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I I 12 I I 100-year storm event and under such a flood condition the road will be overtopped to a depth of approximately two feet. The Lone Tree Creek flood plain remains in a natural condition except for three crossing structures at Orchard Road, Arapahoe Road and the east-west runway of the Arapahoe County Airport. No other improvements have been made in or adjacent to the flood prone area. I I I I The reach from West Parker Road to Interstate 25 contains no development which would be susceptible to flooding. The channel through the reach is well defined and as a result the flood plain becomes considerably narrower than in the lower reaches. The width through this reach is less than 100 feet. Orchard Road is located within the Cherry Creek State Recreation Area. The existing culverts at Orchard Road, as at Arapahoe Road, are inadequate for the one percent flood event. In each case the road will be overtopped to a depth of one to two feet during such an event. A backwater effect is created above Arapahoe Road which widens the flood plain south of the road. I In the reach from Interstate 25 to the upper limits of the study near the Urban Drainage & Flood District boundary, the channel is very steep, having bottom slopes in excess of two percent. The crossing at 1-25 is adequate for the 100-year event. Upstream of 1-25 there is no existing development in or adjacent to the flood plain. The steepness Of the terrain will discourage de- velopment next to the stream. The flood plain width is less than 50 feet and well defined. I I I I Development pressures along Cottonwood Creek will continue to increase due to the influences of 1-25, the Arapahoe County Air- port and the possible construction of 1-470. The third obstruction in the Lone Tree Creek flood plain is the east-west runway of the Arapahoe County Airport. The runway has been constructed across the natural stream on a 23 foot high em- bankment. A 48-inch concrete pipe exists as part of the embank- ment. The 100-year flood event will create a 20 foot deep back water south of the runway embankment for a distance of approximately 1,000 feet. Flood waters will overtop the runway to a maximum depth of approximately 1.5 feet near the eastern end of the run- I I I way. AS a result of overtopping, damage to the runway surface and embankment could result. I I Lone Tree Creek - The flood plain limits and water Surface pro- files for Lone Tree Creek are shown on the Flood Hazard Area Delineation Maps, Drawings LC-l through LC-6. I