ESCONDIDO — Ten years after learning of the need to replace or repair the dam at Lake Wohlford, officials at the city of Escondido are still trying to raise the money.
It’s a substantial sum — $45 million to $50 million — and they’re about halfway to it.
Completion of the project would enable the city to store about twice as much water as it now can in the man-made reservoir and still prevent flooding from the structure in the event of a big earthquake.
The dam is located east of the city. Because it also is about 900 feet higher than the city, a failure of the upper portion could flood the city if the reservoir were filled to capacity. But it isn’t.
In 2007, a seismic analysis indicated that the upper portion of the dam could be unstable in the event of a major earthquake.
“The risk comes if there is a greater than 7.5 magnitude earthquake in close proximity to the dam,” city Utilities Director Chris McKinney said.
The city quickly drew down the reservoir to about 40 percent of its full capacity, which is 6,500 acre feet (an acre foot equals 325,851 U.S. gallons).
City officials say this is not an optimal solution.
“There are a couple of reasons why it’s better to run it at full capacity,” McKinney said. “The first is that when there is more water in storage, it allows us to ride out a period of drought. Second, water quality is improved. It’s better to have a deeper reservoir than a shallow reservoir. Operation at our water treatment plant is more efficient if we have a deeper reservoir … And it’s our storage not just for water, in general, but for our local supply. It allows us to have some water independence.”
The original earthen dam was built in 1895 to create a reservoir for the city’s water supply. It was a rock-fill structure, 76 feet high. In 1924, attempting to increase the reservoir’s capacity, the city added 24 feet of hydraulic fill to the top of the dam. That’s the portion where the seismic analysis found potential instability.
City officials thought they had the final piece of the funding for a new dam in early 2016, a $25 million loan from the state’s revolving fund program for water. But that went by the boards when it was discovered that an obscure regulation prohibits money from that fund to be used for dams.
Once the City Council approves an environmental impact report, the city will apply for another loan from another state source, along with the permits needed to finish the project.
The city already has set aside $8.5 million for the new dam. The state has provided a $15 million matching grant, which originally came with a deadline that has been extended. So, the city still is $25 million short, give or take, depending on the final construction bids.
McKinney said there are a couple of places to look for the additional money. One possibility is federal funding for infrastructure programs. More certainly, the city could go to the State Infrastructure Bank.
McKinney said the water utility has good credit and ought to be able to borrow the money at 3.5 to 4 percent interest from the infrastructure bank.
He said that would be better than paying 4.5 to 5 percent on the bond market, but it still would have been better if the money could have come from the revolving fund program, which would have charged 1.5 to 2 percent interest.
McKinney said that as of about 2012, it was thought that the project would cost $30 million. But that was before the design process got rolling and planners went into the unforgiving details. Among those details is the need for a southward re-alignment of Oakvale Road, which runs along the dam.
“As we finished the design, it was clear there was going to be a lot more done in terms of preparation and excavation of the bedrock, which is expensive,” McKinney said. “ … You have to dig to the point of finding good stable bedrock. The realignment of Oakvale is about $8 (million) or $9 million. As we’re moving the road, we’re excavating that part of the dam abutment.”
City officials now hope the project can begin next summer. Escondido Director of Community Development Bill Martin said an environmental impact report will go before the City Council for approval next month.
“Once we start building a new dam, we have to take down some of the trees,” Martin said. “ … There has been habitat that has grown during the draw-down period.”
The city’s Notice of Preparation for the project said the construction will involve building a new dam that will crest about 200 feet west and downstream from the existing dam. Hydraulic fill composing the upper part of the existing dam will be removed and the new dam will be constructed from roller-compacted concrete.
Once the new dam is complete, the reservoir can be filled to its historic capacity, which would submerge what remains of the existing dam.
To establish a suitable foundation and solid surfaces for the abutments, material would be excavated from the downstream canyon floor and rocky slopes, perhaps by blasting and hydraulic drilling to remove rock. The new dam would rise to about 125 feet above its foundation grade, which would be 1,490 feet above mean sea level. The crest would span about 650 feet from its north abutment to its south abutment.
The dam crest would feature an access path to accommodate vehicles and pedestrians for maintenance purposes only.
The portion of the existing outlet tower that’s more than 1,442 feet above mean sea level would be demolished and the rest of that tower would be filled and abandoned. A new outlet tower will be built in its place.
Before any of that can happen, the city will first have to do the Oakvale Road adjustment. That will involve excavation into the existing hillside to make room for the re-alignment.