Section 3
Evaluation of Current Water Supplies

3.1       Groundwater

There are five major and two minor aquifers supplying water to the region.  The five major aquifers are the Edwards-Balcones Fault Zone, Carrizo-Wilcox, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers (Figure 3-1).  The two minor aquifers are the Sparta and Queen City Aquifers.  Sections 1.7.1 and 1.8.1 contain further descriptions of the aquifers including water quality.  The descriptions presented in this section provide water use information for the aquifers located within the region.

3.1.1    Edwards-Balcones Fault Zone Aquifer (Edwards Aquifer)

The Edwards Aquifer underlies parts of six counties (Uvalde, Medina, Bexar, Atascosa, Comal, and Hays) in the South Central Texas Region.  The aquifer forms a narrow belt extending from a groundwater divide in Kinney County through the San Antonio area northeastward to the Leon River in Bell County.  In the South Central Texas Planning Region, water from the aquifer is primarily used for municipal, irrigation, and recreational purposes.  Historically, about 54 percent of the total water pumped from the aquifer in the region has been used for municipal supply, with 39 percent used for irrigation purposes.  The Edwards Aquifer is projected to supply water for municipal, industrial, and irrigation uses in Atascosa, Bexar, Caldwell, Comal, Guadalupe, Hays, Medina, and Uvalde Counties.

3.1.2    Carrizo-Wilcox Aquifer (Carrizo Aquifer)

The Wilcox Group and the overlying Carrizo Formation of the Claiborne Group form a hydrologically-connected system known as the Carrizo-Wilcox Aquifer, which is referred to in this study as the Carrizo Aquifer.  Historically, municipal and irrigation pumpage account for about 35 percent and 51 percent, respectively, of total pumpage from the Carrizo Aquifer within the region, with irrigation being the predominant use in the Winter Garden region.  The Carrizo Aquifer is projected to supply water for municipal, industrial, steam-electric power, mining, and irrigation uses in Atascosa, Bexar, Caldwell, Comal, Dimmit, Frio, Gonzales, Guadalupe, Karnes, La Salle, Medina, Uvalde, Wilson, and Zavala Counties.

3.1.3    Trinity Aquifer

The Trinity Aquifer consists of early Cretaceous age formations of the Trinity Group.  Trinity Group deposits also occur in the Edwards Plateau region, where they are included as part of the Edwards-Trinity (Plateau) Aquifer.  The Trinity Aquifer is projected to supply water for municipal, industrial, steam-electric power, mining, and irrigation uses in Bexar, Comal, Hays, Kendall, Medina, and Wilson Counties.

3.1.4    Gulf Coast Aquifer

The Gulf Coast Aquifer forms a wide belt along the Gulf of Mexico from Florida to Mexico, supplying water to all or parts of 54 counties in Texas.  Municipal and irrigation uses have historically accounted for 90 percent of the total pumpage from the aquifer in the planning region.  The Gulf Coast Aquifer is projected to supply water for municipal, industrial, steam-electric power, mining, and irrigation uses in Calhoun, DeWitt, Goliad, Gonzales, Karnes, Refugio, and Victoria Counties.

3.1.5    Edwards-Trinity (Plateau) Aquifer

The Edwards-Trinity (Plateau) Aquifer underlies the Edwards Plateau east of the Pecos River and provides water to all or parts of 38 counties in Texas.  This aquifer underlies the northern portions of Uvalde and Kendall Counties in the South Central Texas Region.  The aquifer consists of saturated sediments of lower Cretaceous age Trinity Group Formations and overlying limestones and dolomites of the Comanche Peak, Edwards, and the Georgetown Formations.  The Glen Rose limestone is the primary water-bearing unit in the Trinity (Plateau) Aquifer in the southern areas of its extent.  The Trinity (Plateau) Aquifer is projected to supply water for municipal, mining, and irrigation uses in Kendall and Uvalde Counties.

3.1.6    Sparta Aquifer

The Sparta Aquifer extends in a narrow band from the Frio River in South Texas northeastward to the Louisiana border, and underlies parts of five counties (Atascosa, Frio, Gonzales, La Salle, and Wilson) in the South Central Texas Region.  The southwestern boundary is placed at the Frio River because of a facies change in the formation, which makes it difficult to delineate the boundaries of the Sparta Aquifer and contiguous formations southwestward.  The facies change results in reduced amounts of water and poorer quality water produced from the interval.  The Sparta Aquifer is projected to supply water for municipal, industrial, steam-electric power, mining, and irrigation uses in Atascosa, Frio, Gonzales, La Salle, and Wilson Counties.

3.1.7    Queen City Aquifer

The Queen City Aquifer extends across Texas from the Frio River in South Texas northeastward into Louisiana.  The southwestern boundary is placed at the Frio River because of a facies change in the formation.  This facies change results in reduced amounts of poorer quality water produced from this interval southwest of the Frio River.  The Queen City Aquifer is projected to supply water for municipal, industrial, steam-electric power, mining, and irrigation uses in Atascosa, Caldwell, Frio, Gonzales, La Salle, and Wilson Counties.

3.1.8    Groundwater Availability in the South Central Texas Region

According to TWDB data, the total quantity of water obtained from aquifers of the South Central Texas Region and used within the Region in 1990 was 967,327 acft (Table 3-1).  Of this total, 53.7 percent was from the Edwards Aquifer, 28.8 percent was from the Carrizo, 9.3 percent was from the Gulf Coast, 4.8 percent was from the Sparta, and the remaining 3.4 percent was from the Queen City, Trinity, and Edwards-Trinity (Plateau) Aquifers (Table 3-1).

Projected future groundwater supplies available in the South Central Texas Region during the drought of record are 812,868 acft/yr in 2000, 812,868 acft/yr in 2020, and 675,187 acft/yr in 2050 (Table 3-1).  Supplies available from the Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers are projected to hold steady on an annual basis throughout the 2000 through 2050 projections period (Table 3-1).  However, these aquifers are projected to supply only about 25 percent of the total groundwater available to the region in 2050 (Table 3-1).  The supply available from the Carrizo Aquifer is projected to decline from 304,484 acft/yr for the 2000 through 2020 period to 168,159 acft/yr for the period after 2020 (i.e., withdrawals are projected to exceed recharge).  It is important to note that Underground Water Conservation Districts that have been organized within the Carrizo Aquifer area have developed regulatory policies that limit annual pumping to estimated annual recharge.

In the case of the Edwards Aquifer, SB 1477 limits pumpage withdrawals to 450,000 acft/yr until December 31, 2007, and to 400,000 acft/yr beginning in 2008 (Table 2-10).  In addition, SB 1477 states in Section 1.14(h): “… the authority, through a program, shall implement and enforce water management practices, procedures, and methods to ensure that, not later than December 31, 2012, the continuous minimum springflows of the Comal Springs and the San Marcos Springs are maintained to protect endangered and threatened species to the extent required by federal law.  The authority from time to time as appropriate may revise the practices, procedures, and methods.  To meet this requirement, the authority shall require: (1) phased reductions in the amount of water that may be used or withdrawn by existing users or categories of other users; or (2) implementation of alternative management practices, procedures, and methods.”  Thus, supplies from the Edwards Aquifer may be less than the pumpage limits specified in SB 1477.  For purposes of this analysis, the supply from the Edwards Aquifer is included at 340,000 acft/yr.[1]

3.2       Surface Water

The South Central Texas Region includes parts of the Rio Grande, Nueces, San Antonio, Guadalupe, Colorado, and Lavaca River Basins, and parts of the Colorado-Lavaca, Lavaca-Guadalupe, and San Antonio-Nueces Coastal Basins (Figure 3-2).  The existing surface water supplies of the region include storage reservoirs and run-of-river water rights.

It has not been necessary to pursue aggressively the development of surface water resources in the South Central Texas Region because of the presence of significant quantities of groundwater.  In addition, the comparatively low quantity of developable surface water in the western part of the region presents significant limitations upon surface water development potentials.  Existing reservoirs (Figure 3-2) and run-of-river water rights within the region are described below.

3.2.1    Lakes and Reservoirs

Medina Lake is located on the Medina River, of the San Antonio River Basin, at the boundaries of Medina and Bandera Counties, with Diversion Lake on the Medina River downstream of Medina Lake.  These lakes are owned by the Bexar-Medina-Atascosa Counties Water Control and Improvement District No. 1 and historically have been used to supply irrigation water to farms along the Medina Canal System (Table 3-2).  In addition to supplying irrigation water, seepage through the lake and riverbeds recharges the Edwards Aquifer.  The TWDB has designated Medina Lake as a special water resource located within Region L.

Braunig and Calaveras Lakes, owned by the City of San Antonio City Public Service, are located in the San Antonio River Basin in Bexar County to the southeast of San Antonio and are used for electric power plant cooling water (Table 3-2).  Runoff from the watersheds above the lakes, diversion from the San Antonio River, and diversions from the San Antonio River of San Antonio reclaimed wastewater that has been discharged into the San Antonio River are used to maintain the necessary lake levels and meet the cooling water demands (24,263 acft in 1990).

Constructed by the U.S. Army Corps of Engineers, Canyon Reservoir in the Guadalupe River Basin is located in Comal County on the mainstem of the Guadalupe River.  Uses of the reservoir include water supply for municipal, industrial, steam-electric power generation, irrigation, hydroelectric power generation, flood protection, and recreation (Table 3-2). Diversions from Canyon Reservoir are currently authorized up to an average of 50,000 acft/yr.  GBRA, who holds the water rights, has applied to TNRCC for an amendment to the Canyon Reservoir Certificate of Adjudication (#18-2074) to increase authorized diversions to approximately 90,000 acft/yr.  Stored water is made available by GBRA to water users within their district and the South Central Texas Region. The TWDB has designated Canyon Reservoir as a special water resource located within Region L.

Lakes Dunlap, McQueeny, Placid, Nolte, H-4, and Wood, on the Guadalupe River, form hydroelectric power generation pools and are the sites of hydroelectric power plants on the Guadalupe River in the reach from New Braunfels to about 8 miles west of Gonzales.  The lakes and the water rights are owned by GBRA, and since hydroelectric power generation is a non-consumptive use of water, water available to these rights is not included in the tabulation of water rights for the Guadalupe River Basin. 

Coleto Creek Reservoir, owned by American Electric Power (formerly Central Power & Light Company) and operated by GBRA, is located at the border of Victoria and Goliad Counties in the lower Guadalupe River Basin, and is a cooling reservoir for steam-electric power generation.  The source of water is drainage from the Coleto Creek watershed, with diversions from the Guadalupe River, backed by storage in Canyon Reservoir, when needed.  The reservoir supplies water for steam-electric power generation at a power plant located in Goliad County (12,165 acft in 1990).

3.2.2    Run-of-River Water Rights

In addition to surface water from reservoirs, rights have been issued by the TNRCC and predecessor agencies to individuals, cities, industries, and water districts and authorities for diversion from flowing streams of the South Central Texas Region.  Each right bears a priority date, diversion location, maximum diversion rate, and annual quantity of diversion.  Some rights may include off-channel storage authorization, instream flow requirements, and various special conditions.  The principle of prior appropriation or “first-in-time-first-in-right” is applied, which means that the senior, or oldest, right (earliest priority date) has first call on flows, with the second, third, and more recent rights having second, third, and later standings for diversions.  This procedure gives senior right holders priority when streamflows are low, as in periods of drought, and renders junior rights less reliable during droughts (i.e., the most junior right holders may not be able to divert any water during severe droughts).

It is important to note that many run-of-river rights are for irrigation purposes, where chances are taken at planting time upon whether or not water will be available for crop production during the growing season.  In fact, when reviewing applications for irrigation rights, TNRCC staff has historically considered whether 75 percent of the proposed diversion would be available in 75 percent of the years.  Most of the municipal, industrial, and steam-electric power demands, however, are for more reliable supplies than are available from run-of-river flows.  Thus, reservoirs having firm yields have been permitted by TNRCC and constructed by water suppliers.

Run-of-river permits have been summarized for the streams of the South Central Texas Region (Table 3-3).  For the Nueces River Basin part of the Regional Planning Area, run-of-river water rights total 120,097 acft, most of which are for irrigation purposes (Table 3-3).

In the San Antonio River Basin on the Medina River, downstream of the Medina Lake System to San Antonio, there are 31,794 acft of run-of-river rights (Table 3-3).  On the San Antonio River from San Antonio to the confluence with the Guadalupe River, 28,866 acft of run-of-river rights have been awarded (Table 3-3).  Most of the rights are for irrigation and livestock water with some limited municipal and industrial use, and can be viewed as supply available to meet those needs in areas along the Medina and San Antonio Rivers.

 

Consumptive run-of-river rights in the South Central Texas Region in the Guadalupe River Basin upstream of Canyon Reservoir total 4,674 acft/yr, and downstream of Canyon to Victoria total 46,468 acft/yr.  These rights are primarily for irrigation, municipal, and industrial purposes.

In the Guadalupe River Basin downstream of Victoria, total run-of-river rights are 223,884 acft/yr considering only consumptive rights for municipal, irrigation and industrial process water (Table 3-3).

In the South Central Texas Region, the sum of the major consumptive run-of-river permitted water rights is 455,783 acft/yr (Table 3-3).

3.3       Drought Response

Texas Water Code Sections 16.053(e)(3)(A) and 31 TAC 357.5(e)(7) require that, for each source of water supply in the regional water planning area designated in accordance with 31 TAC 357.7(a)(1), the regional water plan shall identify: (A) factors specific to each source of water supply to be considered in determining whether to initiate a drought response; and (B) actions to be taken as part of the response.  Table 3-4 summarizes the general recommendations of the South Central Texas Regional Water Planning Group (SCTRWPG) regarding identification and initiation of drought responses for current water supply sources in the South Central Texas Region.  As the SCTRWPG is a planning body only, with no implementation authority, it is emphasized that these drought responses are recommendations only.  Local public and private water suppliers and water districts have been required to adopt a Drought Contingency Plan (by TNRCC pursuant to SB1) that contains drought triggers and responses unique to each specific entity.  Furthermore, these entities have the authority and responsibility to manage their particular water supply within the bounds created by applicable law.  Therefore, the SCTRWPG encourages these entities to implement their respective plans with due consideration of the recommendations summarized in Table 3-4.

The Edwards Aquifer Authority (EAA) is presently in the process of developing Critical Period Management (CPM) rules that establish trigger conditions for recognition of drought and recommended reductions in withdrawals from the Edwards Aquifer when these trigger conditions are met.  The draft CPM rules reflect staged reductions in permitted municipal withdrawals ranging from five to 15 percent during periods in which water levels in representative monitoring wells in Bexar, Medina, and Uvalde Counties have fallen below specified trigger levels.  Table 3-5 summarizes the factors specific to the Edwards Aquifer in determining whether to initiate a drought response and the reductions in withdrawal expected as part of the response pursuant to draft CPM rules current as of March 22, 2000.  It must be emphasized that rulemaking at the EAA is presently a dynamic process and that factors and responses identified in Table 3-5 may or may not be applicable in the future.

 

The EAA is also in the process of developing a Habitat Conservation Plan (HCP) and Environmental Impact Statement (EIS) for submittal to the U.S. Fish & Wildlife Service.  It is expected that the HCP and EIS will form the basis for identification of appropriate springflow levels for protection of threatened and endangered species.  Until these springflow levels are identified and approved, appropriate timing for initiation of drought responses is uncertain.  The SCTRWPG encourages the timely implementation of this Regional Water Plan as a pre-emptive drought response so that alternative sources of supply and/or enhanced supplies from the Edwards Aquifer will be available to satisfy regional water needs, maintain springflow, and protect endangered species to the extent required by State and Federal law.

 

Water supplies available from the Carrizo Aquifer and other aquifers in Region L are less subject to transient hydrologic drought conditions than the Edwards Aquifer and more dependent upon water stored in the formation and the acceptability of long-term depletion or drawdown.  If depletion of storage in these aquifers is occurring at an unacceptable pace (typically measured over many years, rather than a few months), there is likely to be sufficient time to amend groundwater district rules and/or develop alternative sources of supply.  As with any source of water supply, production facility constraints may necessitate expedited increases in production capacity or implementation of drought contingency measures during dry periods when peak water demands are greatest.

Supplies from surface water sources such as run-of-river water rights and reservoirs are determined on the basis of minimum year availability and firm yield, respectively.  Hence, the current surface water supplies presented herein are, by TWDB definition, dependable during drought.  Factors that are typically considered in initiating drought response for surface water sources are streamflow and reservoir storage as they may be conveniently measured and monitored.  In contrast to groundwater sources, water right priority with respect to other rights and special permit conditions regarding minimum instream flows can also be important factors in determining whether to initiate drought responses for surface water sources.  In the Guadalupe—San Antonio and Nueces River Basins, coordination with the TNRCC Watermaster is an essential drought response for all entities dependent upon surface water supply sources.

3.4       Methodology to Calculate the Water Supplies Available to the South Central Texas Region and Methodology for Calculating Water Supplies Available for Water User Groups

The water supplies available to the South Central Texas Region during the “drought of record” were calculated from the following data sources:

A.  Groundwater availability by aquifer for the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers was obtained from the TWDB.  The groundwater availability by county was further subdivided into river basin parts of each county according the amount of land area overlying each aquifer.  Groundwater supplies for cities using water from the Carrizo, Gulf Coast, and Trinity Aquifers was based upon an analysis of saturated thickness of the aquifer in which their well fields are located respectively, and well capacities.  The quantities available in Wilson and Gonzales Counties were obtained from the Evergreen and Gonzales County Underground Water Conservation Districts, respectively.

B.   Groundwater availability from the Edwards Aquifer was set at a total of 340,000 acft/yr.  Preliminary permit quantities by the Edwards Aquifer Authority were prorated down to achieve a total value of 340,000 acft/yr as the sum of all permits.

C.  Surface water availability for permits within the Nueces Basin was obtained from the TNRCC Water Rights Availability Model (WAM).

D.  Surface water availability for permits within the Guadalupe-San Antonio River Basin was obtained from the TNRCC Water Availability Model, but with a special run for Canyon Reservoir with hydroelectric rights subordinated.  However, existing supplies from Canyon Reservoir for use in calculating water needs in Section 4 were limited to the TNRCC permitted diversions of 50,000 acft/yr.

E.   Water availability from direct reuse was obtained from input to the TNRCC WAM for the San Antonio and Guadalupe River Basins.  Three sources of supply from direct reuse are used in the supplies report.  Two sources of supply are from the SAWS’ current recycle program and are 18,193 acft/yr for the City of San Antonio in Bexar County and 6,748 acft/yr for industrial use in Bexar County.  The third source of supply from direct reuse is 3,936 acft/yr for steam-electric use in Hays County.

F.      Livestock water supply was allocated from local sources, and set at projected livestock water demands.

G.     See Appendix B for assumptions that underlie water supply calculations.

The methods used to distribute each respective water supply to its appropriate use category are presented below.

1.   Municipal Use from the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers

a.   For cities using water from the Carrizo, Gulf Coast, and Trinity Aquifers their supply was based upon an analysis of saturated thickness of the aquifer in which their well fields are located, respectively, and well capacities.

b.   For rural areas, it was assumed that the rural household (municipal type) demand would be met from aquifers underlying that river basin portion of the county.  The rural supply was calculated from the maximum water demand over the planning horizon (usually in the year 2050), which was then proportioned among the available aquifers based on the area of the aquifer’s extent below the appropriate river basin portion of each county.

2.   Industrial Use from the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers

It was estimated that industrial demand would be met from aquifers underlying that river basin portion of the county.  The industrial supply was calculated from the year 2050 projected demand.  This demand was then proportioned among the available aquifers based on the area of the aquifer’s extent below the appropriate river basin portion of each county.

3.   Steam-Electric Use from the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers

It was estimated that steam-electric demand would be met from aquifers underlying that river basin portion of the county.  The steam-electric supply was calculated from the year 2050 projected steam-electric demand.  This demand was then proportioned among the available aquifers based on the area of the aquifer’s extent below the appropriate river basin portion of each county.

4.   Irrigation Use from the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers (For Edwards Aquifer See No. 6 Below)

It was estimated that irrigation demand would be met from aquifers underlying that river basin portion of the county.  However, when projected total demand for all uses was greater than the estimated total groundwater supply for river basin portions of individual counties, the quantity available for irrigation was the total supply of the river basin portion of the county remaining after municipal, industrial, steam-electric power, and mining uses had been met.

5.   Mining Use from the Carrizo, Sparta, Queen City, Trinity, Gulf Coast, and Edwards-Trinity (Plateau) Aquifers

It was estimated that mining demand would be met from aquifers underlying that river basin portion of the county.  The mining supply was set equal to the projected demand for each year within the planning horizon.  This demand was then proportioned among the available aquifers based on the area of the aquifer’s extent below the appropriate river basin portion of each county.

6.   Groundwater Supply from the Edwards Aquifer

To determine the groundwater availability from the Edwards Aquifer, the prorated permits were placed in the appropriate river basin portion of each county by the permit’s use (municipal, industrial, and irrigation) category.  All agricultural permits (not irrigation) were included in the industrial use classification; e.g.; permits for Lone Star Growers, Living Waters Artesian Springs, a feedyard, and 4 individuals whose type of business is not apparent.  The total of these permits is 5,412 acft. 

7.   Surface Water Availability Within the Nueces Basin

The WAM determined the minimum annual diversion during the drought of record for each permit within the Nueces River Basin.  These permits were then placed in the appropriate river basin portion of each county by the permit’s use category.  (See Appendix C for a list of major water rights sorted by river basin, county, and type of use including the permit number and minimum annual supply).

8.   Surface Water Availability Within the Guadalupe and San Antonio River Basins

The WAM determined the minimum annual diversion during the drought of record for each permit within the San Antonio and Guadalupe River Basins.  The quantities of supply for these permits were then placed in the appropriate river basin portion of each county by the permit’s use category. (See Appendix C for a list of major water rights sorted by river basin, county, and type of use including the permit number and minimum annual supply).  The key technical information and assumptions used in this application of the TWDB Edwards Aquifer Model (GWSIM4) are listed below.[2],[3]

Edwards Aquifer pumpage of 400,000 acft/yr (plus domestic & livestock pumpage of 12,312 acft/yr) subject to Critical Period Management Rules under review on March 29, 2000 by an assessment team for the EAA.  Pro-ration of proposed permits totaling about 484,000 acft/yr to simulated pumpage rates was accomplished by proportional reduction.

Breakdown of use type and geographical distribution was based on EAA proposed permits (without any voluntary transfers from irrigation to municipal use).

Simulations based upon draft Critical Period Management Rules which include staged curtailment of permitted municipal pumpage by up to 15 percent subject to specified levels in monitoring wells located in Bexar, Medina, and Uvalde Counties.  Program code modifications were made by HDR to TWDB Edwards Aquifer Model (GWSIM4) to facilitate application of these rules.

Starting heads and seasonal distributions of pumpage were developed by the TWDB and are consistent with previous applications of GWSIM4.

Historical Edwards Aquifer recharge estimates developed by HDR which reflect current water rights and existing recharge enhancement facilities were used in the computations.[4],[5]

The key technical information and assumptions underlying this application of the Guadalupe—San Antonio River Basin Water Availability Model (WAM) are listed below.[6]

Full exercise of surface water rights.

Subordination of all senior Guadalupe River hydropower rights to Canyon Reservoir.  This assumption is based on previous actions of the GBRA to subordinate its own Guadalupe River hydropower rights and on an existing GBRA contractual agreement with the City of Seguin to subordinate its hydropower rights.

Delivery of GBRA’s full contractual obligations from Canyon Reservoir to point of diversion in all years.  GBRA’s obligations to American Electric Power (formerly Central Power & Light (CP&L)) for make-up water to Coleto Creek Reservoir, however, were supplied only on an as-needed basis.  Contracts simulated total 48,152 acft/yr including an estimated average of 6,000 acft/yr for American Electric Power (CP&L) at Coleto Creek Reservoir.

Effluent discharge/return flow in the Guadalupe—San Antonio and Nueces River Basins is that reported for calendar year 1988 and adjusted for SAWS direct reclaimed water use of 35,000 acft/yr (about 25,000 acft/yr of which is estimated to be consumptive).

Operation of power plant reservoirs (Braunig, Calaveras, and Coleto Creek) subject to authorized consumptive uses at each reservoir, with makeup diversions as needed to maintain full conservation storage subject to senior water rights, instream flow constraints, and/or applicable contractual provisions.

 

It is important to note that the five alternative regional plans, as presented in Volume II, were based upon calculations of water available in the Guadalupe and San Antonio River Basins for the case of Canyon Reservoir Firm Yield (approximately 90,000 acft/yr) with downstream hydropower rights mentioned in D above having been subordinated to Canyon Reservoir.  However, the Initially Prepared Regional Water Plan for the South Central Texas Region is based upon the TNRCC permitted diversion of 50,000 acft/yr from Canyon Reservoir.  In the former case, a part of the difference of 40,000 acft/yr was allocated to meeting projected needs in the Guadalupe River Basin, thus reducing the quantity of new supply required to meet projected needs of the Basin.  In the latter case, the quantity available to meet projected needs is less, thus the projected needs are greater by the difference in supply available from Canyon Reservoir.  But, the quantity involved is included in the Initially Prepared Plan as water management strategies to meet the needs, which in the five alternative regional plans was included as firm water supply since GBRA had already subordinated hydropower rights.  All that was done was to move the quantities from the situation of  “it’s a done deal,” to the situation of  “it’s a water management strategy” that will meet the same quantity of needs.  The results are no different!!  

9.   Livestock Water Supply

For all areas within the planning region, livestock water demand was assumed to be met from local sources such as stock tanks, streams, and windmills.  Livestock water supply was set equal to projected livestock demand.

10. Unallocated Supplies

In counties where projected demands are less than projected supplies, the difference (surplus supply) is listed in the county summary, by river basin, as “unallocated groundwater.”  However, this “unallocated supply” is not necessarily available to meet projected shortages of other parts of the region, since it may not be located in close proximity to demands.  There are 12 counties (Caldwell, Calhoun, DeWitt, Dimmit, Goliad, Gonzales, Karnes, Kendall, La Salle, Refugio, Victoria, and Wilson) that have “unallocated groundwater” supplies.

3.5       Potential for Emergency Transfers of Surface Water

TWDB Rules, Section 357.5(i) direct that the RWPG include recommendations for the emergency transfer of surface water and further direct that a determination be made of the portion of each right for non-municipal use that may be transferred without causing unreasonable damage to the property of the non-municipal water right holder.  SB1, Section 3.03 amends Texas Water Code Section 11.139 and allows the Executive Director of TNRCC, after notice to the Governor, to issue emergency permits or temporarily suspend or amend permit conditions without notice or hearing to address emergency conditions for a limited period of not more than 120 days if an imminent threat to public health and safety exists.  A person desiring to obtain an emergency authorization is required to justify the request to TNRCC. If TNRCC determines the request is justified, it may issue an emergency authorization without notice and hearing, or with notice and hearing, if practicable.  Applicants for emergency authorizations are required to pay fair market value for the water they are allowed to divert, as well as any damages caused by the transfer.  In transferring the quantity of water pursuant to an emergency authorization request, the Executive Director, or the TNRCC, shall allocate the requested quantity among two or more water rights held for purposes other than domestic or municipal purposes.

Surface water availability models have been developed for the streams of the South Central Texas Region (Region L) in which the locations, quantities, and reliabilities of the surface water rights of the region have been determined (Appendix C).  The Regional Water Plan incorporates Appendix C as a primary source of information to water user groups and the TNRCC for use in cases of emergencies that result in a threat to public health and safety.  Water user groups who are located in proximity to one or more existing surface water diversion permits for non-municipal use can readily estimate quantities of water that might be available for emergency use applications, and TNRCC may also consider Appendix C in its administration of this provision of SB1.  With regard to the determination of amounts “that may be transferred without causing unreasonable damage to the property of the non-municipal water rights holder,” the SCTRWPG defers to the judgment of the TNRCC inasmuch as the TNRCC is charged with consideration of sworn applications for emergency transfer authorizations.  The South Central Texas Regional Water Planning Group recommends that water user groups of the region develop emergency water supply plans to be activated in the event that public health and safety are threatened.  Some water user groups will have access to surface water, but it is noted that many do not since they are remotely located, insofar as surface water is concerned, and rely upon groundwater.[7]

 


[1] For planning purposes, an estimate of 340,000 acft/yr of available supply during a drought of record from the Edwards Aquifer was agreed upon by the South Central Texas Regional Water Planning Group and the staff of the Texas Water Development Board.  This quantity was adopted as a placeholder number until the EAA completes and acquires approval from the U.S. Fish and Wildlife Service for a Habitat Conservation Plan (HCP).  TWDB staff, in a letter to Greg Ellis, dated November 16, 1999, agreed to accept water availability from the Edwards Aquifer as 340,000 acft/yr after 2012 in the Regional Water Plan, if it includes actions to be taken to ensure that the required level of protection of the endangered species at San Marcos and Comal Springs will be maintained during a drought of record.

[2] Klemt, W.B., Knowles, T.R., Elder, G.R., and Sieh, T.W., “Ground-water Resources and Model Applications for the Edwards (Balcones Fault Zone) Aquifer in the San Antonio Region, Texas,” Texas Water Development Board Report 239, 1979.

[3] Thorkildsen, D. and McElhaney, P.D.., “Model Refinement and Applications for the Edwards (Balcones Fault Zone) Aquifer in the San Antonio Region, Texas,” Texas Water Development Board Report 340, 1992.

[4] HDR Engineering, Inc., “Guadalupe-San Antonio River Basin Recharge Enhancement Study,” Edwards Underground Water District, September 1993.

[5] HDR Engineering, Inc., “Nueces River Basin Regional Water Supply Planning Study,” Nueces River Authority, et al., May 1991.

[6] HDR Engineering, Inc., “Water Availability in the Guadalupe — San Antonio River Basin,” Texas Natural Resource Conservation Commission, December 1999.

[7] Standards for public water supplies have been established by TNRCC and predecessor agencies to provide for public health and safety.