Dredging to boost capacity too costly
as unsolvable as ever.
Texas started building reservoirs around 1900. Today, the state water development board counts 188 major reservoirs, ones with a built capacity of at least 5,000 acre-feet apiece.
On paper at least, those major reservoirs can hold about 35.4 million acre-feet in Texas territory. (Some reservoirs straddle Texas and other states or Mexico.) About half of that capacity was built between 1960 and 1980 during a reservoir building binge after the 1950s drought.
But taking sedimentation into account, the current estimate for the capacity of those reservoirs is 32.9 million acrefeet, a number that will steadily decline.
The 2012 state water plan estimates that Texas reservoirs lose between 66,000 and 128,000 acre-feet of water storage capacity a year due to sedimentation — enough water to serve all the washing, bathing and landscaping demands of at least 200,000 homes.
Lake Buchanan has lost about 12 percent of its capacity since it was completed in 1939, when it was rated at 992,000 acrefeet. Today its capacity is 875,566 acre-feet.
Lake Travis has collected less sediment — by virtue of being downstream of Lake Buchanan and separated from that sediment-catching lake by a dam — losing roughly 3 percent of its capacity to sedimentation over about 60 years.
Far from measuring changing depths with tools such as a string and anchor, researchers with the state water development board now conduct occasional surveys by measuring the way sound travels underwater. Acoustic devices can measure water depth, currents and sediment buildup.
The most commonly used technique is a depth sounder, which measures the round-trip travel time for an acoustic pulse sent out and then returning to the water’s surface.
The technique has led to rafts of data, Solis said: “We now have much better ability to measure the vol- efforts fell short, and Straus easily cruised back to power with only 15 members opposing him.
Last session, voters sent a record number of Republicans to the House, where 101 of the body’s 150 members were Republicans, a supermajority that could act without the votes of Democrats. Some conservatives hoped 2011 was the year to topple Straus, who was elected by a coalition of Republicans and Democrats. This November, Republicans lost ground, winning 95 House seats.
Cathie Adams, president of the conservative Texas Eagle Forum and one of the people umes of our reservoirs.”
What might seem like an obvious solution — dredging of the lake bottoms — is impractical and cost prohibitive.
Dredging is so expensive because of the intensity of labor and machinery, the permitting involved, the massive moving of material, and the special disposal of waste that when stirred up might be deemed hazardous because of old agricultural chemicals like DDT, said James Kowis, water supply strategist for the Lower Colorado River Authority.
“Most people living around the lake won’t want you to dispose of (dredged-up material) anywhere near them,” he said.
The LCRA estimates that dredging Lake Buchanan would cost at least $17,000 an acre-foot. “Our ratepayers wouldn’t be very happy spending that kind of money per acre-foot,” Kowis said.
The next most expensive way to develop water — desalination — costs $2,890 an acre-foot. Cutting demand by encouraging conservation, the cheapest way to improve water supplies, costs only $450 an acre-foot. spearheading an effort to remove Straus from power, said she believes this time will be different. There is more momentum in conservative circles these days, she said.
“Time has allowed more education of the grass roots,” Adams said in an email. She added that conservatives aren’t happy with Straus and the way he led the House last session. Particularly, she said, conservatives wanted a balanced budget without accounting gimmicks, passage of the bill to ban sanctuary cities and passage of Simpson’s “aggressive patdown” bill that Straus said in 2011 would make Texas look like a “laughingstock.”
“The voters are restless. They want no more excuses,” Adams said. “No more go-along-to-getalong kind of government in Austin.”
Lake Travis has collected less sediment than Lake Buchanan because it’s downstream and separated by a dam. Lake Travis has lost roughly 3 percent of its capacity to sedimentation over 60 years.