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INTRODUCTION EXECUTIVE SU~ARY The City of ~tontrose, through its Cormmnity Development and Planning Departments, is engaged in a cooperative program with the Colorado Water COn<;ervation Board and the Departrnent of Local Affairs to collect and analyze storm runoff and floodplain information for intellige nt and orderly planning of future storm drainage facilities. Thiseffortisbeingconductedinatwo-phasedapproach. The pre- viously completed first phase was directed to gathering the basic facts (Reference 1). Hyctrologicand hydraulic analyses were conducted to deter- mine water surface elevations and to delineate the flooded area boundaries to reduce potential flooddallldges. This second phase is directed toward formulating alternate flood control and drainage plans forwiser. .anagerrent ofthefloodp1ainandrapidlydevelopingurbandrainageareainandaround the City of Montrose. This report presents a plan to reduce flood damage in the City of Montrosewilter service area. This area is affected by the flood flows from Cedar Creek, Montrose Arroyo, and Dry Cedar Creek. At the present ti~e, the culvert crossings on Montrose Arroyo dre insufficient to pass the lOO-year flow; consequently, during such an event, a considerable arnountof flow,lould be lost from the cha.nnel to flow overland. Thi, Shallow flooding would flow away from Montrose Arroyo west, and north- west toward the Uncompahgre River, resulting in average annual damQges to residential andcorranercial areas in the amount of $198,000. There is also some overflow from Cedar Creek in Montrose due to insufficient culvert capacity, which causes $24,000 in average annual damages. The flood dalllaqes Cd used by Dry Cedar Creek are estimated to be minim al. The recolTl1lended Flood Control Plan consists of iOlproving ten culverts on Mont- rose Arrovo. and onl' on Cedar Creek. This plJn would eliminate structural damage from floods up to the 100-yearevent. The economic evaluation was completed based on the following criteria: 73/8% interest rate; project life of 50~years; and 1980 dollar base. This economic analysis yields benefit-cost ratios of 1.20 and 2.49 fOI'Montrose Arroyo and Cedar Creek Au ~hori za tion This report "dS ..utilol'i ,"'0 by til'" Colurddo Water Conservation ~Qard In joint sponsorShip with the City of Nontl'ose, Colorado, and Montr ose County, and the Colorado Department of Local Affairs. Specific tasks were performed according to the terms of a contract between the C010l'o.oo Water Conservation Bodrd and Gingery Associates, Inc. dated March 1, ]980. The respectively. iX",,'0"p<JweranddutY1S: "...todevise and formulatemethods,rneans and plans for bringing aboutthl'gl'eaterlltilizationottnewatersot the state and thepr e- vention of flooddalllages therefrom and to designate ana approve storm or floouwdy runoff channels or hasins. and to ~ake such desig- nations available to legislative bodies of cities and incorporated towns; to county planning conmissions; and to boards of adjustment .j. 4