Lake Gregory

Lake Gregory Dam has been identified by the California Division of Safety of Dams (DSOD) as a “high hazard dam” due the possibility of soil liquefaction that could occur during a major seismic event. The DSOD has mandated the County of San Bernardino to retrofit and bring the dam up to earthquake safety standards.

The project will more than double the existing width at the top of the dam and add 80-foot average thickness to the earthen buttress on the downstream side of the existing dam. This will reinforce a section of the dam that has been identified as being susceptible to seismic activity. A significant portion of the project has been completed, which was the construction of new valves and pipeline to be used to control the lake level and allow for fast drainage in the event that water levels need to be adjusted in the event of an emergency.

Prior to work on this project, most visitors to Crestline driving the north side of the Lake wouldn’t notice the dam. In the 80 years since it was built, the growth of forest vegetation on the downstream side, along with road improvements, have made the dam virtually unnoticeable. That will change with this rehabilitation project.

The reinforcement of the buttress begins by first clearing off trees and old vegetation that has grown wild directly on the dam itself, or in adjacent proximity. Only after the dam has been cleared down to the original dirt layer configuration (beneath the rock protective layer) can the process of reinforcing the dam to meet DSOD mandates begin. When completed, the top of the dam (Lake Drive) will double in width, contain a vegetation-free rock layer for protection, and the downstream face will appear deeper and more clearly visible.

To reduce the risk of potential dam failure in the event of substantial seismic activity, the DSOD has mandated the lowering of the lake by 5 feet as an interim measure of safety. The project is being designed to try to avoid any additional lowering of the lake; however, there are safety variables that may require further precautionary lowering to maintain the integrity of the dam structure and/or ensure a safe work environment. The actual necessity to drop the lake level (beyond the 5-foot DSOD mandate) cannot be ascertained until the retrofit work is substantially underway and any vulnerabilities become known.

The operator of Lake Gregory’s recreational attractions expects the lake’s beaches and swimming areas to continue serving as major attractions, with minimal effect on tourism and revenue.

Every effort will be made during the rehabilitation work to not lower the lake any further; however, there are scenarios that might necessitate additional drainage of the lake.

Specifically, as the earthen buttress is rebuilt on the downstream side of the dam, the DSOD has specific requirements on the control of water seepage. If water seepage levels cannot be maintained at an adequate level through extraction, conditions of stability may force added lowering of the lake to meet the construction requirements.

The project is being overseen by the County of San Bernardino and the project management is through Griffin Structures. RockForce Construction is the awarded contractor.

The rehabilitation process has already begun. Dredging has been done, vegetation has been cleared from the dam, and new outlet valves and catch basins have been installed. San Moritz Way has been widened to allow for two-way traffic and work on the buttress is now in progress. The project is expected to be complete in 2019.

To date $20 million has been funded by the County of San Bernardino. The project will improve the dam and Lake Gregory overall. In addition to the rehabilitation of the Lake Gregory dam, the project includes the installation of two detention basins on the east and west sides of the lake, dredging of the lake, installation of new drain pipes and outlet valves and the widening of San Moritz Way to accommodate two-way traffic.

Construction and earthmoving equipment will share local roads on weekdays, primarily on the northern and eastern portions of the lake. Traffic control measures will be conducted when necessary to facilitate circulation and allow for construction activities.

Any work activity related to the dam rehab will primarily take place Monday through Friday, between the hours of 6:30 a.m. and 4 p.m. To satisfy the demands of the DSOD and work around the Hwy 18 Caltrans project, work hours and days of operations are subject to change. Changes to work hours could potentially be Monday through Friday between 5 a.m. and 7 p.m. and extend to Saturday work days if needed. The public will be notified via the Project Update and www.abetterlakegregory.org if an extended work schedule is confirmed.

Since the project area is concentrated on the dam itself, there will be a closure on Lake Drive between the Crestline Sanitation District and Edelweiss Drive beginning in July 2018 through the remainder of the project period. During this time, motorists will be detoured around the south side of the lake, via San Moritz Drive and San Moritz Way.

San Moritz Way has been permanently widened to allow for two-way traffic. San Moritz Way is a short connector road between Lake Drive with San Moritz Drive, on the east side of the lake. It will be used to shorten detour routes and minimize construction traffic on roads within Crestline. Movement of materials and equipment is not expected to disrupt recreation activities or cause significant delays for residents or motorists.

Finally, there will be a periodic and temporary lane reduction at the mouth of Edelweiss Drive from Lake Drive. Access for residents on Edelweiss will be accommodated throughout construction but could be intermittently disrupted.

The lake’s beaches and swimming areas are open and continue to serve as major attractions to tourists and the local community.

Camp Switzerland, a rustic campground directly adjacent to the dam buttress, will be used for the majority of rehab activity. To that end, the Camp was recently closed to the public and acquired by the County of San Bernardino to facilitate the rehabilitation project. Upon completion of the project, the County will assess the condition and future of the campground.

The County of San Bernardino will continue to share important updates during the improvement project. Status updates will be shared with local media and via the County of San Bernardino and Parks and Recreation Facebook pages. Community members can sign up to receive Project Updates via email at www.abetterlakegregory.org. Questions about the project can be left on our project specific helpline number at 909-294-3977.

These FAQs will be updated periodically and can always be found on the Lake Gregory Dam Improvement Project website at www.abetterlakegregory.org. By visiting the website, community members can sign up to receive Project Updates via email. Updates will also be shared on the County’s Facebook page. Residents and businesses with project questions or concerns can call 909- 294-3977 and leave a message; a member of our public information team will respond within 48 hours.