How Cobbs Creek Reservoir Works
Published 4:14 pm Thursday, November 15, 2012
CUMBERLAND – Since acquiring the Cobbs Creek Reservoir project from Cumberland County in 2010, Henrico has not been idle. The County has submitted two permit modifications to the Virginia Department of Environmental Quality (DEQ). Construction on the utility corridor is scheduled to begin this spring and a meeting with affected landowners was held last month. (See article in today's paper for more details regarding the October meeting.)
The 1,117-acre augmentation reservoir will be located between Columbia Road and Cedar Plains Road, in the far northwest corner of Cumberland County near the James River. The augmentation reservoir is designed to release water into the James to augment river flow during the dry summer months and periods of drought. During times of sufficient river flow, such as the Spring, the reservoir supply will be replenished.
After a severe drought in 2002, the Virginia General Assembly passed legislation directing the DEQ to develop plans for consistent water supply for all Virginia residents. When the 2005 permit request was first submitted to the DEQ, part of the rationale behind the Cobbs Creek Reservoir Project was to provide a means of augmenting the flow of the middle James.
At the time of the request, there was no means to do so between Gathright Dam near the Virginia-West Virginia border and the Richmond metropolitan area, 270 miles down river. Lake Moomaw, created by the Gathright Dam, is drawn down annually to augment the flow of the James.
By the end of the 2002 drought, Lake Moomaw had augmented the flow of the James so much that it was two-thirds depleted.
Henrico is investing in Cobbs Creek Reservoir as part of a 50-year plan to meet its increasing water needs. Henrico's anticipated demand is expected to be at or above 105 million gallons a day by the year 2050, according to the 2005 permit request.
Henrico plans to procure all the property necessary for the reservoir by April 2013, when it hopes to begin construction of the utility corridor. Preparation of the utility corridor will clearing the mile corridor, roughing in a construction road and installing a small part of transfer pipeline that will eventually bring water from the James to the reservoir.
In 2014, the utility corridor should be finished and Colonial Pipeline will come in to remove its two existing pipelines and lay them into the new corridor. Later that year, Virginia Power will run new overhead power lines.
Around the Fall of 2014, Henrico will also advertise the reservoir project as one large bid for a “mega contractor,” according to Mawyer. The winning contractor will build the intake structure at the James River, the pump station, remaining pipeline for the reservoir, both dams and complete final shaping for the reservoir.
Construction is slated to begin in the spring of 2015 and be completed in four years. If all goes as planned, the reservoir will begin to be filled fall of 2019, seven years from now.
The main dam will be made of earth and about 4,000 feet long and 150 feet tall, creating a 1,100 acre reservoir. For comparison, Prince Edward's Sandy River Reservoir is 740 acres. Bear Creek Lake is 40 acres.
The main dam will be located on the northern edge of the reservoir. There will be a secondary saddle dam located on the western side of the reservoir. The reservoir will have a normal pool elevation of 345 feet above sea level and planned flood elevation of 350 feet above sea level. It will hold 14.8 billion gallons of water.
Overhead electric lines and pipelines that run through the proposed dam sight are being relocated to a utility corridor that will run along the western edge of the dam. The corridor will be three miles long and 200 feet wide.
Two underground pipelines, owned by Colonial Pipeline, are part of 5,500-miles of pipeline which run from Texas to New Jersey, transporting petroleum products such as gasoline, diesel fuel and heating oil from the Gulf of Mexico to the East Coast. Colonial's mainline passes through Cumberland. There is also a Colonial tank farm located in northern Cumberland County.
Water for the reservoir will be withdrawn and released from a facility on the James River, located 1.7 miles upstream from the Columbia Bridge. The facility is designed to pump as much as 150 million gallons a day. The project will temporarily impact 25,000 square feet of James River streambed.
The reservoir will permanently impact 15.3 miles of stream, almost 31 acres of wetland and 4.6 acres of open water. One home will be flooded and at least two homes are located in the 150-foot buffer that will surround the reservoir. Four archeological sites found to be of interest in a study conducted by the Virginia Commonwealth University Archeological Resource Center in 1990 will be flooded.
Even though it has been five years since the original permit for Cobbs Creek Reservoir was issued by the DEQ, there was still confusion regarding how the reservoir was designed to work during an October meeting with affected landowners.
The 2007 permit issued by the DEQ to Cumberland County approves an augmentation reservoir, which is unlike many of the other reservoirs in the area, such as Sandy River Reservoir. Residents experience Sandy River primarily as a static lake. Sandy River Reservoir, built by Prince Edward County and completed in 1994, has not had any major withdrawals for public water use since that time, even during the 2002 drought. During this summer, which was dry, the water level only dropped 14 inches below normal pool elevation.
Cobbs Creek Reservoir, however, is not designed to be static. Instead, it is designed to augment the highly variable flow of the James River, harnessing the excess water that travels down the James during high flow periods and holding it in reserve to release when flows are exceptionally low.
Between June and November, Henrico is required by the DEQ permit to release water from the reservoir when river flow is 30 percent below normal.
During the October meeting, William “Bill” Mawyer, assistant director of public utilities of Henrico County, discussed the fluctuation of the James River over the past year and how the reservoir would have been utilized during that time. According to him, during April of this year, there were 24 billion gallons of water flowing in the James River. During such a time of high flow, Henrico would be able to pump water out of the James to replenish the reservoir.
Only three months later, on July 11, there was less than one billion gallons, only 800 million gallons, flowing in the river. Under the DEQ requirement, the reservoir would have been required to release water back into the James.
Paul Peterson, engineering team project manager for the reservoir, stated during the October meeting that this past summer, the river flow would have been “plenty low enough to require large releases from the reservoir.”
Using river flow and participation records from the past hundred years, models generated by the engineering team estimate that the reservoir should drop no more than five feet below normal pool elevation 11 percent of the time in the next 100 years. Under these conditions, 91 acres of reservoir bottom would be exposed, which is eight percent of the 1,117-acre reservoir pool area.
The reservoir is not expected to be drawn down more than 15 feet about 3.4 percent of the time. This would expose 257 acres of reservoir bottom, about 23 percent of the normal pool surface area.
The reservoir could be refilled one vertical foot a day when the flow of the James is adequate and the pump is used to its full capacity.
Because of the reservoir's ability to augment the James River's flow downstream, the DEQ has calculated that the reservoir has a maximum safe yield of 47 million gallons a day, the amount for new or expanded withdrawals from the James.
The reservoir's safe yield is divided between the three counties involved in the project: Henrico with 30 million, Powhatan with 10 million and Cumberland with seven million.
The safe yield is calculated to determine how much more water can be taken from the James River due to the augmentation of the reservoir, but has no baring on the actual intake or output of the reservoir itself. During heavy drought the reservoir could return as much as 100 million gallons a day to the river to augment the low river flow, over double its 47 million gallon a day water benefit. Conversely, during very high river flow, it could be taking out as much as 150 million gallons a day to refill the reservoir.
A permit modification recently submitted by Henrico requests that the County be able to increase its current average daily withdrawals by 30 million gallons a day, its allotted benefit from the reservoir, from its intake station down river, located 2.4 miles above the Huguenot Bridge.
Although the reservoir is not yet augmenting the river, Mawyer says that Henrico has approached the DEQ saying “we're going to spend all this money right now over the next five, six years. You need to give us the permit increase now.”
Mawyer reasoned that since Henrico is already beginning to absorb the cost of the reservoir, it should also begin reaping its benefits. Henrico's withdrawals from the James will increase from an average 45 million gallons a day to 75 million gallons a day.
Cumberland and Powhatan can submit similar requests in the future to claim their shares of the reservoir's safe yield: seven and ten million gallons a day respectively. These permit requests would use the river flow augmentation provided by the reservoir as justification for why they should be allowed to pull water out of the James as well.
Cumberland could submit a request to withdrawal water directly from the reservoir or from the James, down river from the reservoir.
Since its assumption of the project in 2010, Henrico is scheduled to pay Cumberland County $1,131,900 a year for 50 years in lieu of taxes.
Henrico will not be using county taxes or federal money to fund the project, according to Mawyer. It plans to pay for the reservoir entirely from service and connection fees. There are 95,000 connections to the Henrico water and sewer system, reported Mawyer. Money borrowed by Henrico for the utilities project is issued as bonds and is based on expected revenue from these service fees and connection fees.
During the October meeting, Mawyer stated that because Henrico, Cumberland and Powhatan are all receiving the opportunity to apply for new or expanded water withdrawal, they all also have to pay for the reservoir.
When later approached by The Herald to clarify, Mawyer explained that when the citizens of Cumberland are ready to receive their benefit of seven million gallons a day, then they will have to start paying for the cost to build and operate the reservoir.
Because Cumberland is expected to benefit from seven million of the 47 approved million gallon a day expanded withdrawals, it will pay 7/47 of the total cost to build and operate the reservoir each year: “Once they take water, they start paying. But, Cumberland does not pay us anything until you start receiving a water benefit.”
The Memorandum of Understanding between Henrico and Cumberland states that when Cumberland enters into a water agreement with Henrico to access its designated share of water, Henrico will charge Cumberland based on the cost of service methodology determined by Henrico.
According to Mawyer, Powhatan would also only start paying when it begins using the water which is a benefit of the reservoir.
Henrico is required to mitigate for both wetlands and streams that are permanently impacted by the reservoir.
Henrico must mitigate a total of 56 wetland credits. Cumberland procured a contract with Mitigation Services for all of the wetland credits in 2008. When Henrico took over the project in 2010, they also assumed that contract according to Mawyer. The projected cost for those credits is $2,469,600.
In addition to wetland credits, 80,000 stream credits are also required to be mitigated. The original DEQ permit requires that some stream mitigation credits be obtained from the Cumberland State Forest, which is owned by the Department of Forestry.
According to Mawyer, Henrico is negotiating with the Department of Forestry to mitigate 60,000 stream credits. The remaining 20,000 that are required will be mitigated via the private market. Some of these will be purchased through Mitigation Services at $319 a credit. The remainder will be put out for competitive bids.
