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. . . Hydraulic Analysis of Construction Conditions 10 Existing Construction Conditions Survey At the request of the Colorado Water Conservation Board, additional cross sections were surveyed to more accurately describe the conditions on the property during construction. The new cross sections were surveyed by King and Associates of Windsor on January 19, 1992. The survey certification is included at the end of this document with the raw data downloaded from the survey instrument. Five new cross sections were added to the area under analysis to ensure an accurate modeling of the construction conditions. Three of these new cross sections are located upstream of the existing cross section, and two are located downstream. In calibrating all new survey data to the existing FIS survey data, a benchmark in the most recent FEMA Flood Insurance Rate Map with an elevation of 4769.26 feet above mean sea level denoted "RM20" was used. This bench mark is located on the top of the concrete of the Southeast corner of the Northea.st abutment of Weld County Road 17 bridge. The results of this survey are shown on plate 1, included as a supplement to this document. To examine the data used to generate this drawing see 'New Survey Coordinates', page 49 or the supplied data diskette. The data format is x,y,z coordinates and wa.s certified as to its direct translation into HEC-2 format. The formatted data was then added to the existing FIS HEC-2 data and simulations were run. HEC-2 Simulation Analysis In addition to the five n€,w cross sections, the Colorado Water Conservation Board indicated we can not take full advantage of the reduced roughness due to the water surface of the lakes during construction. The reason for this is twofold. First of all, until both of the lakes are completely finished, the full benefit of the reduced roughness will not actually take place. In addition, any stockpiles near the lakes may create ineffective flow areas and therefore the reduced roughness of the lake in certain area.s will not have any effect. For these reasons, the roughness value used for the construction conditions will be the same as existed for the current FIS. Table 3 shows the results of the HEC-2 simulation of construction conditions utilizing the addi- tional cross sections. Note there is no increase in the water levels of the base flood discharge, and in two cases there is actually a drop in the water surface. The topographic cross sections for eight cross sections of interest are shown starting with figure 8 which is one cross section downstream of Laku Landing. Figures 9 and 10 are the two new cross sections downstream of cross section #139690 which was part of the most recent FIS. This cross section is shown in figure 11. Figures 12,13 and 14 are the three new surveyed cross sections just upstream of cross section #139690. Finally, the cross section just upstream of Laku Landing which wa.s part of the current FIS is shown in figure 15.