Updates on the Savannah River Basin Comprehensive and Flood Storage studies

Corporate Communications Chief
Published Nov. 25, 2014
In October 2013 we announced an initiative to assess our flood storage capacity to test the possibility of reducing our current flood storage allotment. More specifically, the study will provide information that will better define the present need for flood storage in the basin. In the announcement we estimated the study would take approximately 12 months. Based on recent updates from the Hydrologic Engineering Center (HEC), the organization conducting most of the study, the results will be delayed about six more months.

To recap, the assessment will look at two things:

1) the ability of the projects to contain the Probable Maximum Flood (PMF), which however unlikely, is the greatest rain event the basin could ever expect; and

2) the ability of the projects to contain a number of smaller and more likely periods of rainfall intensity, from 10- to 500-year rain events. The assessment models intense rain events, and how runoff occurs in the basin with the present level of development. It will compare impacts of each of these rain events using our current 4-foot drawdown with impacts of lesser amounts of flood storage (smaller winter draw downs). The idea is to assess how much flood storage we need and identify what kind of risk we are taking if we reduce the winter drawdown and then get the inevitable large spring rain. If the study indicates that all the present flood storage is not needed, additional studies could be performed to determine how much storage is economically justified.

Update on the Savannah River Basin Comp Study (Interim 2)

In February we provided an update on the progress of the Comp Study. We estimated then, that the draft report would be ready for review in about 12 months (putting us at approximately February 2015). An updated estimate on completion of a draft report for public comments is about January 2016.

After we ran an initial data set through the models, the Corps and the study sponsors agreed that we needed to add data from 2013 to our inflow dataset to have more accurate results. We are obtaining that information to make sure we capture the recovery of the system from the most recent drought, possibly the new drought of record, which occurred from 2011 to 2013. Georgia Environmental Protection Division (GAEPD) is now collecting the needed data and when their work is complete, we will run the reservoir simulation models again to evaluate each of the six proposed alternatives.

Other work continues. The Nature Conservancy (TNC) has been performing research and held a workshop to help define parameters for Alternative 3: “Release Based on Environmental Flow Restriction.” TNC is finalizing their report from that workshop and they will then update the ecosystem functions model to incorporate additional environmental criteria that we will use to evaluate each alternative.

To recap, the purpose of this interim is to answer the following questions:

1) How low can we reduce daily outflows at the Thurmond Dam during drought conditions?

2.) How long can we sustain these minimum outflows before significant negative impacts would occur to the downstream economy and environment?

This portion of the study will examine value, risks and impacts of six alternative operating protocols for the current Drought Contingency Plan. You can see summaries of these alternatives here.