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<br />,< <br /> <br />l <br /> <br /> <br />Federal Emergency Management Agency <br />Washington. D.C. 20472 <br /> <br />CERTIFIED MAIL <br />RETURN RECEIPT REQUESTED <br /> <br />IN REPLY REFER TO: <br />Case No.: 96-08-I8IP <br /> <br />The Honorable Mark Williams <br />Mayor, Town of Castle Rock <br />144 Hillside Drive <br />Castle Rock, Colorado 80 I 04 <br /> <br />Community: Town of Castle Rock, Colorado <br />Community No.: 080050 <br />Panel Affected: 0188 C <br />Effective Date of <br />This Revision: JUN 18 1996 <br /> <br />102-I-A-C <br /> <br />Dear Mayor Williams: <br /> <br />This responds to a request for a revision to the effective Flood Insurance Study (FIS) and National Flood <br />Insurance Program (NFIP) map for your community, Specifically. this responds to a letter dated <br />March 21, 1996. from Mr. Rodrick C. Hamilton, Engineer II, Town of Castle Rock, regarding the <br />effective FIS report and Flood Insurance Rate Map (FIRM) for the Town of Castle Rock, Colorado. <br />Mr, Hamilton requested that the Federal Emergency Management Agency (FEMA) revise the effective <br />FIRM to show the effects of the construction of storm drainage improvements and erosion protection <br />measures along Hangmans Gulch consisting of a storm drain outfall at Prairie Lane, concrete erosion sills. <br />and riprap-lined channel banks from Frontage Road to approximately 2,000 feet upstream of Frontage <br />Road. Mr. Hamilton also requested that FEMA revise the FIRM to show the effects of channel <br />improvements along Hangmans Gulch that were made during the construction of Scott Road and to correct <br />an error in the hydraulic model used to develop the effective FIRM. This request follows up on a <br />Conditional Letter of Map Revision, which was issued on June 29, 1994, <br /> <br />All data required to complete our review of this request were submitted with Mr. Hamilton's letters dated <br />March 21 and April 8, 1996. Because this Letter of Map Revision (LOMR) shows the effects of a <br />publicly sponsored flood-control project that reduces flooding to existing development, fees were not <br />assessed for the review. <br /> <br />We have completed our review of the submitted data and the flood data shown on the effective FIRM. <br />and have revised the FIRM to modify the elevations and floodplain and floodway boundary delineations <br />of l\ flood having a I-percent chance of being equaled or exceeded in any given year (base flood) along <br />Hangmans Gulch from Frontage Road to approximately 4,600 feet upstream. Hangmans Gulch has been <br />realigned and channelized from Frontage Road to approximately 2,000' feet upstream of Frontage Road. <br />The construction of the storm drain outfall routes overland flow from the Scott II Filing No.3 subdivision <br />into the existing channelized portion of Hangmans Gulch. Concrete erosion control sills and riprap were <br />placed within the channelized portion to prevent channel degradation caused by the introduction of flow <br />from the storm drain outfall. <br /> <br />The base flood elevations (BFEs) decreased along the revised reach. The maximum decrease in BFE. <br />10 feet. occurred approximately 2,400 feet upstream of Frontage Road. The widths of the Special Flood <br />Hazard Area (SFHA)-- the area inundated by the base flood-- and floodway increased and decreased <br />compared to the widths shown on the effective FIRM. The maximum increases in SFHA and floodway <br />