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SECTION III AL TERNAn: PLANS The development of alternate concepts for the dr-alnageways Included basic data collection, hydrological studies, field inspections, and the development of various possible alternates whlcr appeared to provide an opportuni ty for a solution to the lon9-range flood pr.oblem on Big Dry Creek. The alternate concepts were presented to officials of 'vIestmlnster, Adams County, Jefferson County, and the Urban Dralnage and Fiood Control District. ThIs study was limited to the flood plain of Big Dry Creek, and, by definition, did not give detaIled consIderation to the channels in the basins tributary to the main channel. Certain .Iternates are signifi- cantly affected by the tributaries to Big Dry Creek, and each al ternate Is defined as to this effect. The Drc,win!)s which show various alternates used for meetings and for the decision-making process are on file wIth the Urban Drainage and Flood Control Distl-ict. Channel encroachment and deterioration of BIg Dry Creek can create a sIgnIficant drainage problem. Paralleling the deterioration of the channel is often the encroachment onto the flooc' plain. ThIs is a typical problem In the urbanIzed areas of the Denver region. As little channel encroachment exists, this study hus a great deal of flexlbi 1 i ty in choice of alternates sInce certaIn altE~rnates havE' not all'eady been eliminated. In many of our cities, the mujor dr,linase system often has not been planned or designed and Its functionIng very often I-esults in flood damage losses. The major system fulfi lIs the maIn damage-prevention function. The major system will operate whether or not It has been de- signed and whether or not urban improvements are situated ,.,Isely in regard to It. The work in thIs assignment deals exclusively with a major drainage system, Big Dry Creek. Once this maJ"r drainage system Is planned, de- signed, and constructed, the smaller tributary major drainage systems and the InitIal draInage system consistIng of storm sewer.s and small channels fall Into order more easily. The alternates presented subsequently were dlscllssed In Phase A and are agaIn presented to make the reader aware of the scope of the study. Alternates Studied 1. Flood PlaIn Zonlnq Without Structllral-'mprov.~~nt:2. -(Non-Structural Alternate) ThIs alternate Is based on the flood plain as it is presently constituted. It Is defined by the 100-'year runoff from the basIn under projected future development with presently-existing channel condi tlons. The approach of "dol ng nothIng" is an economi- cal and legItimate alternate on Big Dr.y Creek and can be compared, cost-wlse, on an annual basis to other alternates considered In thIs 111"1