LAKE JACKSON DAM
THIS PAGE IS DEDICATED TO THE FUTURE OF THE DAM
This page is a source for plans, news and information, links to reports on the designs and effectiveness of spillways as well as the history of the Lake Jackson Dam.
Questions, comments, and suggestions about the County’s plans for the dam may be sent by email to [email protected] If you want to volunteer your time to take an active role in LJCA’s response to the County’s proposal, contact us by email as well. Your participation will help guide our collective response.
Questions, comments, and suggestions about the County’s plans for the dam may be sent by email to [email protected] If you want to volunteer your time to take an active role in LJCA’s response to the County’s proposal, contact us by email as well. Your participation will help guide our collective response.
Tuesday, March 17, 2020: On Thursday evening March 12th, our new Coles District Supervisor, Yesli Vega, Lake Jackson's Road Committee and Lake Jackson Citizens Association hosted a town hall meeting for the residents of Lake Jackson. Among the issues discussed was progress towards a new design for the dam. PWC's Marc Aveni reviewed the options he first presented at a special meeting in August, updated with projected costs for each option. That document is attached below as well as is the original technical report on the dam developed by Dewberry Engineering and published in January 2019. Also attached are the slides from Mr. Aveni's power point presentation.
| pwc_ppt_on_lj_dam.ppt |
| dewberry-lake_jackson_technical_memorandum_2019-01-23.pdf |
| lj_dam_matrix0001.pdf |
Over the past six months, LJCA's Dam Committee has met several times with Marc Aveni and his engineers and communicates regularly with them. While Mr. Aveni favors option 3B as the dam modification, the Dam Committee stressed the importance of adding to any new design a means for draining the lake, not as a way to control lake levels during storms but to flush the lake a few times a year. This option would provide residents the opportunity to perform dock and wall repairs and also to move silt and sediment. The problem of silt and sediment has built over the past few years and Mr. Aveni recognizes this as a priority as well.
The reason the lake was drained over the past week was to allow Dewberry to take measurements along the lower parts of the dam, especially along the gates of the old turbines located below the dam house. Fashioning one of the gates to be lifted and lowered could be the answer to the "sluice" we desire to allow periodic drainage of the lake.
Mr. Aveni has stressed the importance of reaching an agreement with the residents of Lake Jackson, one we can take to the county's Board of Supervisors for approval. Once that occurs, Mr. Aveni doesn't expect work to begin for another three to five years.
Friday, October 11, 2019: On Wednesday, October 9th, Prince William County Environmental Chief Marc Aveni and three county colleagues met at the dam with members of LJCA’s Dam Committee. They gave a tour of the dam’s mechanics and demonstrated how the manually-operated tainter gate is lowered and raised. Mr. Aveni pointed out the dam’s aging equipment and infrastructure, also stressing the costs and risks involved with operating the gate as the reasons he wants the dam modified as a fixed spillway. Committee members raised concerns about silt buildup and losing the flexibility to occasionally lower lake levels if those modifications are made. Those concerns are among a list of questions (see below) the committee sent to Mr. Aveni a few weeks ago to which Mr. Aveni says he is gathering answers and would respond soon. Committee members also gave Mr. Aveni a proposed modification to a dam design he has proposed that could offer the kind of water-level flexibility many in our community desires. Mr. Aveni said he would take that design to Dewberry, the engineering firm the county has hired, to evaluate the idea.
Questions sent to Marc Aveni:
1. We do not understand the relationship between the possible purchase of properties and the five alternatives (1, 2, 3A, 3B, 4A) presented. Are any of the alternatives contingent on the purchase of properties? Please clarify why the purchase of properties is being presented with the alternatives.
2. Has an analysis been performed to determine if the rate of siltation changes under any of the proposed alternatives?
3. We are concerned that the county’s preferred option 3B does not provide a means to lower lake levels. What options are there under this alternative for draining the lake.
4. Analysis only considers 1.5 miles up the dam, are there flood affected properties past that?Monday, September 9, 2019: The new Future of the Dam Committee met on Wednesday, September 4th. Derek Brinkmann agreed to serve as chairman. Members are reviewing the five dam options PWC’s Marc Aveni introduced at the August 27th meeting and as described in Dewberry Engineering’s draft report. The Committee also is waiting for responses from Mr. Aveni to several questions concerning how those options would affect conditions on the lake.
The five options (Dewberry draft report):
* Alternative No. 1 – Replace existing radial gate and hoist system with a new radial gate and hoist system including new steel gate, trunnion assembly, side and bottom seal plates, stainless steel hoisting cables, motorized actuator, and housing. Under this alternative, PWC will continue operation of the new radial gate system during storm events following existing protocols.
It was assumed for modeling purposes that the radial gate was fully open for all storm events (i.e., the gate was opened to its maximum height of 13 feet).
* Alternative No. 2 – Discontinue operation of gate during storm events while maintaining basic functionality of the existing gate system to ensure that it remains operational. The gate would remain in the closed position during all storm events and would only be raised to lower the lake level for maintenance activities or during emergency situations. Gate functionality would be tested at least once a year as part of the dam maintenance plan.
* Alternative No. 3A – Remove radial gate, catwalk, and catwalk piers and replace the radial gate with a concrete ogee spillway section. In this scenario, the existing radial gate would be removed and replaced with a concrete spillway section with the same crest elevation as the existing ogee spillway. The catwalk spanning the length of the dam and the 1’-wide piers which support the catwalk would also be removed, while the 4’-wide thrust piers which currently support the radial gate would remain in place for cost reduction and stability purposes. Removal of the catwalk piers increases the effective weir length of the dam by approximately 13’.
* Alternative No. 3B – Remove radial gate, catwalk, catwalk piers, and thrust piers and replace the radial gate with a concrete ogee spillway section. In this scenario, the existing radial gate would be removed and replaced with an ogee spillway section with the same crest elevation and shape as the existing ogee spillway. The catwalk spanning the length of the dam, the 1’-wide piers which support the catwalk, and the 4’-wide thrust piers which currently support the radial gate would all be removed. Removal of the catwalk piers and thrust piers increases the effective weir length of the dam by approximately 21’.
The existing radial gate provides low-level drawdown capability for Lake Jackson. Removal of the thrust piers would likely require that the replacement spillway section be ogee-shaped (matching the existing ogee weir) to maintain dam stability. Note that for this type of spillway it would be difficult to install a new low-level drain.
* Alternative No. 4A – Remove radial gate and replace with a 25’-wide fixed-crest concrete spillway section with a crest elevation 1’ lower than the crest elevation of the existing ogee spillway (147.18’). The existing catwalk, catwalk piers, and thrust piers would be preserved.
Wednesday, September 4, 2019 was the first meeting of the committee formed to represent the Lake Jackson community in dealing with Prince William County and its proposal to replace or modify the current dam structure.
Membership: Scott Bishop, Derek Brinkmann (Chairman), Sandra Dutemple, Bryon Fugate, Cindy Hall, Sharon Henson, Linda Hostetler, Todd Mason, Larry Phillips, Bill Pierce, Phil Reimers, Valerie Thornton, Jim Trengrove, Mike Trentacoste and Ken Vaughan
Thursday, August 27, 2019 : A special informational meeting for Lake Jackson residents was held on Tuesday, August 27th, 2019 to consider proposals by Prince William County to replace the Lake Jackson Dam with a spillway. Marc Aveni, Chief of Environmental Services for PWC Public Works, who first proposed the spillway option at our LJCA meeting in May, has received clearance from the PWC Board of Supervisors (BOCS) to pursue replacement options and will share his ideas with the community at the meeting. Aveni said a public session with the BOCS will follow sometime in the fall.
Two reports have been added to this page.
The first is a preliminary report from our legal representative researching the requirements Prince William County must achieve to replace or modify the Lake Jackson Dam.
The second report, Addressing Operational Risks for Gated Spillways, was authored and provided to us by Greg Paxson, a dam engineer and expert whom we reached through the United States Society on Dams.
The reason the lake was drained over the past week was to allow Dewberry to take measurements along the lower parts of the dam, especially along the gates of the old turbines located below the dam house. Fashioning one of the gates to be lifted and lowered could be the answer to the "sluice" we desire to allow periodic drainage of the lake.
Mr. Aveni has stressed the importance of reaching an agreement with the residents of Lake Jackson, one we can take to the county's Board of Supervisors for approval. Once that occurs, Mr. Aveni doesn't expect work to begin for another three to five years.
Friday, October 11, 2019: On Wednesday, October 9th, Prince William County Environmental Chief Marc Aveni and three county colleagues met at the dam with members of LJCA’s Dam Committee. They gave a tour of the dam’s mechanics and demonstrated how the manually-operated tainter gate is lowered and raised. Mr. Aveni pointed out the dam’s aging equipment and infrastructure, also stressing the costs and risks involved with operating the gate as the reasons he wants the dam modified as a fixed spillway. Committee members raised concerns about silt buildup and losing the flexibility to occasionally lower lake levels if those modifications are made. Those concerns are among a list of questions (see below) the committee sent to Mr. Aveni a few weeks ago to which Mr. Aveni says he is gathering answers and would respond soon. Committee members also gave Mr. Aveni a proposed modification to a dam design he has proposed that could offer the kind of water-level flexibility many in our community desires. Mr. Aveni said he would take that design to Dewberry, the engineering firm the county has hired, to evaluate the idea.
Questions sent to Marc Aveni:
1. We do not understand the relationship between the possible purchase of properties and the five alternatives (1, 2, 3A, 3B, 4A) presented. Are any of the alternatives contingent on the purchase of properties? Please clarify why the purchase of properties is being presented with the alternatives.
2. Has an analysis been performed to determine if the rate of siltation changes under any of the proposed alternatives?
3. We are concerned that the county’s preferred option 3B does not provide a means to lower lake levels. What options are there under this alternative for draining the lake.
4. Analysis only considers 1.5 miles up the dam, are there flood affected properties past that?Monday, September 9, 2019: The new Future of the Dam Committee met on Wednesday, September 4th. Derek Brinkmann agreed to serve as chairman. Members are reviewing the five dam options PWC’s Marc Aveni introduced at the August 27th meeting and as described in Dewberry Engineering’s draft report. The Committee also is waiting for responses from Mr. Aveni to several questions concerning how those options would affect conditions on the lake.
The five options (Dewberry draft report):
* Alternative No. 1 – Replace existing radial gate and hoist system with a new radial gate and hoist system including new steel gate, trunnion assembly, side and bottom seal plates, stainless steel hoisting cables, motorized actuator, and housing. Under this alternative, PWC will continue operation of the new radial gate system during storm events following existing protocols.
It was assumed for modeling purposes that the radial gate was fully open for all storm events (i.e., the gate was opened to its maximum height of 13 feet).
* Alternative No. 2 – Discontinue operation of gate during storm events while maintaining basic functionality of the existing gate system to ensure that it remains operational. The gate would remain in the closed position during all storm events and would only be raised to lower the lake level for maintenance activities or during emergency situations. Gate functionality would be tested at least once a year as part of the dam maintenance plan.
* Alternative No. 3A – Remove radial gate, catwalk, and catwalk piers and replace the radial gate with a concrete ogee spillway section. In this scenario, the existing radial gate would be removed and replaced with a concrete spillway section with the same crest elevation as the existing ogee spillway. The catwalk spanning the length of the dam and the 1’-wide piers which support the catwalk would also be removed, while the 4’-wide thrust piers which currently support the radial gate would remain in place for cost reduction and stability purposes. Removal of the catwalk piers increases the effective weir length of the dam by approximately 13’.
* Alternative No. 3B – Remove radial gate, catwalk, catwalk piers, and thrust piers and replace the radial gate with a concrete ogee spillway section. In this scenario, the existing radial gate would be removed and replaced with an ogee spillway section with the same crest elevation and shape as the existing ogee spillway. The catwalk spanning the length of the dam, the 1’-wide piers which support the catwalk, and the 4’-wide thrust piers which currently support the radial gate would all be removed. Removal of the catwalk piers and thrust piers increases the effective weir length of the dam by approximately 21’.
The existing radial gate provides low-level drawdown capability for Lake Jackson. Removal of the thrust piers would likely require that the replacement spillway section be ogee-shaped (matching the existing ogee weir) to maintain dam stability. Note that for this type of spillway it would be difficult to install a new low-level drain.
* Alternative No. 4A – Remove radial gate and replace with a 25’-wide fixed-crest concrete spillway section with a crest elevation 1’ lower than the crest elevation of the existing ogee spillway (147.18’). The existing catwalk, catwalk piers, and thrust piers would be preserved.
Wednesday, September 4, 2019 was the first meeting of the committee formed to represent the Lake Jackson community in dealing with Prince William County and its proposal to replace or modify the current dam structure.
Membership: Scott Bishop, Derek Brinkmann (Chairman), Sandra Dutemple, Bryon Fugate, Cindy Hall, Sharon Henson, Linda Hostetler, Todd Mason, Larry Phillips, Bill Pierce, Phil Reimers, Valerie Thornton, Jim Trengrove, Mike Trentacoste and Ken Vaughan
Thursday, August 27, 2019 : A special informational meeting for Lake Jackson residents was held on Tuesday, August 27th, 2019 to consider proposals by Prince William County to replace the Lake Jackson Dam with a spillway. Marc Aveni, Chief of Environmental Services for PWC Public Works, who first proposed the spillway option at our LJCA meeting in May, has received clearance from the PWC Board of Supervisors (BOCS) to pursue replacement options and will share his ideas with the community at the meeting. Aveni said a public session with the BOCS will follow sometime in the fall.
Two reports have been added to this page.
The first is a preliminary report from our legal representative researching the requirements Prince William County must achieve to replace or modify the Lake Jackson Dam.
The second report, Addressing Operational Risks for Gated Spillways, was authored and provided to us by Greg Paxson, a dam engineer and expert whom we reached through the United States Society on Dams.
July, 2019:
The Lake Jackson Citizens Association met July 16, 2019. There was a very good turnout as the primary issue discussed was the future of the dam and an expected proposal by Prince William County that the dam be replaced with a spillway. At the meeting, membership approved $7,500 in LJCA funds to retain the legal services of Walsh, Colucci, Lubeley & Walsh to provide research, clarity of process and, if needed, possibly representation to protect LJCA’s interests. This law firm has worked successfully with LJCA in the past. Membership also passed a resolution urging that LJCA be represented at an expected meeting in August between Mr. Aveni and the PWC Board of Supervisors where the proposed replacement of the dam would be discussed.
For the time being, participants all agreed that we need to educate ourselves on all aspects of this issue, primarily the question of what kinds of changes the replacement of the dam with a spillway would bring to the lake and our community. We reached out to the US Society on Dams and several Society members promptly responded with research and reports and offers of assistance as we move ahead. Posted 7/20/2019
May, 2019:
The July LJCA meeting was changed to July 16, 2019 in order to discuss the implications of PWC’s announcement regarding replacing the Lake Jackson Dam with a spillway. Marc Aveni, Chief of Environmental Services Division for PWC Public Works, announced at the May 28th meeting that he was evaluating proposals to replace our current dam structure with one that would not require manual operation. Mr. Aveni said the safety of workers and annual cost of operating the dam prompted his announcement. The 91 year-old dam is expensive to run and poses liability risks. The current 91 year old gate is very warped. It is dangerous when county workers must open and shut the gate during storms and many times during the night hours. Marc estimates that operational costs to open and close the gate have reached over $250,000 per year.
The function of the dam in preventing flooding was discussed. It is estimated that the dam keeps about 35 homes from flooding. The county is investigating options.
Dam History:
In 1927, the Alpaugh family came to the area to build a dam across Occoquan Creek. The dam was constructed by local workers over a period of two years. The lake bed was excavated by twenty teams of men, horses and mules. The completed dam was 300 feet wide and 25 feet high. In 1928, Mr. Alpaugh sold the dam to Virginia Public Service which later became Virginia Electric & Power Company (VEPCO). Concrete was added over the wooden dam and a concrete walkway built. A hydro-electric power plant built at the dam produced electricity for the surrounding area until 1955 when it became a booster station providing power when needed. Prince William County has owned the dam since 1963 and is responsible for the safety and maintenance of the dam.
The lake level was quite low for many months between 2010 and 2014. In the Spring of 2010, residents were informed that the lake level would be lowered for repairs to be made to the dam; the work would take about 2 months. With the water gone, lake access was almost impossible. Docks rested in the mud. Boats were pulled up onto the hills. Deer grazed on plants sprouting where there had once been water. Those daring to walk across the mud to enter the lake found themselves knee-deep in a substance that resembled quick sand as much as mud.
The repair work took about a year. Then the dam was closed and the lake levels went up. Docks floated, boats were out on the water and residents celebrated. Then there was an earthquake in August 2011 that cracked the Washington Monument in Washington D.C. After the quake, lake residents started complaining that the dam repairs were not successful. The lake would be at normal levels after rain but then slowly drain.
An investigation of the dam that included underwater diving was completed in October of 2012. Results determined that the earthquake of 2011 had cracked the dam and that water was seeping through the cracks. Solutions were investigated, including removing the dam. A decision was made to repair the dam. The repair to the dam cost over $1,000,000 and was completed in the summer of 2014. During these year, the residents often referred to the damn dam.
The dam was repaired but the original, 90+ year old gate, used to control the lake water level, was sticking during warm weather and this prevented the gate from being opened or closed. A 60-page Lake Jackson Dam Radial Gate Inspection Report by Prince William County, dated 8/39/2017 was emailed to LJCA members in May 2018. Repairs were made in in the summer of 2019 but the original 90+ year old gate remained in place. The future is uncertain.....