NC Operational Modes
Roanoke Rapids and Gaston Power Stations
Our Roanoke Rapids and Gaston power stations operate cooperatively and in conjunction with the U.S. Army Corps of Engineers (USACE) Kerr Dam. The USACE operates the Kerr reservoir according to its Rule Curve. In using the rule curve, the Kerr provides us with a weekly volume of water (weekly declaration) to be released from the three dams to the lower Roanoke River.
We are required by our FERC operating license to maintain license-prescribed lake levels and certain downstream flows from the Roanoke Rapids Dam.
The Roanoke Rapids Dam always operates with a continuous release (minimum flow) from the dam to the lower Roanoke River. The Gaston Dam operates in an on/off mode. The operating modes described below will affect the total flow released from Gaston, but except in the case of high flood flows, it will operate in an on/off manner.
The Roanoke Rapids and Gaston power stations have four distinct modes of operation, as described below. Modes are dictated by river conditions or season.
Water released from Roanoke Rapids Dam is used for electric power generation to the greatest extent possible, limited only by the hydraulic capacity of the power station (20,000 cfs). Power generation is scheduled to meet the electric power requirements of the Dominion Energy Virginia and Dominion Energy North Carolina customers, which vary significantly throughout the day and from day-to-day. Flow release may vary from about 2,000 cfs to 20,000 cfs. Large and sudden changes in flow release may occur at any time.
During normal operation Lake Gaston water levels are typically maintained between elevations 199 to 200 feet.
Minimum flows from Roanoke rapids during normal operation:
|December 1 - January 15, Kerr declaration < 6,000 cfs||2,000|
|December 1 - January 15, Kerr declaration > 6,000 cfs||2,500|
|January 16 - February 29, Kerr declaration < 6,000 cfs||2,500|
|January 16 - February 29, Kerr declaration > 6,000 cfs||3,000|
|June 16 - June 30||2,800|
|July 1 - September 15||2,000|
|September 16 - November 15||1,500|
|November 16- November 30||2,000|
Drought Flow Operation
Drought flows released from the Roanoke Rapids Dam are determined in consultation with the US Army Corps of Engineers (Corps) and the North Carolina Department of Water Quality (DWQ). These flows will be determined when a drought has been declared in the Roanoke River Basin by the Corps and DWQ.
At this time, Dominion Energy North Carolina will cease its load following operations at the Roanoke Rapids Dam and will discharge water to the lower river per the consultation. Minimum flows during droughts stated in Dominion Energy's FERC license are 2000 cfs for all months except September through November when minimum drought flows are 1500 cfs.
Fish Spawning Operation
During the anadromous fish spawning season (March 1 - June 15), flow released from Roanoke Rapids Dam is regulated to provide adequate downstream flow for spawning success. A constant sustained flow with little variation is desirable.
Toward the weekend extra water may be stored in Lake Gaston (between elevations 200 and 201 feet) for weekend release.
The recommended flow regime is:
|Period||Target Flow (cfs)||Lower Limit (cfs)||Upper Limit (cfs)|
|March 1 - 31*||Average of Kerr's weekly declaration||3,500|
|April 1 - 15||8,500||6,600||13,700|
|April 16 - 30||7,800||5,800||11,000|
|May 1 - 15||6,500||4,700||9,500|
|May 16 - 31||5,900||4,400||9,500|
|June 1 - 15||5,300||4,000||9,500|
*During March, Dominion may run peak flows on five separate days.
Flood Control Operations
Floodtime flow releases from Roanoke Rapids Dam are under direction of the U.S. Army Corps of Engineers. Release rates are primarily governed by Kerr Reservoir water level and inflow.
During flood control operation, a portion of the 3 feet of Lake Gaston flood storage (between elevations 200 and 203 feet) may be used.
Guidelines for flood releases relative to Kerr Reservoir water level and inflow are:
|Kerr Reservoir Water Level (feet)||Release (cfs)|
|300 - 312||Up to 20,000|
|312 - 315||25,000|
|315 - 320||35,000|
|320 - 321||Greater of 85% of inflow or 35,000|
|> 321||Greater of 100% of inflow or 35,000|