11.3 Water Underground p. 378-381
Objectives • Describe springs and how water moves through underground layers of soil and rock. • Explain what an aquifer is and how people obtain water from an aquifer.
Engage/Explore • Spring water • What was the original source of this water? • Where does the water in springs and wells come from?
Discover - Where Does the Water Go? • Clear jar, pebbles, sand, water • P. 378
Introduction • P. 378 • Digging a hole
Underground Layers • Where does underground water come from? • Answer: Precipitation that soaks in the ground and trickles downward. • Water underground trickles down between particles of sol and through cracks and spaces in layers of rock.
Pores - different types of rock and soil have different-sized spaces. • Permeable - materials that allow water to easily pass through or permeate. • Examples of permeable materials are sand and gravel.
Impermeable - materials that water cannot pass through easily. • Examples of impermeable materials are clay and granite. • Saturated zone - the area of permeable rock or soil tat is totally filled or saturated with water.
Water table - the top of the saturated zone. • Unsaturated zone - the layer of rocks and soil above the water table.
Layers Underground • What is different about the pores in the two pictures? • Which picture represents a permeable rock layer? • In this picture how do the pores differ above and below the water table?
Aquifers • Aquifer - any underground layer of rock or sediment that holds water. • Size - small underground patch of to an area the size of several states.
Aquifers • The huge Ogallala aquifer lies beneath the plains of the west, from S. Dakota to Texas. It provides drinking water and water for crops and livestock.
Aquifers • The water in aquifer moves only a few centimeters a day which equals out to be about 10 meters a year. The movement depends largely on how steeply the aquifer slopes and how permeable the rocks are.
Wells • People can obtain groundwater from an aquifer by drilling a well below the water table. • Fig. 12 - Compare the well and dry well.
Wells • History of wells • Dug by hand • Lined with brick or stone to keep the walls from collapsing. • Lowered and raised a bucket to brink up water. • Today, most are dug with well-drilling equipment.
Wells • Pumping water out of an aquifer lowers the water level near the well. If too much water is pumped out too fast, the well may run dry. • Then it may be necessary to dig deeper to reach the lowered water table or to wait for rainfall to refill the aquifer.
Wells • Recharge - New water that enters the aquifer from the surface. • Artesian well - a well in which water rises because of pressure within the aquifer.
Bringing Groundwater to the Surface • Springs - where the water table meets the ground surface, groundwater bubbles or flows out of cracks in the rock in places.