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Last modified
1/25/2010 6:27:32 PM
Creation date
10/4/2006 11:50:16 PM
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Template:
Floodplain Documents
County
Statewide
Community
na
Basin
Statewide
Title
Procedures for Compliance with Floodway Regulations
Date
5/1/1990
Prepared For
State of Pennsylvania
Prepared By
US Army Corps of Engineers
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />Flow_ <br /> <br />_________~-~:~~~~~~~~:~~:I_____- <br /> <br />F <br /> <br />channel and revised floodwaydelineation. This option is generally limited to <br />relatively small streams. The base flood profile must reflect no increase in <br />elevation unless conditions defined in Section 4 NFloodway Development <br />Impacts" are applied. Adjacent communities and property owners opposite, <br />upstream and downstream of the development must be notified of proposed <br />realignments and of any negative impacts induced by the project. <br /> <br />The community has the option of shifting the floodway to one side of the <br />stream or the other as long as both sides of the stream are within the corporate <br />limits and there are no ownership problems. For example, the designated <br />f100dway boundaries may be shifted to a park area on one side of a stream to <br />allow commercial development on the other side. <br /> <br />The development proposal may require hydraulic design documentation <br />of radical bends, bank erosion and sediment control methods, flow transitions <br />to the existing channel and energy dissipation procedures at the lower end <br />of the development as applicable. The hydraulic analysis must encompass <br />the stream from a downstream point unaffected by the proposed development <br />to the upstream point where original conditions and anticipated post-project <br />profiles converge. <br /> <br />Any environmental impacts associated with the realignment of the channel <br />must be described and documented. <br /> <br />5-4. Equal Conveyance Replacement. The concept of equal conveyance <br />replacement as part of a development proposal is similarto that of the channel <br />realignment. The concept is to replace the cross-sectional area of conveyance <br />taken by the development with an equal area below the Base Flood Elevation <br />so that there is no decrease in cross-sectional conveyance area at the develop- <br />ment location throughout its range of flow depths. See Figure 6. This may be <br />accomplished by excavation of the conveyance area or by replacing a <br />structure below the Base Flood Elevation by one of equal or less volume and <br />cross-sectional area. The excavated area must be adjacent to the main <br />channel to assure that conveyance is maintained so that there is no increase <br />in the Floodway profile. <br /> <br />Other hydraulic design criteria as described in Section 5-3 are also ap- <br />plicable. As in relocation of channel alignments the hydraulic analysis must <br />encompass the stream from a downstream point unaffected by the proposed <br />developmentto the upstream point where original conditions and anticipated <br />post-project profiles converge, and it must be demonstrated that a reasonable <br />flow transition is maintained through the altered cross sections. <br /> <br /> <br />Existing Channel <br /> <br />Proposed Development Site <br />Figure 5: Relocation of Channel <br /> <br />Flood Fringe <br /> <br />Floodway <br /> <br />Flood Fring <br /> <br /> <br />Figure 6: Equal Conveyance Replacement <br /> <br />5-5. Development Elevated on Piers or Columns. Proposed devl <br />elevated on piers or columns may result in a negligible increase in <br />flood elevations, requiring no compensating actions. However, the c <br />must demonstrate that this is the case. Small increases in the base pn <br />be offset by procedures defined in Section 4-2. The developer ma: <br />required to analyze the effect of debris buildup among the piers or ( <br /> <br />5-6. Fill or Barrier Obstruction. The placement of fill or a barrie <br />a levee or floodwall in the f100dway requires remedial actions to ( <br />induced increase in the base flood profiles. These actions are oft, <br />replacement of lost conveyance area through the cross section at the, <br />ment (see Section 5-4). The developer, if a Federal agency or if usi <br />from a Federally sponsored program, must also meet applicable fl, <br />guidelines such as Executive Order 11988. <br /> <br />National Flood Insurance Program regulations (PART 65) include s <br />for levees or f100dwalls. These standards address freeboard requi <br />structure and closure maintenance, interior drainage, etc. Develol <br /> <br />12 <br />
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