Coosa Project
INTRODUCTION TO COOSA PROJECT OPERATIONS
Alabama Power Company's Coosa River and Warrior River hydroelectric projects are operated either locally or remotely from the Alabama Control Center (ACC) in Birmingham. Operations of the Coosa River developments are closely coordinated with each other and with the operation of other facilities in the Coosa River basin, particularly the Army Corps of Engineers' Carters (on the Coosawattee River) and Allatoona (on the Etowah River) Reservoirs (located approximately 120 miles upstream of Weiss Lake). The ACC monitors Alabama Power's electrical system and directs the generation schedule. For additional information about the operation of these hydroelectric developments, click on one of the links below or see the Project Operations and Management (section 3.0) in any of the Initial Information Packages.
Coosa Project
Alabama Power Company operates the Weiss development principally to produce peaking power with seasonal variation in storage and generation. Operation is guided by a lake rule curve which is a set of target lake level elevations (see Weiss IIP). This curve varies seasonally with the lake level normally maintained at or below the curve except when storing floodwater.
Alabama Power normally schedules power operation on the basis of system demands and availability, seeking to keep the pool at or below el. 564 ft above mean sea level (msl) at all times except during flood conditions. The plant normally operates on a weekly cycle and the power generated is available for use in daily peak-load periods (Monday through Friday).
From May through August the lake is held at the normal full pool elevation of 564 ft msl during normal inflows and system generating requirements. Drawdown begins in September and ends in December when the winter pool level of el. 558 ft msl is reached. The lake begins refilling on January 1 and continues until April 30 when full pool is reached.
Flood Control Operations
During periods of flooding, Alabama Power maintains communication with the Army Corps of Engineers (ACOE) and with the Weather Service River Forecast Center in Atlanta. The lake's flood control pool is from 564 to 574 ft msl and provides 397,000 acre-ft of storage. This volume is equivalent to 1.42 inches of runoff from the drainage area.
To the extent possible within the limits of the discharge capacity of the powerhouse, the lake level is maintained below the rule curve. Releases through the powerhouse and spillway are adjusted depending upon inflow and the level of the lake relative to the power pool or flood storage pool. The release rate is limited to 40,000 cubit feet per second (cfs) until the lake rises and/or the inflow increases to a point where a higher release rate is specified by the induced surcharge curve. Similar to a lake rule curve, the induced surcharge curve is used to manage flows during periods of high inflow to ensure protection of downstream lands.
Low Water Operations
During periods of low inflows, water is released from storage to help maintain downstream water quality, aquatic habitat, power generation, navigation, and recreational opportunities.
Nonpower Operations
In addition to power production, operation of the Weiss development provides other benefits to the immediate vicinity and region including recreational and environmental enhancements.
In 1989 Alabama Power made an agreement with the Cherokee Chamber of Commerce, the ACOE, and the Alabama Department of Conservation and Natural Resources (ADCNR) to stabilize lake levels during the spring spawning season for crappie. When Alabama Power is notified by the ADCNR that spring crappie spawning is near peak the lake level is held constant or slightly rising for a period of 14 days.
For a more detailed description of project operations at the Weiss development, see the Project Operations and Management (section 3.0) in the Weiss Initial Information Package.
Alabama Power Company operates the Henry development to produce peaking power and provide downstream flow augmentation. Operation is guided by a lake rule curve which is a set of target lake level elevations (see Henry IIP). The lake level is normally maintained at or below the curve. The compulsory drawdown each year is to el. 505 ft above mean sea level (msl) during the flood season. The plant normally operates on a weekly cycle and the power generated is available for use in daily peak-load periods (Monday through Friday). When the lake level is below target levels on the rule curve, the powerhouse is operated in accordance with the rule curve and system requirements. Whenever the lake reaches the elevation shown on the curve, the powerhouse is operated as necessary up to full-gate capacity in order to discharge the amount of water required to prevent the lake level from exceeding that shown on the curve.
Historically Alabama Power has operated the lake so that from May 1 to October 31 the lake level was maintained at a normal maximum water surface elevation of 508 ft msl, and el. 505 ft msl during the winter (November 5 to April 15). However, FERC recently approved a 3-year temporary variance to the rule curve. Under the revised rule, Alabama Power will maintain the lake at el. 508 ft msl from May 1 to September 30, then draw down to el. 507 ft msl by December 1 and maintain this level until March 31, when the lake will be refilled to el. 508 ft msl by May 1.
Usable storage of 30,640 acre-ft is provided between elevations 508 and 505 ft msl to augment flow into the downstream Logan Martin Lake during periods of low stream flow. The lake is lowered to el. 505 ft msl during the winter months to provide power storage capacity (Verigin, 1995; FERC, 1998). The normal static tailwater elevation varies from el. 465 to el. 460 ft msl, providing a fluctuating gross head of 43 to 45 ft.
Flood Control Operations
There is limited flood control storage in Henry Lake. Alabama Power lowers the lake to minimize river stages in advance of impending floods to reduce potential damage to the Gadsden area (ACOE, 1998). The principal factors in determining when to begin drawdown, the rate of drawdown, and the elevation to which the lake will be lowered are 1) the magnitude of discharges from the upstream Weiss development and 2) runoff estimates for the portion of the drainage basin downstream of Weiss.
Low Water Operations
During periods of low inflows, water is released from storage to help maintain downstream water quality, aquatic habitat, power generation, navigation, and recreational activities.
Nonpower Operations
In addition to power production, the Henry development provides other benefits to the immediate vicinity and region including recreational and environmental enhancements.
Project Operations During a New License Term
Alabama Power anticipates continuing the present mode of operation at the Henry development. One exception is the trial evaluations of alternative lake levels as described above. As part of the relicensing process and in response to stakeholder interest, Alabama Power may reexamine their operations to enhance recreational, operational, environmental, and economic values of the Henry development.
For a more detailed description of operations at the Henry development, see the Project Operations and Management (section 3.0) in the Henry Initial Information Package.
Alabama Power operates the Logan Martin development principally to produce peaking power. Operation is guided by a lake rule curve which is a set of target lake level elevations (see Logan Martin IIP). The lake level is normally maintained at or below the rule curve except when flood inflows cause the pool to rise. The compulsory drawdown each year is to el. 460 ft above mean sea level (msl) during the flood season. The plant normally operates on a weekly cycle and the power generated is available for use in daily peak-load periods (Monday through Friday). When the lake level is below that shown on the rule curve, the powerhouse is operated in accordance with this curve and system requirements. When the lake reaches the elevation shown on the curve, the powerhouse is operated as necessary up to full-gate capacity in order to discharge the amount of water required to prevent the lake level from exceeding that shown on the curve.
Alabama Power operates the lake so that from early May to the end of August the lake level is maintained at or near the normal maximum water surface elevation of 465 ft msl for normal inflows and system generation requirements. The winter drawdown begins at the end of September and reaches el. 460 ft msl in late December.
Usable storage of 67,700 acre-ft is provided between el. 465 and el. 460 ft msl to augment flow into the downstream Lay Lake during periods of low streamflow. The lake is lowered to 460 ft msl during the winter months to provide flood storage. The normal static tailwater elevation of 396 ft msl provides 69 ft of gross head.
Flood Control Operations
To the extent possible within the limits of the discharge capacity of the powerhouse, the lake level is maintained below the rule curve. Releases through the powerhouse and spillway are adjusted depending upon inflow and the level of the lake relative to the power pool or flood storage pool. A regulation schedule specifies the releases corresponding to various combinations of inflow and lake level. The first adjustment is typically to increase the magnitude or duration of powerhouse releases, followed by increased spillway releases.
The release rate is limited to 50,000 cubit feet per second (cfs) until the lake rises and/or the inflow increases to a point where a higher release rate is specified by an induced surcharge curve. Every 6 hours thereafter the release rate is adjusted to conform to the induced surcharge curve. An induced surcharge curve is a graph that shows how high above the normal full pool level a reservoir should be while storing water from flood flows. Similar to a lake rule curve, the induced surcharge curve is used to manage flows during high inflow to ensure protection of downstream lands.
When the rate of inflow decreases to the release rate, the positions of the spillway gates are maintained during the emptying of flood storage which is above the elevation designated by the rule curve until the lake level recedes to the required elevation. Should a second flood enter the lake prior to completion of emptying to the designated elevation, the rate of release is dictated by the induced surcharge curve. When the lake level recedes to the elevation designated by the storage delineation curve, the powerhouse is operated as required to maintain the lake at or below the specified limits.
Flood control operation is normally in accordance with the regulation plan described above. However, the limited amount of storage allocated to flood control at Logan Martin Lake generally will not significantly reduce major flood peaks. When firm forecasts indicate that a major flood is in progress, Alabama Power and the Army Corps of Engineers (ACOE) collaborate in the analysis of available information and determine whether a deviation from the induced surcharge curve is needed. Any departure from the regulation schedule requires approval by the ACOE.
Low Water Operations
During periods of low inflows, water is released from storage to help maintain downstream water quality, aquatic habitat, power generation, navigation, and recreational opportunities.
Nonpower Operations
In addition to power production, operation of the Logan Martin development provides other benefits to the immediate vicinity and region including recreational and environmental enhancements.
For a more detailed description of operations at the Logan Martin development, see the Project Operations and Management (section 3.0) in the Logan Martin Initial Information Package.
Since the Lay development has limited storage capacity, Alabama Power operates Lay principally in a run-of-river mode in which peak flows from upstream project operations are passed directly though the powerhouse. During typical operations the lake normally fluctuates no more than one foot as a result of daily flow releases.
Flood Control Operations
Lay Lake has no flood storage thereby limiting operations during floods to passing inflows.
Low Water Operations
Because the Lay development is a run-of-river project, water releases during low inflow conditions are equal to inflow. The lack of seasonal storage prevents Lay from making sustained releases in excess of inflows.
Nonpower Operations
In addition to power production, the Lay development provides other benefits to the immediate vicinity and region including recreational and environmental enhancements.
For a more detailed description of operations at the Lay development, see the Project Operations and Management (section 3.0) in the Lay Initial Information Package.
Since the Mitchell Project (the Project) has limited storage capacity, Alabama Power operates the Project principally in a run-of-river mode in which peak flows from upstream project operations are passed directly through the powerhouse. During typical operations, the lake fluctuates no more than one foot as a result of daily flow releases.
Flood Control Operations
Mitchell Lake has no flood storage, thereby limiting operations during floods to passage of inflow.
Low Water Operations
Because Mitchell is a run-of-river project, water releases during low inflow conditions are equal to inflow. The lack of seasonal storage prevents Mitchell from making sustained releases in excess of inflow.
Nonpower Operation
In addition to power production, the Mitchell Project provides other benefits to the immediate vicinity and region including recreational and environmental enhancements.
For a more detailed description of operations at the Mitchell Project, see the Project Operations and Management (section 3.0) in the Mitchell Initial Information Package.
Since the Jordan Project and Bouldin development have limited storage capacities, Alabama Power operates Jordan and Bouldin principally in a run-of-river mode in which peak flows from upstream project operations are passed directly through the plants.
Releases through Jordan and Bouldin are coordinated with discharges at other Alabama Power facilities on the Coosa River to achieve the best combination of power generation and flood control. Data from an automatic network of rain gages and stream gages are transmitted to the Alabama Control Center (ACC) which provides an early indication of flows developing in the basin.
Normal operating procedures call for passing Jordan Lake inflow first to the Bouldin powerhouse, except for a minimum discharge to be maintained through the Jordan powerhouse for downstream recreation, water quality, and aquatic habitat enhancement. This minimum flow requirement varies from 2,000 to 10,000 cubit feet per second (cfs) depending on time of year. Flows in excess of the combined minimum flow at Jordan Dam and turbine capacity of the Bouldin powerhouse (27,600 cfs) are discharged through the Jordan powerhouse to the extent of its capacity (19,700 cfs). Flows in excess of the Jordan and Bouldin combined turbine capacity are discharged through the Jordan spillway. Lake fluctuations below el. 252 ft above mean sea level (msl) are normally limited to considerably less than 5 feet (Hendron, 1996). The Jordan Lake level normally fluctuates about 1 foot each day due to minimum flow operations. The Bouldin forebay level fluctuates from 1 to 2 feet due to head loss through the intake channel from normal power operations.
Flood Control Operations
Jordan Lake has little to no flood storage, thereby limiting operations during floods to passing inflows.
Low Water Operations
Because the Jordan and Bouldin operations are basically run-of-river, the lack of seasonal storage prevents them from making any substantial releases in excess of inflows.
Nonpower Operations
In addition to power production, Jordan and Bouldin provide other benefits to the region and immediate vicinity including recreational and environmental enhancements.
Alabama Power currently has mandatory minimum flow releases from Jordan Dam for whitewater boating and aquatic enhancement of the Coosa and Alabama Rivers below the dam. Alabama Power has been operating Jordan Dam under minimum flow requirements since the late 1960's. These have been modified from time to time with the most recent modification implemented in May 2000. The following release schedule is in effect:
- From April 1 through May 31, Alabama Power releases continuous base flows of 4,000 cfs for 18 hours per day from 3:00 p.m. through 9 a.m. For the remaining 6 hours, Alabama Power should release an 8,000 cfs pulse flow from 9 a.m. through 3 p.m.
- Beginning June 1 through June 15, Alabama Power reduces the continuous 4,000 cfs base flow at a rate of 66.7 cfs per day, and the daily 8,000 cfs pulse flow at a rate of 133.3 cfs per day.
- From June 16 through June 30, Alabama Power ceases release of the daily pulse flow but continues to release the continuous base flow reducing it to 66.7 cfs per day.
- From July 1 through March 31, Alabama Power releases a continuous minimum base flow of 2,000 cfs regardless of inflow.
- On weekends only from June 16 through October 31, Alabama Power releases flows of either 4,000, 6,000, or 8,000 cfs continuously from 11 a.m. to 5 p.m. using the schedule presented in table 3.2-1 (Appendix C, pg. C-5) and the following schedule for holidays:
- On one day during the Memorial Day weekend, Alabama Power releases up to 10,000 cfs continuously between 10 a.m. and 6 p.m.
- On one day during the Labor Day weekend, Alabama Power releases up to 10,000 cfs continuously between 10 a.m. and 6 p.m.
- On July 4, Alabama Power releases up to 10,000 cfs continuously between 10 a.m. and 6 p.m. using the following schedule: if July 4 is on Tuesday, a Monday release would be required in addition to the required release on July 4; if July 4 is on a Wednesday, the Monday release would be forfeited for the July 4 release; if July 4 is on a Thursday, the Monday release would be changed to Friday, July 5 to give a 4 day release; if July 4 is on a Saturday, Sunday, or Monday, the normal recreational release schedule would be followed.
