Laserfiche WebLink
<br />Guidelines and Specifications for Flood Hazard Mapping Partners [April 2003] <br /> <br />only by chance. Such analyses are subject to appeal or protest on the basis of being scientifically <br />or technically incorrect. <br /> <br />In watersheds with significant storage, hydrologic routing may be needed in estimating the flood <br />discharges. Some hydrologic routing methods require a relationship between the water-surface <br />elevation and the cross-sectional area, or the floodplain storage area between cross sections. For <br />those methods, a hydraulic model is required as part of the hydrologic analysis, and the hydraulic <br />model used to generate rating curves shall be provided by the Mapping Partner that performed <br />the analysis for review by the reviewing Mapping Partner with the hydrologic model. <br /> <br />The reviewing Mapping Partner shall ensure that the rainfall-runoff model has been calibrated <br />against available data as described in Subsection C.1.1.3. Where reliable gaging station data are <br />available, the rainfall-runoff model must be calibrated against them. <br /> <br />In Ullgaged watersheds where high-water marks from major flood events are available, the <br />reviewing Mapping Partner shall ensure that the rainfall-runoff model and the hydraulic model <br />have been calibrated against the high-water marks. If no high-water marks from major events <br />exist, and regression equations are determined not to be applicable, the Mapping Partner that <br />performed the hydrologic analysis shall provide a detailed explanation of the rainfall-runoff <br />model, and the designated Mapping Partner shall review the model in detail to deterrnine flood <br />discharge reasonableness. <br /> <br />C.2.4 <br /> <br />Hydrologic Review Documentation <br /> <br />[February 2002] <br /> <br />The reviewing Mapping Partner shall document the results of the review in a memorandum or <br />letter that will be sent to the RPO and to the Mapping Partner that performed the hydrologic <br />analysis. The documentation shall describe the review approach and conclusions (whether flood <br />discharges are reasonable or unreasonable) and shall provide options for resolving any concerns. <br /> <br />If the proposed flood discharges are determined to be unreasonable, the options may include, but <br />are not limited to the following: <br /> <br />· Requesting further justification or documentation that the proposed 1-percent-annual- <br />chance flood discharges shall be used; <br /> <br />. Suggesting an alternate method; or <br /> <br />. Revising the analysis to obtain more reasonable results. <br /> <br />C-15 <br /> <br />Section C2 <br />