Corps updates on DSMP

By Kathe Malouf
Special to the Sun

Kern River Valley residents were given an update on the progress of construction for the Isabella Dam Safety Modification Project (DSMP) last week, when representatives of the U.S. Army Corps of Engineers hosted two public meetings in Kernville and Lake Isabella.

The meetings, held April 3 and 4, drew a small crowd of area residents but allowed Corps representatives to present an overview of the Highway 155 detour route, as well as the planned improvements for three recreation areas that are part of the multi-million-dollar DSMP.

Mike Ruthford, Tech Lead with the Corps, opened the meeting by displaying a diagram of the fluctuating levels of Isabella reservoir has since the DSMP began in early 2017. Ruthford noted that late last year, the lake was dropped to about 68,000-acre feet during the Borel decommissioning, when crews closed and capped the water outlet at Borel. Ruthford noted that the low level of last winter would be the one and only low water draw down during the DSMP.

“We do not need to go back to that pool level,” Ruthford said.

Isabella Lake is now into its high-pool season, which typically runs from April through September. The lake level is currently at about 229,500 acre feet. Ruthford said that it is estimated that the lake elevation will reach approximately 361,000 acre feet by early June, which is the maximum restricted operational pool established by the Corps for the duration of the DSMP.

Through an illustrated PowerPoint presentation, Ruthford presented the work plan as proposed for 2019 and 2020.

This year’s work will include the detour along Highway 155, excavation and concrete work at the service spillway, excavation and concrete work on the new emergency spillway, excavation and earthwork at Auxiliary Dam and improvements to the recreation facilities at South Fork, Auxiliary Dam and Old Isabella Road.

Later this year, work will begin on the emergency spillway.

Work proposed for 2020 includes continued work along Hwy. 155, as well as continued work on the emergency spillway and Auxiliary Dam.
Ruthford stated that work will also begin on raising Main Dam during 2020.

Work is already underway on the Hwy. 155 detour that is being developed at the crest of Main Dam. While work was temporarily halted due to winter rains, work is expected to resume on the detour that will take motorists over the dam, in preparation for construction of a 17-foot-tall wall that will be located at the crest of the Main Dam.

The DSMP will raise both Main and Auxiliary Dams by 16 feet in order to minimize the risk of overtopping, improve stability of the existing spillway and create a new emergency spillway in order to reduce the risk to public safety in the event of a catastrophic flood.

In order to accommodate the increased height of the Main Dam, a 17-foot tall wall will be constructed along Highway 155 at the crest of the Main Dam’s right abutment. According to Ruthford, the length of the wall will be approximately 425 feet and will follow the slope of the Main Dam.

Ruthford explained that the wall is necessary in the event of a rare but catastrophic flood event that could result with heavy water flows onto Hwy. 155. Although considered to be a 1 in 6,000 event, should that event happen, the concrete abutment wall, along with a smaller wall on the opposite side of the highway would serve as a spillway shoot, similar to a third spillway.

Ruthford stated that the Hwy. 155 detour and wall construction project would take about 12 months. During the majority of that timeframe, there will be two-way traffic, although at some point, traffic will be reduced to one-way. During that time, a 24-hour traffic signal will be installed for traffic control.

Having the wall in place is critical to the Main Dam height increase, as Main Dam cannot be raised until the wall, which will hold materials needed for raising the height, is completed.

Once the wall is in place, Hwy. 155 will be returned to its current alignment and Ruthford stated that there will be no change to the highway’s current alignment or grade.

Because of the impacts the DSMP will cause to recreation, improvements are scheduled to be made to the three recreation areas: Auxiliary Dam, Old Isabella Road and South Fork Recreation area.
Melanie Tymes, Project Manager, presented an outline of the improvements slated for the recreation areas.

Tymes assured attendees that renovations at the three areas would only occur Monday through Thursday from 7 a.m. to 7 p.m. She noted that work will continue until the Memorial Day weekend then be halted until after Labor Day weekend.

The recreation areas will remain open to the public at all times during construction, and no construction activity will take place during the fishing derby.

Construction of facility utilities will get underway this spring with construction of the replacement facilities and roadways occurring sometime during the fall.

The Corps noted that replacement facilities would be completed before the existing facilities are demolished.

Construction renovations include:

At Auxiliary Dam recreation area:
• Adding pavement and aggregate base to the existing dirt road
• Construction of an entrance station and RV dump station
• Replacement of existing restrooms with a new 4-unit vault restrooms
• Adding an additional 4-unit vault restroom
• Demolishing existing host camp area and RV dump station

At Old Isabella:
• Paving a new section of road
• Construction of an entrance station and RV dump station
• Installation of two new 4-unit vault restrooms
• Refurbishing the parking spaces
• Adding signage and incorporating ADA requirements at the existing restrooms

At South Fork:
• Construction of a new 2-unit vault restroom
• Refurbishing the parking spaces
• Adding signage and incorporating ADA requirements

The Isabella Dam Modification Project will be completed in December 2022.

Debra Matthews - April 17, 2019

I though the the dam was unsafe now i hear we are going to driving across it. I am confused. save a million and go around the back side.
totally confused.

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