5.2.4    Cumulative Effects

Sophisticated hydrologic models have been employed to quantify the cumulative effects of implementation of the South Central Texas Regional Water Plan through the year 2050.  These cumulative effects are quantified through long-term simulation of natural hydrologic processes including precipitation, streamflow, aquifer recharge, springflow, and evaporation as they are affected by human influences such as aquifer pumpage, reservoirs, diversions, and the discharge of treated effluent.  Cumulative effects of plan implementation on the Edwards Aquifer are measured against a baseline representative of full utilization of proposed permits prorated to a total of 400,000 acft/yr subject to Critical Period Management Rules without any additional recharge enhancement projects.  Edwards Aquifer simulations with implementation of the Plan do not reflect the activation of available Management Supplies as may be necessary to offset Edwards Aquifer pumpage reductions necessary to maintain springflow.  The baseline for consideration of effects on streamflow reflects the baseline for the Edwards Aquifer, full utilization of existing water rights, and treated effluent discharge representative of current conditions.  Cumulative effects of plan implementation on Carrizo and Simsboro Aquifer levels are measured against a baseline of projected local pumpage.

The potential cumulative effects of plan implementation on Comal Springs discharge from the Edwards Aquifer are shown in Figure 5.2-26 for a 56-year historical simulation period.  Springflows would increase much of the time and particularly in the summer due to Edwards Recharge – Type 2 Projects (L-18a) and SAWS Aquifer Storage & Recovery (ASR) Program in southern Bexar County (SCTN-1a), respectively.  However, springflow increases would be offset to some degree by increased pumpage closer to the springs associated with Edwards Irrigation Transfers (L-15) and Irrigation Demand Reduction (Conservation) with Transfer (L-10 Irr.).  As shown in Figure 5.2-27, simulated San Marcos Springs discharges would increase substantially because the Edwards Recharge – Type 2 Projects (L-18a) include a recharge enhancement dam on the Blanco River with pumped diversions to the outcrop in the Upper San Marcos River watershed.  Overall pumpage from the Edwards Aquifer would increase (Figure 5.2-28) due to potential EAA authorizations for recharge recovery (see Appendix C in Volume III) pursuant to development of the Edwards Recharge – Type 2 Projects (L-18a).  Figure 5.2-29 shows

simulated water levels at key monitoring wells in Uvalde, Medina, and Bexar Counties with implementation of the Plan.  Percentages of time under Critical Period Management in Uvalde and Medina Counties would be less with the Plan than for baseline conditions.

The potential cumulative effects of phased implementation of water management strategies involving pumpage from the Carrizo Aquifer are summarized in Figures 5.2-30  (Figures 5.2-31  Figures 5.2-32  Figures 5.2-33  Figures 5.2-34  Figures 5.2-35)   through 5.2-36.  Figure 5.2-30 shows the projected pumpage from Wilson, Gonzales, and Bastrop Counties associated with the following water management strategies: Carrizo Aquifer–Wilson & Gonzales (CZ-10C); Carrizo Aquifer – Gonzales & Bastrop (CZ-10D); and Schertz-Seguin Water Supply Project (SSWSP).  Projected drawdown associated with CZ-10C and SSWSP is referenced to simulated 1994 aquifer levels and shown in plan view in Figure 5.2-31 along with monitoring well locations for the simulated well hydrographs presented in Figures 5.2-32  (Figure 5.2-33 Figure 5.2-34)  through 5.2-35.  Note that projected drawdown shown in these figures is a result of both projected local demands and the development of two water management strategies in the Plan.  Drawdown associated with CZ-10D in northern Gonzales County and southern Bastrop County, in addition to that associated with projected local demands, is shown in Figure 5.2-36.

Simulated cumulative effects of implementation of the Simsboro Aquifer (SCTN-3c) strategy in Milam, Lee, and Bastrop Counties are summarized in Figures 5.2-37 (Figures 5.2-38) through 5.2-39.  Projected drawdown associated with SCTN-3c between years 2000 and 2050 is shown in plan view in Figure 5.2-37.  Figures 5.2-38 and 5.2-39 illustrate the simulated incremental effects on Simsboro Aquifer levels associated with local demands and mining operations (baseline) and the implementation of the Plan for the Aluminum Company of America (Alcoa) and San Antonio City Public Service (CPS) well fields.

Potential cumulative effects of implementation of the South Central Texas Regional Water Plan on streamflows at selected locations in the Guadalupe – San Antonio River Basin are summarized in Figures 5.2-40  (Figure 5.2-41) through 5.2-42.  Streamflow comparisons for the Guadalupe River at Cuero (Figure 5.2-40) and the San Antonio River at Falls City (Figure 5.2-41) indicate that streamflows are expected to increase with full implementation of the Plan.  Increased streamflow at Cuero will be primarily due to Edwards Recharge – Type 2 Projects (L-18a) and the associated increases in Comal and San Marcos springflow.  Note that average annual freshwater inflows to the Nueces Estuary will be reduced by approximately three percent due to enhanced recharge

associated with Edwards Recharge – Type 2 Projects (L-18a).  Increased streamflow at Falls City will be a direct result of net projected increases in treated effluent discharge associated with increasing water use and expansion of SAWS Recycled Water Program in Bexar County.  Figure 5.2-42 shows increased streamflows (as compared to the baseline) in the Guadalupe River at the Saltwater Barrier in 2050.  This is particularly evident during low streamflow periods.

Potential effects of implementation of the South Central Texas Regional Water Plan on streamflows in the Colorado River at Bay City are summarized in Figure 5.2-43.  Results of statistical analyses of simulated streamflows from each of two potential Regional Water Sharing Alternatives proposed by the LCRA are presented in Figure 5.2-43.  The Plan includes diversions from both Bastrop and Bay City totaling 150,000 acft/yr, which is the same annual diversion from the Colorado River as simulated by LCRA.  Median streamflow in months during which irrigation use is limited or non-existent (October through March) may be reduced by more than 300 cfs once this management strategy is fully implemented in 2050.

 

5.2.5    Environmental Assessment

5.2.5.1     Environmental Setting

Brief discussions of the predominant land uses, vegetation, topography, habitats, and important species are included in the descriptions and environmental effects assessments of the individual water management strategies in Volume III of this document.  The South Central Texas Regional Water Plan must meet the municipal, industrial, mining, and steam-electric power water needs of a region that spans southern Texas from Hays and Caldwell Counties in the north to the Colorado and Guadalupe Estuaries on the Gulf Coast, to the headwaters of the Nueces River in Uvalde County.  The South Central Texas Region (Region L) exhibits a unique biological diversity as a consequence of its location in an area of transition between major vegetational and faunal regions to the north, east and south (respectively, the Kansan, Austroriparian and Tamaulipan), and its position astride migration corridors important to numerous bird, bat and insect populations.  Locally, the prairie and coastal ecoregions circumscribe sets of habitats, plants and animals distinct from those of the Central Texas Plateau, and the more tropical affinities of the Southern Texas Plains.  The eastern and southern margins of the Edwards Plateau are incised by a series of rugged, wooded canyons traversed by a series of streams where clear, spring fed waters intimately associated with a cavernous limestone aquifer provide the present primary water supply for Region L. 

The Edwards Aquifer itself, together with the karst geology of its recharge zone and the major perennial springs, constitute a unique set of habitats in which a significant concentration of isolated, endemic species have developed.  The porous to cavernous formation making up the Edwards and associated limestones constitute the Edwards Aquifer, the ground water source that presently supplies the City of San Antonio, and numerous other users, and which is critical to maintenance of spring habitats containing several endemic, endangered species.  The Edwards Aquifer is the only important aquifer habitat in Texas in which vertebrate species live[1] and it supports a surprisingly diverse ecosystem.  The aquifer has three parts: the drainage, or catchment area, the recharge zone, and the reservoir zone.  Input to the aquifer comes from  rainfall over the watershed and recharge occurs primarily in the beds of streams crossing the recharge zone, which consist of a band of fractured and cavernous limestone (Karst geology) that harbors a growing number of endemic, terrestrial cave species.  Where rivers flowing across the plateau have carved deep canyons and exposed the base of the Edwards Limestone, spring fed streams arise and flow south and eastward over the impermeable older formations to the recharge zone, at the base of which a set of larger springs (e.g., Leona, San Antonio, San Pedro, Comal, Hueco, and San Marcos Springs) emerge that support still more species of limited distribution.

Omernik[2] utilized criteria that included topography, climate, vegetation type and land use characteristics to divide the United States into ecological regions, or ecoregions, that exhibit more or less distinct sets of physical habitats and species.  According to Omernik’s classification Region L includes parts of five Ecoregions: the Central Texas Plateau, Southern Texas Plains, Texas Blackland Prairies, East Central Texas Plains, and the Western Gulf Coastal Plains (Figure 5.2-44).  Focusing specifically on Texas and excluding explicit land use criteria, Gould[3] delineated 10 vegetational areas, which generally correspond with the portions of Omernik's Ecoregions that extend into the state. The corresponding names for the vegetational areas in Region L are Edwards Plateau, South Texas Plains, Blackland Prairies, Post Oak Savannah, and the Gulf Prairies and Marshes (Figure 5.2-45).

The Edwards Plateau vegetational area encompasses approximately 24 million acres of tall or mid-grass understory and a brushy, savanna-type overstory complex of live oak (Quercus virginiana) and other oaks (Q.fusiformis, Q. buckleyi, Q sinuata var. breviloba), ashe junipers (Juniperus ashei), cedar elm (Ulmus crassifolia), mesquite (Prosopis glandulosa), various species of acacia (Acacia sp.), and sumacs, including the prairie flame-leaf (Rhus copallina var. lanceolata).  The most important climax grasses include switchgrass (Panicum virgatum), several species of bluestem (Schizachyrium and Andropogon spp.), gramas (Bouteloua spp.), Indian grass (Sorghastrum nutans), Canadian wild rye (Elymus canadensis), buffalo grass (Buchloe dactyloides) and curly mesquite (Hilaria belangeri).[4]

Juniper and mesquite brush are generally considered invaders into a presumed climax of largely grassland or savannah, except on the steeper slopes which have continually supported a dense cedar-oak thicket. Bald cypress (Taxodium distichum) occurs along perennial streams and rivers, while pecan (Carya illinoiensis), Arizona and little walnut (Juglans major, J. microcarpa) hackberry (Celtis laevigata), black and sandbar willow (Salix nigra, S. interior), and eastern cottonwood (Populus deltoides) are more widely distributed in riparian areas of both perennial and intermittent streams.  Cultivated fields are generally in the relatively broad, level stream valleys where deeper soils have accumulated.[5]  Upland agriculture consists primarily of livestock grazing and harvest of cedar and oak for fence posts and firewood, respectively.

The Post Oak Savannah vegetational area, which covers approximately 8.5 million acres, consists of gently rolling or hilly country, with elevations ranging from 300 to 800 ft-msl.  Upland soils of the region are light-colored, acid sandy loams or sands.  Bottomland soils are light brown to dark gray and acid, with textures ranging from sandy loams to clays.  The area is characterized by pastureland with frequent stands of woodland and occasional cropland.  The dominant species of the Post Oak Savannah is post oak (Quercus stellata), which occurs in open stands with a ground cover of grasses.[6]  Other associated species include blackjack oak (Quercus marilandica), black hickory (Carya texana), cedar elm (Ulmus crassifolia), and eastern redcedar (Juniperus virginiana).  This vegetation type is either considered to be a part of the Eastern Deciduous Forest association or as part of the Prairie association.[7],[8],[9],[10]  During the last few decades, open savannah has been converted into dense woodland stands of post oak and winged elm (Ulmus alata).  This has occurred as a result of overgrazing, abandonment from cultivation, and removal of fire.  Grazing is the major land use of both upland and bottomland sites within the vegetation type.  Large acreages of both upland and bottomland forests have been cleared for grazing and most of this is in tame pasture.

The Blackland Prairies is considered true prairie because of its native vegetation, which includes little bluestem as the climax dominant of the region.  Elevations for the region as a whole range from 300 to 800 ft-msl.  Uniform, dark-colored calcareous clays, which are interspersed with gray acid sandy loams, constitute the fertile Blackland soils.  According to Thomas, most of the region is under cultivation, although there are some excellent native hay meadows and a few ranches remaining.[11]  Big bluestem, Indiangrass, switchgrass (Panicum virgatum), sideoats grama (Bouteloua curtipendula), hairy grama(Bouteloua hirsuta), tall dropseed (Sporobolus asper), silver bluestem (Bothriochloa saccharoides), and Texas wintergrass (Stipa leucotricha) are other important grasses in the region.[12]  If heavy grazing is allowed, Texas wintergrass, buffalo grass (Buchloe dactyloides), Texas grama (Bouteloua rigidiseta), smutgrass (Sporobolus indicus) and many annuals may increase or invade the prairies, causing deterioration of the native community.[13]  Other invasive species are mesquite (Prosopis sp.) in the southern portion of the Blackland Prairies, and post oak and blackjack oak in areas of medium to light-textured soils. Grasses that have been used to seed improved pastures within the Blackland Prairies are dallisgrass (Paspalum dilatatum), common and coastal bermudagrass (Cynodon dactylon), and some native species. 

The South Texas Plains vegetational area (corresponding to the Southern Texas Plains Ecoregion) encompasses approximately 20 million acres of level to rolling topography, with elevations ranging from 1,000 feet to about sea level. Soil types cover a wide range, from clays to sandy loams, creating variations in soil drainage and moisture-holding capacities.  Though there are large areas of cultivated land, most of the area is still rangeland.  The South Texas Plains region originally supported a grassland or savannah climax vegetation.[14]  A long period of grazing and the reduction of fire have affected the plant communities and have led to an increase of brush.  Species which have increased in the area include honey mesquite (Prosopis glandulosa), post oak, live oak (Quercus virginiana), several acacias (Acacia spp.) and members of the cactus family (Cactaceae).  Distinct differences in climax plant communities and successional patterns occur on the many range sites that are found in the region.

The Gulf Prairies and Marshes vegetational region of Texas consists of about 9,500,000 acres.  This nearly level, slowly drained plain is less than 150 feet in elevation and is cut by sluggish rivers, creeks, bayous, and sloughs.  Habitats include coastal salt marshes, dunes, prairies, riverbottoms, and fresh water ponds.  Soils are acid sands, sandy loams and clays.  The upland prairie soils tend to be heavier textured acid clays or clay loams.  Much of the region is fertile farmland or pastureland.  The climax vegetation of the region is mostly tall grass prairie or post oak savannah.[15]  Principal grasses are big bluestem (Andropogon gerardi), little bluestem (Schizachyrium scoparium), seacoast bluestem (S. scoparium var. litoralis), indiangrass (Sorghastrum nutans), eastern gamma grass (Tripsacum dactyloides), Texas wintergrass (Stipa leucotricha) and switchgrass (Panicum virgatum) and gulf cordgrass (Spartina spp.).  Seashore saltgrass (Distichlis spicata) occurs on moist saline sites.  Since the region is heavily used for ranching and agriculture, extensive disturbance has allowed invader species, such as mesquite (Prosopis glandulosa), huisache (Acacia smallii), prickly pear (Opuntia spp.), Acacia (Acacia spp.), ragweed (Ambrosia psilostachya), broomweed (Xanthocephalum spp.) and others to become well established.[16],[17]  Heavy grazing and/or abandoned farmland has changed the predominant grasses to species such as broomsedge (Andropogon virginicus), smutgrass (Sporobolus indicus), threeawns (Aristida spp.) and introduced bermudagrass (Cynodon dactylon), fesque (Vulpia spp.) and dallisgrass (Paspalum dilatatum).

Large acreages of both upland and bottomland forests have been cleared for grazing and much of this land is planted with domestic grasses.  Major creek and river floodplains may retain more or less well-developed hardwood forests, but upland areas are generally cleared for cultivation or pasturage.  However, uplands support scattered, dense, shrubby thickets of oak, huisache and mesquite and occasional freshwater marshes in relict drainages.  Principal tree and shrub species observed in uplands include live oak (Quercus virginiana), post oak (Q. stellata),


cedar elm (Ulmus crassifolia), hackberry (Celtis laevigata), honey mesquite, huisache, and yaupon (Ilex vomitoria).[18],[19],[20]

Species listed by the Federal and state governments as Endangered or Threatened (see Volume III, Appendices D and E for lists by county), species that are candidates for listing as endangered and threatened, and other resources of concern are listed and discussed in terms of the potential impacts of each water management strategy in Volume III.  Stream segments nominated by Texas Parks and Wildlife Department for designation as Ecologically Unique River and Stream Segments in Region L are listed, along with the listing criteria employed in the nomination process, in Table 8-7 in Volume II.  Tables 8-4 and 8-4a list the potential effects on the nominated segments for each water management strategy, and Table 8-8 presents additional information on potential impacts by nominated segment.

With respect to Cultural Resources, Region L is the location of much of the earliest European activity in Texas, including concentrations of important historical sites on Matagorda bay, along the Guadalupe and San Antonio Rivers, in Bexar County and at the perennial spring along the margin of the Edwards Plateau.  Prehistoric sites also tend to be concentrated in many of the same areas, and Region L contains some of the oldest Native American habitation sites known in the United States.  Large National Historic Districts encompass areas on the lower Guadalupe and San Antonio Rivers that are particularly rich in both historic and prehistoric remains.

5.2.5.2     Environmental Effects

A number of the Water Management Strategies included in the Regional Water Plan are expected to involve little potential impact to environmental or cultural resources, except with respect to changes in land use practices that may affect wildlife habitats and uses in both rural and urban areas.  These include the conservation options (L-10), transfer of Edwards irrigation water to municipal uses (L-15), rainwater harvesting (SCTN-9), and aquifer storage and recovery in the Carrizo-Wilcox Aquifer (SCTN-1).  Some concern has been expressed that implementation of L-15 might adversely affect Comal springflows when a portion of the water that has been pumped from the aquifer for irrigation in Uvalde and Medina Counties is withdrawn instead from Bexar County wells.

Potential adverse environmental and cultural resources impacts are minimized in the Regional Water Plan by the inclusion of options which maximize the efficient use of existing surface water resources (G-15C and G-24), or which develop groundwater supplies (SCTN-2a, SCTN-3c, CZ-10C, CZ-10D), thereby avoiding the extensive habitat conversions and streamflow changes that can accompany comparable surface water development.

Construction of pipelines and well fields, and similarly dispersed facilities that typically have substantial flexibility in terms of alignment or site selection, will generally result in relatively localized disturbances of vegetation and habitats.  While a major pipeline may disturb several hundred acres in total, effects are generally minor at the landscape scale because construction and maintenance activities are dispersed among the much larger physiographic and habitat elements in which they are placed.  In addition, field studies conducted prior to design and easement procurement can substantially reduce the potential to adversely affect individual members of Endangered and Threatened species populations, historic and prehistoric sites, and other resources that are present only at particular locations.  Where sensitive resources at stream crossings cannot be adequately protected or avoided, boring or tunneling can be considered as construction options to avoid disturbance to aquatic habitats. 

Pipeline or well field construction are features of water management strategies that are present in all the Ecoregions.  Recharge reservoir or pipeline construction associated with water management strategies L-18a and G-24 (and other facilities located in northern Bexar, Comal, and Hays Counties) have the potential to encounter a number of Endangered and Threatened species occurring in association with the margin of the Edwards Plateau (e.g., golden-cheeked warbler, Dendroica chrysoparia) and the Edwards Aquifer or its associated Karst recharge zone and springs.  Many of these species are currently being affected by the urban and suburban development of the City of San Antonio and the Interstate Highway 35 corridor, and pipeline construction in these areas should be preceded by consultation with U.S. Fish and Wildlife Service.

The species mapped by the Texas Parks and Wildlife Texas Biological and Conservation Data System maintained by the Texas Parks and Wildlife Department Wildlife Diversity Branch and designated Endangered, and which inhabit extensive areas (or more correctly inhabit fragments of habitat dispersed over a large area) along pipeline alignments in the Coastal Plain, Blackland Prairies, and Central Texas Plains Ecoregions include Attwater’s Prairie Chicken (Tympanuchus cupido attwateri), Houston Toad (Bufo houstonensis), Two-Flower Stickpea (Calliandra biflora),  and Welder Machaeranthera (Psilactis heterocarpa).  The relatively large number of protected species mapped within the one mile pipeline corridors associated with water management strategies SCTN-16, SCTN-17, and LCRA Colorado River Diversions include a number of marine species, some of which may be affected by changes in estuarine inflows as a result of diversions from the Guadalupe and Colorado Rivers, or by discharge of reject water (brine) from a desalination facility.  Pipeline construction by itself is unlikely to significantly affect any marine species.

The water management strategies that include development of groundwater (CZ-10C, CZ10D, SCTN-3c, SCTN-16, and LCRA Colorado River Diversions) all avoid the potential environmental and cultural resources impacts usually attendant to development of similar volumes of surface water.  However, local residents of the areas that would be affected have expressed concerns about declining well levels and potential impacts to springs and streamflows.  Hydrogeological studies have indicated that substantial aquifer drawdowns will be largely limited to the vicinity of the well fields and effects on nearby wells can be mitigated.  With respect to effects on the flow of springs, and streams crossing the aquifer outcrops, existing information indicates that most of the springs in the vicinity of the Simsboro Aquifer well fields (SCTN-3c) originate in local alluvial aquifers and are presently being impacted by local groundwater users.  None have been identified that would be adversely affected by a drawdown in the Simsboro Aquifer.  Likewise, hydrogeological and surface water modeling shows that streamflows in the Brazos and Colorado Rivers, and in the intervening streams crossing the Simsboro outcrop, would not be significantly affected by this strategy. 

In contrast to the Simsboro Aquifer project, development of groundwater from the Carrizo-Wilcox Aquifer (CZ-10C, CZ-10D) is projected to result in reductions in streamflow in both the San Antonio and Guadalupe Rivers, and in inflows to the Guadalupe Estuary.  Proportionally, reductions in flow would be greatest in the middle San Antonio River and least at the Saltwater Barrier (estuary inflows).  Unlike the river diversions discussed below, flow reductions resulting from implementation of these options are most pronounced during dry weather to drought conditions, when aquatic communities are most stressed.  Potential reductions in Guadalupe and San Antonio River streamflow as a result of groundwater pumpage will be largely offset by enhanced Edwards springflow (L-18a) and increasing treated effluent discharge, respectively.

The large river diversion water management strategies, the Lower Guadalupe River Diversion (SCTN-16) and the LCRA Colorado River Diversion, include diversion of water under existing water rights. SCTN-16 includes unappropriated streamflow for which rights have to be obtained through the state permitting process.  Under both strategies, water supplies from off-channel and upstream reservoirs and from newly developed groundwater may be used to insure firm supplies throughout a drought comparable to the most severe on record.  The additional water is necessary because the unused water rights and the unappropriated water are either not physically present during low flow periods, are unavailable due to senior water rights demands, or are assigned to environmental streamflow needs.  The bulk of these diversions will occur during higher flow periods – when streamflows exceed the monthly medians (for a given month in the period of record, half the time flows were less than the median, and half the time flows were greater than the median), and low flow regimes will be affected to a much lesser degree.  Operations of both water management strategies are consistent with the inflow needs outlined in the Inflow Needs Reports for the two estuaries.[21],[22] 

Water management strategy L-18a includes dams where selected streams cross the Edwards Aquifer recharge zone to increase the amount of water entering the aquifer.  Most of the recharge occurs during heavy rains that result in streamflows exceeding the maximum possible recharge rate of the reach over the recharge zone and contributes instead to downstream flow.  In addition, most of the time, streambeds in the recharge zone (and for substantial distances downstream) are dry, and streamflows entering the zone are usually well below maximum recharge amounts.  Slowing the flow of water in order to increase the amount of time water remains over the recharge zone would increase recharge to the aquifer without substantially impacting stream habitats and populations, because water is not present in most of the stream reaches recommended at frequencies sufficient to support aquatic communities in the recharge and downstream reaches.  Because these projects involve natural recharge, no changes in water quality are expected.  The brief retention times for the impounded water are not expected to significantly alter the types and amounts of suspended and dissolved materials entering the recharge zone.

Major exceptions include the Nueces and Blanco River sites that do ordinarily exhibit surface water and aquatic communities at the proposed recharge sites.  However, permanent aquatic habitats are not generally maintained in the Nueces River between US 90 and the “braided reach” of the Nueces River, while the Blanco River joins with the San Marcos River only a few miles below the proposed recharge dam site.  Most of the water entering the aquifer from the Blanco River is expected to be discharged from the nearby springs in San Marcos and flow down the San Marcos River.  Recharge sites proposed for northern Bexar County may be near caves in which reside populations of endemic invertebrates that may be listed by U.S. Fish and Wildlife Service as Endangered or Threatened, and one site is in Government Canyon State Park.

As a result of diverting flood flows in the upper Nueces River basin into the Edwards Aquifer, thence to the Guadalupe-San Antonio River Basin through enhanced springflows and wastewater discharges, implementation of L-18a would result in small decreases in the firm yield of the Choke Canyon Reservoir/Lake Corpus Christi System and inflows to the Nueces Estuary.  At the same time, instream flows would increase in the Guadalupe-San Antonio River Basin, as would inflows to the Guadalupe Estuary.

Several stream segments that contain proposed recharge project sites have been nominated by Texas Parks and Wildlife Department for designation as Ecologically Unique Segments.  Table 5.2-23 lists the nominated streams in Region L together with the criteria that were used to select these segments.  All of the streams having segments that would have recharge projects (Blanco, Frio, Nueces, and Sabinal) have Edwards Aquifer recharge as a hydrologic criterion.  The other criteria tabulated include nomination for inclusion in Texas Natural River Systems, the presence of Garner State Park, overall use, and aesthetics.  As the recharge projects are all located at the downstream end of perennial flow, none of the criteria used to nominate these stream segments will be affected adversely.  Table 5.2-24 summarizes the potential effects on Ecologically Unique Segments of all the water management strategies included in the Regional Water Plan.

The cultural resources of Region L include historical markers designated by the Texas Historical Commission.  One concentration of markers is located in central Bexar County within the City of San Antonio.  Other areas where substantial numbers of historical markers are found within the mile-wide pipeline corridors discussed and assessed in the presentation of individual water management strategies CZ-10C, SCTN-17, LCRA Colorado River Diversions, SCTN-3c, and SCTN-16 in Volume III of this document.  Stream terraces, particularly where they are in proximity to a tributary confluence, are thought to have substantially higher probabilities of holding significant archaeological sites than do either floodplains or more upland areas.  In addition, terrace and floodplain (riparian) areas are likely to include deep, geologically recent sediments in which archaeological sites may be buried.  Finding and investigating such sites can be a lengthy and difficult process, and may significantly affect implementation of options that include reservoir construction or substantial lengths of pipeline in such settings.

Potential environmental and cultural resources impacts associated with water management strategy SCTN-17, desalination of seawater, would result primarily from construction of the facility and its intake, discharge and water delivery pipelines.  Field studies conducted prior to design and easement procurement can substantially reduce the potential to adversely affect individual members of Endangered and Threatened species populations, historic and prehistoric sites, and other resources that may be present.  Because the reject water (brine) can be 3 to 4 times more saline than seawater, and could amount to as much as 100 acft per day, the outfall will likely need to be sited in the Gulf of Mexico because of potential salinity impacts that may occur in an enclosed estuarine environment.

5.2.6    Implementation Issues

5.2.6.1     Summary of Key Information

Pursuant to TAC 357.7(a)(7), regional water plan development shall include evaluations of water management strategies providing certain key information pursuant to TWDB criteria.  Key information regarding the South Central Texas Regional Water Plan is summarized by subject area below.  In addition, Table 5.2-25 provides a summary of key information, pursuant to TWDB evaluation criteria, for each water management strategy included in the Regional Water Plan.

Quantity, Reliability, and Cost

·        Plan reflects substantial commitment to Municipal and Irrigation Demand Reduction (Conservation) (L-10) throughout the South Central Texas Region, thereby encouraging efficient utilization of existing water supplies and reducing quantities of new supply needed.

·        Plan includes reliable new water supplies sufficient to meet projected drought needs for municipal, industrial, steam-electric power, and mining uses through the year 2050.

·        Plan recognizes that water management strategies such as brush management, weather modification, rainwater harvesting, and small recharge dams contribute positively to storage and system management of diverse sources of supply.

·        Annual costs associated with new supplies delivered to each water user group range from about $120,000,000 dollars early in the planning period to about $420,000,000 in 2040.  Unit costs range from $530 per acft to $737 per acft and average $617 per acft or $1.89 per 1,000 gallons over the 50-year planning period.

·        During the more immediate planning period extending through 2030, the Regional Water Plan has the least average unit cost of the alternative plans considered.

Environmental Factors

·        See Section 5.2.6.2 for summary of environmental benefits and concerns.

Impacts on Water Resources

·        Plan implementation results in no unmitigated reductions in water available to existing rights.

·        Generally modest long-term reductions in water levels in the Carrizo Aquifer as withdrawals associated with management strategies in the Plan are in conformance with the policies of the Evergreen and Gonzales County Underground Water Conservation Districts.

Impacts on Agricultural and Natural Resources

Inclusion of water management strategies to meet projected irrigation needs (shortages) in full is estimated to be economically infeasible at this time.  Irrigation Demand Reduction (Conservation) (L-10 Irr.) through the installation of Low Energy Precision Application (LEPA) systems is recommended to offset a portion of projected irrigation needs (shortages) in six counties.

·        Plan includes Brush Management (SCTN-4) and Weather Modification (SCTN-5) which are expected to contribute positively to storage and system management of diverse water management strategies.  Weather Modification (SCTN-5) assists irrigation and dry-land agriculture (crops and ranching) and increases water supply for wildlife habitat.

·        Plan includes about 53 percent of potential maximum voluntary transfer of Edwards Aquifer irrigation permits to municipal use through lease or purchase.

·        Plan includes installation of LEPA systems on about 53 percent of applicable acreage in Uvalde, Medina, and Bexar Counties with conserved water being transferred to municipal use.

Other Relevant Factors per SCTRWPG

·        Potential effects of Plan implementation on Edwards Aquifer springflows has been identified as a relevant factor by the South Central Texas Regional Water Planning Group (SCTRWPG).  As shown in Section 5.2.3, implementation of Plan is expected to increase discharges from both Comal Springs and San Marcos Springs.

·        Flexibility in the phasing and order of implementation of management strategies comprising the Plan has been identified as a relevant factor or concern by the SCTRWPG.  Major Water Providers and water user groups need the ability to expedite or reschedule implementation of any specific management strategy as necessary and appropriate.

Comparison of Strategies to Meet Needs

·        Selection of water management strategies comprising the Regional Water Plan was based upon guiding principles and assumptions of the SCTRWPG as discussed in Section 6.3.

Interbasin Transfer Issues

·        Plan includes at least three potential interbasin transfers: (a) from the Lower Colorado River near Bastrop to Hays County; (b) from the Lower Colorado River near Bay City to Bexar County; and (c) from San Antonio Bay near Seadrift to Bexar County.  Interbasin transfer(s) may also be associated with Edwards Aquifer Recharge & Recirculation Systems once this management strategy is more completely defined.

·        Projected needs (shortages) in basin(s) of origin are met throughout the planning period.

Third-Party Impacts of Voluntary Redistribution of Water

·        Positive effects for municipal water user groups and potentially negative effects upon rural economies associated with Edwards Irrigation Transfers (L-15) and Irrigation Demand Reduction (Conservation) (L-10 Irr.) with Transfers.

·        Payment to farmers for voluntary irrigation water transfer provides capital for farmers to install higher efficiency irrigation systems.  In many cases, this allows irrigation to continue at present levels so that the transfer does not adversely affect the regional economy.

·        Lower water levels in some portions of the Carrizo Aquifer.

Regional Efficiency

·        Edwards Irrigation Transfers (L-15) require no new facilities.  Transferred water would likely be available at or very near locations having projected municipal, industrial, steam-electric power, and mining needs in Uvalde, Medina, Atascosa, and Bexar Counties.

·        Regional water treatment and balancing storage facilities in Bexar County increase efficiency, improve reliability, and reduce unit cost.

·        San Antonio Water System Regional Aquifer Storage & Recovery System (SCTN-1a) substantially reduces peak summer pumpage from the Edwards Aquifer.

Effect on Navigation

·        Not applicable.

5.2.6.2     Environmental Benefits and Concerns

The South Central Texas Regional Water Planning Group has identified the following environmental benefits and concerns associated with the implementation of the Regional Water Plan.

Environmental Benefits

·        Substantial commitment to water conservation through adoption of Texas Water Development Board (TWDB) advanced conservation water demand projections results in fewer water management strategies necessary to meet projected water needs.  The South Central Texas Region is the only planning region in the state to adopt the advanced conservation water demand projections.

·        Additional commitment to accelerated conservation (above and beyond that in the TWDB’s advanced conservation water demand projections) through Demand Reduction (L-10) results in fewer water management strategies necessary to meet projected water needs.  Demand Reduction (L-10) accounts for more than 22 percent of the total new water supplies for municipal, industrial, steam-electric, and mining uses in 2010.  Even in 2050, Demand Reduction (L-10) accounts for more than 10 percent of the total new water supplies for the referenced uses.

·        Development of new water supply sources for Bexar, Comal, and Hays Counties reduces reliance on the Edwards Aquifer during drought thereby contributing to maintenance of springflow and protection of endangered species.  The Regional Water Plan recognizes the on-going initiatives of the Edwards Aquifer Authority (EAA) to develop a Habitat Conservation Plan and implement Critical Period Management rules which will help to define the requirements for maintenance of springflow and protection of endangered species.

·        Phased implementation of the Regional Water Plan (including timely utilization of Management Supplies) results in increased instream flows in the Guadalupe and San Antonio Rivers and increased freshwater inflows to the Guadalupe Estuary, particularly during the drier months and more extended drought periods.

·        Edwards Aquifer Recharge Enhancement through the construction of Type 2 recharge dams (L-18a) contributes not only to municipal water supply, but also to maintenance of springflow, protection of endangered species, increased instream flows, and increased freshwater inflows to the Guadalupe Estuary.

·        The Regional Water Plan makes greatest beneficial use of existing surface water rights and major storage facilities (Canyon Reservoir, Highland Lakes System) thereby minimizing the development of new water supply sources and associated environmental impacts.  Examples include reliance on presently under-utilized water rights held by the Guadalupe-Blanco River Authority (GBRA) and Union Carbide Corporation (UCC) below the confluence of the Guadalupe and San Antonio Rivers (SCTN-16) and by the Lower Colorado River Authority (LCRA) on the Lower Colorado River.  Enhanced use of existing surface water rights and major storage facilities accounts for more than one third of the total new water supplies for municipal, industrial, steam-electric, and mining uses by 2050.

·        The Regional Water Plan avoids large-scale development of new reservoirs having associated terrestrial and aquatic habitat and cultural resources impacts and focuses on smaller, off-channel balancing reservoirs essential for efficient operations and meeting peak seasonal water needs.

·        Inclusion of Edwards Aquifer transfers from irrigation use to municipal use through lease/purchase of pumpage rights (L-15) and development of conserved water through installation of LEPA irrigation systems (L-10 Irr.) results in substantial increases in municipal water supply without construction of additional transmission and storage facilities having associated environmental effects.

·        The San Antonio Water System (SAWS) goal of meeting 20 percent of projected water demand through its Recycled Water Program makes greatest use of developed water resulting in fewer water management strategies necessary to meet projected water needs.

·        Inclusion of modest Carrizo Aquifer groundwater development (CZ-10C, CZ-10D, and SCTN-2a) has minimal associated environmental effects as compared to those typically associated with development of new surface water supplies.

·        Inclusion of Desalination of Seawater (SCTN-17) is perceived to have fewer associated environmental effects, as compared to those typically associated with development of new (fresh) surface water supplies.

Environmental Concerns

·        Potential reductions in freshwater inflows to bays and estuaries including associated effects on wetland and marsh habitats and marine species are identified as matters of concern.  Primary concerns focus upon the potential effects of the New Colorado River Diversion Option (LCRA) on freshwater inflows to Matagorda Bay.  Secondary concerns are identified for the Nueces Estuary as a result of implementation of Edwards Recharge—Type 2 Projects (L-18a).

·        Concentration of Edwards Aquifer pumpage closer to Comal Springs as a result of implementation of Edwards Irrigation Transfers (L-15) and additional transfers of conserved water developed by installation of LEPA irrigation systems (L-10 Irr.) tends to reduce discharge from Comal Springs.

·        Potential conflicts with stream segments identified by TPWD as ecologically significant are associated with the New Lower Colorado River Diversion Option (LCRA), Lower Guadalupe River Diversions (SCTN-16), and Edwards Recharge—Type 2 Projects (L-18a).

·        Potential effects on small springs may be associated with the development of groundwater supplies from the Carrizo Aquifer (CZ-10C, CZ-10D, and SCTN-2a) and from the Simsboro Aquifer (SCTN-3c).

·        Intake siting, brine discharge location(s), and potential effects on marine habitat and species are environmental concerns associated with Desalination of Seawater (SCTN-17).

5.2.7        Special Water Resources

The Texas Water Development Board has designated Canyon Reservoir and the Medina Lake System as special water resources located within the South Central Texas Regional Water Planning Area (Region L).  This designation is pursuant to TAC 357.5 (g) & (h) as surface water supplies from these reservoirs may be obligated to meet demands outside of Region L.  Water rights to Canyon Reservoir are held by the Guadalupe-Blanco River Authority (GBRA) which is headquartered in Guadalupe County.  Water rights to the Medina Lake System are held by the Bexar-Medina-Atascosa Counties Water Control & Improvement District #1 (BMA) which is headquartered in Medina County.  TAC 357.5 (h) requires that “the regional water planning group for the regional water planning area which contains the special water resource shall protect the water rights, water supply contracts, and water supply option agreements associated with the special water resource(s) so that supplies obligated to meet demands outside the regional water planning area shall not be impacted.”  Present and potential obligations of supplies from these special water resources to meet demands outside Region L are summarized in the following paragraphs.

5.2.7.1    Canyon Reservoir

There is only one current contractual obligation with an entity located outside of Region L for water supply from Canyon Reservoir.  This upstream diversion contract is between GBRA and the City of Kerrville and represents a commitment of up to 26 acft/yr from the firm yield of Canyon Reservoir for irrigation use in Kerr County.  The South Central Texas Regional Water Plan includes approximately 300 acft/yr from Canyon Reservoir to meet projected needs for the City of Blanco located in Blanco County in the Lower Colorado Regional Water Planning Area (Region K).  Pursuant to a Memorandum of Understanding (MOU) between GBRA and the Commissioners’ Court of Kerr County, the South Central Texas Regional Water Planning Group (SCTRWPG) recognizes a potential commitment of approximately 2,000 acft/yr from the firm yield of Canyon Reservoir for the calendar years 2021 through 2050.  Subject to and conditioned upon the Texas Natural Resource Conservation Commission (TNRCC) granting, in whole, GBRA’s application to amend the Canyon water right, this MOU states:

Upon request from Kerr County, at any time after  January 1, 2021 and prior to December 31, 2050, GBRA will support and assist Kerr County in obtaining from the TNRCC permits to divert water from the Guadalupe River or its tributaries at one or more diversion points within Kerr County for use within the County, up to a total diversion of not to exceed 6,000 acft/yr, pursuant to GBRA’s then-standard agreement for “upstream sales of water from storage.”

GBRA’s hydrology studies have indicated that a commitment of 2,000 acft/yr is necessary to allow permits for 6,000 acft/yr to be issued by TNRCC for diversion in Kerr County.  No additional supplies from Canyon Reservoir are specifically reserved for entities within the Plateau Regional Water Planning Area (Region J) at this time.

5.2.7.2    Medina Lake System

The South Central Texas Regional Water Plan does not specifically include any supplies from the Medina Lake System to meet present or projected needs for water user groups within Region L or any adjacent planning regions.  Simulations using the Guadalupe—San Antonio River Basin Water Availability Model (GSA WAM) indicate that there would be no dependable surface water supply from the Medina Lake System in a repeat of the drought of record if operated in accordance with its current Certificate of Adjudication (19-2130C).  It is recognized, however, that the Medina Lake System may supply up to an authorized 66,750 acft for municipal (20,144 acft), irrigation (45,856 acft), and domestic and livestock (750 acft) uses in many years.  Most of these supplies are contractually committed to irrigators in Region L and to the Bexar Metropolitan Water District (BMWD).  The South Central Texas Regional Water Planning Group (SCTRWPG) recognizes that some supplies from the Medina Lake System may be committed to Region J pursuant to a March 1997 Memorandum of Understanding (MOU) between BMA, BMWD, Bandera County, and the Springhills Water Management District.[23] This MOU indicates that BMA will make up to 5,000 acft/yr available to Bandera County when Medina Lake exceeds 1,035 ft-msl (BMA datum) and up to 1,000 acft/yr when Medina Lake falls below this level.  It is assumed that interests upstream of Medina Lake will obtain the necessary water rights permit(s) for diversion from the Medina River and/or its tributaries and will mitigate any associated impacts upon recharge of the Edwards Aquifer within Region L.

 

 


[1] Edwards, Robert J., Glen Longley, Randy Moss, John Ward, Ray Mathews, and Bruce Stewart, “A Classification of Texas Aquatic Communities with Special Consideration Toward the Conservation of Endangered and Threatened Taxa,” Vol. 41, No. 3, The Texas Journal of Science, University of Texas at Austin, Austin, Texas, 1989.

[2]  Omernik, James M., “Ecoregions of the Conterminous United States,” Annals of the Association of American Geographers, 77(1) pp. 118-125, 1987.

[3] Gould, F.W., “The Grasses of Texas,” Texas A&M University Press, College Station, Texas, 1975.

[4] Correll, D.S., and M.C. Johnston, “Manual of Vascular Plants of Texas,” Texas Research Foundation, Renner, Texas, 1979.

[5] Ibid.

[6] Correll, D.S., and M.C. Johnston, Op. Cit., 1979.

[7] Tharp, B.C., “The Vegetation of Texas,” Texas Acad. Sci., Anson Jones Press, Houston, 1939.

[8] Braun, E.L., “Deciduous Forests of Eastern North America,” Hafner Publ. Co., Inc., New York, 1950.

[9] Weaver, J.E. and F.E. Clements, “Plant Ecology,” 2nd Ed., McGraw-Hill Book Co., New York, 1938.

[10] Daubenmire, Rexford, “Plant Geography with Special Reference to North America,” Academic Press, New York, 1978.

[11] Thomas, G.W., “Texas Plants – An Ecological Summary,” In: F.W. Gould. 1975. Texas Plants – A Checklist and Ecological Summary, Texas Agricultural Experiment Station, MP-585/Rev., College Station, Texas, 1975.

[12] Correll, D.S., and M.C. Johnston, Op. Cit., 1979.

[13] Ibid.

[14] Thomas, G.W., OP. Cit., 1975.

[15] Correll, D.S., and M.C. Johnston, “Manual of the Vascular Plants of Texas,” Texas Research Foundation, Renner, Texas, Second printing, 1979.

[16] Johnston, M.C., “The Vascular Plants of Texas, A List Updating the Manual of the Vascular Plants of Texas,” Austin, Texas, 1988.

[17] Thomas, G.W., Op. Cit., 1975.

[18] Bureau of Reclamation, “Palmetto Bend Project – Texas Final Environmental Impact Statement,” Bureau of Reclamation, U.S. Department of the Interior, 1974.

[19] Soil Conservation Service (SCS), “Soil survey of Calhoun County, Texas,” SCS, Temple, Texas, 1978.

[20] Texas Department of Water Resources, “ Land Use/Land Cover Maps of Texas,” Austin, Texas, LP-62, Reprinted 1978, 1977.

[21] Martin, Q., D. Mosier, J. Patek, C. Gorham-Test.  1997.  Freshwater Inflow Needs of the Matagorda Bay System.  Lower Colorado River Authority, Austin, Texas.   

[22] TPWD and TWDB, “Freshwater Inflow Recommendation for the Guadalupe Estuary of Texas,” Coastal Studies Technical Report No. 98-1, TPWD and TWDB, Austin, Texas, 1998.

[23] Memoram of Understanding to Facilitate Regional Cooperation for the Maximization of Beneficial Development of the Water Resources Available from Medina Lake Pursuant to BMA’s Certificate of Adjudication No. 19-2130 and to Settle and Compromise Issues and Disputes Among the Parties, March 19, 1997.