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9 As mentioned, floodways have been computed for each stream. A floodway represents a part of the flood plain which is required to pass a lOa-year flood event without raising the flood profile more than an acceptable amount and also represents that part of the flood plain most hazardous to personal safety and welfare. In this study, the floodway was defined as being the limit of en- croachment into the flood plain where existing flood profiles are not increased more than 0.5 feet. Also, flood plain areas where average velocities exceeded two to three feet per second were considered to be within the floodway. Areas where significant portions of the flood flow were directed to alternate paths, such as along Monaco Boulevard, were also considered to be within the floodway. Floodway widths, which represent the maximum limits of enc~oachment into the flood plain, are tabulated in Tables 5 and 6. The flood plain limits presume planned, future development in the basin, existing, mapped flood plain conditions, no peak flood flow reduction or interception by the Highline Canal and no blockage at the existing culvert and bridge structures. Even with these assumptions, floods of greater magnitude can and will occur in which the limits of flooding will exceed those shown in this report. Flood Velocities presently, the majority of potential damages on Goldsmith Gulch exist in the reaches below Yale, with some minor damages such as channel erosion and crossing damages in the reaches above this location. In the area below Yale there has been development within the 100-year flood plain and the capacity of the channel has been severely restricted. In this reach, all the road crossings will be overtopped and Monaco will become a carrier of flood waters. The flood hazard not only includes the potential damage to public and private property but also involves the inability of the City to provide emergency service to the area because of the flood waters inundating the major transportation system. Average flow velocities, characteristic of a 100-year flood event on Goldsmith Gulch and tributaries, are shown on the profile por- tion of the Flood Hazard A,rea Delineation Drawings. The flow velocity in the channel would range generally between 4 to 10 feet per second for a lOO-year event in the study area. Overbank velocities range between 1 to 4 feet per second. - Sm'lJl1ARY - Presently, the lower reaches of Goldsmith Gulch and the Southmoor Park tributary are considered to have a high flood damage potential. The preservation of the flood plain will serve, at least, to maintain the present level of damage potential while any improve- ments will minimize or reduce the flood damage potential. Re- ducing the flood hazard potential can be accomplished through structural improvements to culverts and channels, flood proofing and an operational and effective flood plain management program. The upper reaches of Goldsmith Gulch and the entire west tribu- tary are considered to have a low flood damage potential. The preservation or improvement of the lOa-year flood plain in these areas will maintain and possibly reduce flood damage potential through these reaches. Current master plans and flood plain ordinances in Greenwood Village and Arapahoe County will regulate development in the flood plain. Water flowing at a rate greater than 6 to 8 feet per second will cause severe erosion of stream banks and is capable of trans- porting large rocks. Velocities in the range of 6 to 8 feet per second could erode fill around bridge abutments. Water flowing at about 2 feet per second or less will deposit debris and silt. This report has identified the probable flooding limits of a po- tential lOa-year flood event in the Goldsmith Gulch drainage basin.