Dredg­ing to boost ca­pac­ity too costly


Austin American-Statesman - - THE SECOND FRONT - A Jay JAN­NER / AMER­I­CAN-STATES­MAN ‘This thing is pretty wide open in my es­ti­ma­tion.’ Rep. David Simp­son Con­tact Asher Price at 445-3643. Con­tact Tim Ea­ton at 445-3631.

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.

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