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Karst Connections A Virtual Field Experience Welcome to the Edwards Aquifer Region. The three colors on the map represent the Drainage Area (green), Recharge Zone (blue), and Artesian Zone (tan) of the aquifer. Learn about all three zones and what the Edwards Aquifer Authority does to protect them by taking a virtual field experience. Click on a focus area on the map to zoom in and investigate. Welcome to Seco Sinkhole Click on the arrow to enter the aquifer, or click the focus area to learn about the Seco Creek Recharge Enhancement Project. A sinkhole is a type of geologic feature, created by the collapse of a cave, or dissolution of the bedrock found in karst terrains. Karst topography describes a landscape containing soluble rocks typified by the presence of caves, sinkholes, and other natural dissolution features produced by the interaction of water, minerals within the rock, and many other natural processes. Click the focus area to learn more about the recharge project. Back The sinkhole is about 60 feet in diameter at the surface entrance with vertical walls. The Woodward Cave Fault crosses about 0.3 miles north of the Seco Sinkhole and has a total displacement of around 500 feet. There are 60 to 100 feet of Edwards limestone below the floor of the cave system above the Glen Rose/Edwards contact. The water level in the cave is the approximate local water table in the Edwards Aquifer. Click the arrow to continue the repel. Click the focus area to discover more about aquifers. Back Upon entering the sinkhole you’ll reach a ledge at about 90 feet, and then the bottom of the cave at about 160 feet below land surface. The cave system has been explored to approximately 4,000 feet. The main cavern system was formed by the solutioning of fractures in the lower portion of the Edwards limestone, aligned along the northeast-southwest axis of the Balcones fault system. Choose an arrow to explore a cave passageway. Check out the left passage Back Check out the right passage You’ve reached the water table of the Edwards Aquifer! The water table is the uppermost surface of the water filled zone within an aquifer. Click the blue circle to find out where the water goes after entering the aquifer at the recharge zone. Click on the focus area to see how the EAA monitors water quality. Back Having the right equipment can make the difference between an enjoyable field experience and potential disaster. Cavers typically carry three dependable light sources with them during expeditions. It’s important to have backup systems ready so you’re not left in the dark. Most Texas caves are on private property and you must always get the permission of the landowner and be properly trained prior to entering any cave. Back The Edwards Aquifer is divided into three hydrologic zones; the drainage area, recharge zone, and artesian zone. Rain that falls on the drainage area, and that emerges from various springs along the Edwards Plateau enters several streams and creeks that flow south, crossing the recharge zone. Precipitation and stream flow then percolate through the highly porous and permeable Edwards limestone, exposed at the ground surface in the recharge zone. Once in the aquifer, the water generally flows south and then east towards large springs and other smaller discharge points within the artesian zone, or confined zone of the aquifer. You are here Back The Seco Creek Recharge Enhancement Project The Seco Creek Recharge Project, completed on November 15, 1982, was the fourth structure built by the former Edwards Underground Water District (EUWD) to enhance natural recharge to the Edwards Aquifer. The dam is 13 feet high, 310 feet long, with the crest of the dam at 1,201 feet above mean sea level. When Seco Creek is flowing at high levels, excess water is diverted through a man-made channel, terminating at the entrance to the sinkhole. Recharge structures, on average, contribute nearly 5000 acre-feet to the aquifer annually. Back The Seco Creek Recharge Enhancement Project Click on the arrow to see how the water reaches the sinkhole, or click on the focus area learn more about recharge stuctures. Back Two words that describe an aquifer’s flow characteristics are porosity and permeability. Porosity refers to the amount of pore (or open) space within a rock and permeability describes how interconnected those pores are with each other, and how well water can travel through it. Connections How would you describe the porosity and permeability of this section of the Edwards limestone? Does it have low or high porosity? Could water be easily transmitted through this rock body? Back Water Quality Sampling Every month the EAA samples water quality from numerous wells and springs from across the region. In the middle – A team collects storm water samples in an effort to assess potential contaminants that may be present in surface water runoff generated by storm events. The storm water sampling effort was designed to assess what changes in water quality occur within each surface water system during a storm event. On the right – Surface water samples are taken downstream of San Marcos Springs to establish a baseline of water quality within the river system. Back Recharge Structures The EAA operates four recharge structures in Medina County on the Edwards Aquifer Recharge Zone. The total recharge for each site is calculated using data from Stage recorders near these structures. The approximate historical median annual recharge contributed by the combined structures is 853 acre-feet, whereas the approximate historical mean annual recharge contributed by the combined structures is 4,970 acre-feet. The dams slow down the creek’s flow during rain events, giving the impounded water more time to percolate into the aquifer. Back Welcome to San Marcos Springs Click on the arrow to follow the river’s course south of the springs, or click on a focus area to lean about the unique attributes of San Marcos Springs. San Marcos Springs, located just northeast of San Marcos, comprise the second largest spring system in Texas. Some 200 springs emerge from large fissures and many smaller openings at the bottom of spring lake, along the San Marcos Fault. Click the focus area to learn more about the springs. Back The San Marcos River Beginning with it’s headwaters at the springs, the San Marcos River flows south, eventually meeting its confluence with the Guadalupe River. The crystal clear waters offer habitat to an endangered plant, the Texas wild rice. Texas wild rice is only found in the upper reaches of the San Marcos River. Riparian, or riverside habitat can be adversely effected by exotic and invasive species. Click on the riparian focus area to learn more. Back Texas Wild Rice Zizania texana Texas wild rice exists in only one place: a small segment of the San Marcos River. In 1967, the plant was headed toward extinction, with only a single clump appearing anywhere in the river. After a researcher began a long-term restoration project of the species, the plant began to again appear in the water, favoring swift currents, shallow areas near the middle of the stream, and still pools of water as much as ten feet deep. Texas wild rice requires thermally constant temperatures, clear water, undisturbed stream-bottom habitat, protection from floods, and unimpeded light. Back Invasive Species These elephant ear plants may look lush and aesthetically pleasing, but the are considered an invasive species along the banks of the San Marcos river and elsewhere in south Texas. An invasive species is a plant or organism that has been introduced into an environment where it competes for food and/or habitat with native species. One component of the Edwards Aquifer Habitat Conservation Plan is to control non-native species by removing them and replacing them with native species. Back Spring Sampling Water quality samples are taken a few different spots at the springs. This location is known as ‘San Marcos Deep’. Divers take a sampling tube more than 28 feet deep to extract pure spring water from an opening at the base of the lake. Click on the samplers to learn more about water quality parameters, or click on the water to discover more about sampling. Back Water Quality Parameters This water quality meter takes four different types of readings: temperature, conductivity, dissolved oxygen, and pH. Parameters can give early indications of water quality problems. For example if a pH reading is coming back too low or too high it could indicate potential impact from an accident spill or wastewater discharge. Back Water Quality Sampling Every month the EAA samples water quality from numerous wells and springs from across the region. In the middle – A team collects storm water samples in an effort to assess potential contaminants that may be present in surface water runoff generated by storm events. The storm water sampling effort was designed to assess what changes in water quality occur within each surface water system during a storm event. On the right – Surface water samples are taken downstream of San Marcos Springs to establish a baseline of water quality within the river system. Back Glass Bottom Boats Years ago San Marcos Springs was home to an amusement park featuring Ralph the Swimming Pig, Mermaids, an underwater submarine, and glass bottomed boats. The theme park is gone, but the boats remain. Texas State University now operates the boats and manages they spring system at the Meadows Center. Click on the boat to look through the glass, or click on the water to learn about the endangered and threatened species of San Marcos Springs. Back A Look Through The Glass The glass bottomed boat tours offer visitors to the springs a unique view at the hydrogeological, and biologic features below. Numerous springs and a variety of wildlife can be easily seen by peering through the glass. Click on the glass to get a view. Back Cream of Wheat Springs The aptly-named Cream of Wheat Springs can be easily viewed through glass of the Meadows Center boat. These are high pressure springs that add thousands of gallons of water to Spring Lake each day. Because of down faulting the Edwards Aquifer drops deep below land surface in the artesian zone. The rocks above the Edwards are relatively less permeable, creating a confined condition that adds pressure to the aquifer. Where pressure is sufficient, and natural faults or fractures or present, water will be forced to the surface in the form of springs. Back Endangered and Threatened Species San Marcos Springs is home to three endangered, and one threatened species: The Texas Blind Salamander, San Marcos Gambusia, Fountain Darter, and San Marcos Salamander. These species serve as indicators These species serve as indicators to health the health of the springs and aquifer. Each need clean, fresh at a near constant temperature springs and aquifer. Each need clean, fresh water at a near constant temperature. If they begin to die out , what does that say about our aquifer system? If they begin to die out , what does that say about our aquifer system? Back The Wetlands Boardwalk Welcome to the wetlands boardwalk, a floating dock that extends out into the marsh area of the springs. Why are wetlands important? What benefit do they bring to the ecosystem? Enter the boardwalk to find out… Back Wetlands Some people may consider wetlands to be useless swamp land, but in fact wetlands play an important role in the ecosystem for a number of reasons. Wetlands provide natural filtration for runoff water entering the system. The diversity of plants here allows for the filtration of many harmful contaminates as the water slowing passes through the dense cover. . Check out two different views of the wetlands area. Back Wetlands area, viewing west. Back Wetlands area viewing southwest. Back Welcome to Government Canyon State Natural Area Government Canyon State Natural Area is a 9,084 acre preserve in Northwest Bexar County, on all three aquifer zones – Drainage, Recharge, and Artesian. The natural area was purchased by Texas Parks and Wildlife in 1993, in cooperation with the EAA, San Antonio Water System, the Trust for Public Land, and the federal government Land and Water Conservation Fund. (TPWD.state.tx.us) Click the focus area to learn more about the canyon. Back Welcome to the Government Canyon State Natural Area Visitor Center Government Canyon State Natural Area provides excellent protection for both the watershed and wildlife within the Edwards Aquifer Region. Much of the canyon is situated on top of the highly sensitive Edwards Aquifer Recharge Zone. A couple of things that make this visitor center unique are it’s examples of rainwater collection and use of xeriscaping. Click on red boxes to discover more. Back A Closer Look – Rainwater Collection Rainwater collection is the process of capturing runoff water from rooftops and other impermeable surfaces with the use of cisterns and smaller barrels. The captured water can then be later used for landscape watering and other non-potable uses. When equipped with special filters, some home owners live exclusively on the captured rainwater. Rainwater collection has gained more popularity as the drought continues and other water sources have declined. Connections What are other alternative sources of water besides the aquifer that South Texas could utilize? Back A Closer Look – Xeriscaping Xeriscaping uses a combination of native and drought resistant plants together with mulch or decorative rocks to save water while maintaining aesthetic appeal. Drought resistant plants and mulch can replace turf grass to save hundreds or even thousands of gallons of water for a home annually. Connections Some Cities, particularly in the western United States, require drought tolerant landscaping. Is this a policy south central Texas should consider? Why or why not? Back After a few miles of hiking down the Joe Johnston trail, the mail trail of Government Canyon’s backcountry, you’ll encounter a nice exposure of both the Edwards (younger) and Glen Rose (older) limestones. Although the Glen Rose is also limestone, it is relatively less permeable than the Edwards and serves as the lower confining member to the Edwards Aquifer. Take a closer looks to discover some unique features within both limestone formations. Back Trace fossils are the tracks, trails, or borings of once living organisms. (Hamblin, Christiansen 2004) Trace fossils can be found throughout the Edwards Aquifer Region. Connections This dinosaur print is located in the Glen Rose limestone, the first geologic unit below the Edwards limestone. What clues can this trace fossil tell us about the relative age of the Edwards limestone? Back Marine fossils can be found in both the Glen Rose and Edwards Limestones. Over millions of years the bodies of ocean organisms accumulated in layers on the sea floor, eventually being compacted and lithified, or converted into rock. Connections Try to determine the geologic history of Texas based on the clues found within the rocks. Hint – you may want to check the other focus area on the previous image to determine the relative age of the rock. Back Monitoring the Effects of Drought The photo on the left was taken in 2004, during a normal year for precipitation. The photo on the right is from 2013 after three years of lingering severe to exceptional drought. The water in the creek originates from a series of small springs within Government Canyon. Connections What differences do you spot between the two photos? What effects, besides declining water levels could prolonged drought have on an ecosystem? 2004 Back 2013 References: Adapted from Lukes, L. (2014, January). A new take on the field trip. The Science Teacher, 81(1), 24-29. Hamblin, W. K., & Christiansen, E. H. (2004). Earth's dynamic systems (10th ed.). Upper Saddle River, N.J.: Prentice Hall, Pearson Education. Government Canyon State Natural Area. (2014, January 1). - Texas Parks & Wildlife Department. Retrieved April 30, 2014, from http://www.tpwd.state.tx.us/state-parks/government-canyon All photos copyright, Edwards Aquifer Authority, 2014.