Sunday, April 22, 2012


Published in the Sun March 18, 2012 

While the population of Williamson County is projected to increase by more than 100 percent during the next 50 years, groundwater supplies will remain unchanged.  Dr. Robert Mace of the Texas Water Development Board explains there is “only so much blood you can squeeze out of a turnip.”
 
Where Does Our Water Come From?

Aquifers

Jennifer McKnight has a low opinion of raindances.  “I tried them and they didn’t work.”  As general manager of the Chisholm Trail Special Utility District, McKnight is responsible for supplying water to a huge service area that extends from the west part of Georgetown all the way into Burnet and Bell Counties.  Forty percent of her water comes from two wells into the Edwards Aquifer.  One of those wells went dry during the drought this summer, and the other was pumping less than expected.  In McKnight’s experienced opinion, groundwater is just not as reliable as surface water.  Next summer she plans on getting 80 percent of her water from Lake Georgetown.


Mary Condon, mayor of Florence, has also had her share of nailbiting experiences involving wells.  Florence gets all its water from four wells into the Trinity Aquifer, but one of them stopped flowing last summer.  After $19,000 in repairs, it would still pump dry in about three minutes.  She has been told by her consultants that groundwater is just not a viable source of water in this part of the country any more.


The city of Georgetown pumps about 35% of its water from the Edwards Aquifer, 9 million gallons a day.  Under normal circumstances most of Georgetown east of IH 35 is supplied with well water.  During the dry summer of 2009 those essential wells came perilously close to failing, and were at risk again this past summer.  Fortunately it was discovered that water from the San Gabriel River can partially recharge the aquifer as it flows through town, slowly seeping into sinkholes in the riverbed.  During the summer of 2011 when the San Gabriel ceased to flow naturally, an intentional release of water from Lake Georgetown kept the wells pumping.


From a human perspective, an aquifer is like a huge rain barrel, storing clean water collected during rainy seasons in an underground honeycomb of rock.  Before 1940, Texans got almost all of our water from aquifers and the springs that flowed from aquifers, but the entire demand was less than 1 million acre-feet per year.  (An acre-foot is the amount of water required to cover one acre of land with water to a depth of one foot.  An acre-foot equals 325,851 gallons.)  Population growth has increased the demand on Texas aquifers by a factor of ten, but even that increased amount satisfies only 60 percent of our needs.  The rest of our water comes from lakes and reservoirs which have been constructed since the 1950s in response to increased demand and water shortages during droughts.


Although the state government clearly controls usage of all the surface water in Texas’ reservoirs through agencies such as the Brazos River Authority and the Lower Colorado River Authority, once the water seeps into the aquifers its ownership is murkier.  Groundwater usage is governed by the “Rule of Capture,” otherwise known as the rule of the biggest pump.  This rule, adopted by the Texas Supreme Court in 1904, states that if a landowner has a well, he is entitled to pump as much water out of that well as he wants.  In other words, if your well goes dry because your neighbor is pumping large amounts of water, too bad for you.  Your only recourse is to dig a deeper well.  Texas is the only western state that still uses the Rule of Capture.  Groundwater conservation districts in some counties try to regulate how much water can be pumped from underlying aquifers, but that control may be diminished by a Texas Supreme Court ruling last month.  In Edwards Aquifer Authority vs. Day, the court reaffirmed the 1904 ruling that landowners own the water beneath their land and access to that water may not be restricted without just compensation.  Groundwater conservation districts will be hesitant to restrict a landowner’s access to the water beneath his property if the landowner has to be compensated.  The question is moot in this county because Williamson County has never had a groundwater conservation district.


Williamson County has three important aquifers: the Trinity, the Edwards, and in the far eastern corner of the county, the Carrizo-Wilcox.  Fortunately, after periods of drought or overpumping, all three can be easily recharged when normal rainfall resumes.   Even after 6 years of drought in the 1950s, two years of normal rainfall restored the springs of the Edwards Aquifer to normal flows.  The prompt recharge of the Edwards is in marked contrast to the enormous Ogallala Aquifer which extends from the Texas Panhandle to Nebraska and is heavily used for irrigation.  The Ogallala recharges at an almost insignificant rate.  The water in that aquifer is “paleowater,” unchanged since the last ice age.  If the Ogallala is depleted by overpumping, which at current usage rates could happen in 25-50 years, it will take 6000 years to refill.


Since 2002, two NASA satellites orbiting 300 miles above the earth have been measuring tiny changes in the earth’s gravity based on the quantity of water stored in underground aquifers.  These satellites are part of the Gravity Recovery and Climate Experiment (GRACE).  Every week, maps are produced by the Goddard Space Flight Center, the Jet Propulsion Laboratory, and University of Texas Center for Space Research in Austin.  The maps compare the current status of the aquifers to historical data since 1948.  Like a gas gauge, the maps tell if our “tanks” of water are full or empty.  The week of December 5, 2011, the central Texas aquifers measured at a lower volume than at almost any other time since 1948.  The rain during the winter has improved the situation in our area, but the Ogallala Aquifer continues to show a major deficit.


Dr. Robert Mace, deputy executive administrator for water science and conservation at the TWDB, is not convinced that measuring gravity is the best way to evaluate aquifers.  He explains that the GRACE project is experimental and the best way to evaluate aquifers is to measure water levels.  He confirms however that some Texas aquifers are being overpumped.  In the Dallas area the Trinity Aquifer is down 1000 feet and probably won’t recover as long as the present rate of pumping continues.   Last year he told the Texas Tribune that the Ogallala is being pumped at six times the rate of recharge.  He explains that there is “only so much blood you can squeeze out of a turnip.”


The Texas Water Development Board estimates that Williamson and Bell counties can count on 11,200 acre-feet of water per year from the Edwards from now through 2060.  To put this quantity in perspective, currently 47,000 acre-feet per year are being pumped from Stillhouse Hollow to Lake Georgetown for the use of Georgetown, Round Rock, and surrounding communities.  Williamson County is projected to have a municipal water usage of 92,000 acre-feet per year by 2020, so clearly the Edwards Aquifer will fulfill only about 12% of our water needs.  In contrast, the Carrizo-Wilcox Aquifer, third largest aquifer in Texas, is still underutilized and will play a larger role in the future.  Plans are already underway for what the Texas Water Development Board calls the Conjunctive Use Project in which the Carrizo-Wilcox is tapped to augment water in Lake Granger and supply the eastern part of the county and Round Rock.  Capital cost to complete this project is $644 million.


2 comments:

  1. Wow Mom, 8 posts at once is a little much. I've got a question about this one. Measuring water level sounds way easier than taking a gravity reading from space. Why are these methods being compared? Is there some major flaw with the water level approach?

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