55
degrees average
Bear Valley Dam
First Bear Valley Dam Constructed in 1884
The first Bear Valley Dam was constructed in 1884 at a cost of $75,000. It was built to create a reservoir for downstream irrigation uses in Redlands, resulting in the largest man-made body of water in the world at the time. When Frank E. Brown engineered this dam, he couldn't possibly have envisioned the role Big Bear Lake would play in the future development of the surrounding mountain communities.
The storage capacity of the newly created Lake was 25,000 acre feet (one acre foot is enough water for a family of four for one year). Many engineers claimed that this single arch granite dam would not hold. Sometime later, those same doubting engineers declared it "The Eighth Wonder of the World". This dam is still generally intact, but is usually submerged beneath the higher 1912 dam.
1884 Dam Still Visible After Construction of the
1912 Dam.
Following the completion of this first dam, the valley experienced many years of above average snowfall and plans were made to create an even larger storage reservoir. this included construction of a 65 foot high rock-filled dam, located 300 feet downstream from the original dam. However this project ended in bankruptcy and in 1909 new designs were considered. In 1910, Bear Valley Mutual Water Company retained an engineer to design and oversee the construction of the current concrete dam.
Frame of the 1912 Dam
1912 Multiple Arch Dam
Prior
to Addition of Highway in 1924
The present multiple arch dam was built from 1910-1912 at a cost of $138,000 and is located about 100 yards downstream from the Old Bear Valley Dam. The top of the arches is 72 feet 4 inches from the Lake bottom and its construction nearly tripled the storage of the reservoir to 73,000 acre feet. In 1924, a highway bridge was constructed over the top of the buttresses. This road is now part of State Route 18.
Bear Valley Dam As It Exists Today
Dam Improvement Projects
Seismic Retrofitting
In 1980, as a result of an inspection by the California Division of Safety of Dams
(DSOD), Big Bear Municipal Water District was directed to repair the multiple arch dam to
withstand an 8+ seismic event. It was eventually determined that filling the arches with
concrete would be the most efficient and cost effective solution.
Retrofit Work in Progress.
In the fall of 1986, DSOD notified MWD that the seismic repairs to the dam must be completed by October 1988 or the Lake would be subject to a twenty foot drawdown. The project was well underway by the October deadline and the drawdown was not required. All work was completed in the summer of 1989 at a total cost of about $8.5 million.
Beginning in 1951, DSOD had required a three-foot drawdown form November to March each year because of spillway capacity. Following the completion of the 1988 modification project, DSOD rescinded the order as a result of improved dam safety. These seismic repairs were completed as Phase I of the total modification project.
Spillway Improvements/Repairs
Phase
II work was originally scheduled to begin in 1990 and was dependent upon
Caltrans' relocation of the highway bridge to accommodate the installation
of the spillway in bays 5, 6 and 8. However, the project was never
implemented because the California Department of Transportation (Caltrans) has
not yet constructed the new bridge. In 2002, the District's Board of Directors determined that in the many years since the seismic retrofit was completed, the service spillways
had
deteriorated to the point that repairs were critical. Consequently, the Phase II work
was divided into two separate
projects, Phase IIA (Service Spillway Gate Repair) and Phase IIB (Installation
of Auxiliary Spillways). The most recent information indicates that
Caltrans may be prepared to begin construction of a new bridge by Bear
Valley Dam by 2008.
The original Bear Valley Dam service spillways consisted of five openings 4 feet
wide by 6 feet high in bay 1 (north side of the Dam) and an identical arrangement
in bay 10 (south side of the Dam). Each opening was closed by wooden
bulkheads, which could be removed by hand-driven hoists as needed. In
addition to reliability and safety, a major goal of Phase IIA was to
maximize the release capacities of the spillway gates during a major storm
event.
Old Gates in bay
#1
A Request for Proposal was prepared for the engineering
services for Phase IIA and Christensen Associates Incorporated was awarded the
project. In
February 2003, construction bids were solicited
and the projected was awarded to John S. Meek Co. in the amount of $1,249,920.
The final construction cost was $1,490,583, with most of the increase due
to overages in excavation and concrete requirements.
The method selected for the spillway gate repairs made it possible for the work to be performed at any time regardless of Lake level, with all construction activity occurring downstream of the existing gates. The support structure was left in place until the new spillway system was completed. The project involved replacement of the existing wooden slide gates which were difficult to open and close. They were replaced with new stainless steel slide gates with remotely controlled motor operators in a configuration similar to the original gates. The timber operating deck and the deteriorated concrete piers and gate support structure were removed to below the gate sill level and new concrete piers and support structure were constructed. Due to the new location of the spillway gates, the highway precluded installation of a steel gate in the No. 10 gate position. This gate opening will contain wooden stoplogs until such time as the highway is removed by Caltrans and the new steel gate is installed. The combined release capacity of the new gates is estimated at approximately 3,690 cubic feet per second (cfs) as compared to the previous release capacity of approximately 1,300 cfs.
New
gates in bay #1
In addition to the gate and concrete repairs, the project involved significant erosion control work downstream of the dam. All costs for Phase IIA were paid from Assessment District 88-1 and Davis-Grunsky grant funds.
Construction of erosion apron
downstream of bay #1
Erosion wall downstream of bay #10
In February 2005, the District commissioned MWH Americas, Inc. to complete an assessment of the Bear Valley Dam. Issues included: repairs to the face of the dam, evaluation of the structural integrity of bays 5, 6 and 8, improvement to the dam outlet works, remote control of the spillway gates, cameras at the dam to verify releases and record downstream impacts, and evaluation of spillway capabilities. The report confirmed that bays 5, 6 and 8 are in need of repair as they constitute a “seismic risk”. When the 1988 seismic retrofit of the dam was completed, the top sixteen feet of these three bays were not filled with concrete. It was planned to install auxiliary spillway gates in each of these bays to accommodate Lake releases in major storm events. However, that project required the removal of the highway and this has not yet occurred. Consequently, the District determined it was critical that the three remaining bays be rehabilitated to eliminate the seismic risk, along with reducing the seepage that occurs in all three bays. The final engineering was completed and the bid process was initiated in June 2006. The project was awarded in July to John S. Meek Company at a construction cost of $614,555, and it will be completed before November 30, 2006. Upon issuance of the permit to complete the project, the Division of Safety of Dams required that the District submit a work plan by October 15, 2006 to address the following issues: completion of further hydrologic analyses for the 100-year storm and the PMP; protection of the cross-bracing bars in bays 5, 6 and 8 against corrosion; and repair and maintenance of the cracked and spalled concrete on the upstream face of the upper arches The work plan was submitted by the deadline and the work will be completed as financing, weather and lake level conditions allow.
In addition to the increased spillway capacity gained by rehabilitation of the service spillway gates, the District has improved its flood control capabilities with the adoption of a new Lake Release Policy. This policy allows the District to maintain the Lake at one foot below full between December 31 and March 1. This will improve the District's ability to manage Lake releases in a major storm event.
Lake Water Release from Bays 1 and 10
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