is the area of land which is inun- <br />dated by the base flood (1 DO-year flood), The area oubide the base flood that is affected by <br />larger floods or by seepage and groundwater from the regulatory flood and is called the <br />secondary flood hazard area (SFHA). This area of land lies between the 100-year and the <br />500-year flood plain limit boundaries, <br /> <br />The designated flood plain is broken down into two areas, the floodway and the flood fringe <br />(see Figure 5.1). The floodway is the channel and the adjacent area required to pass flood <br />flows without increasing the water surface elevation by a specified rise criteria above the <br />existing BFE. No development is recommended within the floodway. The flood fringe is the <br />remaining flood plain from the floodway boundary to the boundary of the BFL Regulations <br />apply to development within the floodway and the flood fringe in accordance with the <br />Model Flood plain Regulations for local governments (Reference 22). <br /> <br />DESIGNATED FLODDPLAIN-, <br /> <br />- <br /> <br />FLOODWAY <br />FRINGE <br /> <br />- FI,.OODWA,(-~"~- <br /> <br />FLOODWA~ <br />FRINGE <br /> <br />STREAM <br />....----- <br />CHANNEL <br /> <br /> <br />FLOOD ELEVATION WHEN <br />CONFINED WITHIN FLOODWAY <br />ENCROACHMENT, I <br /> <br />"::, :,:,:,:,:,:,:;,,:,:::;:::::;:;:,:,:,:,:;,,:,:,:: ",:;:,:,' C <br />A ":'::;~;~~~;~ffi~~I~~~~~~~fi~~~~~i/:;~f~~ -- <br /> <br />ENCROACHMENT <br /> <br />- D1..::::::::::,:,::::::::::::ri, :::, :." <br />S'JRCHARGE* 3............. , <br />..........". ... <br />--'---ft ".;.;.;.;.;...-"" <br />.. }mrr:;:~~~;jp B <br /> <br />FLOOD ELEVATION <br />\.____ BEFORE ENCROACHMENT <br />ON FLOODPLAIN <br /> <br /> <br />AREA OF FLOODPLAIN THAT <br />COULD BE USED FOR DEVELOPM~NT <br />BY RAISING GROUND <br />LINE AB IS THE fLOOD ELEVATION BEfORE ENCROACHME>JT, <br />LINE CD IS THE fLOOD ELEVATION AfTER ENCROACHMENT, <br />-SURCHARGE IS NOTTO EXCEED 1.0 fOOT (lEMA REQUIRIM'NT) OR [ISSIR AMOUNT AS <br />SPECifiED BY STilTE. <br /> <br />Figure 5.1. Floodway and floodway fringe <br />