An abundance of rain has prompted Wichita to significantly increase the amount of water it is pulling from Cheney Reservoir even as malfunctioning equipment has diminished how much water the city can store from the overflowing Little Arkansas River.
The city began pulling 70 percent of its water from Cheney this week after more than 15 inches of rain over the past three weeks filled the lake.
Only two months ago, the City Council approved a move to drop the amount the city takes from Cheney from the normal 60 percent to 40 percent. But not only had the lake’s conservation pool – where the city draws its water – filled to capacity early Thursday, its flood control level was almost 10 percent full by 4 p.m. and increasing.
The flood control level is the excess water. At some point, the U.S. Army Corps of Engineers has to start spilling that water into the north fork of the Ninnescah River, but Corps officials said they are a long way from doing that.
City officials, however, don’t want to get to that point.
Plus, they want to go back to taking as much from Cheney as possible to help protect the Equus Beds aquifer – the city’s other main water source. The aquifer was providing 40 percent of the city’s water until it was bumped to 60 percent in June; now it will be at 30 percent.
“We want to make sure we use as much water out of Cheney as possible,” said Alan King, the city’s public works and utilities director.
High rainfall this year has dramatically changed the picture for Cheney. Last February, when the lake’s conservation pool was 58 percent full after two years of drought, city officials were predicting it would run dry by August 2015.
Rain and conservation efforts have left the city using about half as much water as it did a year ago at this point.
Since the council members approved the original switch to a smaller draw from Cheney, King planned to wait and get their permission to change again at a meeting on Aug. 27. But King said City Manager Robert Layton told him Wednesday to make a temporary “operational adjustment” and let the council know about the change at the meeting.
“The council can still pull it back,” King said, “but I don’t think they will.”
There is a limit in the percentage of how much water the city can take from Cheney, said Mike Jacobs, the city’s water resources engineer, adding that the amount depends on numerous factors. There are different treatments for water pulled from Cheney and the Equus Beds.
As of mid-afternoon Thursday, Cheney would have to go up almost 7 feet before its flood level was full. While the Corps doesn’t want the lake to get close to that level, there isn’t a point that triggers when the Corps starts spilling water into the Ninnescah.
“Part of the trigger is what’s the capacity downstream,” said Ross Adkins, a spokesman for the Tulsa district of the Corps, which oversees Cheney. “You have to consider the capacity of the streams and rivers before you start releasing water.”
He said it also was important to wait until the rain stops, so there can be an accurate capacity measurement of Cheney and downstream tributaries. Rain is in the forecast for this weekend.
The only exception to that rule is if the flood level is full.
“Once it gets to the top of the pool, all bets are off,” Adkins said. “Once you get over the top, you lose all control. But it’ll take quite a bit to fill that pool.”
Meanwhile, the city is making adjustments to its Aquifer Storage and Recovery project – a $244 million plant northwest of Wichita that was built to help recharge the Equus Beds – to take full advantage of the high river flow.
The project takes water out of the Little Arkansas, treats the water and puts it in underground storage in the aquifer.
But there have been a couple of hitches.
First, when the city tried to push the plant to full capacity of 30 million gallons a day earlier this summer, some equipment malfunctioned after operating at that level for about half a day. A manufacturer’s representative has been at the plant trying to get it fixed, Jacobs said.
“Rather than just pack it up, we ran it at 15 (million gallons per day),” King said.
In addition, the plant couldn’t take any water out of the river during a four-day stretch since Friday because the river level was too high, Jacobs said.
When the water is too high, it covers the river intake structure, he said.
Another issue that has to be addressed, King said, is the chemistry of the water. A higher river level means higher amounts of Atrazine – a weed-control product used in agriculture – and bromides, a naturally occurring chemical that comes out of the soil.
Since Tuesday, the equipment has been tweaked so the plant can handle those issues.
“We’re learning and going beyond what it was designed to do,” Jacobs said.
The plant was never meant to operate around the clock or to be a primary water supply, he noted. It was designed to treat the river water before it is stored in the aquifer, he added.
“Therefore, it doesn’t have the redundancies (backup equipment) like our other treatment plants that are designed to run 24/7,” he said. “If this doesn’t run, we can still provide water to our customers. It can break, and we can still make water.”
But, King added, “We want to run it when we want it to run, so we’re pulling the wrinkles out.”
King said working out the kinks of a plant that has been operating only a short while is part of the process.
Construction on the Aquifer Storage and Recovery project began in 2006, but it wasn’t available to operate at full capacity until mid-April.
A low river flow slowed the process considerably, King and Jacobs said.
“You need water to test it and fine tune it as it’s being built,” Jacobs said. “And since there wasn’t water, we couldn’t do it.
“There were many months when there wasn’t any construction because the next step was to test a piece of it. It didn’t get dragged out because no one wanted to do it.”
Since April, the plant has operated at a rate of 15 million gallons a day for nearly 170 hours. Low river flow prevented it from operating more frequently, Jacobs said.
As of this week, the plant has processed 105 million gallons and sent it into storage.
When the drought’s effect was still in full effect earlier this summer, about half of that 105 million gallons briefly was put in storage to satisfy water rights requirements before being pulled back up and sent directly to the city’s distribution center.
“Now that we’re out of the drought,” King said, “we won’t continue to do that.”
More adjustments to how much is taken out of Cheney and the aquifer could be made after this rainy stretch stops, Jacobs said.