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<br />1.3 INSTRUCTIONS ON GUIDELINES USE <br /> <br />The users of this methodology may apply the regression equations to stream reaches where only <br />approximate or no floodplain mapping exists (where no detailed hydrologic data or floodplain <br />studies are available). The procedure for using the equations in this docwnent for a particular <br />stream reach is as follows: <br /> <br />I. Establish the major drainage basin and the hydrologic subregion where the stream reach <br />(hydrologic point of interest) is located by referencing the basin and subregion maps within this <br />docwnent. <br /> <br />2, Select the regression equation or regression curve for the subregion where the hydrologic point <br />of interest is located, <br /> <br />3. Establish the drainage area at the hydrologic point of interest by planimetering the drainage <br />basin on a topographic map or by obtaining a published value for the drainage area. <br /> <br />4. Estimate the 100-year peak flow value for the hydrologic point of interest by applying the <br />appropriate equation (or regression curve) to the drainage area found in step 3, <br /> <br />1.4 RELATED STUDIES <br /> <br />The TM-1 publication (Reference 2), which was prepared in 1976 by the CWCB in cooperation <br />with the U.S, Geological Survey, has been used in many hydrologic analyses. The manual was <br />developed to provide a simplified method for estimating approximate limits of flood-prone areas <br />along streams in Colorado in response to House Bill 1041 (Local Government Land Use Control <br />Enabling Act of 1974). The manual presents regional regression curves which were developed <br />from stream gage data, Over the past 20 years, it has been discovered that the methods presented in <br />TM-I may not accurately estimate 100-year peak flow values in some geographic areas. Therefore, <br />any usage of that manual should be checked by comparing results with results derived using other <br />hydrologic methods, TM-1 has been essentially superseded by more recent USGS methodologies. <br />Additional information regarding USGS publications can be obtained from the U.s. Geological <br />Survey at the Denver Federal Center in Lakewood, Colorado, <br /> <br />Several USGS and other publications contain hydrologic methodologies for various regions of the <br />state. For basins with drainage areas that fall outside of the applicability of the Guidelines, the user <br />should conduct a detailed hydrologic analysis or use other available methodologies, <br /> <br />6 <br />