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23 24 V. EV ALVA nON OF CONCEPTUAL ALTERNA TIVE$ By reviewing the relative impact of future stonnwater runoff upon the major drainagewlIYs. each of the evaluation parameters wcn: ranked. A minimal impact was assumed wherever the future flows wcre consirlerecl to cause little physical change with respect to a specific parameter. Neutral impact upon a given parameter WlIS considered wherever the negative effects of future flows could be planned for and mitigated. High impact was considered wherever the existing channel soction would be rendered unsuitable to provide for a given parameter in the future flow condition, Using the input from the individuals and agencies who participaled in the meetings and field reviews, flood hazard,operationsand ma intenance, habitat preservation, open space/aesthetics. and water quality were judged to be of high concern in the Dirty Woman and Crystal Creek drainage basins. Introduction Alternative drainageway improvement concepts have been examined that address the existing and future stonnwater management needs of the basin. Alternatives have been identified for each reach of the Diny Woman and Crystal Creek drainageways. Quantitative and qualitative comparisons are presented, and a recommendation made as to which concepts are most feasible to advance to preliminary design and eventually implementation. The general planning goals to be achieved during the alternative evaluation phase were: I. Identify stonnwater facilities which will reduce existing floodplains and flooding problems within urbanized areas: 2. Provide stonnwater management within developing areas of the basin in order to reduce the denimental effects ofnmoff and sedimentation from disturbed areas; Flood Control ErosionConrrol Operation and Maintenance Recreation Right-of-Way Transportation-Roadwayand Trails Open Space/Aesthetics Landllse Water Quality Habitat ConstIUctionOJst Administration and Implementation Environmental Review of Sand Creek Draina~e Basin A preliminary description of the environmental resoun:es in thc Dirty Woman and Cryslal Creek drainage basins is contained in this section. The environmental resources for the purposeofthisreviewconsistsofadescriptionandcompilationofthebiological and land use resources in the basin. their present condition. and an analysis of abiotic and human factors affecting the environment. A reconnais.\ance survcy was conducted during which the environmental conditions were studied by driving and walking the areas and drainages in thc basin. The area was mapped and interpreted in the field based on 7-112 minute topogmphic map~ and ortho-corre-cted aerial pllOwgraphs at a scale of l-inch to 400 feel. panicular allcntion was given to conditions in the drainages <U1<1 spring/>eep areas for biological reSOU;l;CS in the riparian zones and wetlands. Dominant plant species for each habitat type were observed and recorded. The Dirty Woman and Crystal Creek dminage basins trend in a west to southwest diroc:tion from their headwaters in the Black Forest/Palmer Divide area, Dirty Woman Creek cxtends about 5 miles 10 its confluence with Monument Cn:ek, Crystal Creek estends about 3 miles to it confluence with Monument Creek just upstream of Monument Lake These areo.s are in the transilion zone of high plains grasslands and wctlands to the f oothillsand.lowermontane pine forests. The drainage basins have a mixture of scmi,natura] vegetation am.! habitat, somewhat altered by development. specifically Ifansportation corridors. and commercial and. residemialdevelopmenl. The basin has a hi,lOry of human aetiv;ty and disturbance. The western. Iowa drdinage axa has suppOI1ed the Town of Monumer.t ami wa, and continues to be a major nonh"outh roadwa,' and railroad corridor for traffic between Denver and Colorado Spl'lllp, 11\e ea,;rem, upper draInage, area has historically b.:en a ranching district with e,'idencc of heavy ]ivestoL'k 3. Provide stonnwater facilities which preserve and/or enhance the existing drainageway and areas adjacent to the drainageway which provide an environmental resource in the ~, 4. Identify facilities which will minimize fUillre operations and maintenance costs: and 5. Provitk stonnwater management facilities which will at least maintain and/or enhance the water quality characteristics of the basin. The City/Coumy Drainage Criteria Manual was used as a guide in tile conceptual sizing of facilities. Planning goals were developed through the agency/individualcoortlination proce Sl_ Common and/or mutual goals of the interested agencies were itkntified prior to the initiation of the altemative evaJuation phase. Evaluation Parameters OJord!nation meetings were held th.roughout the planning process in order to discuss the overall goals of the study and to solicit specific concerns from governmcntal agencies, individuals. and private community groups. One result of this coordination effort was the development of the following Est ofparametel'l which should be considered when evaluating altcrnatives.