Laserfiche WebLink
<br />Colorado Water Conservation Board <br />Department of Natural Resources <br />721 Centennial Building <br />1313 Sherman Street <br />Denver, Colorado 80203 <br />Phone, (303) 866.3441 <br />FAX, (303) 866.4474 <br /> <br />- 1-:J2.... <br />STATE OF COLORl\DO <br />tM\ <br />. <br /> <br />I/' <br /> <br />~ <br /> <br />December 18,1997 <br /> <br />Roy Romer <br />Guvernor <br /> <br />Iilmes S. lochheild <br />E:<ecuti"e Director, DNR <br /> <br />Dilries C.lile, PE <br />Director, eWe8 <br /> <br />Ms, Cindy L. Edwards, P,E., Program Manager, Stormwater <br />Department of HighwayslEngineering <br />5334 South Prince Street <br />Littleton, CO 80166-0001 <br /> <br />Dear Cindy: <br /> <br />We have received the materials related to the request for a Conditional Letter of Map <br />Revision (CLOMR) for Unnamed Creek and "Tributary A" to Unnamed Creek in the <br />proposed Saddle Rock Ridge Subdivision (Filing No. I) in unincorporated Arapahoe <br />County. We have reviewed the request and would like to offer some comments. <br /> <br />Hackl!round <br />The current floodplain delineation is an approximate delineation with no supporting <br />hydrologic data provided by FEMA. The developer's engineer, Ms. Ann Woods of <br />Carroll & Lange, Inc., has computed drainage areas of 89.5 acres for Unnamed Creek <br />(approximately 0.14 sq. mi.) and 73.3 acres for Tributary A (approximately 0.11 sq. mi.) <br />The depth of 100-year flooding would be less than one foot and the 100-year floodplain <br />width is less than 50 feet. At a mapping scale of 1" = 1000', the delineated floodplain <br />would be 1/20 inch wide, About half of the 1 OO-year flows would be contained in the <br />local drainage storm sewers and the other half would be contained between the street <br />curbs. No 100-year flows would directly affect private property. <br /> <br />Should Storm Drainal!e Areas He MaDDed? <br />There is a somewhat vague transition between "local storm drainage problem" areas and <br />the "floodplains" into which they ultimately flow. Drainage area (in square miles) and <br />peak flow (in cubic feet per second) are the usual parameters evaluated to make such a <br />distinction. If drainage area or peak flow is below some value, then an area is a storm <br />drainage problem area instead of a floodplain, While we feel it is important for local <br />govemments, developers of land and homeowners to be aware of storm drainage <br />problems, we feel that there are very special circwnstances when they should actually <br />appear on a FIRM and be subject to NFIP regulation. The first criterion is: do local <br />drainage regulations fail to adequately address this storm drainage area? The second <br />criterion is: willflooding affect private property or pose a serious risk to life or property <br />within public property (i.e. preventing vehicular access during a flood, posing a danger <br />