The Water Table
Date: 2015-10-07; view: 430.
The water table depends on the distribution of groundwater. The open spaces in the rocks of the upper part of the crust are filled mainly with air. This is the zone of aeration. Water moves downward through this zone into the zone of saturation, where openings are filled with water. The upper surface of this saturated zone is the water table. In most areas, the water table is only a few tens of feet below the surface, but in arid regions, it is much deeper. Water-bearing rocks are rarely found below 2.000 feet. Rock pores are closed by pressure at depth, and this determines the lower limit for groundwater. Most rocks will give off water whenever they intersect the water table. But the level of the water table falls after a dry season, so rock formations must be deep enough to penetrate the water table all year round. Sometimes a perched water table results when a pocket of water is held above the normal water table by a saucer of impervious rock. Any water-producing rock formation is called an aquifer.
Exercise 6. Answer the following questions using information from the text above:
- The water table depends on the distribution of groundwater, doesn't it?
- Are the open spaces in the rocks of the upper part of the crust filled with water?
- Which is the aeration zone?
- Where does water move?
- What is the water table?
- The water table is only a few tens of feet below the surface everywhere on earth, isn't it?
- How deep are water-bearing rocks found?
- Why are rock pores closed at depth?
- The lower limit for groundwater is determined by the water circulation process, isn't it?
- When will most rocks give off water?
- When does the level of the water table fall?
- When does a perched water table occur?
| <== previous lecture | | | next lecture ==> |
| Part 1.Geological Work of Ground Water | | | Part 2. Geysers |