Editor's Note: This article is part of an operator profile on Leslie Carreiro of Asheville, North Carolina. Watch for a special feature in the November 2015 issue of Treatment Plant Operator. Not a subscriber? Take care of that right here and now. Click here to have TPO delivered monthly to your mailbox.
During the 1998 drought that affected North Carolina, the City of Asheville imposed mandatory water restrictions and purchased an emergency water supply for $300,000, despite demand being 20 percent less than the safe yield.
When the next drought hit in 2007, the city used a different approach. While other communities imposed water restrictions in July and August, Leslie Carreiro, water production superintendent, looked at the data from the computerized drought management model (Hydrologics) and knew it wasn’t time to ask customers to conserve.
The drought model, based on some 80 years of data entered weekly on the lake level and amounts of precipitation, balances the three water plants’ capacity of 20 mgd with data on the worst drought to create a probability chart.
“For example, it may show that in eight to 10 weeks there is a 10 percent probability the lake will be down 3 feet,” says Carreiro. “Remain calm. The lake is 110 feet deep. In a few more weeks, the model may show the lake will be down 10 feet. Still not bad, because the model also shows there is an 80 percent probability the lake will be full.”
The drought plan also calls for the city’s North Fork water plant to decrease production if the lake level drops, and to increase demand from the Mills River and William DeBruhl plants. Despite pressure from city and state officials to restrict water usage during the last drought, Carreiro and upper management stood firm.
“We had spent $400,000 on this hard-core scientific model,” says Carreiro. “If we didn’t follow it, how could we ever trust it?”
In October, the probability chart called for conservation measures, months after other communities had initiated theirs. The drought broke three weeks later. City officials and customers now had confidence in the model.
“The nerve-wracking part is balancing the drought model with our flood operation plan,” says Carreiro. “The latter calls for lowering the lake 3.5 feet in summer to retain heavy rains. My operators feel more comfortable when the spillway is overflowing. However, we have to trust the plan to prove it right or wrong.”
That moment has yet to arrive.
