Sunday, April 22, 2012

In August 1956, during the sixth year of the drought of record, Dr. H. R. Gaddy read a resolution to the Georgetown City Council stating that “the present water supply in Georgetown is not adequate,” and “future rainfall cannot be depended upon to supply our needs.”  It was time to build a reservoir.


During the drought of record in the 1950s, the leaders of Williamson County realized that they could no longer rely on aquifers for water during prolonged dry spells.  It was time to take matters into their own hands and build some reservoirs.

Williamson County has two man-made lakes.  Lake Georgetown was completed in 1979, and Lake Granger in 1980.  Both were built to control devastating flooding on the San Gabriel River, and also to provide reliable water during times of drought.  Lake Georgetown supplies 65% of Georgetown’s municipal water supply, as well as water to Round Rock, and Chisholm Trail and Brushy Creek utility districts.

But here’s the catch.  Lake Georgetown can only supply its customers with water from the San Gabriel River if there is plenty of rain, as there was in 2010.  During a drought, not only do the municipal customers begin to use more water, but the river stops refilling the reservoir.  The lake starts dropping and has to be filled with water pumped from Stillhouse Hollow Lake on the Lampasas River near Belton.  Every day since July 2011, when Lake Georgetown dropped to a trigger level of 781.5 feet above sea level, 42 million gallons per day have been piped in from Stillhouse to keep our lake at a safe level, and it is still not full.  That water is purchased from the Brazos River Authority and costs $3,000,000 per year, plus the cost of the electricity required to pump it, which is about $1,000,000 per year.  And that is just the cost of the raw water, sitting in the lake.  It still has to be purified and pumped to our houses.  By the way, that $3,000,000 per year has to be paid whether we need the water or not.

Mary Condon, mayor of Florence, would love to get her hands on some of that Lake Stillhouse water.  Florence is completely reliant on well water.  For the past four years the city has been paying $30,000 a year for rights to 500 acre-feet of water (163 million gallons) from Lake Stillhouse, but the citizens of Florence have yet to receive a single drop.  They have not been able to secure the funds (about a million dollars) necessary to build a pipeline and storage capacity.  There are 80 acres of prime undeveloped real estate within Florence city limits, but until adequate water arrives from the lake, no developers will invest.  Condon states that if they hadn’t reserved the rights four years ago, those rights would not be available today.

Even though Stillhouse is six times larger than Lake Georgetown, at some point in the next 10-20 years it will not be large enough to meet the demand.  Lake Stillhouse will have to be filled with another pipeline bringing water from Lake Belton.  This is not just speculation.  Glenn Dishong, utilities director for the city of Georgetown, states that Georgetown has already reserved rights to 10,000 acre-feet of Lake Belton water per year, and has been paying $625,000 a year for those rights for the last three years.

Lakes may be more reliable than groundwater, but they have one big disadvantage:  evaporation.  During a hot, dry, windy summer such as 2011, evaporation rates can be astronomical.  Brad Brunett of the Water Services Management Department, Brazos River Authority, calculated this past summer that the eleven BRA reservoirs, which include Lakes Georgetown and Granger, were being depleted by 4000 acre-feet per day.  Half of that amount was going to customers.  The other 2000 acre-feet were evaporating into thin air.

Another issue with man-made reservoirs is sedimentation.  When a river is dammed, sediment washes into the river during rain events and settles out behind the dam, diminishing the capacity of the lake.  When Lake Granger was first built, its capacity was 62,000 acre-feet.  By 2008 sedimentation had decreased its volume to 50,779 acre-feet, a loss of 18%.  Studies over the last three decades demonstrate that the rate of sedimentation is actually increasing.  The volume loss was 129 acre-feet per year when the dam was new.  The loss has now accelerated to 304 acre-feet/year.  Lake Stillhouse Hollow has only lost about 3.5% of its volume since 1967.  Fortunately, sedimentation has not been a problem for Lake Georgetown.

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