Detailed Instructions: Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.
Problem:Context: To be a good aquifer, the rock in the aquifer must have good: porosity: small spaces between grains permeability: connections between pores To reach an aquifer, surface water infiltrates downward into the ground through tiny spaces or pores in the rock. The water travels down through the permeable rock until it reaches a layer that does not have pores; this rock is impermeable (Figure 1.1). This impermeable rock layer forms the base of the aquifer. The upper surface where the groundwater reaches is the water table. Groundwater is found beneath the solid surface. Notice that the water table roughly mirrors the slope of the lands surface. A well penetrates the water table. For a groundwater aquifer to contain the same amount of water, the amount of recharge must equal the amount of discharge. What are the likely sources of recharge? What are the likely sources of discharge? What happens to the water table when there is a lot of rainfall? What happens when there is a drought? Although groundwater levels do not rise and fall as rapidly as at the surface, over time the water table will rise during wet periods and fall during droughts. In wet regions, streams are fed by groundwater; the surface of the stream is the top of the water table (Figure 1.2). In dry regions, water seeps down from the stream into the aquifer. These streams are often dry much of the year. Water leaves a groundwater reservoir in streams or springs. People take water from aquifers, too. Groundwater meets the surface in a stream (Figure 1.2) or a spring (Figure 1.3). A spring may be constant, or may only flow at certain times of year. Towns in many locations depend on water from springs. Springs can be an extremely important source of water in locations where surface water is scarce. A well is created by digging or drilling to reach groundwater. It is important for anyone who intends to dig a well to know how deep beneath the surface the water table is. When the water table is close to the surface, wells are a convenient method for extracting water. When the water table is far below the surface, specialized equipment must The top of the stream is the top of the water table. The stream feeds the aquifer. A spring in Croatia bubbles to the surface and feeds the river Cetina. be used to dig a well. Most wells use motorized pumps to bring water to the surface, but some still require people to use a bucket to draw water up (Figure 1.4). An old-fashioned well that uses a bucket drawn up by hand.
Question: the surface of a stream is
Solution:
the top of the water table.