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studies for the struoture providing the most economic degree of ,pro- tcction at Sopris Dam site and for a ohannel improvement through Tt'4>.idad, that a combination of these structures is not feasihle at this time. (See project justification, par. 94.) ,,' . 78. Plan oj improvement recommended.~The most feasible plan for the protection of Trinidad, where the largest concentration of losses, occurs, provides a channel improvement within the city of Trinidad for the protection of the urban areas which are overflowed by flooda from Purgatoire River. In order not to induce a sense of false secu- rity inpoople in the flood plain, it was considered that the"..trncture .should,'provide '(lood ,protcction equal to that of the maliOimum flood , of'recerd, ,jfeeonomically justified. To obtainthe,.mo"t economical, design which,would provide the greatcst degree of e<;lonomic protec-, tion, various channel sections and types were considered., Limiting channel widths and velocities governed the design of the re<;lommended plan of improvement. For peak discharges up to and ineluding a flood with a probable occurrence of once in 100 years, 45,000 cubic feet per second, and the maliOiffium of record, a channel with an un- paved invert would not produce eliOeessive velocities. To provide for diseharges above 45,000 cubic feet per geeond would necessitate it wider unpaved channel section to control sufficiently the velocities. A wider channel section would involve eliOpensive eonstruction of sev- eral bridges and removal of commereial and industrial property. A channel with a paved invert which would control ,floods above,45,000' . cubic feet per second, although of lesser width than an unpaved sec- tion, would require a mare expensive design to control the resulting high velocities. Tho recommended improvement would consist of two typi<;lal.sections and levM construction abovo and belowtheso soctions. Qne,typioal section would be an unpaved rectaI\gular chann<\! andre- inforccd concrcto ,cantilever walls, with back,up levees having rip- rapped slopes capable of passing a peak discharge of 45,000 cubic feet per,second with a 2,foot freeboard. The other typical section would be an unpavcd trapezoidal channel witb riprapped sido slopes. Trap- ezoidal reaches would be constructed above and below the cantilever wall section. Upstream from the trapezoidal channel, levees with rip- rapped side .lopes are provided to collect the flow into the channel pl'Oper. Below tbe downstream trapezoidal section, a lever. with rip-, rapped sido slopes would bo constructed on the right bank to confine the flow below Linden Avenue. Two dropatruc,tures'are provided to obtain the most economical channel design. A two span deck girder bridge, witb150 feet between abutments, would be constructed at Commercial Street to repll1,ce the present two spa,n concrete arch struc' ture. The intake of tho Baca irrigation ditch would be moved about 2,450 fcet upstrcam and would be constructed as an integral part of the drop structure above Animas Street. A concrete conduit from the intake would carry the water diverted to the present ditch at Chestnut Strcet. Concrcte channel weirs would be constructed at criticalloca- tions to control the channel slopes to the desired grade. ' The COI\struc- tion of the improvoment would entail special construction provisions, at, the abutments and piers of some of the existing bridges. The plan and cultural details are shown on map No.9, appendix A. The plan and sections of the recommended improvement are shown on map No., I .