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FLOOD01647
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Last modified
11/23/2009 10:40:31 AM
Creation date
10/4/2006 10:13:54 PM
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Floodplain Documents
County
Statewide
Title
Optimal Sizing of Urban Flood Control Systems
Date
3/1/1974
Prepared For
US
Prepared By
COE
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />" <br /> <br />flood control and major drainage projects. The methodology is in fact not limited <br />to urban flood-control studies and is equally applicable to other flood-control <br />studies for which the assumptions of the operating characteristics of storage <br />reservoirs, pumping, and diversions apply. The information needed to apply <br />the technique is essentially no different than the usual procedures used in Corps <br />of Engineers flood-control plan formulation studies. <br />Data Requirements,- The level of data refinement needed to model the <br />rainfall-runoff response of the basin, characterize the operation of system <br />components, compute system costs, and perform e,conomic damage computations <br />can vary but should be at least feasibility level. The hydrologic data required <br />are the size and topology of the subbasin subdivision of the basin, precipitation <br />for each subbasin for a representative storm, unit hydrograph, loss rates, and <br />base flow recession for each subbasin, .streamflow routing criteria for each <br />channel reach, and reservoir routing criteria for all reservoirs. Exceedence <br />frequency relations for each damage center for existing conditions must be <br />developed and provided. <br />The system cost functions require tabulation of capital costs for a range <br />of facility sizes, the capital recovery factor for each facility, the annual operation, <br />maintenance, and replacement costs, power costs, and costs of any fixed facilities <br />(not considered variable) to be included. A range of capital recovery factors <br />should be developed for use in assessing the sensitivity of the solution to discount <br />rates and investment timing. <br />The economic functions required are flow-damage or stage-damage relationships <br />for each damage center. The functions should reflect all economic consequences <br />of a flood event and should be present worth for any assumed future change <br />in flood-plain land use. A number of damage functions should be prepared <br />representative of a range of assumed future conditions. The study of nonstructural <br />measures requires manipulation of the damage functions, e.g" flood-proofing <br />measures are reflected by displacing a portion of the damage function within <br />the elevation range that flood proofing is considered. <br />As might be expected when a tool becomes available that provides expanded <br />capability, there is the tendency to attempt to more precisely define the hydrologic <br />and economic performance than would be done otherwise. For example, in <br />the usual study procedure, two damage centers might be used as index points <br />for a reach of stream whereas with the capability available herein twice that <br />many damage centers might be used which would generate additional study. <br />An even stronger urge seems to arise to answer more "what if" questions. <br />While this is somewhat the objective of a technique like this one, the urge <br />should be at least mildly resisted, <br />Development of general performance and cost functions for the system <br />components requires additional analysis. In a study that is of necessity not <br />considering a wide range of component sizes, a single or perhaps two detailed <br />cost estimates might be developed. For the optimization methodology, cost <br />functions that relate to component size are needed which requires a different <br />philosophy of cost estimating. General cost functions are needed initially and <br />the detailed cost estimates deferred until approximate component scales have <br />been determined by the studies. The generalized reservoir performance charac- <br />teristics require additional hydraulic analysis to develop preliminary sizes for <br />outlet works and spillways. <br />
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