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1 i j I 1 j I 1 , ~ ! j I I I , 1i:.~ :~O''''tl' . ,~"",:1l.... .',..,0:, l",'';'~ ~'.... ': ,'"',,,.... ,', ',,'" . Boxelder Creek was investigated using the "special bridge routine" option. A design discharge of 4,700 cubic feet per second (cfs) was used for the investigation to represent the , 100-year, or Regulatory Flood, quantity of flow. This discharge quantity was estimated by the Soil Conservation Service in 1969 or earlier as being that portion of the total.ll,900 cfs reaching Interstate 25 during the 100-year flood that would pass through the concrete box culverts and over the highway lanes westerly into Section 16, T7N, R6SW. The remaining flow was assumed to flow southerly on the east side of 1-25. As a result of their study of Boxelder Creek four structures (detention areas or reservoirs) were planned to reduce peak storm discharges throughout Boxelder Creek. The estimated 100-year flood flow quantity reaching 1-25 after completion of all four structures was 3,140 cfs, with only 1,625 cfs passing westerly onto Section 16. Currently, two of the structures have been completed, a third is under construction, and the fourth and last structure is designed with bids for construction to be opened later this fall. Essentially this means that the flood control program is well under way, and that our flood- plain investigation using 4,700 cfs should be considered conservative. Due to the complexity of establishing a more refined quantity of flow at the present status of improve- ments and of determining floodplain characteristics up- stream of 1-25, this office has used 4,700 cfs for this study. In the more comprehensive study report to follow, the effect of the reduced flow from completion of all four structures will be addressed in detail. III. RESULTS OF THE INVESTIGATION Copies of the computer printout of the 100-year water surface profiles for the natural, or existing, conditions