Misplaced Pages

#551448

87-745: Located in South Central Texas, the Edwards Aquifer encompasses an area of approximately 4,350 square miles (11,300 km) that extends into parts of 11 counties. The aquifer's boundaries begin at the groundwater divide in Kinney County, East of Brackettville, and extend Eastward through the San Antonio area and then Northeast where the aquifer boundary ends at the Leon River in Bell County. The aquifer

174-399: A well field in an aquifer with the aim to control the water table , the anisotropy is to be taken into account, otherwise the result may be erroneous. Because of their high porosity and permeability, sand and gravel aquifers have higher hydraulic conductivity than clay or unfractured granite aquifers. Sand or gravel aquifers would thus be easier to extract water from (e.g., using

261-517: A few geographical exceptions. Groundwater conservation plans are required for permit holders who withdraw more than 3 acre-feet per year (2,700 U.S. gal/d; 10 kL/d), unless irrigators can prove more than 60 percent efficiency in their water use. Conservation plans require the use of Best Management Practices, as determined by the Edwards Aquifer Authority. Balcones Fault The Balcones Fault or Balcones Fault Zone

348-445: A pumping well ) because of their high transmissivity, compared to clay or unfractured bedrock aquifers. Hydraulic conductivity has units with dimensions of length per time (e.g., m/s, ft/day and ( gal /day)/ft ); transmissivity then has units with dimensions of length squared per time. The following table gives some typical ranges (illustrating the many orders of magnitude which are likely) for K values. Hydraulic conductivity ( K )

435-472: A short period of time (hours to days). Aquifers can be easily contaminated when pollutants enter the recharge zone. Because of this vulnerability to contamination, organizations have formed to protect the Edward's Aquifer recharge zones. Anthropogenically sourced pollutants (pesticides, VOCs, and synthetically derived compounds) can be found within the Edwards Aquifer at minuscule levels. The Edwards Aquifer supports

522-571: A significant increase in development. From 1996 to 1998 residential land use increased 9 percent in the Edwards aquifer recharge zone; even so, 72 percent remains undeveloped. The region atop the Edwards aquifer continues to increase in population today. In 2012, the US Census Bureau noted four counties located within the Edwards Region; Kendal, Comal, Hays and Travis were among the fastest growing in

609-485: A specimen of length L and cross-sectional area A , as well as the head h , the hydraulic conductivity ( K ) can be derived by simply rearranging Darcy's law : Proof: Darcy's law states that the volumetric flow depends on the pressure differential Δ P between the two sides of the sample, the permeability k and the dynamic viscosity μ as: In a constant head experiment, the head (difference between two heights) defines an excess water mass, ρAh , where ρ

696-620: A transient model simulation allows for a change in water storage over time. Steady-state results suggest water leaving the aquifer occurs through springs (73.3 percent), water well pumping (25.7 percent), and to the Colorado River (0.6 percent). Inflow of water to the aquifer mostly occurs through natural recharge (93.5 percent) and water delivered through the aquifer's regional boundaries (6.5 percent). The transient simulation model also suggests discharge primarily occurs through springs, followed by water well pumping; however, changes in water storage

783-571: A wide variety of organisms, and several endemic species. The ecosystem is one of the most diverse subterranean aquatic ecosystems in the world. The widemouth blindcat ( Satan eurystomus ), a unique species of blind catfish, has been pumped out of wells almost 610 meters deep along the FW-SW boundary. However, all aquatic-dependent plants and wildlife in the Edwards Plateau area rely on the aquifer to support essential components of their habitats. Currently,

870-466: Is a property of porous materials , soils and rocks , that describes the ease with which a fluid (usually water) can move through the pore space , or fracture network. It depends on the intrinsic permeability ( k , unit: m ) of the material, the degree of saturation , and on the density and viscosity of the fluid. Saturated hydraulic conductivity, K sat , describes water movement through saturated media. By definition, hydraulic conductivity

957-432: Is a specialized empirical estimation method, used primarily in the soil sciences , but increasingly used in hydrogeology. There are many different PTF methods, however, they all attempt to determine soil properties, such as hydraulic conductivity, given several measured soil properties, such as soil particle size , and bulk density . There are relatively simple and inexpensive laboratory tests that may be run to determine

SECTION 10

#1732844555552

1044-460: Is an area of largely normal faulting in the U.S. state of Texas that runs roughly from the southwest part of the state near Del Rio to the north-central region near Dallas along Interstate 35 . The Balcones Fault zone is made up of many smaller features, including normal faults , grabens , and horsts . One of the obvious features is the Mount Bonnell Fault. The location of

1131-479: Is called semi-confined when a saturated layer with a relatively small horizontal hydraulic conductivity (the semi-confining layer or aquitard ) overlies a layer with a relatively high horizontal hydraulic conductivity so that the flow of groundwater in the first layer is mainly vertical and in the second layer mainly horizontal. The resistance of a semi-confining top layer of an aquifer can be determined from pumping tests . When calculating flow to drains or to

1218-456: Is difficult, but modeling segments within an aquifer is common and provides useful information for water users throughout the aquifer. Aquifer storage is correlated with water levels recorded in the J-17 Bexar index well which serves as the sole official monitoring well in the Edwards Aquifer. The J-17 well, is located in the artisanal confined Edwards Aquifer at a location AY-68-37-203 based on

1305-487: Is found mainly in the layers with high horizontal permeability while the layers with low horizontal permeability transmit the water mainly in a vertical sense. When the horizontal and vertical hydraulic conductivity ( K h i {\textstyle K_{h_{i}}} and K v i {\textstyle K_{v_{i}}} ) of the i -th {\textstyle i{\mbox{-th}}} soil layer differ considerably,

1392-494: Is heavily dependent upon the amount of monthly precipitation and water well pumping volumes. Edwards Aquifer Authority regulates withdrawal permits, transfers, and groundwater conservation plans under authority granted by the Texas legislature. Groundwater law in the state of Texas is governed by the Rule of Capture, which gives landowners the right to pump groundwater beneath their land, with

1479-539: Is hydrologically separated into the Austin and San Antonio regions by a groundwater divide near the town of Kyle in Hays County. The total area of the aquifer forms roughly the shape of a slight upward curve and approximately measures 160 miles (260 km) east to west at its furthermost boundaries and 80 miles (130 km) north to south at its widest section. The aquifer is geographically divided into four distinct regions:

1566-422: Is related to the falling head by Δ V = Δ hA . Plugging this relationship into the above, and taking the limit as Δ t → 0 , the differential equation has the solution Plugging in h ( t f ) = h f {\displaystyle h(t_{f})=h_{f}} and rearranging gives the result. In compare to laboratory method, field methods gives the most reliable information about

1653-435: Is the density of water. This mass weighs down on the side it is on, creating a pressure differential of Δ P = ρgh , where g is the gravitational acceleration. Plugging this directly into the above gives If the hydraulic conductivity is defined to be related to the hydraulic permeability as this gives the result. In the falling-head method, the soil sample is first saturated under a specific head condition. The water

1740-478: Is the largest public water utility system that serves the eight counties of the San Antonio metropolitan area. A total of 92 water wells with a daily pumpage rate of 203.7 million U.S. gallons (771 megaliters) supply water to SAWS' customers. In addition to the 2.3 million San Antonio residents are the communities of New Braunfels and San Marcos that depend on the aquifer for clean drinking water. Farming and ranching communities are other significant dependents of

1827-454: Is the month with the lowest precipitation, averaging 1 inch (25 mm), while May and September average the most, 3 inches (76 mm). The proximity of the Edwards Plateau to the Gulf of Mexico and its location in the middle latitudes creates variation in the weather patterns experienced between different years, seasons, and months. Approximately 1.5 million people obtain their drinking water from

SECTION 20

#1732844555552

1914-686: Is the ratio of volume flux to hydraulic gradient yielding a quantitative measure of a saturated soil's ability to transmit water when subjected to a hydraulic gradient. There are two broad approaches for determining hydraulic conductivity: The experimental approach is broadly classified into: The small-scale field tests are further subdivided into: The methods of determining hydraulic conductivity and other hydraulic properties are investigated by numerous researchers and include additional empirical approaches. Allen Hazen derived an empirical formula for approximating hydraulic conductivity from grain-size analyses: where A pedotransfer function (PTF)

2001-423: Is then allowed to flow through the soil without adding any water, so the pressure head declines as water passes through the specimen. The advantage to the falling-head method is that it can be used for both fine-grained and coarse-grained soils. . If the head drops from h i to h f in a time Δ t , then the hydraulic conductivity is equal to Proof: As above, Darcy's law reads The decrease in volume

2088-466: Is to oversee the permitting system for water withdrawals from the aquifer system. A subdivision of state government, EAA is more of a liaison between federal agencies (e.g. USFWS, USEPA, USGS), state agencies (e.g. Texas Water Development Board, Texas Commission on Environmental Quality, etc.) and non-governmental organizations (e.g. Texas Water Conservation Association, Texas Association of Groundwater Districts). Spanish missionaries who arrived in Texas in

2175-404: Is transported near the surface to the recharge zone, extends about 40 miles (60 km) north of the recharge zone at the west end, and tapers to end at a point in the east. The artesian zone , where water springs from wells naturally due to the higher elevation of the recharge zone, extends 10 to 20 miles (15 to 30 km) south on the west end to only a few miles south on the east end. Across

2262-466: The Barton Springs segment of the Edwards Aquifer. Between 1990 and 2015, the population increased by two thirds, at this rate, the population of the basin will be doubled in 2050. The population across the counties have approximately the same growth rate of 10% per year. However, Comal and Guadalupe have a greater growth rate of more than 25% per year. This will increase the number of people relying on

2349-510: The Blanco blind salamander , is unlisted because it is unknown whether the species is extant or extinct. Land use through the region atop the Edwards aquifer varies between rangeland, agricultural and residential/urban. The northern portion is primarily rangelands and contains most of the streams feeding the recharge zone. Until the late 1990s much of the land area that recharged the aquifer was undeveloped rangeland, but since that time it has undergone

2436-535: The Texas Hill Country and the western boundary of the Texas Coastal Plain, and consists of cliffs and cliff-like structures. Subterranean features such as Wonder Cave and numerous other smaller caves are found along the fault zone. Many cities are located along this fault zone. Springs such as San Pedro Springs , Comal Springs , San Marcos Springs , Barton Springs , and Salado Springs are found in

2523-482: The i th soil layer with a saturated thickness d i and horizontal hydraulic conductivity K i is: Transmissivity is directly proportional to horizontal hydraulic conductivity K i and thickness d i . Expressing K i in m/day and d i in m, the transmissivity T i is found in units m /day. The total transmissivity T t of the aquifer is the sum of every layer's transmissivity: The apparent horizontal hydraulic conductivity K A of

2610-569: The 1700s looked to the Edwards Aquifer as their primary source of water. Springs fed by the aquifer played a key role in deciding the location of the Alamo mission and other settlements in the Texas Hill Country. As Europeans continued to settle the region, and as Texas was acquired by the United States, the Edwards Aquifer continued to supply water for farming, ranching, and rural domestic use. In

2697-629: The 1950s Texas experienced the worst drought on record . Legislature for protection of the Edwards aquifer began in 1959 with the creation of the Edwards Underground Water District, which created and supplied maps and worked with licensing departments for development interests. Starting in the 1970s, the Texas Water Quality Board (TWQB) first recognized the aquifer and issued regulations regarding surface recharge zones. Following these first steps, regulations began to include

Edwards Aquifer - Misplaced Pages Continue

2784-557: The Edwards Aquifer Protection Plan in 2000 (renewed in 2005, 2010 and 2015). The plan allows the city to purchase conservation easements for land in Bexar, Medina and Uvalde counties. The landowners retain and upon agreement the landowners cannot divide or develop the land and are paid 40-45% of market value for the easement. The plan has over 130,000 acres (525 km) enrolled. More than 1.7 million people rely on water from

2871-411: The Edwards Aquifer for municipal, industrial and daily use. One of the major cities on the aquifer is San Antonio, America's 7th largest city, with a population of over 1 million. San Antonio is heavily dependent on the Edwards Aquifer for their municipal, industrial and daily use. Another major city on the aquifer is Austin. More than 50,000 people in the city of Austin (6% of Austin's population) rely on

2958-658: The Edwards Aquifer in two ways: it either falls as precipitation and percolates directly into the aquifer, or it enters as streamflow flowing through the Recharge Zone. The Recharge Zone occurs along the Balcones Fault Zone where the Edwards Plateau drops steeply and meets the Gulf Coastal Plain. Here, highly fractured limestones are exposed at the Earth's surface, which allow rain and streamflow to infiltrate directly into

3045-473: The Edwards Aquifer some water may barely move, while in other areas water may travel miles (thousands of meters) in a single day. On average, the Edwards aquifer has been modeled with a transmissivity of about 100 square feet per day (9 m/d). In the south, the Edwards Aquifer dips beneath the lowland plains of the gulf coast. This area south of the recharge zone is referred to as the Artesian Zone, where

3132-602: The Edwards Aquifer. At present, the water quality of the aquifer has satisfied drinking water standards and there have been no significant issues with pollution contamination. Regular water quality testing through the USGS NAWQA Program occurred between 1996 and 2006. On a yearly basis, ions, metals, nutrients, bacteria, pesticides, VOCs , and synthesized chemicals remained below the EPA's published Maximum Contaminant Levels (MCLs) . Dissolved nitrates (NO3) are detected throughout

3219-510: The Edwards Plateau and the Gulf. The main geologic unit, known as the Edwards Limestone , is tilted downward toward the south and east and is overlain by younger limestone layers as well as several thousand feet of sediments. The Edwards Aquifer is a group of limestones and is considered a highly heterogenic aquifer . Three stratigraphic columns across the San Antonio area represent the Edwards Aquifer. These stratigraphic units are known as

3306-464: The Kainer, Person, and Georgetown Formations. The Edwards Aquifer is a highly productive karst aquifer made up of Edwards Group limestones . The Edwards limestone is variable in hydrologic character, but is generally highly porous and permeable, which makes it able to hold and move a lot of water. The limestone is broken by faults and joints. Water flows through these fractures and continues to dissolve

3393-715: The Maverick Basin. the Devils River Trend, and the San Marcos Platform. The Maverick Basin portion of the Edwards Aquifer consists of the West Nueces, McKnight, and Salmon Peak Formations. The Devils River Trend unit of the Edwards Aquifer is composed mostly of Devils River Limestone with a thickness of approximately 550 feet (170 m). The third unit of the Edwards Aquifer, the San Marco Platform, consists of

3480-566: The Texas Comptroller and Texas Water Development Board, the Southern region's economic growth and irrigation practices have put pressure on water demands that exceed supply, and this is expected to increase with economic and demographic trends between 2010 and 2060. All of these economic practices in the region put pressure on both the quantity and quality of water in the Edwards Aquifer. A recent study showed that salinity in groundwater wells in

3567-515: The United States Geologic Survey have developed numerical groundwater flow models for the San Antonio and Barton Springs aquifer segments to determine the amount of water in the aquifer, the direction it is flowing, and its velocity. These are used to estimate the sustainable levels of groundwater withdrawal throughout the aquifer. Given ample data is needed for numerical simulations, yet often lacking, regional modeling of large aquifers

Edwards Aquifer - Misplaced Pages Continue

3654-628: The United States Geological Survey (USGS) have monitored annual well and spring discharges since 1934. Annual well discharge—the sum of all well discharges in a year— ranged from 219,300 to 542,500 acre-feet (271 to 669 GL) between 1955 and 2012. The average well discharge for this period was approximately 371,667 acre-feet (458 GL), equivalent to 183,000 Olympic-sized swimming pools. Annual spring discharge ranged from 69,800 to 802,800 acre-feet (86 to 990 GL) between 1955 and 2012. The average spring discharge for this period

3741-464: The United States, only the fauna of the Edwards Aquifer of Texas has a significant component of marine-derived species. Of the major karst regions in the United States, it is the only one with a significant marine component. Of the 64 stygobionts known from the Edwards Aquifer, 17 are marine relics. The U.S. Fish and Wildlife Service (USFWS) consider the Comal and San Marcos Springs ecosystems to have one of

3828-457: The adopted state water plan (2005, 79th Texas Legislature HB 1763). Senate Bill 2 of the 77th Texas Legislature also required the groundwater conservation districts to submit groundwater management plans to the Chair of any Regional Water Planning Group in which any part of the district is located so that they may specify any area(s) that conflict with the approved Regional Water Plan[1]. In addition to

3915-468: The aquifer for daily water use. The Edwards Aquifer underlies 38 counties in South and Western Texas. West Texas is regionally defined by jobs in the oil and gas industries, but is also home to mining support, agriculture, and transportation support, among other sectors. South Texas is regionally defined by recent economic growth in shipping industries, irrigation based farming, and manufacturing. According to

4002-403: The aquifer is high, potentially affected by adjacent, natural salt deposits as well as brine seepage from nearby oil fields. Additionally, irrigated agriculture is a significant user of the Edwards Aquifer groundwater, with a variety of crops cultivated, including: " vegetables, hay sesame, soybeans, peanuts, cotton, corn, sorghum, wheat, and oats". Also, the city of San Antonio is located along

4089-446: The aquifer is the sum of each layer's resistance: The apparent vertical hydraulic conductivity ( K v A ) of the aquifer is: where D t is the total thickness of the aquifer: D t = ∑ d i . {\textstyle D_{t}=\sum d_{i}.} The resistance plays a role in aquifers where a sequence of layers occurs with varying horizontal permeability so that horizontal flow

4176-435: The aquifer is: where D t , the total thickness of the aquifer, is the sum of each layer's individual thickness: D t = ∑ d i . {\textstyle D_{t}=\sum d_{i}.} The transmissivity of an aquifer can be determined from pumping tests . Influence of the water table When a soil layer is above the water table , it is not saturated and does not contribute to

4263-499: The aquifer, follows the Balcones Fault line, from Brackettville (roughly along U.S. Highway 90 ), through San Antonio , and north to Austin along but a few miles west of Interstate 35 . On certain stretches of highway in Austin and San Antonio, signs indicate that the driver is entering or leaving the recharge zone, as the zone's easternmost edge sits beneath heavy urban and suburban development. Its drainage area, where water

4350-503: The aquifer, including the Edwards Aquifer Authority (EAA), New Braunfels, San Marcos, San Antonio, and Texas State University. Additionally, federal entities including US Geological Survey, US Fish and Wildlife Service, and US Environmental Protection Agency have been involved in water steward activities and recovery management plans of the Edwards aquifer system. The EAA was created as a result of Edwards Aquifer Authority Act enacted by Texas State Legislature in 1993. The main purpose of EAA

4437-536: The aquifer. Although between 25 and 55 million acre-feet (30 and 70 teraliters) of water may be present in the Edwards aquifer, only a small portion of this water is practically or legally available for use. Storage is the difference between recharge (inputs) and discharge (outputs) from the Edwards Aquifer. Annual storage can be negative during dry years with high water use and positive during wet years with relatively low water use. A long-term negative imbalance between recharge and discharge in an aquifer may lead to

SECTION 50

#1732844555552

4524-473: The aquifer. The Contributing Zone, which occurs on 5,400 square miles (14,000 km) of the Edwards Plateau (Texas Hill Country), collects precipitation and streamflow that drain to the Recharge Zone. Major streams draining the Contributing Zone include Cibolo Creek , Helotes Creek , Barton Creek , and Onion Creek . Water is unable to percolate into the aquifer in the Contributing Zone because much of

4611-426: The aquifer. From the 1930s to the 1980s, withdrawals have quadrupled with over half of the current withdrawals serving municipal water purposes while the remaining goes to agricultural needs. More than 50,000 people in the city of Austin (6% of Austin's population) rely on the Barton Springs segment of the Edwards Aquifer. Five groups of stakeholders have played significant roles in shaping the use and conservation of

4698-455: The augerhole method in an area of 100 ha. The ratio between the highest and lowest values is 25. The cumulative frequency distribution is lognormal and was made with the CumFreq program. The transmissivity is a measure of how much water can be transmitted horizontally, such as to a pumping well. An aquifer may consist of n soil layers. The transmissivity T i of a horizontal flow for

4785-408: The depletion of the available water in the aquifer. Annual storage between 1955 and 2012 estimated from data provided by a continuing program between the U.S. Geologic Survey and the Edwards Aquifer Authority ranged from −633,000 to 1,653,000 acre-feet per year (−780 to 2,000 gigaliters per year). The average storage during this period was 37,000 acre-feet per year (46 GL/a). Water mainly enters

4872-422: The eastern edge of the aquifer and was listed as the 7th largest city in the United States by population in 2014. Historically, the Edwards Aquifer has served as the sole source of water for the city of San Antonio. This eight-county metropolitan area is the second fastest-growing area in the state of Texas and depends on the aquifer for both recreational use and clean drinking water. San Antonio Water System (SAWS)

4959-461: The eastern half of the aquifer, the recharge and artesian zones occupy common area. Approximately 70 million years ago, activity of tectonic plates caused a revival of the Rocky Mountains . As these tectonic processes were occurring, millions of tons of sediments were deposited by alluvial and fluvial processes across Texas. The tremendous weight of these sediments resulted in faulting between

5046-475: The entire aquifer at concentrations that exceeded the national background levels, but that are well below the MCL (10 mg/L). These nitrates may be the result of agricultural runoff that enters the aquifer through its recharge zone. Due to the karst hydrogeology of the Edwards Aquifer, chemicals that enter the system have the potential to rapidly travel through the aquifer and contaminate down-gradient water sources in

5133-474: The equivalent of 5.3 million Olympic sized swimming pools. The average annual recharge rate between 1934 and 2013 is estimated to be 699,000 acre-feet (862 GL). The median annual recharge is 556,950 acre-feet (687 GL), or only 6% of the total inputs to the system. Water from the Edwards Aquifer is discharged in two ways: it is either pumped from wells (well discharge) or it leaves as stream outflow (spring discharge). The Edwards Aquifer Authority (EAA) and

5220-414: The exception of drilling a lateral well extending under a neighbor's property, wasting water, or pumping with the intention of causing harm to a neighbor's well. In order to construct a well to withdraw water from the Edwards Aquifer, however, a user requires a permit that is granted by the Edwards Aquifer Authority. Permits for existing users are determined by maximum historical use, taking into consideration

5307-657: The fault zone and provide a source of fresh water and a place for human settlement. The Balcones Fault Zone is a demarcation line for certain ecological systems and for species distributions, e.g., the California fan palm ( Washingtonia filifera ) is the only species of palm tree native to the continental United States west of the Balcones Fault. Transmissivity (earth sciences) In science and engineering , hydraulic conductivity ( K , in SI units of meters per second),

SECTION 60

#1732844555552

5394-547: The fault zone may be related to the Ouachita Mountains , formed 300 million years ago during a continental collision. Although long since worn away in Texas, the roots of these ancient mountains still exist, buried beneath thousands of feet of sediment . These buried Ouachita Mountains may still be an area of weakness that becomes a preferred site for faulting when stress exists in the Earth's crust . The Balcones Fault has remained inactive for nearly 15 million years, with

5481-513: The field. When the water table is shallow, the augerhole method, a slug test , can be used for determining the hydraulic conductivity below the water table. The method was developed by Hooghoudt (1934) in The Netherlands and introduced in the US by Van Bavel en Kirkham (1948). The method uses the following steps: where: where: The picture shows a large variation of K -values measured with

5568-550: The greatest known diversities of organisms of any aquatic ecosystem in the Southwestern United States. This is due in part to the constant nature of the temperature and flow of the aquifer waters that have created unique ecosystems supporting a high degree of endemism . The Edwards Aquifer is the sole environment for the rare Barton Springs salamander ( Eurycea sosorum ), which is a federally listed endangered species. At Comal and San Marcos Springs, their openings and in

5655-431: The groundwater management plan, the Edwards Aquifer Authority board of directors maintains a three-year rolling strategic plan that is updated annually. The 2015-2017 strategic plan adopted on October 14, 2014 identifies six major goals: With the growth of regional cities such as San Antonio, municipal demand for water increased. The second half of the twentieth century saw a high volume of legal activity regarding rights to

5742-408: The groundwater management plans were that they address the efficient use of groundwater, methods of controlling and preventing waste of groundwater, conjunctive surface water issues, natural resource issues that affect the use and availability, of groundwater, and methods of controlling and preventing subsidence. The requirements of groundwater management plans have since undergone expansion to require

5829-406: The hydraulic conductivity of a soil: constant-head method and falling-head method. The constant-head method is typically used on granular soil. This procedure allows water to move through the soil under a steady state head condition while the volume of water flowing through the soil specimen is measured over a period of time. By knowing the volume Δ V of water measured in a time Δ t , over

5916-426: The inclusion of planning requirements for addressing drought conditions and conservation (2001, the 77th Texas Legislature Senate Bill 2), estimates of the managed available groundwater, the amount of groundwater used within each district, the amount of recharge from precipitation, projected surface water supply, total water demand within the district, and consideration of water management strategies that were included in

6003-573: The last activity being during the Neogene period. This activity was related to subsidence of the Texas Coastal Plain , most likely from the large amount of sediment deposited on it by Texas rivers. The Balcones Fault is in one of the lowest-risk zones for earthquakes in the United States. The surface expression of the fault is the Balcones Escarpment, which forms the eastern boundary of

6090-590: The latitude and longitude. Water levels have been recorded in the J-17 well since the 1910s, and is used to generalize the entire aquifer system. Changes in aquifer storage are used to estimate recharge rates. In the Edwards aquifer, groundwater flow models have been developed for the San Antonio and Barton Springs aquifer segments in the San Antonio region of Texas. Two model simulations were conducted: steady state and transient. A steady-state groundwater flow model requires magnitude and direction of flow remain constant, whereas

6177-423: The layer is said to be anisotropic with respect to hydraulic conductivity. When the apparent horizontal and vertical hydraulic conductivity ( K h A {\textstyle K_{h_{A}}} and K v A {\textstyle K_{v_{A}}} ) differ considerably, the aquifer is said to be anisotropic with respect to hydraulic conductivity. An aquifer

6264-676: The limestone, creating larger and larger pore spaces over time. Some units also store water in eroded fossil burrows that formed through the burrowing action of worms and crustaceans at the seafloor. The effective porosity , or the amount of water that is capable of being recovered, of the Edwards aquifer is estimated to be about 5%. The aquifer ranges in thickness from about 300 to 700 feet (90 to 200 m). Unlike sand and gravel aquifers that store water in very small pore spaces, karst aquifers store water in large pockets or caverns, forming underground "rivers" and "lakes". The rate at which groundwater moves through these conduits can vary tremendously. In

6351-421: The nation, all with growth rates between 25 and 50 percent. An estimated 4.6 percent of the recharge zone is now covered with impervious surfaces which decrease aquifer recharge and can negatively affect water quality. Almost all of agricultural lands and a large portion of San Antonio overlie the confined portion of the aquifer (Barker 1996). In an effort to preserve undeveloped land the city of San Antonio passed

6438-472: The need for geologic assessments prior to development, design standards for underground storage tanks and pipes, and fees for development. In 1992, the TWQB declared the Edwards aquifer an underground river due to the presence of endangered species, but this was overturned later the same year. In 1993, Texas Senate Bill 1477 established the Edwards Aquifer Authority to manage the aquifer and to limit pumping to protect

6525-457: The overall availability of water in the aquifer. Wells that produce less than 25,000 gallons per day, wells that are solely for the purpose of watering livestock, and a few other exceptions are considered exempt wells that do not require a permit. Permits for withdrawal can be transferred to another user, provided that the new use is beneficial and occurs within the boundaries of the Authority, with

6612-413: The permeability of soil with minimum disturbances. In laboratory methods, the degree of disturbances affect the reliability of value of permeability of the soil. Pumping test is the most reliable method to calculate the coefficient of permeability of a soil. This test is further classified into Pumping in test and pumping out test. There are also in-situ methods for measuring the hydraulic conductivity in

6699-686: The rivers and lakes originating from the springs, one threatened and seven endangered species have been listed by USFWS under the Endangered Species Act of 1973. The San Marcos salamander ( Eurycea nana ) is listed as threatened. The San Marcos gambusia ( Gambusia georgei ), Texas wild rice ( Zizania texana ), fountain darter ( Etheostoma fonticola ), Texas blind salamander ( Typhlomolge rathbuni ), Comal Springs riffle beetle ( Heterelmis comalensis ), Comal Springs dryopid beetle ( Stygoparnus comalensis ), and Peck's cave amphipod ( Stygobromus pecki ) are listed as endangered. Another species,

6786-639: The spring flow levels. In 1997, Chapter 36 of the Texas Water Code was amended by Senate Bill 1 of the 75th Texas Legislature to require all underground water conservation districts in Texas to develop a groundwater management plan and submit it for approval by the Texas Water Development Board every five years on the anniversary of initial approval (September 17, 1998 for the Edwards Aquifer Authority). The initial requirements of

6873-406: The terrain is dominated by oak – juniper parks. The dominant woody plant on the Edwards Plateau is Ashe juniper ( Juniperus ashei ). Edwards Aquifer is home to a large number of invertebrate species, 40 of which have been described. The most diverse groups are the prosobranch gastropods and amphipod crustaceans. The Edwards Aquifer has the highest recorded diversity of stygobites in the world. In

6960-403: The total drainage area, recharge zone, artesian zone, and saline zone. These zones run east to west, with the drainage area forming the northernmost portion of the aquifer and the saline zone forming the southernmost portion. The artesian zone intersects the saline zone to the south and west at the fresh water - saline water boundary (FW-SW). The aquifer's recharge zone, where surface water enters

7047-416: The transmissivity may vary accordingly. In a semi-confined aquifer, the water table is found within a soil layer with a negligibly small transmissivity, so that changes of the total transmissivity ( D t ) resulting from changes in the level of the water table are negligibly small. When pumping water from an unconfined aquifer, where the water table is inside a soil layer with a significant transmissivity,

7134-416: The transmissivity. When the soil layer is entirely below the water table, its saturated thickness corresponds to the thickness of the soil layer itself. When the water table is inside a soil layer, the saturated thickness corresponds to the distance of the water table to the bottom of the layer. As the water table may behave dynamically, this thickness may change from place to place or from time to time, so that

7221-404: The underlying geology is impermeable. Average precipitation in the region is around 30 inches (760 mm) per year. Only precipitation that falls on the contributing area is available for infiltration. With a contributing and recharge area of over 26,650 square miles (17,000 km), the mean annual volume of precipitation that is available for recharge is 10,660,000 acre-feet (13.1 TL), or

7308-518: The water is held under pressure by low permeability layers, and can flow to the surface without the assistance of pumps through openings like springs and artesian wells . The Edwards aquifer underlies a portion of the Edwards Plateau thus the climate of the Edwards Plateau can be used to describe the climate in the aquifer's region. The eastern portion of the Aquifer falls in a Humid subtropical climate ( Köppen climate classification Cfa or Cwa ), while

7395-418: The water table may be drawn down whereby the transmissivity reduces and the flow of water to the well diminishes. The resistance to vertical flow ( R i ) of the i th soil layer with a saturated thickness d i and vertical hydraulic conductivity K v i is: Expressing K v i in m/day and d i in m, the resistance ( R i ) is expressed in days. The total resistance ( R t ) of

7482-557: The western has a semi-arid steppe climate ( BSk and BSh) The average annual temperature on the Edwards Plateau is 66 °F (19 °C) and the average annual precipitation amounts to 25.24 inches (641 mm). The temperatures vary by season with the lowest average temperature occurring in January, 50 °F (10 °C), and the highest temperature occurring in July or August, nearing 85 °F (29 °C) for both months. Conversely, January

7569-433: Was approximately 392,991 acre-feet (485 GL). During dry years, more water is discharged from wells while during wet years, more water is discharged from springs. Annual total groundwater discharge from pumping and springs ranged from 388,800 to 1,130,000 acre-feet (480 to 1,394 GL), and the average total groundwater discharge for 1955 to 2012 period was approximately 764,431 acre-feet (943 GL). Scientists with

#551448