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<br />Guidelines and Specifications for Flood Hazard Mapping Partners [April 2003] <br /> <br />The Mapping Partner performing the Mapping Needs Assessment shall consider the following <br />factors that affect the hydrologic conditions in evaluating the community's need for a flood data <br />update: <br /> <br />. Changes in land use in the watershed; <br /> <br />. Publication of new regional regression equations;: <br /> <br />. Changes in design storm data; - <br /> <br />. Increase in length of stream record; and <br /> <br />. Construction of flood-control structures. <br /> <br />Each factor is discussed in more detail below. <br /> <br />Changes in Land Use in the Watershed <br /> <br />Significant development or other changes in land use in the watershed (both within the <br />community and in any upstream communities) can significantly change the discharges. Often, <br />the increase in impervious areas associated with urbanization causes an increase in the stream's <br />peak discharge. The Mapping Partner performing the 1-bppine; Needs Assessment can evaluate <br />the amount of development in a community by reviewing a variety of information, including: <br /> <br />. Community Comprehensive Plan; <br /> <br />. Community zoning maps; <br /> <br />. Site plans for large projects; <br /> <br />. Storm water utility plans; and <br /> <br />. Letters of Map Change (LOMCs) issued by JFEMA smce the effective FIRM was <br />published. <br /> <br />The Mapping Partner performing the Mapping Needs Assessment should refer to Volume 2 of <br />these Guidelines for more information on LOMes issued by FEMA, which include Letters of <br />Map Amendment (LOMAs), Letters of Map Revision Based on Fill (LOMR-Fs), and Letters of <br />Map Revision (LOMRs) based on conditions other than fill. <br /> <br />Publication of New Regional Regression Equations <br /> <br />The U.S. Geological Survey (USGS) records, studies, and publishes streamflow data, including <br />the magnitude and frequency of flood peaks. From the:se data, the USGS develops or revises <br />regional regression equations and publishes them in Water Resources Investigation Reports. If <br />effective base (l-percent-annual-chance) flood discharges were estimated using regression <br />equations and the analyses are more than 10 years old, there is a reasonable chance that the <br />regional regression equations have been revised since those analyses were conducted. The <br />Mapping Partner performing the Mapping Needs Assessment shall compare the effective base <br /> <br />1-17 <br /> <br />Section 1.2 <br />