Gathright Dam Action Plan Update
Posted December 9, 2009
November 30, 2009
The Norfolk District, U.S. Army Corps of Engineers (NAO) i s executing the overall plan as briefed Oct. 2, 2009, and as outlined below. The intensified surveillance/monitoring conducted to date indicate no unusual conditions and Gathright Dam is functioning as designed. NAO will issue the December 2009 status report Jan. 4, 2010
Immediate Risk Reduction Measures Taken
- Maintain current pool level decline of 1 foot per week - We have lowered Lake Moomaw 20 feet from its normal pool elevation of 1582.0. The current pool elevation (1562.0) allows for the project's flood control storage to be contained in a pool with a maximum elevation of 1594.8; an elevation below both the record (high) pool the dam experienced in 1996 and the extreme flood events identified in the DSAC II Report as carrying higher risks. We plan to maintain the pool at elevation 1562 pending the completion of the short term risk reduction measures outlined below. At which time the Corps will implement additional operational modifications, as required.
- Increased staff routine surveillance of dam from once per day to twice per day - Started Sept. 18, 2009 and continues to date. No unusual conditions observed, conditions remain unchanged.
- Increased downstream toe piezometer readings from monthly to daily - Started Sept. 18 2009 and continues to date. No unusual conditions observed.
- Updated the Gathright Dam Safety Plan - All key personnel contact information and contractors for emergency supplies were validated and/or updated. Plan is posted (Oct. 1, 2009) on the NAO SharePoint web site for internal use.
- Provide 24/7 staff - 24/7 staffing started Sept. 29, 2009, and continued for 30 days - Reduced staffing to 12/7 based in part on: lack of risks identified in the DSAC report for normal pool levels (current pool level is 20 feet below normal pool level), no changed conditions observed during the intensified monitoring/surveillance period, and an assessment of historic instrumentation and lake level data which indicates the dam is functioning as designed.
Short-Term (within 90 days) Risk Reduction Measures
- Prepare Interim Risk Reduction Measures Plan - Currently under development and scheduled for completion by Dec. 15, 2009.
- Increase remote electronic monitoring - Contract awarded (Oct. 27, 2009) to set up remote monitoring of key downstream toe piezometers and adit weir instrumentation. Installation is scheduled to commence on 7 December and be completed by Dec. 20, 2009.
- District data compilation and analyses - Compiled and analyzed historic data for toe trench weir and adit weirs. Trends observed to date do not indicate an increase in seepage with time or that seepage is connected to pool elevation. The Corps will continue to evaluate existing historical instrumentation data and documents. Completion of the evaluation is scheduled for Dec. 21, 2009.
- Contract with dam safety consultants to provide an independent assessment of existing data and conditions at Gathright Dam - Contract awarded 30 September 2009. Site meeting with consultants and NAO staff held 19 and 20 October 2009. Draft report scheduled for submission by December 2009.
2010 Initiatives
- Update inundation mapping – NAO is currently working with Corps North Atlantic Division (NAD) and Corps Mapping, Modeling and Consequence (MMC) Center to schedule an inundation mapping update in 2010.
- Conduct a dam safety exercise w/local and state officials - NAO Emergency Management Office met with VA Department of Emergency Management (VDEM) on 13 October. VDEM expressed an interest to partner with NAO to develop and execute a dam failure exercise. VDEM scheduled a meeting for December with local planners to determine if they will support the exercise. If supported, exercise would be scheduled for Spring 2010
- Conduct a series of field investigations and analyses in an effort to confirm or repudiate the preliminary DSAC II rating - Upon completion of NAO analyses and dam safety consultants' analyses/findings, NAO will determine the appropriate path forward.
Updated: 11-Feb-2010