Women for Wise Growth drought forum

Kevin, of course, has an excellent wrap up of last night's Women for Wise Growth forum on the drought. There's also supposed to be a podcast of the forum available here at some time in the future.

Here's my two cents.

First thing i noticed, far fewer people at this even than at the forum in January. A couple of possible explanations. First, much less publicity around this event. Second, location. This was at the Durham Public Library downtown, the earlier forum was on duke campus, at the Sarah P. Duke Gardens. The third possibility, which i really hope was not the case, people think the drought is over because the reservoirs are filled.

Both the Herald Sun and BCR noted the number of elected officials and office seekers in attendance. I myself was rather disappointed that Mike Woodard was the only City Council person in attendance. I didn't notice anyone from Patrick Baker's office either, though i could have missed them.

What caught my ear was a number mentioned by both Syd Miller, of Triangle J Council of Governments, and Bill Holman of the Nicholas Institute at Duke. That is, the 50 year safe yield for Durham's water supply is 37 million gallons per day. That number seemed significant, since we peaked last year at around 33 million gallons per day before mandatory conservation measures were enacted. So i chatted with Syd Miller this morning to get a better understanding of how that number is derived and what it means.

Here's the deal.

First off, "50 year safe yield" means that, over each of the next 50 years, there's a 98% chance that we can count on being able to provide that amount of water, on an average basis. The 37 million gallons per day is the 50 year safe yield number. So, on an average daily basis, there's an overwhelming statistical chance that amount of water will be available. That number is derived from a number of factors, including the historical record over time of rainfall patterns in the drainage basins for our two current reservoirs. It also assumes that all available water would be used. In other words, we could essentially drain the reservoirs on occasion to meet that average daily demand.

Syd put my mind at ease as far as the 33 mgd peak usage recorded last year by stressing that the 37 mgd figure is based on average use, and can accommodate peaks above that number.

I don't have the data in front of me, but I'm reasonably certain that for 2006, average daily demand was at or below 27 mgd. According to Syd, warning bells should start to go off at city planners' desks when average daily demand hits 80% of the safe yield. In our case, that would be a 29.6 mgd figure.

The short term steps being taken to increase the safe yield number for Durham include bringing the Teer Quarry online (7mgd) and some soon-to-be-announced conservation programs that are outside the Stage III and Stage IV mandatory measures. Reducing average demand by 15 - 20% on a long term basis (we're about 15% below last year as a result of the short-term Stage III and Stage IV restrictions), and adding the Teer Quarry storage to the equation could put us somewhere near the 65% mark by increasing safe yield to 44 mgd, and keeping usage below 28 mgd, even allowing for 2.25% annual population growth.

Whether that gets us through 2 or 3 consecutive years of drought is still a thought experiment i hope we don't have to actually conduct. Meanwhile, it's raining again. Now that the reservoirs are full, let's hope this helps to replenish our ground water, which remains depleted.