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NEW STUDY The flow estimates developed in the 1977 study for the 100 year event were utilized for this study. There have been little, if any, changes in the physical characteristics of the basin contributing to the peak flows at the proposed development. The procedure used in determining the floodplain elevations for the proposed conditions was the revised 1991 HEC-2 Water Surface Profiles program (Version 4.6.0) by the Army Corps of Engineers. The information used to develop the proposed cross sections were the approved final grading plans for Westwoods Golf Course. The grading plans were developed from a 1991 aerial topographic map, with 2' contours, produced at 50 scale. Culverts, crossings and other details were surveyed in the field. The cross sections were surveyed in the field. Ralston Creek, as it flows through the site, contains both subcritical and supercritical flows between various cross sections. Two runs were performed to evaluate the floodplain elevations for both subcritical and supercritical conditions. The elevations were evaluated in both conditions and the worst case, or higher elevation, was chosen for that particular cross section. The difference between the two conditions are minimal but warranted comparison. In nearly all cases the subcritical condition prevailed. See Table A for a list of cross sections and the floodplain elevations. Twenty cross sections plus a special bridge card were utilized in the 1 mile stretch between the west and the east property lines. A new box culvert has been designed for the Quaker St. crossing for which the special bridge card was used. The culvert consists of two con-span arches, side by side, each 135' long, 24' wide and 12' high. It has been overdesigned to allow a horse and rider to pass through one side with plenty of head clearance. Cross section #16 is a section down the length of the Farmers Highline Canal at the crossing with Ralston Creek. This section is intended to illustrate the high water elevation in relation to the top of the headwalls of the canal siphon under Ralston Creek. The intent in developing a grading plan for the proposed golf course community was to keep the golf course along the creek corridor and to develop the residential areas away from the creek and out of the 100 year floodplain. A series of 9 golf course ponds also provide 3 1/2 and 100 year storm water management in accordance with the City of Arvada's drainage ordinance. Reference is made to the Westwoods Golf Course Floodplain Designation Map. ~