Updated: May 29, 2014
The concrete work to repair and fill the Lake Jackson Dam is now complete, and the once hollow dam is now a stable, concrete-filled structure and the toe drains have stopped flowing. The contractor also repaired the undermining that had developed on the downstream side of the dam.
It has come to our attention that the seal on the dam gate has suffered some pretty extensive damage due to its exposure to the elements. You may know that it was necessary to keep the gate up prior to and during the construction process to minimize the pressure that the lake water put on the upstream face of the dam, and to allow the contractor to do the repair work. This prolonged exposure is causing the seal to leak, and the seal must be replaced for it to function properly.
Staff has been notified that the contractors will return Monday, June 2, to begin performing the replacement of the seal on the dam gate. The gate will be raised to allow the contractor to do their work and complete the project. It is unknown how long the installation will take and therefore how long the gate will be open, but it is estimated to take approximately one week. We encourage Lake Jackson residents to make any necessary preparations and take appropriate precautions for the water level to recede temporarily while the gate is open, and then rise once the installation of the new seal is complete and the dam gate is lowered once again.
Please note, due to the rain we are currently experiencing, it may become necessary to raise the gate earlier than the anticipated Monday opening. If it is determined to be necessary, staff will raise the gate before Monday to allow a buildup of excess stormwater to dissipate.
As a reminder, please be aware that citizens are not allowed in the fenced area around the dam nor on the dam for safety reasons. It is also very important that the workers on-site be allowed to do their work without interruption. Please direct any questions you have to Supervisor Nohe’s office at (703)792-4621 or ColesDistrict@pwcgov.org and his staff will respond as quickly as possible.
The County has received questions from residents about whether there is an opportunity to dredge the lake and/or remove vegetation as part of the dam repair project. At this time, the County has no plans or funding to dredge the lake, make any improvements to the shoreline, or remove vegetation. Residents can certainly address those issues now themselves on their own property when the water level is low, being sure to follow any applicable county, state and federal guidelines. County staff can assist residents in figuring out which guidelines may apply to their particular situation, but unfortunately the funding approved by the Board of County Supervisors is not sufficient to cover any additional efforts beyond the dam repair.
ADVISORY: Please be aware that no repairs have taken place, and residents are still advised to stay clear of the area in and around the dam due to the small whirlpool in the water. It poses a significant safety hazard so please do not swim or boat anywhere near the dam.
In May of 2012, County staff observed the activation of two “toe” drains on the downstream side of the Lake Jackson Dam (see photo) that are releasing a significant amount of water. The County is closely monitoring the flow from the toe drains, as well as researching the purpose of the toe drains and the significance of the water flow. The toe drains are believed to drain water from the inside of the dam, however the dam was built in 1928 and there are no construction plans or as-builts to reference to confirm this conclusion. If the drains are active because of water in the core of the dam, this is a possible concern for dam safety. Since the toe drains are draining water, this would also explain the low lake water levels water front owners are experiencing. Other factors could also be contributing to low lake water levels as well.
The County engaged the services of a nationally known dam consultant, the Michael Baker Corporation, to investigate the cause(s) of the toe drain activation, and consulted with the State Dam Safety Engineer for the NOVA region. The investigative work included:
- Underwater diving investigation of both the upstream and downstream face of the dam
- coring holes into the dam crest to investigate the dam interior with remote control cameras
- dewatering the interior of the dam with pumps
- use of dye tracer tests to determine seepage areas.
Please note this work was exploratory in nature and did not include any repairs or remediation. The Michael Baker Corporation submitted their final report which contains information on the investigation of the dam as well as several rehabilitation options. The report can be viewed and downloaded at http://www.colesdistrict.org/news/lakejacksondam/. Please note that the report is very large and as such, had to be uploaded into many sections.
On April 23, 2013, the Board of County Supervisors approved the County’s FY14 budget which provides full funding to repair the Lake Jackson dam. The funding will cover the cost to repair the dam as recommended in the consultant’s report as Alternative A: Fill All Chambers with Concrete.
An Invitation for Bid (IFB) to repair the Lake Jackson dam was issued in August 2013 and the contract was awarded.
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