Water Level Monitoring

Keeping Near Full Pond

Each year SML lake levels often vary by several feet due to variance in rainfall, and about every 5 to 7 years, SML will experience drought conditions that can, but rarely, lower levels as much as 5’. SML water levels are regulated primarily by AEP and the dam power generation project and its association water release schedule.  But often our members and residents ask SMLA questions regarding why Lake levels are so low or so variable.  SMLA conducts scientific assessments of a variety of factors, including: water release and inflow rates, evaporation rates, rainfall, groundwater discharge, and water removal rates by local water authorities. The following conclusions have been consolidated and approved by our partner organizations for publication:

  • Annual rainfall affects Lake level more than any other factor. Lake levels tend to drop during late summer and usually returns to normal level in Oct/Nov when the hurricane remnants come through and the plants and trees go dormant. You may view of the actual lake level chart at smithmountainlakelevel.com.
  • Appalachian Power’s dam generates power but is required to follow an approved release protocol, which remains constant until certain “triggers” are activated based on weather forecasts, inflow models, power generation needs, and the adjusted water level of Smith Mountain Lake.  Current lake levels are available on Appalachian’s website at http://www.aep.com/environment/conservation/hydro/. Appalachian continues to monitor lake levels to determine if any triggers can be implemented.
  • Evaporation rates at the lake are substantial – about 73M gallons a day.
  • The Bedford County Regional Water Authority (BRWA) Smith Mountain Lake Water Treatment Facility currently withdraws about 1.8M gallons a day from the Lake – which is 40 times less than the rate of evaporation.

In summary, rainfall has the greatest impact on Lake level; BRWA withdrawal has the least impact on the lake. Other factors will cause variable impacts, but only Leesville Dam releases can be negotiated.  With each renewal of the FERC license, SMLA is fighting for reduced outflows. SMLA was actually successful the last time, however downstream advocates have a strong lobby in the House of Delegates.  SMLA has made Appalachian Power aware that they were releasing MORE than the required amounts.  There subsequent adjustment has had a positive impact on lake levels over the past few years.

The following recommendations were provided to AEP in the Spring of 2015        (* indicates recommended responsibility):

  • Use actual Leesville discharges since 2010 to improve predictive accuracy in the June-December timeframe (Hydrologics*)
  • Maintain closer adherence to following the minimum Leesville discharges specified in the Water Management Plan (AEP*)
  • Request adding a probability value for the lake falling below 791 ft. in the Trigger 3 definition (Bedford Regional Water Authority*)
  • Request that DEQ renew the AEP permit for the next 5 years and review our recommendations and issues (DEQ*)
  • Continue to assess predictive model performance and address issues during the next 5 years (SMLA*) Water Level Monitoring Committee Plans
  • Continue to analyze the factors that control SML water levels over the next 5 years
  • Expand the committee membership to include additional expertise from the SML community
  • Specific areas of interest include:
    • Evaluate using more realistic groundwater models
    • Explore the utility of NOAA drought predictions for identifying low rainfall periods further ahead of their occurrence
    • Examine whether there is a better scaling relationship between the USGS streamflow gages and the larger SML drainage area
    • Improve estimates of the groundwater loss from the Smith Mountain and Leesville Lakes
    • Examine alternate methods for generating synthetic streamflows
    • Provide appropriate comments to AEP in the Spring of 2020

Interested parties can follow the drought outlook for our area on this website. http://www.deq.virginia.gov/Programs/Water/WaterSupplyWaterQuantity/Drought/CurrentDroughtConditionsMap.aspx.

Study of Water Level and Release Issues at Smith Mountain and Leesville Lakes

Smith Mountain Lake Association Water Management Committee February 15,    2015

View the report archive

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