The Savannah River Basin has had a significant rain deficit throughout the last year, which has continued to produce low lake levels that severely impact recreation, hydropower, and other authorized purposes. Rainfall in the last 60 days has been well below normal for the upper basin.
This time of year, the reservoirs typically decline, even with normal rainfall, because they lose a significant amount of water to evaporation, transpiration, and groundwater recharge. For the pools to remain flat or climb, we would need a sustained rainfall well above normal amounts for this time of year. The only real solution to this drought is more rainfall over the upper part of the basin.
We have seen rainfall over parts of the basin in the last few weeks. However, much of that water has been absorbed into the ground (infiltration). Under our current conditions, it will take a substantial amount of rain before the ground is sufficiently saturated to produce runoff into the reservoirs. Typically, 60 to 90 percent of rainfall is lost to infiltration for a 1-to-2 inch rain event on unsaturated soil. It’s not until there is rainfall on saturated soil, or a lot of rain in a short period of time, before a significant amount of runoff occurs.
We are doing everything we can within our authorities to respond to the current drought. The basin has been in drought since July 2011, when the reservoirs entered Drought Level 1. We immediately reduced the outflows from the reservoirs to a maximum weekly average of 4,200 cubic feet per second (cfs) at the Thurmond Dam. In August of 2011, the reservoirs entered Drought Level 2, so immediately; we further reduced outflows to a maximum weekly average of 4,000 cfs. In October, the District Engineer exercised his authority to reduce outflows beyond the Drought Level 2 rate, down to 3,800 cfs. This is the lowest outflow we can release under our authorities at this time.
We manage water based on the Drought Contingency Plan, which was decided and agreed upon by the Corps and other federal and state agencies that all have a stake in the basin. Those agencies include:
– Georgia Environmental Protection Division
– Georgia Department of Natural Resources
– South Carolina Department of Natural Resources
– South Carolina Department of Health and Environmental Control
– Southeastern Power Administration
– U.S. Fish and Wildlife Service
– The National Oceanic and Atmospheric Administration
– National Marine Fisheries Service
– Environmental Protection Agency
Our plan relies on coordination with these agencies to address environmental impacts, and to ensure we remain in compliance with the National Environmental Policy Act. We continue to use this balanced approach when evaluating potential changes to the drought plan, as we are currently doing with a draft Interim Drought Plan Environmental Assessment (EA).
The proposed EA would allow us to determine water releases from the three-reservoir system during drought based on inflow and pool elevation. The current drought management strategy only uses pool elevation as a drought criteria that designates how much the Corps should release from the reservoirs. We would use the 28-day average flow at the U.S. Geological Survey (USGS) gage on the Broad River at Bell, Ga., as the index site for the inflow-based trigger. The Broad River is an unregulated drainage basin with 1,430 square miles above the gage site. The Broad River flows into the Thurmond reservoir downstream of Richard B. Russell Dam.
At this time, we are still evaluating and addressing comments we’ve received from the public, state and federal agencies, and other stakeholders about the proposed EA. We are working to make a decision as soon as possible and will keep the public informed through this e-newsletter and other communication.