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. . . 2-08. Departures from the Phase I GDM DesiEn. The extent of channel improvement has been modified from the recommended plan in the Phase I GDM. This modification resulted from comments by SWD and HQUSACE personnel at a design field conference held in Pueblo in December 1983. The Phase I GDM recommended a channel width from 270 feet to 570 feet and excavation to the existing thalweg, resulting in a broad flat-bottomed channel. The General design meeting comments limited channel excavation to a depth not to exceed 3 feet above the stream invert in the overbank area. The low flow channel would remain in it s pres ent cond it ion. The length of the channel improvement was increased to 1,450 feet downstream of the Missouri Pacific Railroad bridge. This was required to lower the design water surface elevation 1.5 below the Missouri Pacific Railroad bridge. 2-09. The west bank levee upstream of the 8th Street Bridge was revised due to space restrictions between the railroad and Interstate 25 limiting the width of the levee section. A soil cement levee and concrete flood wall are incorporated into the design of the west levee above the 8th Street Bridge. 2-10. The east bank levee in the Phase I CDM presented a tie-back levee which ran parallel to the Missouri Pacific Railroad at the lower end of the project. This levee was intended to tie to natural high ground to create a ponding area for interior drainage and to maintain adequate freeboard (the water surface profile was higher than the railroad bridge approach fill). Subsequent investigations, field reconnaissance and improved aerial photography revealed no high ground for the levee to abut to. The lengthening of the channel improvement as presented in this design memorandum reduced the design water surface to an elevation which allows the levee to tie to the Missouri Pacific Railroad abutment. Also, an economic analysis of the need to improve interior drainage in this area revealed that improvements were not justified. 2-11. Changes in the design of levee freeboard agreed to at the general design conference have eliminated the overflow section between the 4th and 8th Stre~t bridges On the east bank. The freeboard will gradually be reduced from 4-feet at the upstream end to 3-feet at the downstream end of the project. This along with increased channel improvements reduced the levee height requirement at the Missouri Pacific railroad and so eliminated the need for a tie back levee. The levee will now tie into the railroad fill about 200 feet east of the Missouri Pacific east bridge abutment at Fountain Creek. 2-12. BridEe Modifications. The Phase I GDM recommended that two bays of the 8th St. bridge be opened by excavation of channel material for flow and that modifications to the bridge piers would be made. Information obtained from the city of Pueblo during Phase II investigations showed that the bridge piers were founded On a shale bedrock layer. During subsurface exploration the shale was determined to be competent and the existing piers would not require modification. Two bays will be excavsted under the recommended plan to a depth not to exceed three feet above the present low flow Thalweg. 2-13. Other Plans Investi~ated. A constricted area was revealed during site ~SLts on the east bank of Fountain Creek between Sta 28+20 and the 4th Street bridge. The constricted area is defined by existing buildings on Erie Street " , and the high east bank. A typical earth leveeCsection would require either condemnation of the existing buildings or extension of the earth levee section 80 feet into the low flow channel, severely reducing flow capacity. II-3