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GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions Vol. 58 (2008), Pages 903-904

EXTENDED ABSTRACT: Development of Desired Future Conditions of Aquifers in Texas Groundwater Management Area 8

Charles R. Williams1, Cheryl Maxwell2, and Horace Grace2

1TCB, Inc., 400 W. 15th St., Austin, Texas 78701
2Clearwater Underground Water Conservation District, 2180 N. Main St., Belton, Texas 76513

EXTENDED ABSTRACT

The State of Texas is currently divided into 16 areas of common groundwater use and cooperative management called Groundwater Management Areas (GMAs). The GMA process was initiated in the 2001 session of the Texas Legislature (Legislature) with a charge to the Texas Water Development Board (TWDB) to develop the boundaries of GMAs. In general, the GMA boundaries reflect the limits of the “Major Aquifers” recognized by TWDB. GMA membership consists of Groundwater Conservation Districts (GCDs). Initially, GMA members were only required to meet from time to time, share management plans, and provide for common approaches to groundwater management. However, in the 2005 session, the Legislature expanded the responsibilities of GMAs to include the development of a Desired Future Condition (DFC) of aquifers within their boundaries.

The purpose of expanding GMA responsibilities is to address the potential for conflict between Regional Water Planning Groups (RWPGs) and GCDs over the amount of groundwater, which may be used annually from aquifers. The basic purpose of the GCDs is determining the appropriate level of use for aquifers in their jurisdiction and managing that use. In developing 50-year water supply plans, RWPGs also assess the amount of groundwater that may be used from aquifers. In some instances conflicts arose over the amount of groundwater that could be used from an aquifer that was rooted in differing visions of the future condition of the aquifer (0 ft [0 m] versus 400 ft [122 m] draw down of artesian heads). Under the prior statute, GCDs were suborned to the RWPGs if they wanted less pumping.

A DFC is essentially a vision statement of a future aquifer condition that describes a measurable aspect of the aquifer. DFCs are submitted to TWDB, and TWDB calculates the amount of water that can be pumped from the aquifer and meet the DFC specifications for aquifer conditions. The resulting value for the amount of pumping which can be sustained under a DFC is termed the Managed Available Groundwater (MAG) value. After the finalized MAG values are published, RWPGs must use TWDB MAG values for water supply planning. GCDs must use the MAGs as the amount of water that can be permitted for use in their aquifers.

GMAs must submit DFCs to TWDB by September 2010. However, the GMA process is not synchronized with the RWPG 50-year water planning schedule. DFCs submitted by September 2010 will not be reflected in Regional Water Plans (RWPs) until 2016. TWDB provided an administrative schedule adjustment with an interim deadline of January 2008 for GMA submittal of DFCs to guarantee use of the resulting MAGs by the RWPGs in their 2011 RWPs.

Each of the 16 GMAs in Texas faces a significant challenge in meeting their statutory responsibilities. To meet the requirements, the GMAs must essentially serve as the interface of science and policy development. Among the 16 GMAs in Texas, GMA-8 arguably faces among the greatest challenges meeting its responsibilities.

The first challenge relates to the sheer size of GMA-8. The boundaries incorporate all or part of 45 of the 254 counties in the State of Texas. GMA-8 stretches from the north bank of the Colorado River, north to the Red River, and east to the Arkansas state line. Although membership to the GMA is restricted to GCDs, the GMA is responsible for developing a DFC for the entire area of the GMA. The original six GCDs, with jurisdiction in seven counties, were later joined by four new GCDs; however, the 31 unprotected counties outnumber the 14 GCD-protected counties. The number of counties for which information on groundwater availability, groundwater use, and projections of future demands had to be processed added significantly to the workload of the GMA.

A second challenge posed to GMA-8 is the diversity of aquifers for which a DFC is required. The bounds of GMA-8 are oriented generally on the extent of the northern segment of the Trinity Aquifer, which is recognized by TWDB as a Major Aquifer. However, GMA-8 also includes a second Major Aquifer, the northern segment of the Edwards (Balcones Fault Zone [BFZ]) Aquifer . The GMA-8 diversity of aquifers is further expressed with the existence of all or portions of seven “Minor Aquifers” within its bounds. The Woodbine, Blossom, Nacatoch, and Marble Falls aquifers lie wholly within GMA-8. The Ellenburger – San Saba, Hickory, and Brazos River Alluvium aquifers are only partially incorporated in GMA-8.

Where a TWDB groundwater availability model (GAM) exists for an aquifer; GMAs are required to use the GAM in developing the aquifer DFC. In GMA-8, two GAMs were available. The Northern Trinity / Woodbine Aquifer GAM was available for DFC development on the Trinity and Woodbine aquifers, and the Northern Edwards Aquifer GAM was available for development of the Edwards (BFZ) Aquifer DFC. For the remaining six aquifers, GMA-8 developed 2D models to project the use of groundwater in support of DFC development.

A third challenge posed to GMA-8 was the creation of new GCDs after initiation of the DFC development process. Initially the GMA membership was composed of six GCDs with jurisdiction in all or portions of seven counties. In its 2007 session, the Legislature created four new GCDs with jurisdiction in seven additional counties. The Central Texas GCD, Clearwater Underground Water Conservation District (UWCD), Fox Crossing Water District, Middle Trinity GCD, Post Oak Savannah GCD, and the Saratoga GCD welcomed the Northern Trinity GCD, McLennan County GCD, Tablerock GCD, and Upper Trinity GCD with open arms. However, significant effort was required by all concerned to orient the new GCDs on the GMA process in general, and the GMA-8 process specifically in order to stay on-track in development of aquifer DFCs.

The general approach taken by GMA-8 was to combine resources and data available locally from the GCDs and state agencies with targeted consulting assistance in order to most efficiently and effectively develop aquifer DFCs. GMA-8 resolved to develop DFCs in time to be used in the next round of RWPs and approached meeting the interim DFC deadline with inexperienced hubris. The process proved more complex than anticipated in several key areas: educating GCDs on groundwater modeling, estimating groundwater use in new or immature GCDs, and the effort required to reach consensus on aquifer DFCs.

However, GMA-8 met the TWDB interim DFC deadline for the Edwards (BFZ), Woodbine, Blossom, Nacatoch, and Brazos River Alluvium aquifers. In all, DFCs were submitted to TWDB for five of the nine aquifers in the GMA. GMA-8 was the only GMA, which developed DFCs by the TWDB interim deadline. Since January 2008, GMA-8 has submitted DFCs to TWDB on the Ellenburger – San Saba, Hickory, and Marble Falls aquifers, and anticipates prompt completion of DFC development on the Trinity Aquifer.

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