1 2 Direct withdrawals are limited to major rivers and lakes. - PDF document

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Direct withdrawals are limited to major rivers and lakes. Minimum in-stream flow requirements are more than drought period flows, so safe yield without storage is zero. Withdrawals from an existing reservoir is a reservoir alternative, not a direct river withdrawal. 3

On-stream reservoirs capture water from within the reservoir’s watershed and use stored water for supply. 4

Review bullets Depending upon the physical setting and the location of the demand center, these projects can be operated as direct withdrawals from the reservoir or for flow augmentation releases to a downstream diversion. If the reservoir releases into a much larger receiving stream, the project’s yield can be significantly enhanced. 5

Water withdrawn directly form the reservoir generally provides high quality source water because it is pre-settled and and the watershed can be monitored for spills and releases. As an example, Greensboro, North Carolina’s Lake Townsend project is a direct- withdrawal, on-stream reservoir (with a recently added emergency backup diversion). The Lake Townsend project is a 6.3 billion gallon reservoir on about a 105 sq. mi. watershed. It has a safe yield of about 35 mgd. 6

However, if the reservoir releases to a fairly large watershed with enough flow to meet needs during normal to high flow periods, augmentation operation of the reservoir can be quite beneficial. Water supply needs can to drawn from the larger receiving stream when flows are high and water supply releases need be provided from the reservoir only when the receiving stream flows are insufficient to meet those needs and the receiving stream in-stream flow requirements. Therefore, more storage can be conserved for use during droughts, thereby increasing safe yield yield. 7

Most modern water supply reservoirs are constructed on smaller watersheds and provided with diversions from a larger nearby stream or river. Nearly all diversion reservoirs are supplemented by pumping. Occasionally, an adjacent watershed is located at a higher elevation, allowing a gravity flow diversion. 8

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Discuss bullets Similar to on-stream reservoirs, these projects can also be operated as direct withdrawals. In these circumstances, natural runoff is supplemented with diversions and water supply is taken directly form the reservoir. 10

In the right setting, they can also be effective as augmentation reservoirs with releases to a downstream water supply diversion. As discussed previously, if the reservoir releases into a much larger receiving stream, the project’s yield can be significantly enhanced. Like Greensboro’s Lake Townsend Reservoir, Cobb-Marrietta Water Authority’s Hickory Log Creek project is a 6 billion gallon reservoir. Unlike Lake Townsend, it is on an 8 sq. mi. watershed and receives up to 39 mgd in pumped diversions from the 600 sq. mi. Etowah River (located immediately downstream). This project provides augmentation releases to an intake located further downstream on the Etowah River. Since water supply releases are only made when flows in the Etowah are low, this project yields nearly 50 mgd. 11

To illustrate some of the permutations and combinations considered, I’ll touch on Carroll County, GA’s proposed Indian Creek Reservoir Project. The county (outlined in green) is divided into two major river basins. To avoid interbasin transfer issues, the Carroll County Water Authority has planned for separate supplies to meet needs in each basin. For the Tallapoosa, the primary demand center is to the northeast, near I-20 and closest to Atlanta. The best reservoir site is located in the northwest corner of the county It’s a 4 8 sq The best reservoir site is located in the northwest corner of the county. It s a 4.8 sq. mi. watershed that can accommodate 10 Bg of water supply storage. The major long-term diversion to the reservoir is the Little Tallapoosa River – far enough downstream to have a large watershed and far enough away from the Alabama state line to address interstate concerns. Since the reservoir is located well downstream of the demand center, an augmentation reservoir would not serve the county. Therefore, this project needs to be a direct withdrawal that sends water back to the eastern demand center. 12

Here’s the whole project in schematic format. This shows only the western end of the county. The proposed reservoir would be located in the headwaters of Indian Creek. For initial operations - up to 6 mgd – a 10 mgd diversion would be located downstream on Indian Creek. However, Indian Creek can’t provide much more yield, so the second and third phases of the project - 6 mgd each in safe yield – would require additional diversions from the Little Tallapoosa River (10 mgd and 20.5 mgd increments). This project’s yield is 18 mgd despite 40 mgd of diversions and 10 Bg of storage because Georgia, like many states, bases yield on the drought of record. The Tallapoosa River was hit with a very severe drought in 2007 and 2008. Feb. 2007 to Feb. 2008 flows were 54% of the previous minimum 365 day average for the prior 55 years of record. 13

Now let’s take a look at some interesting planning process considerations. 14

You know that you are in a drought once reservoir storage becomes sufficiently depleted to command your attention. Also, it’s impossible to know if conditions will improve or get worse, so water managers must assume the latter. Since supplies can’t be planned, permitted and developed in time to help, unless supplies are ample, demand management is the water managers only viable tool. With our evolving awareness of climate change and not knowing if the current drought is going to be the “big one”, I recommend ample supplies. 15

It is imperative to plan ahead, well ahead. … 16

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Environmental regulators and advocacy groups want to maintain high levels of flow throughout the year. For a given safe yield, the higher the in-stream flow standard, the larger the reservoir and the larger the diversion pumps. Also, stream and wetland impacts weigh heavily in project selection and mitigation costs are very high. Also, higher in-stream flows require bigger reservoirs which increase stream and wetland impacts. It can get incredibly complex, so finding and retaining the very best team (based on track record) is a wise investment. 18

Because of the time and cost and complexity of these projects … Review bullets From initial planning to operation can take from 10 to more than 20 years. Very few projects approach the lower limit. Let’s tune up the time machine! 19

That’s right, it’s 1961. We’ve mastered time travel. Gunsmoke is the #1 TV show, Alfred Hitchcock Presents is in its last year of production and for you folks from Georgia, Hank Aaron and the Braves are still in Wisconsin, along with a 20 year-old catcher named Joe Torre. Take a minute to tell me what your world looks like, and think about how accurate you could project service conditions to appropriately meet water supply needs in 2011? 20

“To better understand the context and difficulty of the challenge, let’s reflect for a moment on our world of 50 years ago” 21

Having put ourselves in a 1961 perspective, would anyone have been able to picture today’s world? Would we have estimated that the state of North Carolina would more than double its population in 50 years or that Georgia would grow to more than 2.5 times its 1961 population. Remember that phones still had wires and many of them still needed an operator interface to work. Most people would have laughed at the concept of a ‘personal’ computer computer. … and there would have been no doubt that our climate was firmly fixed and there would have been no doubt that our climate was firmly fixed within the bounds of weather cycles we had experienced. Brace yourselves – we’re going Back to the Future. 22

Here we are back in 2011, and now we’re charged with planning for a water supply to meet needs through 2061. How accurately can we define what our grandchildren’s world will look like and what its needs will be. 23

Fast forwarding and looking from our current perspective … to plan well, we need to get a handle on a number of issues and develop educated guesses for others. I’d be 114, so it doesn’t matter much to me. It will be critical for our younger people and for the many people not yet born! 24

We all recognize that long-term water supply planning necessarily includes measures of uncertainty. The recognized uncertainties most commonly play out in population projections, per capita demand and industrial demand forecasts. Many regulators and project opponents jump on these issues because they know that the numbers can readily be questioned. In recent years, the opposition has attacked each of these elements and fought to minimize each. 25

We also have unrecognized or, at the least, unspoken uncertainties – climate and streamflow records are at the top of the list. 26