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<br />'. . <br /> <br />. <br /> <br />. <br /> <br />---:..;:~. <br /> <br />. <br /> <br />UNITED STl\TES <br />DEPARTMENT OF <br />l\GRICULTURE <br /> <br />SOIL <br />CONSERVATION <br />SERVICE <br /> <br />\T . OFFIC<: <br />15~O 12TH STREET <br />ALAMOSA, CO B1101 <br /> <br />Date: October 4, 1990 <br /> <br />subject: ENG - Lake San Cristobal <br />Outlet Structure <br /> <br />To: Jim Mietz, RC&D Coordinator <br />scs, Alamosa CO <br /> <br />File Code: 390-13-23 <br /> <br />Purpose: <br />The purpose of this trip was to investigate problems at the <br />outlet of Lake San cristobal. We were also to look into its <br />potential as an RC&D measure. <br /> <br />Findinqs: <br />Hinsdale County is requesting financial and technical <br />assistance to replace the grade control structure located at <br />the outlet of Lake San Cristobal. On October 2, 1990, I met <br />with John Scott, DC, Gunnison; Jim Mietz, SLV RC&D <br />Coordinator, Alamosa; and the Hinsdale County Road <br />supervisor to discuss the proposed project. <br /> <br />Lake San Cristobal is a natural lake that formed when the <br />Slumgullion Slide blocked the Lake Fork of the Gunnison <br />River. The slide material blocking the river channel, being <br />highly erosive, continued to erode as it was replaced by the <br />movement of the slide. The channel gradually stabilized and <br />streambed armor developed as the movement of the slide <br />slowed. <br /> <br />In the 1950's, a large streamflow occurred and caused the <br />stream channel armor to be eroded. This resulted in highly <br />erosive materials being exposed to the erosion process. The <br />channel rapidly degraded to the point that the lake was <br />placed in serious jeopardy. The water surface of the lake <br />was lowered significantly. The rapid lowering of the lake <br />added additional water to the already high water and caused <br />severe flooding of the properties downstream. The <br />properties sustained damage to buildings and land from water <br />and. -'sediment_-:depoSi:ts ~- '~~.';': :--:.. . -: =7'- -~- . - '. .~_.. ::::='. :-::: - - - <br /> <br />The damaged channel was later restored to its pre-runoff <br />elevations with the State Engineer of Colorado apparently <br />providing the engineering. Earth and rockfill was placed in <br />the eroded channel and a grade control structure constructed <br />across the channel at the outlet of the lake for protection <br />of the restored channel. The structure was constructed of <br />timber and provided a sufficient level of protection until <br />the mid 1980's. <br /> <br />. _ ,u_ __.-...._ _. ___ <br />