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I "'-1/ .- I jf:lJ t!J~if'iNC I I il I. . . . I I I I I I . I I I July 31, 1991 Me, William DeGroot, P.E. Urban Drainage and Flood Control District July 31, 1991 Page 2 Mr. William DeGroot, P.E. Urban Drainage and Flood Control District 2480 West 26th Avenue, Suite 156B Denver, CO 80211 The City of Lafayette's floodplain regulation defmes the floodway based on a maximum I-foot rise, as opposed to the City of Louisville's and the District's O,5-foot rise standard. Due to the varying standards regulated by the sponsors of this study, it was considered appropriate to define both the one-foot and the one-half foot rise floodways in this report, The floodway data and other floodplain data have been tabulated within this report. This report is supplemented by a Technical Appendix which contains considerable additional information. This related document provides the engineering background for the hydrology and hydraulics which are represented herein. A copy of this Technical Appendix is on file at the District's office. In addition, we will remain available to provide interpretations or updates to the information in this report. We have enjoyed the opportunity to work with you and the representatives of the City of Lafayette and the City of Louisville during the preparation of this study. The cooperation and guidance of the contributing staff members has been very beneficial to the completion of this study, We look forward to a continued involvement in the project during the preparation of the Outfall Systems Planning study, as well as in the future as the master plan is implemented. RE: Flood Hazard Area Delineation, Bullhead Gulch and Tributaries, Lafayette, Louisville, and Boulder County ASI No. 8162 Dear Mr. DeGroot: Presented with this letter is the final report entitled "Flood Hazard Area Delineation, Bullhead Gulch and Tributaries." This document presents the I OO-year floodplain delineations for 10 miles of Drainageways 3012 and 3014 located in the northeastern portion of the Urban Drainage and Flood Control District. This report represents the completion of one part of a contract between our firm and the District which began in February, 1991. The contract also includes the preparation of the "Outfall Systems Planning, Bullhead Gulch Watershed" study, which will follow this report. Very truly yours, The Flood Hazard Area Delineation (FHAD) represents the horizonal and vertical extent of the 100-year floodplain based on existing channel conditions and future basin imperviousness. The results of this study will provide a valuable tool to the sponsoring agencies, and other governmental agencies with jurisdiction over floodplain management regulations within this watershed. This study will also provide a basis for the recommended master plan improvements which will be developed and presented in the "Outfall System Planning, Bullhead Gulch ~i2 Tyler D. Smart, P.E. Project Manager Watershed." 405 Urban Stret't. Suite 401 L<kewood, CO 80228-1236 (303 J 980-0036 FAX (303) 9SC'~ 12l~(i ~\,,\\Umlllml/flJ. ~\~ OI3ER f l.?II~, #e:, ~ ..D.fU~r;"rIU/l~ Reviewed by: t'*,..t,&\STEIl~(;.--'1:~ ~~..'q;O D.~~ ~-~. .~~ q: fZ - ->!." 16922 g;:*~ := ::Il w: S ~ ~~ ~:O~ ~~~~~ ~~"Q ~ J sR. Kunkel, PhD, c-~":...$IONAL ~,''n..~ff . . . ~ 'it ........ 0'(0 ~ Semor Project Engmeer ~Il OF CO'-- ,# '1111I111"'1II\\\""\~ Authorized for ASI by: .~6-~ Timothy D. Steele, PhD Manager, Physical Sciences Group