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Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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1

Introduction

The Edwards Aquifer is located in south-central Texas and is one of the most productive karst aquifers in the United States. It underlies several Texas counties, covering an area about 180 miles long and from 5 to 40 miles wide (see Figure 1-1). It is the primary water source for the growing city of San Antonio and its surrounding communities, home to over 2.3 million people. Many of these cities (Uvalde, San Antonio, New Braunfels, and San Marcos) were originally founded around the large springs that discharge from the Edwards Aquifer. The aquifer also supplies irrigation water to thousands of farmers and livestock operators in the region, which can account for as much as 30 percent of the total annual water withdrawals from the aquifer system.

In addition to providing drinking water for many communities, the Edwards Aquifer supplies several springs, including the two largest freshwater springs in Texas—Comal Springs in New Braunfels and San Marcos Springs in San Marcos. Many people use these springs and their associated river systems for recreation, but they are also home to a number of endemic species of fish, amphibians, insects, and plants found nowhere else. Because of the potential for reduced spring flow during times of drought, seven of these species are listed under the federal Endangered Species Act (ESA) as endangered species: the fountain darter, the San Marcos gambusia (presumed extinct), the Texas blind salamander, the Comal Springs dryopid beetle, the Comal Springs riffle beetle, Peck’s Cave amphipod, and Texas wild rice. One other species, the San Marcos salamander, is federally listed as threatened, and the U.S Fish and Wildlife Service is currently decid-

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

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FIGURE 1-1 The Edwards Aquifer, showing the jurisdiction of the Edwards Aquifer Authority.
SOURCE: Figure 1-1 from EARIP (2012).

ing whether to list three other species in the system in response to citizen petitions.

The hydrology of the Edwards Aquifer allows for the extremely high yield wells and springs in the system (see subsequent section on Water Budget), with large volumes of groundwater being transported through the system very quickly, on the order of days. Indeed, in some parts of the Edwards Aquifer, groundwater velocities exceed two miles per day (Johnson et al., 2012). As a result, the aquifer responds quickly both to rainfall events (known as recharge) and to withdrawals, such as pumping for irrigation and water supply. During the 1950s, central Texas experienced what is now called the “drought of record,” the most severe drought recorded for the region. During this drought, flows at Comal Springs ceased for 4 months and flows at San Marcos Springs were severely reduced. At current pumping levels, a similar drought today could result in complete cessation of flow at Comal Springs for more than 3 years and near cessation of flow at San Marcos Springs (EARIP, 2012). Such reductions in spring flow would be catastrophic to the ESA-listed (and other) species living in the Edwards Aquifer and its springs. As discussed later in this chapter, climate change in

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

this region may potentially increase the risk of such drought events, exacerbating the future threat to these species.

To protect the ESA-listed species, the Edwards Aquifer Authority (EAA) and four other local entities applied for an Incidental Take Permit under the ESA, creating a 15-year Habitat Conservation Plan as part of the application process. The EAA is a regional government body tasked with managing domestic, industrial, and agricultural withdrawals from the Edwards Aquifer while maintaining spring flows at quantities that can support recreation and ESA-listed species. Among other duties, the EAA implements the Habitat Conservation Plan, which the U.S. Fish and Wildlife Service (FWS) finalized and approved in 2013 after a years-long development process.

Despite the high yields of the Edwards Aquifer, increased pumping and other uses of Edwards Aquifer water pose significant threats to the listed species at Comal and San Marcos Springs. Given the uniqueness of these two ecosystems, the many diverse projects that make up the Habitat Conservation Plan, and the persistence of drought conditions across the region, the EAA has requested the input of the National Academy of Sciences as it (the EAA) implements the Habitat Conservation Plan. This report is the first product of a three-phase study to provide advice to the EAA on various scientific aspects of the Habitat Conservation Plan that will ultimately lead to improved management of the aquifer.

THE EDWARDS AQUIFER

Because the major impacts to endangered species residing in the springs and river systems of the Edwards Aquifer are believed to be related to flow reductions, this section focuses on aquifer physiography and hydrology, regional climate, and the water budget. Local water quality impacts from changes in land use and land cover are thought to be of secondary importance to the springs and are discussed in Chapter 4.

Physiography and Hydrology

The Edwards Aquifer is a karst aquifer that spans three major physiographic zones: the Edwards Plateau, the Balcones fault zone (system), and the Gulf Coastal Plain. The Balcones fault zone is the principal focus of the Habitat Conservation Plan. Along this fault system, the Edwards Aquifer is highly productive, with high-capacity water wells and high spring discharges. In addition, at least six springs occur within this zone, including two first magnitude springs (i.e., flows are at least 100 cubic feet per second or CFS), the San Marcos and Comal.

The Edwards Aquifer is subdivided into zones reflecting hydrologic function (see Figure 1-1). Contributing and recharge zones lie largely to the

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

north of the aquifer, while pumping and artesian wells occur largely over and to the south of the aquifer. The contributing zone, which is also known as the drainage area or the catchment area, includes 5,400 square miles and represents areas where rainfall is directed by streams toward the recharge zone. The catchment area lies within the Edwards Plateau, also known as the Texas Hill Country, and includes elevations ranging from 1,000 to 2,300 feet above sea level. The recharge zone of the Edwards Aquifer is approximately 1,250 square miles. This zone reflects the area where precipitation percolates and flows into the groundwater to replenish the aquifer. The zone extends along the central east-west axis of the aquifer and is generally unconfined, with exposures of the Edwards Limestone along the Balcones fault system. Recharge occurs through dissolution-enhanced features, including faults, fractures, bedding planes caves, and conduits. Surface streams become sinking streams (or swallets) in the recharge zone. Recharge within this zone is a function of overland drainage from the contributing zone and reflects volumes remaining after precipitation and infiltration in the contributing zone as well as losses resulting from evapotranspiration.

The artesian zone encompasses 2,650 square miles and comprises the region in which the Edwards Aquifer is under artesian conditions, meaning that pressure levels in the aquifer cause water levels in wells to rise to elevations above the top of the aquifer. The Edwards Aquifer in this area is generally under confined conditions, where a regional clay-rich unit called the Del Rio Clay occurs on top of the carbonates of the Edwards Aquifer. Where these confined conditions exist, which maintain pressure in the aquifer, groundwater flow from the aquifer to land surface locally occurs in the form of springs and seeps.

The Edwards Aquifer underlies approximately 4,000 square miles in 18 counties and ranges to more than 900 feet thick (Lindgren et al., 2004). Three hydrogeological segments have been delineated within the Edwards Aquifer: the southern (San Antonio) segment, the Barton Springs (Austin) segment, and the northern segment (Figure 1-2). A groundwater divide in the vicinity north of San Marcos Springs in Hays County separates the San Antonio segment from the Barton Springs segment. Under most hydrologic conditions, groundwater from the San Antonio and Barton Springs segments does not mix; however, during drought conditions there is potential for water to bypass San Marcos springs and flow north to the Barton Springs segment (HDR, 2010). The Colorado River hydrologically separates the Barton Springs segment from the northern segment. Comal and San Marcos Springs are located within the San Antonio segment of the Edwards Aquifer, which spans approximately 3,600 square miles and is the focus of the Habitat Conservation Plan and this report.

One important boundary in the Edwards Aquifer system is the southern boundary, which is defined by the freshwater/saltwater transition zone

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

images

FIGURE 1-2 Segments of the Edwards Aquifer recharge and artesian zone.
SOURCE: Figure 3-16 from EARIP (2012).

as demarcated by the 1000 mg/L total dissolved solids (TDS) concentration line. Saltwater intrusion into the artesian zone is one of the risks that pumping of the Edwards Aquifer poses to the system. It is for that reason that the Edwards Aquifer Data Collection Program includes salinity monitoring at 11 wells. Water level elevations collected from index well J-17 correlate strongly with those from the salinity monitoring wells. As shown in Figure 1-3, while J-17 water levels have fluctuated by more than 30 feet, no trend between water levels and TDS levels has been observed, indicating that the salinity concentrations are not sensitive to water levels over the observed period of record.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

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FIGURE 1-3 Total dissolved solids as a function of water level in the J-17 index well.
SOURCE: Johnson et al. (2009).

The geological composition and history of the Edwards Aquifer provides for a complex groundwater flow system. Soluble carbonate rocks, such as limestones, comprise the aquifer rocks and give rise to karst features, such as springs, caves, and sinkholes. Tectonic stresses in the geologic past have produced faults and fractures. Groundwater flowing along these features can dissolve the rock and increase their role in groundwater movement through the system. In addition, groundwater flows through the microscopic connected pore spaces (permeability) in the limestones. This triple-permeability nature of the Edwards Aquifer—matrix, karst, and fracture flow—contributes to vast local differences in groundwater flow regimes. In some areas, flow is intergranular and slow, whereas in other areas, the aquifer is highly responsive to changes in pressures, or hydraulic head, because of conduit or fracture flow. Because of the highly karstic nature of the Edwards Aquifer, much of its recharge is rapid and unfiltered, making it highly vulnerable to surface sources of contamination. Movement of groundwater in the Edwards aquifer is generally from west to east to northeast.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

Climate

Precipitation

More than a foot of variability occurs in precipitation across the Edwards Aquifer region (Figure 1-4), with annual precipitation values ranging from approximately 22 inches in the western extent to over 34 inches in the eastern extent. The mean annual precipitation for San Antonio from 1934 through 2013 is approximately 30.38 inches, although annual precipitation may vary from year to year by more than 20 inches.

Figure 1-5 demonstrates this variability for the San Antonio area. Periods of high rainfall (in excess of 40 inches per year) are separated by

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FIGURE 1-4 Average annual precipitation 1971-2000. The dashed black line outlines the Edwards Aquifer region.
SOURCE: Adapted from Figure 3-3 in EARIP (2012).

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

images

FIGURE 1-5 Annual precipitation in San Antonio, Texas.
SOURCE: Edwardsaquifer.net (accessed October 23, 2014).

periods of drought, the most significant having occurred from 1950 to 1956, during which time precipitation was well below the mean annual average of 30.38 inches for 6 concurrent years. This period is recognized as the “drought of record” and coincides with a 144-day cessation of flow at Comal Springs in 1956 (Longley, 1995).

Evapotranspiration

Evapotranspiration along the extent of the Edwards Aquifer ranges from more than 60 inches per year in the western extent to 30 inches per year in the eastern extent (Scanlon et al., 2005). Moving westward across the region, evapotranspiration increasingly exceeds precipitation, reaching an annual average difference of more than 30 inches in the western-most area. This pattern declines and slightly reverses moving eastward across the Edwards Aquifer region, such that average annual precipitation exceeds evapotranspiration by more than 5 inches in the most eastern area. Comparison of the two parameters underscores the importance of aquifer recharge that minimizes the influence of evapotranspiration, especially in the west. Unlike other parts of the country where recharge can occur pre-

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

dominantly through infiltration, the high rates of evapotranspiration limit recharge to rapid focused events through exposed karst features within surface-exposed limestone.

Climate Change

Scenarios for climate change in the Edwards Aquifer region indicate that long-term declines in precipitation may occur. For example, projected precipitation differences between 2009 and 2050 based on just a “low greenhouse gas emission” scenario indicate more than 7 inches of annual precipitation loss may occur locally in the region (Darby, 2010). Not only is the Edwards Aquifer vulnerable to potential contamination because of its karstic nature, it is among the most vulnerable in the state in relation to changes in climate (Loáiciga et al., 2000; Mace and Wade, 2008). With dryer climate and an anticipated population increase, it is reasonable to expect increased demands on water resources from municipal, agricultural, and industrial users. As stated succinctly in the EARIP (2012): “The historical evidence and the results of this research indicate that without proper consideration to variations in Aquifer recharge and sound pumping strategies, the water resources of the Edwards Aquifer could be severely impacted under a warmer climate.”

Water Budget

Variations in seasons and climate during the recent history of the Edwards Aquifer are manifested in the variable nature of the aquifer’s water budget. Recharge into the system occurs primarily through stream flow networks in the recharge area, which contribute between 60 and 80 percent of the system input (Klemt et al., 1979; Maclay and Land, 1988; Thorkildsen and McElhaney, 1992; Ockerman, 2005), most of which is through open solution channels like fractures and sinkholes (Maclay and Land, 1988). Sharp and Banner (1997) indicate that the remaining 20 to 40 percent of the recharge occurs as direct infiltration within the recharge zone, as well as leakage from the underlying Trinity Aquifer. Leakage from lateral aquifer segments into the San Antonio segment of the Edwards Aquifer and also from adjacent aquifers occurs where hydrologic connections exist, such as along fault zones and through low-confinement border conditions. In Medina County, inflows also occur through recharge structures like surface reservoirs and surface-water diversion to a sinkhole. Based on drainage basin data collected during a period of record from 1934 to 2012, median annual recharge is 556,900 acre-feet1, with a range from 43,700 acre-feet

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1 1 acre-ft = 1,233 m3.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

during the drought of record to 2,486,000 acre-feet in 1992 (EAA, 2013; Figure 1-6). Annual mean and median recharge attributed to structures, from date of construction through 2012, are 853 acre-feet and 4,970 acre-feet, respectively (EARIP, 2012). Recharge estimates of inter-aquifer flow range from 5,000 to more than 100,000 acre-feet per year.

Edwards Aquifer discharge is composed of spring flows and consumptive use through wells (Figure 1-7). Total annual discharge from six of the most significant springs in the region monitored between 1934 and 2012 has varied from 69,800 acre-feet in 1956 to 802,800 acre-feet 1992, with a median annual discharge of 383,900 acre-feet (EAA, 2013). Well discharge estimates during the same period of record range from a low of 101,900 acre-feet in 1934 to a high of 542,400 acre-feet in 1989, with a median annual discharge of 327,800 acre-feet. Total discharge ranged from a low of 388,800 acre-feet in 1955 to a high of 1,130,000 acre-feet in 1992, with

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FIGURE 1-6 Estimated Annual Recharge and 10-Year Floating Median Estimated Recharge for San Antonio Segment of the Edwards Aquifer, 1934–2012.
SOURCE: Figure 8 from EAA (2013).

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

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FIGURE 1-7 Groundwater Pumping Compared with Spring Flow from Edwards Aquifer, 1934–2012.
SOURCE: Figure 11 from EAA (2013).

a median of 692,900 acre-feet. In 2012, springs comprised 44 percent of total discharge.

ECOLOGY OF THE EDWARDS AQUIFER REGION

The springs flowing from the Edwards Aquifer and their resulting streams support a number of species, many of which are endemic to the aquifer area. These species include a variety of submersed aquatic vegetation (SAV) like Texas wild rice; several fish, including the fountain darter; amphibians such as the Texas blind salamander; birds like the whooping crane; and a variety of invertebrates. These species’ individual habitats range from deep underground in the springs themselves (blind salamander) to the larger streams and lakes (fountain darter and Texas wild rice) within the Edwards system. Some species, like the fountain darter and Texas wild rice, have been well studied, while the ecology of others, like the Comal

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

Springs riffle beetle, is poorly understood. These species are described extensively in later chapters.

The complete Edwards Aquifer-based ecosystem is complex and not yet comprehensively understood. However, to greater or lesser extent, all species in the system depend on spring flow, and reduced flow in Comal and San Marcos Springs has resulted in the intermittent loss of habitat. This loss of habitat from reduced flow is a primary threat to all of these species and the main reason that eight species have been listed, with three more proposed for listing, for protection under the federal ESA (Table 1-1). Spring flow loss is the combined result of naturally fluctuating rainfall patterns, regional pumping of groundwater, and the resulting intermittent drawdown of the Edwards Aquifer. Beyond reduced spring flow, other threats include increased competition and predation from invasive species, direct or indirect habitat destruction or modification by humans (e.g., recreational activities and reservoir construction), and other factors such as high nutrient loading and bank erosion that negatively affect water quality (USFWS, 1996). Invasive species of concern include the Asian trematode Centrocestus formosanus, a parasite that attaches to fish’s gill filaments, including fountain darters; the giant ramshorn snail, which grazes on aquatic plants and could negatively impact fountain darter habitat during low flow conditions; non-native fish such as tilapia and suckermouth catfish; and

TABLE 1-1 Common and Scientific Names of Species Proposed for Coverage under the Edwards Aquifer Habitat Conservation Plan and Their Status According to the Endangered Species Act

Common Name Scientific Name ESA Status
Fountain Darter Etheostoma fonticola Endangered
Comal Springs Riffle Beetle Heterelmis comalensis Endangered
San Marcos Gambusia Gambusia georgei Endangered
Comal Springs Dryopid Beetle Stygoparnus comalensis Endangered
Peck’s Cave Amphipod Stygobromus pecki Endangered
Texas Wild Rice Zizania texana Endangered
Texas Blind Salamander Eurycea rathbuni Endangered
San Marcos Salamander Eurycea nana Threatened
Edwards Aquifer Diving Beetle Haideoporus texanus Petitioned*
Comal Springs Salamander Eurycea sp. Petitioned**
Texas Troglobitic Water Slater Lirceolus smithii Petitioned

*Listed as under review by the USFWS.

**Listed as undefined status by the USFWS.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

non-native plants, three of which—Hydrilla verticillata, Hygrophila polysperma, and Colocasia esculenta—have significantly altered both the Comal and San Marcos ecosystems.

OVERVIEW OF THE ENDANGERED SPECIES ACT

Congress enacted the current ESA in 1973 to replace several precursor statutes. According to the U.S. Supreme Court in its 1978 decision in Tennessee Valley Authority v. Hill, 437 U.S. 153, 174, 184 (1978), “the language, history, and structure of the [ESA] indicates beyond doubt that Congress intended endangered species to be afforded the highest of priorities,” and “[t]he plain intent of Congress in enacting this statute was to halt and reverse the trend toward species extinction, whatever the cost.”

There are four operative provisions of the ESA that are relevant to the Edwards Aquifer. First, Section 4, 16 U.S.C. § 1533, governs the listing of species and the establishment of their critical habitat. Until either the U.S. Fish and Wildlife Service (FWS) or the National Marine Fisheries Service formally lists a species for protection pursuant to Section 4, that species receives no federal protection. All of the Edwards Aquifer ESA-listed species were listed under the FWS’s jurisdiction.

Second, once a species is listed, it is protected from federal agency actions that might affect its continued survival. Under Section 7, 16 U.S.C. § 1536, federal agencies must consult regarding listed species; must use their discretionary authorities to conserve listed species; and cannot engage in, fund, or authorize/license/permit activities that will either jeopardize the continued existence of listed species or damage or destroy a listed species’ critical habitat—that is, the designated habitat that the species requires to survive and to recover.

Third, under Section 9, 16 U.S.C. § 1538, endangered species are protected from individual actions that could hurt both members of the species and the species as a whole. Unlike Section 7, Section 9 applies to everyone. It prohibits most trade and commerce in endangered species. In addition, and more importantly for the Edwards Aquifer, with respect to endangered species of fish and wildlife, Section 9 prohibits the “take” of such species, which the ESA defines to mean “harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or collect, or to attempt to engage in any such conduct” (16 U.S.C. § 1532(9)). With regard to endangered species of plants, like Texas wild rice, Section 9 makes it illegal to “remove and reduce to possession any such species from areas under Federal jurisdiction; maliciously damage or destroy any such species on any such area; or remove, cut, dig up, or damage or destroy any such species on any other area in knowing violation of any law or regulation of any State or in the course of any violation of a State criminal trespass law” (16 U.S.C. § 1538(a)(2)(B)). Through

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

a default regulation, threatened species receive all of the same protections that endangered species do unless the relevant Service promulgates a special regulation for a specific threatened species.

Fourth, both federal agencies and private entities can receive exemptions from Section 9 “take” liability. For federal agencies, the relevant Service can issue an Incidental Take Statement during a Section 7(a)(2) consultation, authorizing a limited number of incidental “takes” in the course of an activity that the agency is conducting, funding, or permitting. In turn, private individuals and entities and non-federal governments can acquire, pursuant to Section 10, 16 U.S.C. § 1539, a variety of different permits that allow activities that would otherwise violate the Section 9 take prohibition. The most important of these is the Incidental Take Permit [16 U.S.C. § 1539(a)], which is the permit that the EAA sought with respect to the ESA-listed Edwards Aquifer species.

In order to receive an Incidental Take Permit (ITP), the applicant must, inter alia, develop a Habitat Conservation Plan (HCP). Thus, it is Section 10 that governs the Edwards Aquifer Authority’s ITP and HCP.

THE EDWARDS AQUIFER AUTHORITY AND THE HABITAT CONSERVATION PLAN

The Edwards Aquifer ESA-listed species have been the subject of litigation since at least 1991. For example, one lawsuit, Sierra Club v. Glickman, 156 F.3d 606 (5th Cir. 1998), alleged that the U.S. Department of Agriculture was violating Section 7 through its incentives to local agriculture. Another lawsuit, Sierra Club v. City of San Antonio, 112 F.3d 789, 791-92 (5th Cir. 1997), alleged that the City’s pumping of the aquifer causes Section 9 takes at the springs. Yet another lawsuit, Shields v. Babbitt, 229 F. Supp. 2d 638, 646-47 (W.D. Tex. 2000), alleged that other individual groundwater pumpers were causing Section 9 takes of the Edwards Aquifer ESA-listed species.

The EAA came into being as a result of Sierra Club v. Lujan, No. MO-91-CA-069, 1993 WL 151353 (W.D. Tex. Feb. 1, 1993), which the Sierra Club filed in 1991 against the U.S. Department of the Interior (which houses the FWS). In its 1993 decision resolving this case, the U.S. District Court for the Western District of Texas threatened to effectively federalize management of the Edwards Aquifer unless the State of Texas regulated withdrawals from the aquifer in compliance with the ESA (Sierra Club *33-*35). To avoid federal regulation of the aquifer (Bennett, 2012; Miles, 1997), the Texas Legislature enacted the Edwards Aquifer Authority Act in 1993, which the Texas Supreme Court unanimously upheld as facially constitutional in 1996 in Barshop v. Medina County Underground Water Conservation District, 925 S.W.2d 618, 623 (Tex. 1996).

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

The Edwards Aquifer Authority Act created the EAA, which regulates groundwater withdrawals from the Edwards Aquifer. Specifically:

“The Act imposes an aquifer-wide cap on water withdrawals by nonexempt wells of 450,000 acre-feet of water per year through the year 2007 and 400,000 acre-feet per year thereafter. The Authority can increase the withdrawal caps if it determines that additional water supplies are safely available from the aquifer. The Authority will allocate these caps among wells by a permit system. However, all wells producing no more than 25,000 gallons of water a day for domestic or livestock purposes are exempt from the permit system and the caps. This exemption allows all landowners, except those within or serving a platted subdivision, to drill wells for household purposes, watering animals, or irrigating a family garden.”

(Barshop 624 n.2). While the permitting program gives preference to existing users of water from the Edwards Aquifer, it also allows the Authority to reduce those established uses (Barshop 624 n.2).

Then-existing water users who have either been denied permits or been issued permits to pump reduced amounts of water from the Edwards Aquifer have sued continuously to stop implementation of the Edwards Aquifer Authority Act. These lawsuits include, for example, Edwards Aquifer Authority v. Bragg, 21 S.W.3d 375 (Tex. App. 2000); Bragg v. Edwards Aquifer Authority, 71 S.W.3d 729 (Tex. 2002); Edwards Aquifer Authority v. Peavy Ranch, 199 S.W.3d 312 (Tex. App. 2006); Edwards Aquifer Authority v. Chemical Lime, Ltd., 212 S.W.3d 683 (Tex. App. 2006), rev’d, 291 S.W.3d 392 (Tex. 2009); In re Edwards Aquifer Authority, 217 S.W.3d 581 (Tex. App. 2006); and Edwards Aquifer Authority v. Day, 274 S.W.2d 742 (Tex. App. 2008), aff’d, 369 S.W.3d 814 (Tex. 2012). While the Authority has continued since 1996 to issue groundwater permits, the Texas Court of Appeals in August 2013 deemed the Authority’s permits limiting historical pumping to be an unconstitutional taking without compensation of landowners’ rights to groundwater (Edwards Aquifer Authority v. Bragg, No. 04-11-00018-CV, 2013 WL 4535935, Tex. App. Aug. 28, 2013). The court amended its opinion—but not its conclusion—in November 2013 in Edwards Aquifer Auth. v. Bragg, No. 04-11-00018-CV, 2013 WL 5989430, at *14–15 (Tex. App. Nov. 13, 2013; “Bragg decision”). If upheld on appeal, this decision has potentially significant financial and legal implications for the viability of the Edwards Aquifer permitting system and hence for the Edwards Aquifer HCP.

The Incidental Take Permit and Habitat Conservation Plan

Despite litigation over the groundwater permitting program, the EAA and several other entities pursued an ESA Section 10 ITP to limit their

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

potential Section 9 liability for permitting the continued pumping and use of Edwards Aquifer water. The ITP application process, as noted, required an HCP. Importantly, given the potential conflict between the ESA’s requirements to protect threatened and endangered species endemic to the Edwards Aquifer and its primary springs and the region’s reliance on the Edwards Aquifer for its freshwater needs, it took years and the involvement of many parties to craft the approved HCP.

In 2006, FWS issued an invitation to stakeholders in the Edwards Aquifer region to collaborate in a voluntary effort to contribute to the recovery of threatened and endangered species in the Edwards Aquifer region (USFWS, 2012), an initiative that came to be known as the Edwards Aquifer Recovery Implementation Program. In 2007, the Texas Legislature directed the EAA, the City of San Antonio acting through the San Antonio Water System, the City of San Marcos, the City of New Braunfels, and Texas State University to participate in the Edwards Aquifer Recovery Implementation Program and to develop a plan for managing the Edwards Aquifer in a manner that would protect and conserve the federally listed species in the event of conditions similar to the drought of record. In January 2012, the Edwards Aquifer Recovery Implementation Program submitted the Edwards Aquifer HCP to be used in support of an ITP application to the FWS.

FWS granted the ITP on March 18, 2013 (USFWS, 2014). The permit will last 15 years, until March 31, 2028. The five official Permittees are the EAA; the City of San Antonio, acting through the San Antonio Water System; the City of San Marcos; the City of New Braunfels; and Texas State University. The ITP allows incidental take for the 11 covered species as detailed in Table 1-2. Importantly, although the HCP supports the FWS’s decision to issue the Section 10 Edwards Aquifer ITP, legally it is compliance with the ITP that insulates the EAA and other Permittees from liability under ESA Section 9.

While the subject of monitoring incidental take in the Edwards Aquifer system is not this Committee’s main charge, the Committee nevertheless notes that the numerical incidental take allowances in the ITP (Table 1-2) are unrealistically precise. It is not clear that the EAA could meaningfully monitor incidental take, such as from human-induced habitat modification. Nevertheless, total incidental take could become important to other EAA implementation activities because while maintaining the HCP’s required minimum flows constitutes compliance with some of the ITP’s incidental take allowances, that is not true for all of them, and the ITP’s take limits take priority over HCP implementation (ITP, p. 1, ¶ E).

A timeline of important events in the creation of the HCP for the Edwards Aquifer is shown in Table 1-3.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

TABLE 1-2 Allowances under the Edwards Aquifer Incidental Take Permit

SPECIES INCIDENTAL TAKE ALLOWED
(over 15 years)
Fountain Darter 797,000 in Comal system; 549,129 in San Marcos system
San Marcos Gambusia Presumed extinct, but otherwise judged by implementation of the HCP.
Comal Springs Dryopid Beetle 1,543
Comal Springs Riffle Beetle 11,179
Peck’s Cave Amphipod 18,224
Texas Wild Rice Plant; different standards.
Texas Blind Salamander 10
San Marcos Salamander 263,857
Texas Cave Diving Beetle Judged by minimum flow requirements
Comal Springs Salamander Judged by minimum flow requirements
Texas Troglobitic Water Slater Judged by minimum flow requirements

Species Covered by the HCP

The HCP applies to 11 Edwards Aquifer species—the eight already listed under the federal ESA and three others that have been proposed for listing (Table 1-1). The Permittees considered extending the HCP to an additional 34 species, based on the following criteria: (1) the likelihood that the species would be listed during the permit term; (2) the possible effect of HCP Covered Activities2 on the species; (3) the status of knowledge about the species (in relation to meeting permit issuance criteria regarding demonstrating the link between the Covered Activities and take); and (4) potential problems with implementation of the HCP regarding requirements by the species. Thirteen of these species are listed in Table 1-4; the HCP did not identify the other 21 species that the applicants considered.

Species were eliminated for coverage for a variety of reasons. For example, the Permittees decided not to have the HCP cover the Mimic Cavesnail,

_____________

2 Covered Activities refer to four categories of activities that may result in incidental take of endangered fish and wildlife: (1) the regulation and use of the aquifer; (2) recreational activities in the Comal and San Marcos spring and river ecosystems; (3) other activities in, and related to, the Comal and San Marcos spring and river ecosystems; and (4) activities involved in and related to the implementation of the minimization and mitigation measures in these ecosystems.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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TABLE 1-3 Timeline of Important Events for the Edwards Aquifer Habitat Conservation Plan

1950s Drought of record in Edwards Aquifer region, which now provides the benchmark for the HCP.
June 13, 1956 Comal Springs stops flowing for the first time in recorded history.
1959 Texas legislature forms Edwards Underground Water District in response to the drought.
March 11, 1967 U.S. FWS lists the Texas blind salamander as an endangered species under a precursor statute to the current ESA.
Oct. 13, 1970 U.S. FWS lists the fountain darter as an endangered species under a precursor statute to the current ESA.
1973 Congress enacts the federal Endangered Species Act (ESA).
May 27, 1978 U.S. FWS lists Texas wild rice as an endangered species under the ESA.
July 14, 1980 U.S. FWS lists the San Marcos gambusia as an endangered species and the San Marcos salamander as a threatened species under the ESA.
1984 ESA petition filed to list the Edwards Aquifer diving beetle.
1991 Sierra Club files Sierra Club v. Lujan, alleging that the U.S. FWS has failed to protect ESA-listed species in the Edwards Aquifer region.
Feb. 1, 1993 The U.S. District Court for the Western District of Texas decides Sierra Club v. Lujan, finding a violation of the ESA and threatening to federalize management of the Edwards Aquifer if the Texas Legislature does not act.
1993 Texas Legislature enacts the Edwards Aquifer Authority (EAA) Act, creating the EAA and a permit system for water withdrawals from the aquifer.
1996 Texas Supreme Court upholds the EAA Act as facially constitutional.
Dec. 18, 1997 U.S. FWS lists the Comal Springs riffle beetle, the Comal Springs dryopid beetle, and the Peck’s Cave amphipod as endangered species under the ESA.
2006 U.S. FWS invites interested parties to discuss approaches to the challenges of aquifer management to balance the region’s water needs with those of listed species. This leads to the Edwards Aquifer Recovery Implementation Program.
2012 Texas Supreme Court decides Edwards Aquifer Authority v. Day, concluding that landowners along the Edwards Aquifer have a property right to the aquifer’s groundwater in situ.
Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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Feb. 15, 2013 U.S. FWS approves the Edwards Aquifer Incidental Take Permit and its HCP.
March 18, 2013 Edwards Aquifer ITP and HCP take effect. Phase I begins.
Aug. 2013 Texas Court of Appeals decides Edwards Aquifer Authority v. Bragg, concluding that the implementation of the Edwards Aquifer permit program effectuated a constitutional “taking” of landowners’ property rights in groundwater.
Jan. 2014 Natural Research Council Committee to Review the Edwards Aquifer Habitat Conservation Plan is constituted.
March 2020 Phase I of the HCP scheduled to end. Phase II, utilizing adaptive management, scheduled to begin.
March 31, 2028 The current Edwards Aquifer ITP and HCP will expire.

the salamander Eurycea robusta, and two catfishes because they exist only in the deeper portions of the aquifer. The Permittees concluded that the HCP activities, which would affect only the “top” of the aquifer, would not directly affect these species. The Permittees excluded the six mussel species in Table 1-4 because these species do not occur in the headwaters of the Comal and San Marcos Springs. Similarly, the two salamanders Eurycea tridentifera and Eurycea neotenes do not occur in Comal or San Marcos Springs. The whooping crane, which overwinters far downstream in the river system near Aransas National Wildlife Refuge, was not included for coverage under the HCP because the Permittees believed that: (1) factors affecting the crane and its habitat are not under the control of the EAA and its partners and (2) whooping cranes would not be affected adversely by the Covered Activities (EARIP, 2012). This issue is revisited in the final chapter of this report.

The Role of Indicator Species under the HCP

Rather than attempting to devise an HCP that would address all 11 covered species individually, the HCP identifies three indicator species—the fountain darter, the Comal Springs riffle beetle, and Texas wild rice—to represent all covered species. The HCP assumes that all of its habitat minimization and mitigation measures for these three species will be sufficient to protect all covered species (EARIP, 2012). In addition, the use of indicator species potentially reduces the cost of implementing activities to minimize species impacts and of implementing mitigation measures, as well as the costs and time-consuming efforts associated with processing individual incidental take permits (USFWS, 2013).

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

TABLE 1-4 Common and Scientific Names and ESA Status of Species Considered but Not Proposed for Coverage in the Edwards Aquifer HCP

Common Name Scientific Name ESA Status
Mimic Cavesnail Phreatodrobia imitate Under review
Blanco Blind Salamander Eurycea robusta Not listed*
Comal Blind Salamander Eurycea tridentifera Under review
Texas Salamander Eurycea neotenes Under review
Toothless Blindcat Trogloglanis pattersoni Under review
Widemouth Blindcat Satan eurystomus Under review
Whooping Crane Grus americana Endangered
Texas Fatmucket Lamspilis bracteata Candidate
Golden Orb Quadrula aurea Candidate
Texas Pimpleback Quadrula petrina Candidate
False Spike Mussel Quincuncina mitchelli Under review
Salina Mucket Disconaias salinasensis Not listed**
Mexican Fawnsfoot Truncilla cognata Under review

*Threatened status as determined by the Texas Parks and Wildlife Department.

**Endangered status as determined by the International Union for Conservation of Nature.

The fountain darter (Etheostoma fonticola) is a subtropical, benthic freshwater fish of the family Percidae that was federally listed as an endangered species in 1970 (USFWS, 1970). First documented and described in 1886 by Jordan and Gilbert, fountain darters are found only in the San Marcos and Comal Springs and their effluent rivers (Guadalupe River system) in south central Texas (Page and Burr, 1991). Fountain darters are small (maximum total length of about 4.3 cm) and inhabit clear, clean, flowing, and thermally constant waters with undisturbed sand and gravel substrates, rock outcrops, and areas of submerged vegetation (algae, moss, vascular plants) for cover (EARIP, 2012). They generally eat small aquatic invertebrates, such as copepods, aquatic insect larvae, and amphipods (EARIP, 2012).

The Comal Springs riffle beetle (Heterelmis comalensis) is a small (~0.2 cm), flightless member of the Elmidae, native to the headwaters of the Comal and San Marcos Rivers (Bosse et al., 1988). It was listed under the ESA as an endangered species in 1997, along with two other co-occurring invertebrates, the Comal Springs dryopid beetle (Stygoparnus comalensis) and Peck’s Cave amphipod (USFWS, 1997). Both immature and adult Comal Springs riffle beetles are aquatic. The adults are known to feed

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

primarily on algae and detritus scraped from submerged weeds and rocks (EARIP, 2012), and larval food resources are likely to be similar but have not been documented. Comal Springs riffle beetles are found in flowing waters of the spring runs, as well as in spring flow areas along the Landa Lake shoreline and in spring flow upwelling areas in the lake (BIO-WEST, 2002). In 2007, the FWS designated 19.8 acres of the Comal Springs complex and 10.5 acres of the San Marcos Springs complex as critical habitat for Comal Springs riffle beetles, dryopid beetles, and Peck’s Cave amphipod (USFWS, 2007).

Texas wild rice (Zizania texana) is an aquatic perennial grass from the family Poaceae. It was originally collected in 1892, described in 1932 as southern wild rice (Z. aquatica), recognized as a new species in 1933 by W. A. Silveus, and re-described by A. C. Hitchcock in 1933 (EARIP, 2012). Texas wild rice is an aquatic, monoecious, perennial macrophyte. It is found growing and submerged primarily at a depth of one meter or less in swift moving, shallow areas of the San Marcos River. Flowering typically occurs in the spring and fall but may be seen throughout the year because of the constant water temperatures in the Edwards Aquifer system. Texas wild rice also reproduces vegetatively by stolons and appears to reestablish readily when uprooted and relocated during flood events (EARIP, 2012).

Other Covered Species

The Comal Springs dryopid beetle (Stygoparnus comalensis) is subterranean species inhabiting the Comal Springs system that was listed as endangered in 1997 (USFWS, 1997). Comal Springs dryopid beetles are small (~3mm), slender, reddish-brown beetles restricted to the headwaters of the springs and spring upwelling areas (EARIP, 2012).

Peck’s Cave amphipod (Stygobromus pecki), also a subterranean species found in the Comal and Hueco Springs, was first described using specimens collected from Comal Springs in 1964 and 1965 (Holsinger, 1967). The Peck’s Cave amphipod was listed as endangered in 1997 (USFWS, 1997). Like all members of the genus Stygobromus, Peck’s Cave amphipods are eyeless, unpigmented, and approximately 3 mm long. Like the Comal Springs dryopid beetle, the Peck’s Cave amphipod appears to be restricted to the headwaters of the springs and spring upwelling areas (EARIP, 2012).

The San Marcos salamander (Eurycea nana) is a member of the plethodontid lungless salamanders (Bishop, 1943). San Marcos salamanders are known only from a pool at the source of the San Marcos River (San Marcos Springs, Spring Lake) and a short distance downstream (Chippindale et al., 2000) and have been listed as threatened since 1980. San Marcos salamanders are small (maximum length of about 58 mm), slender, and light brown in color. They are found in Spring Lake in rocky areas around spring open-

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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ings and downstream of the dam at Spring Lake (Tupa and Davis, 1976; Nelson, 1993).

The Texas blind salamander (Eurycea rathbuni) is a smooth, unpigmented subterranean species found only in San Marcos Springs (Longley, 1978). It has a maximum length of about 120 mm, a large and broad head, reduced eyes (two small dark spots beneath the skin), long and slender limbs, four toes on the forelegs and five on the hind legs. As evidenced by the presence of juveniles year round, the Texas blind salamander appears to be sexually active throughout the year because of the thermally constant waters of the Edwards Aquifer (EARIP, 2012).

The Edwards Aquifer diving beetle (Haideoporus texanus), Comal Springs salamander (Eurycea sp.), and Texas troglobitic water slater (Lirceolus smithii) are not presently listed under the federal ESA, but petitions to list them have been filed with the FWS. The Edwards Aquifer diving beetle, also known as the Texas cave diving beetle, is a small (typically less than 13 mm), elongate, oval-shaped and somewhat flattened member of the family Dytiscidae (Young and Longley, 1976). This species is restricted to the subterranean waters of the Edwards Aquifer in Hays and Comal counties, where it has been collected from artesian wells and from Comal Springs (EARIP, 2012). Little is known of the Comal Springs salamander, which exists as a single population in the Comal Springs and has been the subject of systematic debate since the 1970s. The Texas troglobitic water slater is a small, blind, non-pigmented asellid isopod (Bowman and Longley, 1975). This species is known from two localities in Hays County—San Marcos Springs (Diversion Springs) and the artesian well that is located very close to San Marcos Springs. Specimens are rarely collected (EARIP, 2012).

Covered Activities Under the HCP

As ESA Section 10 requires, the Edwards Aquifer HCP specifies the steps that the EAA and other Permittees will take to minimize and mitigate the incidental take of ESA-listed species associated with the Covered Activities (e.g., permitted water withdrawals for drinking water supply, agriculture, and other purposes, and recreation). The Permittees will implement the HCP in two phases (Phase I is the first 7 years, followed by Phase II for the remainder of the permit). During the first phase, they will put in place habitat minimization and mitigation measures to maintain continuous minimum spring flow during a repeat of the drought of record. The minimization and mitigation measures fall roughly into two categories (see Box 1-1).

First, there are four spring flow protection measures designed to provide additional water during drought periods. These include critical period management, regional water conservation, a voluntary irrigation suspension program, and aquifer storage and recovery. Critical period manage-

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

ment refers to reductions in permitted discharges when the spring flow at Comal Springs and well levels at J-17 fall below certain levels. The HCP instituted a new stage, Stage V, which would mandate reductions in pumping of 44 percent. The second measure builds upon the demand management already being conducted by the City of San Antonio. It is envisioned that new municipal conservation activities can save approximately 10,000 acre-feet/year. The third item, the voluntary irrigation suspension program option (VISPO), targets the 30 percent of annual Edwards Aquifer pumping that is withdrawn for irrigation. VISPO relies on permitted irrigators relinquishing their pumping rights when well levels and spring flows drop below certain triggers; it is intended to conserve another 40,000 acre-feet/year. Finally, the San Antonio Water System (SAWS) runs an aquifer storage and recovery (ASR) operation in the Carrizo Aquifer that will be expanded and is predicted to make the greatest contribution to overall Edwards Aquifer water savings (as much as 100,000 acre-feet/year).

As the largest retail water agency that pumps water from the Edwards Aquifer, SAWS has taken steps to develop additional supplies that are not dependent upon the Edwards Aquifer and are separate from the HCP. By developing these supplies, SAWS reduces San Antonio’s reliance on the Edwards Aquifer, particularly during times of drought. Additional water supplies being developed by SAWS include brackish groundwater from the Wilcox Aquifer, recycled water, and the Vista Ridge Pipeline (http://www.saws.org/Your_Water/WaterResources/projects/; accessed 10-27-2014). SAWS is developing a desalination facility to produce 13,400 acre-feet/year from brackish groundwater in the Wilcox Aquifer in southern Bexar County. The desalination facility could be expanded in future phases to produce up to 33,600 acre-feet/year. SAWS has developed a recycled water system capable of providing up to 25,000 acre-feet/year. Recycled water is supplied for irrigation and industrial uses and to supplement flows in the San Antonio River and Salado Creek. SAWS approved the Vista Ridge Pipeline Project in October 2014, and it is projected to provide water to San Antonio by year 2020. The project includes 142 miles of pipeline to provide San Antonio up to 50,000 acre-feet/year of groundwater pumped from the Carrizo Aquifer in Burleson County.

Second, beyond spring flow protection measures there are a variety of minimization and mitigation measures designed to maintain and restore the habitat of ESA-listed species at both Comal and San Marcos Springs (see Box 1-1). These measures include such activities as riparian zone restoration, removal of invasive plant species, replanting of native species, management of recreational activity, pollution prevention, and public education.

Phase II of the HCP adds the possibility of adaptive management. More specifically, the Permittees will continue to implement all of the Phase I measures throughout the 15-year permit term unless information developed

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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Box 1-1
Minimization and Mitigation Measures (M&M) in the Habitat Conservation Plan Modified from EARIP, 2012

Numbers in parentheses indicate the HCP Section
where the activity is described.
Note that all 38 activities are line items in the HCP budget.

Flow Protection Measures

  1. Critical Period Management Stage V (5.1.4)
  2. Use of SAWS Aquifer Storage and Recovery (ASR) for spring flow protection trade off (5.5.1)
  3. Regional Water Conservation Program (5.1.3)
  4. Voluntary Irrigation Suspension Program Option (5.1.2)

M&M measures specific to San Marcos Springs

  1. Texas wild rice enhancement and restoration (5.3.1 and 5.4.1)
  2. Sediment removal in Sewell Park (5.3.6 and 5.4.4)
  3. Aquatic vegetation restoration (non-native removal, native reestablishment) (5.3.8, 5.4.3, 5.4.12)
  4. Management of floating vegetation mats and litter removal (5.3.3 and 5.4.3)
  5. Non-native animal species control (5.3.5. 5.3.9, 5.4.11, 5.4.13)
  6. Sessom Creek sand bar removal (5.4.6)
  7. Low impact development/best management practices (BMPs) (5.7.3)
  8. Recreation control in key areas (5.3.2, 5.4.2)
  9. Restoration of riparian zone with native vegetation (5.7.1)
  10. Bank stabilization/permanent access points (5.3.7)
  11. Biomonitoring (6.3.1)
  12. Water quality monitoring and protection (5.7.2, 5.7.6)
  13. Household hazardous waste program (5.7.5)
  14. Other measures
  1. Management of public recreational use (5.3.2.1)
  2. Prohibition of hazardous materials route (5.3.4)
  3. Diversion of surface water (5.4.5)
  4. Diving classes in Spring Lake (5.4.7)

during Phase I indicates that they should implement additional or alternate measures during Phase II as part of a formal adaptive management process (EARIP, 2012). The Permittees expect that some of the initial minimization and mitigation measures will require modification after 7 years because of the current uncertainty associated with both their hydrologic and ecological models and to incorporate knowledge gained during Phase I.

Several of the minimization and mitigation measures found in Box 1-1

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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  1. Creation of scientific areas (5.6)
  2. Research programs in Spring Lake (5.4.8)
  3. Boating in Spring Lake and Sewell Park (5.3.10)
  4. Septic system registration and permitting program (5.7.3)
  5. Management of golf course grounds (5.4.9)

M&M measures specific to Comal Springs

  1. Old Channel Environmental Restoration and Protection Area (ERPA) (5.2.2.1)
  2. Flow-split management (5.2.1)
  3. Landa Lake and Comal River aquatic vegetation restoration/maintenance (5.2.2 except 5.2.2.1)
  4. Non-native animal species control (5.2.5, 5.2.9)
  5. Decaying vegetation removal program (5.2.4)
  6. Riparian improvements and sediment removal specific to the Comal Springs riffle beetle (5.2.8)
  7. Gill parasite control and non-native snail removal program including optimization research (5.2.6)
  8. Restoration of riparian zone with native vegetation (5.7.1)
  9. Prohibition of hazardous materials route (5.2.7)
  10. BMPs for stormwater control (5.7.6)
  11. Incentive program for Low Impact Development (LID) (5.7.6)
  12. Biomonitoring (6.3.1)
  13. Water quality monitoring (5.7.4)
  14. Household hazardous waste program (5.7.5)
  15. Other measures
  1. Creation of state scientific areas (5.6)
  2. Management of public recreational use (5.2.3)

Measures for both systems

  1. Development of a mechanistic ecological model (6.6.3)
  2. Applied environmental research at the FWS National Fish Hatchery and Training Center (6.3.4)
  3. Science Review Panel
  4. Improve Groundwater Model
  5. National Fish Hatchery and Training Center Refugia (5.1.1)

are specifically intended to provide information that will feed into the formal adaptive management process separating Phase I from Phase II. In particular, the EAA is conducting extensive water quality and biological monitoring of the aquifer and spring systems to gather baseline information, document trends, and eventually determine whether HCP minimization and mitigation measures are leading to species recovery. Biological monitoring of the Comal and San Marcos Spring systems has been in place

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

since 2000 and focuses on the full suite of ESA-listed species as well as SAV. Water quality monitoring began much earlier and encompasses the aquifer, the springs, sediments, and the river systems downstream.

A second major activity that the EAA expects will provide the basis for adaptive management is improving the groundwater hydrologic model for the Edwards Aquifer. Two parallel efforts are ongoing: (1) updating the existing USGS MODFLOW model of the aquifer, which uses a finite difference code, and (2) creating a new finite element model of the aquifer. According to the HCP, the creation of two models, both of which can be adapted for karst terrain, is expected to help quantify the uncertainty associated with groundwater modeling. Along with model development, the EAA has also undertaken the refinement of the conceptual model of the Edwards Aquifer, including a better understanding of recharge and discharge.

A third major activity specified in the HCP is the creation of predictive ecological models for Comal and San Marcos Springs. Although the HCP does not say specifically what models should be pursued for what organisms, the EAA’s initial efforts are focusing on mechanistic models for the fountain darter, SAV (which is prime fountain darter habitat and could eventually be useful for modeling Texas wild rice), and Comal Springs riffle beetle. These efforts are meant to build upon the HCP’s habitat suitability analyses, which led to the current minimum recommended spring flows at Comal and San Marcos Springs to maintain viable populations of the ESA-listed species. A major goal of the ecological modeling is to more accurately establish threshold levels for these taxa and associated species relative to potential environmental stressors, such as a reduction in spring flow. Another goal of the ecological modeling is to be able to predict the long-term effects of the Covered Activities on these species.

Finally, the HCP created an Applied Research Program to fund individual research projects to study the ecological dynamics within the Comal and San Marcos Spring systems. The goals of these year-long projects are to inform the ecological modeling program and also to fill gaps in knowledge about the various species. Given the EAA’s Aquifer Science Research Program and the more advanced state of hydrologic modeling, the Applied Research Program has focused exclusively on ecological topics.

The budget for the HCP varies between $15-20 million per year over its 15-year tenure (see Chapter 7 of EARIP, 2012).

THE EAA REQUESTED STUDY

In late 2013, the EAA formally requested the involvement of the National Research Council (NRC) to provide advice on the many different scientific initiatives under way to support the HCP. An expert committee of the NRC was asked to focus on the adequacy of the scientific informa-

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
×

tion being used to, for example, (1) set biological goals and objectives, (2) determine what minimization and mitigation measures to use and their effectiveness, and (3) make decisions about the transition from Phase I to Phase II of the HCP. The NRC will conduct its study from 2014 to 2018 and produce three reports. Box 1-2 gives the Statement of Task for this first report.

As Box 1-2 indicates, this report focuses on improving modeling efforts for the Edwards Aquifer. Subsequent NRC reports will review the performance of minimization and mitigation measures, including the four spring flow protection measures, as well as the adequacy of the biological goals and objectives to protect the endangered species.

Report Roadmap

Chapter 2 of this report addresses the hydrologic modeling being conducted by the EAA and their contractors. It reviews both the updates to

Box 1-2
Review of the Edwards Aquifer Habitat Conservation Program—Phase 1 Statement of Task

A committee of the National Research Council will review and provide advice on four scientific initiatives within the Edwards Aquifer Habitat Conservation Program (EAHCP): (1) ecological modeling, (2) hydrologic modeling, (3) biological and water quality monitoring programs, and (4) applied research. The committee’s report will address:

  • hydrologic and ecological modeling approaches,
  • accuracy and reliability of the assumptions used to support development of both conceptual and quantitative models,
  • adequacy of data for model calibration and verification,
  • identification and description of uncertainties,
  • additional monitoring data needs,
  • additional research needs, and
  • other issues deemed relevant by the committee.

In addition, the committee will assess the sufficiency of the modeling, research, and monitoring under development to support the EAHCP Phase II strategic decisions and questions regarding relationships among conservation measures, biological objectives, and biological goals.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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the MODFLOW model and the creation of the finite element model, and it discusses changes to the conceptual model of the aquifer and improvements to estimating recharge—two issues that could impact both models. The chapter ends with a consideration of uncertainty in groundwater modeling and the identification of knowledge gaps. This and all subsequent chapters reflect consideration of EAA reports through November 2014.

Chapter 3 describes the state of ecological modeling for Comal and San Marcos Springs, focusing on the initial modeling efforts for the fountain darter, SAV, Texas wild rice, and the Comal Springs riffle beetle. It reviews the HCP’s habitat suitability analyses, which have led to the creation of minimum spring flow requirements in the HCP to maintain the ESA-listed species. It then turns to the development of the new ecological models for the fountain darter and SAV.

Chapter 4 delves more deeply into both the comprehensive water quality monitoring program and biomonitoring program. It considers the adequacy of the biomonitoring program to provide the necessary data and information for the mechanistic ecological models and makes recommendations for what should continue to be sampled as the HCP moves forward.

Chapter 5 critiques the Applied Research Program, which is populated with short-term research projects that are intended to either inform the ecological modeling or fill critical information gaps.

The final chapter tackles overarching issues, such as the need for data management within the HCP, the benefits of taking a more holistic ecosystems approach, and planning for worst-case scenarios.

It should be noted that each chapter ends with conclusions and recommendations that synthesize more technical and specific statements found within the body of each chapter. The most important conclusions and recommendations are repeated in the report summary.

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BIO-WEST. 2002. Comal Springs riffle beetle habitat and population evaluation. Final Report. Prepared for Edwards Aquifer Authority, San Antonio, TX.

Bishop, S. C. 1943. A Handbook of Salamanders. The Salamanders of the United States, of Canada, and of Lower California. Comstock Publishing Company, Ithaca, New York.

Bosse, L. S., D. W. Tuff, and H. P. Brown. 1988. A new species of Heterelmis from Texas (Coleoptera: Elmidae). The Southwestern Naturalist 33:199-203.

Bowman, T. E., and G. Longley. 1975. Redescription and assignment to the new genus Lirceolus of the Texas troglobitic water slater, Asellus smithii (Ulrich) (Crustacea: Isopoda: Asellidae). Proceedings of the Biological Society of Washington 88:489-496.

Chippindale, P. T., A. H. Price, J. J. Wiens, and D. M. Hillis. 2000. Phylogenetic relationships and systematic revision of central Texas hemidactyliine plethodontid salamanders. Herpetological Monographs 1-80.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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Holsinger, J. R. 1967. Systematics, speciation, and distribution of the subterranean amphipod genus Stygonectes (Gammaridae). Bull. U.S. Nat. Mus. 259:1-176.

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Johnson, S., G. Schindel, G. Veni, N. Hauwert, B. Hunt, B. Smith, and M. Gary. 2012. Tracing Groundwater Flowpaths in the Vicinity of San Marcos Springs, Texas. Edwards Aquifer Authority Report No. 12-01, 139 pp.

Klemt, W. B., T. R. Knowles, G. R. Elder, and T. W. Sieh. 1979. Ground-water resources and model applications for the Edwards (Balcones fault zone) aquifer in the San Antonio region. Texas Department of Water Resources Report 239.

Lindgren, R. J., A. R. Dutton, S. D. Hovorka, S. R. H. Worthington, and S. Painter. 2004. Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas. USGS Scientific Investigations Report 2004–5277, 143 pp.

Loáaiciga, H. A., D. R. Maidment, and J. B. Valdes. 2000. Climate change impacts in a regional karst aquifer, Texas, USA. Journal of Hydrology 227:173-194.

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Longley, G. 1995. The relationship between long term climate change and Edwards Aquifer levels, with an emphasis on droughts and spring flows. Paper delivered at the 24th Water for Texas Conference, Austin, TX.

Mace, R. E., and S. C. Wade. 2008. In hot water? How climate change may (or may not) affect the groundwater resources of Texas. Gulf Coast Association of Geological Societies Transactions 58:655-668.

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Ockerman, D. J. 2005. Simulation of streamflow and estimation of recharge to the Edwards Aquifer in the Hondo Creek, Verde Creek, and San Geronimo Creek watersheds, south-central Texas, 1951–2003. USGS Scientific Investigations Report 2005–5252, 37 pp.

Page, L. M., and B. M. Burr. 1991. A field guide to freshwater fishes of North America north of Mexico. Houghton Mifflin Company, Boston.

Scanlon, B., K. Keese, N. Bonal, N. Deeds, V. Kelley, and M. Litvak. 2005. Evapotranspiration estimates with emphasis on groundwater evapotranspiration in Texas. Prepared for the Texas Water Development Board, December, 2005, 54 pp. plus appendices.

Sharp, J. M., Jr., and J. L. Banner. 1997. The Edwards Aquifer: A resource in conflict. GSA Today 7(8):2-9.

Suggested Citation:"1 Introduction." National Research Council. 2015. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1. Washington, DC: The National Academies Press. doi: 10.17226/21699.
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Thorkildsen, D., and P. D. McElhaney. 1992. Model refinement and applications for the Edwards (Balcones fault zone) aquifer in the San Antonio region, Texas. Texas Water Development Board.

Tupa, D. D., and W. K. Davis. 1976. Population dynamics of the San Marcos, salamander Eurycea nana. Texas Journal of Science 27(1):179-195.

USFWS. 1970. 35 Fed. Reg. 16047-16048 (October 13, 1970). U.S. Fish and Wildlife Service.

USFWS. 1996. San Marcos and Comal Springs and associated aquatic ecosystems (revised) recovery plan. Department of Interior, Fish and Wildlife Service.

USFWS. 1997. 62 (243) Fed. Reg. 66295 (December 18, 1997). U.S. Fish and Wildlife Service.

USFWS. 2007. Part 3 Department of the Interior, Fish and Wildlife Service endangered and threatened wildlife and plants; designation of critical habitat for the Peck’s cave amphipod, Comal Springs dryopid beetle, and Comal Springs riffle beetle; final rule. 72 Fed. Reg. 39,247 (July 17, 2007). Federal Register Vol. 72 No. 136. U.S. Fish and Wildlife Service.

USFWS. 2012. Final Environmental Impact Statement: Edwards Aquifer Recovery Implementation Program Habitat Conservation Plan. Department of Interior. Fish and Wildlife Service.

USFWS. 2013. News Release: Service Approves Edwards Aquifer Recovery Implementation Program’s Incidental Take Permit. Department of Interior. Fish and Wildlife Service.

USFWS. 2014. Record of decision: Edwards Aquifer Recovery Implementation Program Habitat Conservation Plan: Issuance of an Incidental Take Permit for Federally Listed Threatened and Endangered Species in Texas. Department of Interior. Fish and Wildlife Service.

Young, F. N., and G. Longley. 1975. A new subterranean aquatic beetle from Texas (Coleoptera: Dytiscidae-Hydroporinae). Ann. Entomol. Soc. Amer. 69:787-792.

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The Edwards Aquifer in south-central Texas is the primary source of water for one of the fastest growing cities in the United States, San Antonio, and it also supplies irrigation water to thousands of farmers and livestock operators. It is also is the source water for several springs and rivers, including the two largest freshwater springs in Texas that form the San Marcos and Comal Rivers. The unique habitat afforded by these spring-fed rivers has led to the development of species that are found in no other locations on Earth. Due to the potential for variations in spring flow caused by both human and natural causes, these species are continuously at risk and have been recognized as endangered under the federal Endangered Species Act (ESA).

In an effort to manage the river systems and the aquifer that controls them, the Edwards Aquifer Authority and stakeholders have developed a Habitat Conservation Plan (HCP). The HCP seeks to effectively manage the river-aquifer system to ensure the viability of the ESA-listed species in the face of drought, population growth, and other threats to the aquifer. The National Research Council was asked to assist in this process by reviewing the activities around implementing the HCP. Review of the Edwards Aquifer Habitat Conservation Plan: Report 1 is the first stage of a three-stage study. This report reviews the scientific efforts that are being conducted to help build a better understanding of the river-aquifer system and its relationship to the ESA-listed species. These efforts, which include monitoring and modeling as well as research on key uncertainties in the system, are designed to build a better understanding of how best to manage and protect the system and the endangered species. Thus, the current report is focused specifically on a review of the hydrologic modeling, the ecological modeling, the water quality and biological monitoring, and the Applied Research Program. The fundamental question that Review of the Edwards Aquifer Habitat Conservation Plan: Report 1 addresses is whether the scientific initiatives appropriately address uncertainties and fill knowledge gaps in the river-aquifer system and the species of concern. It is hoped that the successful completion of these scientific initiatives will ultimately lead the Edwards Aquifer Authority to an improved understanding of how to manage the system and protect these species.

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