CHAPTER – 10 Ground Water • Section – 10.1 Movement and Storage of Groundwater • Section – 10.2 Groundwater – Weathering & Deposition • Section – 10.3 Groundwater - Supply
Section – 10.1Movement and Storage of Groundwater Objectives: • Describe how groundwater storage and underground movement relate to the water cycle. • Illustrate an aquifer and an aquiclude. • Relate the components of aquifers with the presence of springs.
Groundwater reservoirs provide water to streams and wetlands wherever the water table intersects the surface of the ground. Review Vocabulary hydrologic cycle: a never-ending natural circulation of water through Earth’s systems
New Vocabulary • infiltration • zone of saturation • water table • zone of aeration • permeability • aquifer • aquiclude • spring • hot spring • geyser
The Hydrosphere The water on and in Earth’s crust makes up the hydrosphere, named after hydro,the Greek word for water. Freshwater is one of Earth’s most abundant and important renewable resources. However, of all the freshwater, between 70 and 80 percent is held in polar ice caps and glaciers.
Groundwater and Precipitation • Evaporation of seawater cycles water into the atmosphere in the form of invisible water vapor. Water vapor can condense to form visible clouds. • Precipitation brings atmospheric moisture back to Earth’s surface. • Infiltration is the process by which precipitation that has fallen on land trickles into the ground and becomes groundwater.
Groundwater Storage Although Earth’s crust appears solid, much of it is composed of soil, sediment, and rock that contain countless small openings called pore spaces. Because of the enormous volume of sediment and rock beneath Earth’s surface, enormous quantities of groundwater are stored in the pore spaces.
Groundwater Storage Porosity, the amount of pore space in a material, depends on the size and variety of particles in a material.
Zone of Saturation The region below Earth’s surface in which groundwater completely fills all the pores of a material is called the zone of saturation.
Zone of Saturation The upper boundary of the zone of saturation is the water table. Above the water table, in the zone of aeration, the materials are moist in nature. Since they are not saturated with water, air occupies much of the pores. Water in the zone of saturation and zone of aeration can be classified as either gravitational water or capillary water. Gravitational water trickles downward as a result of gravity. Capillary water is drawn upward through capillary action above the water table and is held in the pore spaces of rocks and sediment because of surface tension.
The Water Table The depth of the water table often varies depending on local conditions. Because of its dependence on precipitation, the water table fluctuates with seasonal and other weather conditions.
Groundwater Movement The tendency of a material to let water pass through it is its permeability. An aquifer is a layer of permeable subsurface material that is saturated with water.
Groundwater Movement Impermeable layers, called aquicludes, are barriers to groundwater flow. Flow Velocity - The flow velocity of groundwater is proportional to both the slope of the water table and the permeability of the material through which the water flows.
Springs Groundwater tends to discharge at Earth’s surface where an aquifer and an aquiclude are in contact. These natural discharges of groundwater are called springs. Springs can emerge from sides of valleys, at the edges of perched water tables, along faults, and from underground pathways. A spring is the result of groundwater that emerges at Earth’s surface. Springs can be caused by a variety of situations.
Temperature of Springs The temperature of groundwater that is discharged through a spring is generally the average annual temperature of the region in which it is located. In some regions around the world, springs discharge water that is much warmer than the average annual temperature. These springs are called warm springs or hot springs.
Temperature of Springs Geysers are explosive hot springs in which water is heated past its boiling point, causing it to vaporize The resulting water vapor builds up tremendous pressure, which fuels eruptions at the surface.
Summary Groundwater reservoirs provide water to streams and wetlands wherever the water table intersects the surface of the ground. Some precipitation infiltrates the ground to become groundwater. Groundwater is stored below the water table in pore spaces of rocks and sediments. Groundwater moves through permeable layers called aquifers and is trapped by impermeable layers called aquicludes. Groundwater emerges from the ground where the water table intersects the Earth’s surface.