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I ! , Introduction This SpecIal flood Hazard Information Report for the South Platte RI~er In Morgan County and Washington County, Colorado ~as prepared by the Omaha DistrIct, Corps of Engineers, under contlnu- tng authority provided by Section 206 of the 1960 flood Control Act <PUblic Law 86-645), as amended. The report was requested by the Colorado Water ConservatIon Board, The purpose of this report Is to present Infor~tlon describIng the South Platte RIver and Its flood plain In Morgan County and In Washington County relative to past flooding as well liS +0 potenttal future floodIng. This report basIcally shows the relllttonshlpof the 1973 flood on tha South Platte River In Morgan County end Washington County to the 100~year f food. I nformatlon on the 10-, 50-, ilInd 50o-yaillr floods Is also presented. The Information provided varies from stage- discharge relationships at each cross section In the rural areills to water surface profiles In the urban areas. Throughout the study reach,ftoodwldthshavabeen lndlcafed at each cross section loca- tlon. The information In this report is Intended for use primarily by planners concerned with the area, This report does not Imply any Federal interest or ilIuthorlty to ~one or regulat.. the uSe of the South Platte River flood plein In Margilln County or in Washington County; this Is a 10<:",1 responsibility. The report provides a suitable billsis for the edoptlon of land use controls to guide flOOd plein development with consideration for environmental attributes, thereby preventing Intenslflcetlon of loss problems. Since It Identifies flood problems. the report will stimulate the develop- ment of other flood d~ge reduction techniques such as flood control, removal of obstructions and flood proofing. which might be used In an overall Fiood Plain M"nagement crf'l.1) program. Distribution of the report to officials, agencies, and Indi- viduals concerned with planning In the aroa covered Is made by Morgan County and by WilIshlngton County. The Corps of Engineers will provide interpretilltlon and technical asslstillnce, If requested, In appllcilItlon of the report dillta. Other guidelines available from the Corps of Engineers are a pamphlet, "Guidelines for ReduC- Ing Flood Damages", ilInd a booklet, "Introduction to Flood Proofing". Basin and Stream Characteristics The South Platte River In Morgan County flows In a general easterly dIrection from the Weld-Morgan County line to about Fort Morgan,Coloredowhereitgraduallyturnsandflowslnanorth- easterly direction Into Washington County to the Washington-logan County line. Throughout this reach the South platte River flows Inarelatlvelywelldeflnedchannel. This channel Is typically braIded and Is situated Ina bro"d shallow valley ranging In width from about 1,500 feet to about 21,000 feet and Is flanked by roil- Ing plains, The streambed slope of the South Platte RIver In Margilln and Washington Counties Is relatIvely uniform generally ranging between 9 feet per mile and 5 feet per mile and averaging 6.5 feet per mile. The dralnillge area of the South Platte River In Morgan and WashIngton Counties varies considerably from the Weld-Morgan County line to the WashIngton-Logan County line due mainly to the number of relatively !erge tributaries draining orl- marlly the plains region Io<:ated to the south of Morgan and Washington Counties. Table I gives dralnillge areas of the South Platte River ~t stre~m gage locations within Morgan and WashIngton Counties. ,