Agenda Item 12: Lake San Cristobal Natural Lake Stabilization Issues

Home Browse Search

UNITED STATES SOIL 1T OFFICE DEPARTMENT OF CONSERVATION 15y0 12TH STREET AGRICULTURE SERVICE ALAMOSA, CO 81101 Subject: ENG - Lake San Cristobal Outlet Structure To: Jim Mietz, RC &D Coordinator SCS, Alamosa CO Purpose: The purpose of this trip was outlet of Lake San Cristobal. potential as an RC &D measure. Date: October 4, 1990 File Code: 390 - 13 - 23 to investigate problems at the We were also to look into its Findings: Hinsdale County is requesting financial and technical assistance to replace the grade control structure located at the outlet of Lake San Cristobal. On October 2, 1990, I met with John Scott, DC, Gunnison; Jim Mietz, SLV RC &D Coordinator, Alamosa; and the Hinsdale County Road Supervisor to discuss the proposed project. Lake San Cristobal is a natural lake that formed when the Slumgullion Slide blocked the Lake Fork of the Gunnison River. The slide material blocking the river channel, being highly erosive, continued to erode as it was replaced by the movement of the slide. The channel gradually stabilized and streambed armor developed as the movement of the slide slowed. In the 1950's, a large streamflow occurred and caused the stream channel armor to be eroded. This resulted in highly erosive materials being exposed to the erosion process. The channel rapidly degraded to the point that the lake was placed in serious jeopardy. The water surface of the lake was lowered significantly. The rapid lowering of the lake added additional water to the already high water and caused severe flooding of the properties downstream. The properties sustained damage to buildings and land from water -- and ;_q mein z3epo� s - - _ _ The damaged channel was later restored to its pre- runoff elevations with the State Engineer of Colorado apparently providing the engineering. Earth and rockfill was placed in the eroded channel and a grade control structure constructed across "the channel at the outlet of the lake for protection of the restored channel. The structure was constructed of timber and provided a sufficient level of protection until the mid 1980's.