Since our last progress report on the flood storage study published November 2014, we received a few inquiries on when the results would be released. In the above linked post we estimated the study would take approximately six more months to complete, which projected a late spring/early summer completion date.
Off by a few months, the study concluded in July 2015. Although we now have a complete data set and hydrology models, our water managers report that the Corps’ Hydrologic Engineering Center (HEC), the organization conducting most of the study, is in the process of releasing a report of their analysis on the management of the Probable Maximum Flood (PMF).
With this report, HEC will also be releasing a set of design storms which will require further calibration. Once calibrated, we can assess the reallocation of flood storage at Hartwell.
Data analysis on the reallocation of flood storage at Hartwell is scheduled to take a few months, dependent on available funding and resources.
Recommendations will then be forwarded to the District’s Planning Division to determine whether a reduction in flood pool can be considered as a viable alternative in the next phase of the basin’s comprehensive study, said Corps water manager Stan Simpson.
For those needing a recap or overview of the study, our October 2013 announcement detailed why the Corps began the study.
The story explained how the flood pool analysis intended to examine whether the established 4-foot winter drawdown could be reallocated according to new data.
To summarize, HEC developed rainfall models to analyze the ability of the projects to contain:
- the greatest rain event the basin could expect, known as the Probable Maximum Flood (PMF); and
- the 2- to 500-year storm events at the three Savannah River projects for future analysis. The HEC models, once calibrated, can later be used to analyze possible reductions in flood storage at the projects.
Since then, HEC has developed and run several scenarios to test the ability of the projects to pass the Probable Maximum Flood. These same models are being further refined by the Mapping and Modernization Center for incorporation into the Corps Water Management System (CWMS), a tool that offers features that most Corps water managers need to perform operation analyses on a daily basis.
The CWMS suite can be used to test the feasibility of different scenarios and develop estimates of increased damages due to reduced flood storage, according to Simpson.
Water managers and members of the District’s Planning Division will use these results to evaluate the impacts associated with changes in project operations. If decreasing the winter drawdown is feasible, then reallocating the proposed 2 feet of flood storage to conservation storage would become a viable alternative considered in the third and last phase of the Savannah River Basin Comprehensive study.
If the proposed reduction alternative is the chosen alternative for that phase, the district would recommend a reallocation of flood storage which requires congressional approval.
Thanks for reading us, and as always, we welcome your comments and feedback!
~Chelsea Smith, public affairs specialist
Please help, the terminology confuses the HEC out of me.
The study concluded in July, but “the study” does not include analyzing all of the data or issuing a report. I have eagerly looked forward to the study conclusion and a preliminary report to review.
It appears the schedule goes something like this.
2015 Jul- Study Concluded
2015 Nov?- HEC issues report on Probable Maximum Flood
2016 Mar?- SAS completes analysis of reallocation of flood storage at Hartwell
2016 Apr?- SAD determines whether to consider a flood storage reduction in the next phase of the comprehensive study, Interim III
2016 Nov- Public and Agency Review of Interim II Draft EA and Report
2017 Jun- SAD Approves Interim II
201? Interim III obtains funding
202? Interim III issues EIS for public review that includes the flood storage assessment
Will the HEC report be available to the public?
What about Thurmond flood storage reallocation?
Am I correct to not expect the flood storage assessment report until 202??
All these tax payer funded studies that seem to never end or have any meaningful reports for the payee. What’s the purpose?
Actually our studies do have and end and do serve a purpose. We’ve had multiple updates to our Drought Management Plan over the years, for example. Each required a study. Each study began and ended. The studies resulted in changes to the DMP including the current plans that set outflow reduction rates at various reservoir levels. Thanks for bringing this up so we could mention this to new readers.
— Billy Birdwell, Corporate Communications Office
Ferris: Your research makes your comments always interesting to read.
Your anticipated timeline seems to be within the ballpark. Your past posts show you understand the reasons, but I’m glad you asked so I can address any new BtB readers’ obvious follow-up question, “So why does it take so long?” A simple equation answers the question.
t = $
In this equation t is time and $ is money. There two things drive each other.
Money drives first. To conduct any study, the Corps of Engineers must have money authorized and appropriated from Congress to conduct the study. Congress also requires such studies to be cost-shared with the states. So the states also must appropriate funds. Since two states are involved in the Savannah River basin, both states must appropriate funds or provide work-in-kind services (an equal value of money in labor). Getting funds appropriated through Congress and two state legislatures spans months or years. Then studies can begin.
With money issues initially set, time drives for a while. Field work takes time. Sometimes data must be gathered over multiple seasons. Data must be entered into evaluation systems or computerized models for calculations. Computers crunch data numbers quickly, but humans interpret that number-crunching. To ensure the reliability and validity of the data, others need to review it. More time; more money.
As to your other questions: We plan to make the HEC report available to the public. The Hartwell flood storage analysis will likely only contain an executive summary, also available to the public. While we haven’t made a final decision, we will likely look at Thurmond storage at the same time as we do Hartwell.
— Billy Birdwell, Corporate Communications
I can understand the desire to be protected in the worst imaginable rain event but I don’t understand why congressional approval would be required to back off to 2′ rather than 4′. We didn’t have congressional approval to increase flood storage when we doubled it by adding Hartwell and Russell. So going back to what it was originally when we had just Lake Thurmond flood storage should not require special approval. I guess I am missing something.
Additionally, unless lake interests are taken into account the conclusion will undoubtedly be to stay with 4′ drawdown. You could even reason why not go down a lot more if you leave lake interests and recreation out of the equation. Conservative lake interests need to be represented in all corps decisions regarding the drought plan if we are ever to get to a reasonable solution to protecting the recreational infrastructure associated with the lakes.
Jerry, thanks for contributing to our lively discussions on BtB. You mentioned you may be “missing something” concerning winter drawdown. You concluded drawdown should have been changed with the additional storage gained with the impoundment of Hartwell and Russell lakes. What you are missing is the fact all conservation storage was considered before the dams were constructed – including for multiple potential reservoirs, most of which were never built. In other words, we had all the reservoirs in mind when we set conservation storage.
— Billy Birdwell, Corporate Communications Office
Reducing the flood storage seems like such a logical decision but, I certainly don’t have
my hopes up.
The graph from a 1990 USGS study for the Savannah River at Augusta illustrates that changing the drawdown will make little difference for the PMF and that the reservoirs provide greater flow reduction benefit for higher frequency floods. The 1990 study included all current project reservoirs.
The 1990 study estimates that reservoirs reduce flow rates as follows.
50% Frequency Flood: Reduced from 92,000 to 34,500 cfs, or by 62.5%; green line
20% Frequency Flood: Reduced from 138,000 to 51,500 cfs, or by 62.7%; red line
1% Frequency Flood: Reduced from 316,000 to 180,000 cfs, or by 43.0%
0.2% Frequency Flood: Reduced from 445,000 to 345,000 cfs, or by 22.5%
Probable Maximum Flood: No Reduction- 1,000,000 to 1,000,000 or by 0%
Because higher frequency floods will determine any drawdown adjustments, my frustration emanates from expectations of pending study results, i.e. a public report that analyzes drawdown levels. I now understand these will wrap into the comprehensive study.
The Thurmond plate illustrates the effect of 330′ versus 325′ pool elevations for a roughly 50% Frequency Flood, with peak discharge rates of 46,000 cfs and 44,000 cfs respectively. The current study revisits this type of analysis with higher quality data in an effort to fine tune the drawdown amount. In other words, the data is new but not the concept. Flood storage studies analyze expected elevations for past events based on current operations, which for the current study include the combination of a modified drawdown and drought plan.
Clark Hill and Hartwell approval happened simultaneously in 1944, along with nine other projects. Neither the vision nor plan proposed a permanent solitary Clark Hill project. The inevitable Hartwell authorization came in 1950, before Clark Hill operation. It would have been silly to perform an extra set of laborious hand calculations that applied to just a few years when anecdotal comments indicate the intent was to use as much conservation storage as possible by winter, presumably to demonstrate the value of the huge expenditure.
See graph and comments near the bottom of the Aug 12, 2015 topic.
The Thurmond Plate messed up when I changed the order.
I blame the drawdown study schedule on the political influence that determines funding priorities. As Chelsea wrote, data analysis depends on funding and resources. Later results could be a good thing if the results encompassed a Thurmond bathymetric survey. I think that unrealistic expectations based on a questionable premise generated the pressure to fund the drawdown study before the bathymetric survey.
It appears that USGS topographic maps available prior to filling Thurmond largely employed technology available prior to WWII. Contour line measurements calculate surface areas that calculate storage volume. About half of the surface area calculations would have come from 20′ contour interval maps dated around 1943. The other half would have come from 50′ contour interval maps dated around 1900.
In addition to less accurate survey data based on the technologies available at the time of Thurmond construction, intervals of 20′ to 50′ required wide interpolation. To say it another way, Thurmond storage calculations would have derived from old technology maps at 250′, 300′, and 350′ elevations for one area that were combined with other old technology maps for a different area at 220′, 240′, 260′, 280′, 300′, 320′, and 340′ elevations. Although sufficient for project purposes, the current fine tuning studies could benefit from data that are more accurate. I cannot help but wonder how much a bathymetric survey would affect study results.
Quick question for the COR, why are we down almost 5 ft when Lake Keowee is almost at full pool? Aren’t both in the business of producing power?
Good question Brad. A quick correction on the numbers: Hartwell is 4.8 feet below full, and Thurmond is 5.4 feet below full. By contrast, Keowee is 3.5 feet below full. However, the Duke run pools cannot be compared to the Corps pools because, although they do share a similar purpose in hydropower, they differ in many other areas. The Corps projects have six other mandated purposes besides hydropower. Additionally, there is a minimum discharge requirement for Thurmond because it is the last major dam in the system and feeds a river, whereas Keowee feeds another reservoir. There’s also variances in precipitation, geography, runoff, etc. in each sub basin. I hope this helps. And thanks for commenting :-) -Russell
What I’d really like to know is why, with stevens creek flow at 12000cfs (and the savanna river in augusta at the same), why any release from Thurmond was necessary yesterday. And this has nothing to do with lake inventory… it is a pure downstream flooding question.
Thanks for your comments and question. I contacted our
resident hydrologist & water manager Stan Simpson, who said:
The channel capacity at Augusta is 30,000 cfs. If it looks like our release will cause the gage at Augusta to exceed 30,000 cfs, we will curtail releases from Thurmond until after the peak has receded.
While the concept doesn’t save a lot of water, even we are at drought flows, it does save some.
For this reason, this is one of the topics we will be addressing in the comp study, “How do we manage flows during refill of the
reservoirs.”
Scott, as you note, Stevens Creek is currently contributing massive amounts of local flow to the Savannah River. Unfortunately, it joins the river about 13 miles below the dam and after the environmentally critical Augusta shoals and the city of Augusta. Other upstream tributaries contributed little to Thurmond releases. Kiokee Creek, the major measured contributor, averaged 25 cfs on Sat, 900 cfs on Sun, and 270 cfs today; not a massive amount and difficult to predict. Channel capacity changes the situation as noted below. ~Ferris
Stevens creek joins the river upstream of stevens creek dam. Which is upstream of augusta. This dam backs up water to Thurmond dam and “reregulates” the daily output back into a steady flow. Yes, the flow through augusta was less than 30,000cfs. But downstream of Augusta more than 20,000 cfs can have significant impact.
The fact that the lakes are not full, the basin had more than enough ability to produce the declared output without Thurmond releases, and downstream flow was more than 5 times the minimum should have warranted a couple days of ZERO Thurmond releases but hey, it was within the rules.
Scott, I reversed the dams and stand corrected. The higher flows do affect us, and I had this backwards in my minds eye. Good catch about the releases. ~Ferris