How large is Edward's Aquifer in Texas?
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Located in South Central Texas, the Edwards Aquifer incorporates an area of approximately 4,350 square miles 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 is hydrologically separated into the Austin and San Antonio regions by a groundwater divide near the town of Kyle in Hays County.
Edwards Aquifer
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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 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.
Edwards Aquifer
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The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of the Edwards Plateau in the U.S. state of Texas, it is the source of drinking water for two million people, and is the primary water supply for agriculture and industry in the aquifer’s region. In addition, the Edwards Aquifer feeds the Comal and San Marcos springs, provides springflow for recreational and downstream uses in the Nueces, San Antonio, Guadalupe, and San Marcos river basins, and is home to several unique and endangered species.
Edwards Aquifer
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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 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 the Maverick Basin. the Devils River Trend, and the San Marcos Platform.
Edwards Aquifer
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The Edwards Aquifer is 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 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 (100 – 200 meters).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 will move through these conduits can vary tremendously. In 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 ft2/day (9.29 m2/day).
Edwards Aquifer
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Encompassing an area of 8 counties across south-central Texas including the City of San Antonio and its surrounding communities, the Edwards Aquifer is the main water supply source for the region, providing water for agricultural and industrial purposes and necessary water flow for endangered species habitat, as well as recreational purposes. As a result of a lawsuit filed by the Sierra Club under the Federal Endangered Species Act in 1991, the Edwards Aquifer Authority (EAA) was created to oversee the aquifer in its conservation efforts.
Edwards Aquifer
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The Contributing Zone, which occurs on 5,400 mi2 (14,000 km2) 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 the underlying geology is impermeable.
Edwards Aquifer
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The Texas Legislature directed the EAA to regulate pumping from the aquifer, implement critical period management restrictions, and pursue measures to ensure minimum continuous spring flows of the Comal and San Marcos Springs are maintained to protect endangered and threatened species to the extent required by federal law. In 2013, the U.S. Fish and Wildlife Service approved Edwards Aquifer Authority’s Habitat Conservation Plan (HCP), which is a regional 15-year plan designed to protect the water flow and species in the Edwards Aquifer region.
Edwards Aquifer
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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 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 is heavily dependent upon the amount of monthly precipitation and water well pumping volumes.
Edwards Aquifer
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The EAA was created as a result of Edwards Aquifer Authority Act enacted by Texas State Legislature in 1993. The main purpose of EAA 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).
Edwards Aquifer