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4 2 of the 6.4 miles to incorporate non-structural related flood control measures in an effort to reduce potential flood damages. The city is acquiring and annexing property included within the 100-year flood plain limit within this two mile reach, and plans to retain the rural, open spacE~ environment -of the area. (References 10 and 11). ,; On the remaining 4.4 miles of the South Platte River which is located in both Arapahoe County and the City of Littleton, the U. S. Army Corps of Engineers had proposed a structural solution to flood control, incor- porating channelization and diking. State funds have been appropriated for right-of-way acquisition, but no action will be taken until a Federal Environmental Impact Report is prepared, reviewed, and accepted for the project. Major drainageway planning reports have been completed for Little Dry Creek, Sand Creek, and Big Dry Creek (References 7, 11, and 12). These reports designate various structural measures and non-structural actions which would be appropriate to alleviate potential flood damage along these streams. 3.0 ENGINEERING METHODS For flooding sources studied in detail in Arapahoe County, standard hydrologic and hydraulic study methods were used to determine the flood hazard data required for this study. Floods having recurrence intervals of 10-, 50-, 100-, and SOO-years have been selected as having special significance for flood plain management and for flood insurance premium rates. The analyses reported here reflect current conditions in the watersheds of the streams. 3.1 Hydrologic Analyses Hydrologic analyses were carried out to establish the peak discharge-frequency relationships for floods of the selected recurrence intervals for each stream studied in detail in the county. .. 11 ~ I