1 00:00:00,506 --> 00:00:13,036 [ Music ] 2 00:00:13,536 --> 00:00:19,886 >> Geology is the study of planet Earth, its history, and all the processes that act on it. 3 00:00:19,886 --> 00:00:24,156 Hydrogeology is the branch of geology which studies how water 4 00:00:24,326 --> 00:00:27,966 and rocks interact underground mainly in aquifers. 5 00:00:30,646 --> 00:00:35,876 An aquifer is a rock unit that can hold enough water to supply water to wells. 6 00:00:36,736 --> 00:00:41,916 Aquifers can be found in many types of rocks including sandstone, conglomerate, 7 00:00:42,356 --> 00:00:47,986 unconsolidated sand and gravel, and fractured rocks composed of limestone or igneous rocks. 8 00:00:48,766 --> 00:00:53,056 Here at Barton Springs in Austin, Texas, we are standing on top 9 00:00:53,056 --> 00:00:56,526 of the Edwards aquifer composed mostly of fractured limestone. 10 00:00:57,326 --> 00:01:02,056 Over time, these fractured rocks can dissolve to create large cave 11 00:01:02,056 --> 00:01:04,416 like systems called karst aquifers. 12 00:01:05,076 --> 00:01:08,476 So, when you hear the word karst, think cave. 13 00:01:09,246 --> 00:01:10,546 Some of these caves are big. 14 00:01:11,066 --> 00:01:12,386 Some of them are small. 15 00:01:13,176 --> 00:01:19,186 Karst aquifers are different from sedimentary aquifers where water mostly flows through gravel 16 00:01:19,186 --> 00:01:22,826 and sand grains similar to a sponge. 17 00:01:23,056 --> 00:01:29,416 Hydrogeologists use two terms when investigating aquifers, porosity and permeability. 18 00:01:30,166 --> 00:01:35,796 Porosity is call the empty pore space inside a rock given in a percent volume. 19 00:01:36,336 --> 00:01:40,766 Porosity represents the volume of the water a rock formation can potentially hold. 20 00:01:41,526 --> 00:01:47,906 Permeability is how well a fluid can flow within the pore spaces of the rock within the aquifer. 21 00:01:49,186 --> 00:01:54,016 For water, we describe this property as hydraulic conductivity. 22 00:01:54,656 --> 00:02:00,106 For example, clay and rocks like pumice often have high porosity. 23 00:02:00,866 --> 00:02:06,576 But because their pores do not connect well with each other, they are often low in permeability. 24 00:02:07,486 --> 00:02:13,176 Low permeability materials such as clay and shale, typically act as barriers 25 00:02:13,246 --> 00:02:18,796 to ground water flow and may often function as an aquatard in ground water flow systems. 26 00:02:20,636 --> 00:02:26,616 Aquifers that are bounded and the top and bottom by aquatards are called confined aquifers. 27 00:02:27,266 --> 00:02:30,276 In confined aquifers, the ground water is under pressure. 28 00:02:30,806 --> 00:02:33,576 If penetrated by a well, the water level 29 00:02:33,576 --> 00:02:37,266 in a confined aquifer will rise above the top of the aquifer. 30 00:02:37,846 --> 00:02:43,596 In some cases, the water will reach the surface resulting in a flowing or artesian well. 31 00:02:44,286 --> 00:02:47,806 Confined aquifers function differently than unconfined aquifers 32 00:02:48,146 --> 00:02:50,236 which have no overlying aquatard. 33 00:02:50,816 --> 00:02:54,166 Unconfined aquifers occur near the Earth's surface. 34 00:02:54,526 --> 00:02:59,776 So, they may interact better to the processes that occur near or above land surface. 35 00:03:01,456 --> 00:03:04,766 Because unconfined aquifers are exposed to the atmosphere, 36 00:03:05,246 --> 00:03:09,626 they may interact with surface water features such as rivers or lakes. 37 00:03:10,806 --> 00:03:14,916 If the water level in the aquifer is higher than in the adjacent rivers 38 00:03:14,916 --> 00:03:17,826 or lakes, the rivers or lakes gain water. 39 00:03:18,566 --> 00:03:24,106 In other words, water from the aquifer flows into the rivers or lakes. 40 00:03:25,056 --> 00:03:29,506 If the water level in the aquifer is lower than in the rivers or lakes, 41 00:03:30,406 --> 00:03:32,816 then the rivers or lakes lose water. 42 00:03:33,796 --> 00:03:39,296 That's saying that water flows from the rivers or lakes into the aquifer. 43 00:03:41,206 --> 00:03:44,996 Rainwater may infiltrate the shallow soil and into the aquifer. 44 00:03:45,796 --> 00:03:51,006 Plant roots may extend down into the aquifer and use the water to survive. 45 00:03:51,716 --> 00:03:55,136 Ground water close to the Earth's surface may also evaporate. 46 00:03:56,156 --> 00:03:59,906 Hydrogeologists use the terms recharge and discharge 47 00:04:00,196 --> 00:04:03,976 to describe how water enters and leaves and aquifer. 48 00:04:05,516 --> 00:04:07,606 [ Water Sounds ] 49 00:04:08,106 --> 00:04:11,136 One way an aquifer can discharge is through a spring. 50 00:04:11,766 --> 00:04:15,026 Springs occur when the water table intersects the land's surface. 51 00:04:15,786 --> 00:04:18,676 The Barton Springs pool is fed by this spring here. 52 00:04:19,286 --> 00:04:22,136 Notice the large fracture which the water flows out of. 53 00:04:22,736 --> 00:04:26,886 Here at upper Barton Spring, water is flowing out of the ground 54 00:04:26,886 --> 00:04:29,366 from a karst aquifer or small saves. 55 00:04:32,426 --> 00:04:36,496 To understand better how aquifers work, many hydrogeologists 56 00:04:36,496 --> 00:04:39,026 and scientists develop physical models. 57 00:04:39,776 --> 00:04:43,546 To see the physical model in action, continue on to Part 2. 58 00:04:44,516 --> 00:05:26,550 [ Music ]