WaterWaterChapter 11Chapter 11

The Water CycleThe Water Cycle

Water molecules travel between earth and earth’s atmosphere – renewable resourceWater evaporates at surface –> Water vapor rises –> Condenses to form clouds –> falls back as precipitation

Water is essential to life on Water is essential to life on EarthEarth•Two kinds of water found on Earth:Two kinds of water found on Earth:•1. Fresh water1. Fresh water, the water that people , the water that people

can drink, contains little saltcan drink, contains little salt• 77 percent is frozen in glaciers and 77 percent is frozen in glaciers and

polar icecaps.polar icecaps.

•2. Salt water2. Salt water contains a higher contains a higher concentration of dissolved salts. concentration of dissolved salts.

• 71 percent of the Earth’s surface is 71 percent of the Earth’s surface is covered with watercovered with water

• Nearly 97 percent of Earth’s water is Nearly 97 percent of Earth’s water is salt water in oceans and seas.salt water in oceans and seas.

Global Water DistributionGlobal Water Distribution• The fresh water we use comes The fresh water we use comes

mainly from lakes and rivers and mainly from lakes and rivers and from a relatively narrow zone from a relatively narrow zone beneath the Earth’s surface.beneath the Earth’s surface.

• Surface waterSurface water -all the bodies of fresh -all the bodies of fresh water, salt water, ice, and snow, above the water, salt water, ice, and snow, above the ground people build cities and homes near ground people build cities and homes near waterwater

• River systemRiver system -flowing network of rivers and -flowing network of rivers and streams draining a river basin.streams draining a river basin.

• The Amazon River system is the largest river The Amazon River system is the largest river system in the world as it drains an area of system in the world as it drains an area of land that is nearly the size of Europe.land that is nearly the size of Europe.

• WatershedWatershed - area of land that is drained by - area of land that is drained by a water system.a water system.

• The amount of water that enters a watershed The amount of water that enters a watershed varies throughout the year depending on varies throughout the year depending on rain and snow fall. rain and snow fall.

WatershedsWatersheds

• GroundwaterGroundwater is the water that is is the water that is beneath the Earth’s surface.beneath the Earth’s surface.

• Water Table - a level where the rocks Water Table - a level where the rocks and soil are saturated with water. and soil are saturated with water.

• In wet regions, the water table may In wet regions, the water table may be at Earth’s surface. But in deserts, be at Earth’s surface. But in deserts, the water table may be hundreds of the water table may be hundreds of meters beneath Earth’s surface.meters beneath Earth’s surface.

• The water table has peaks and The water table has peaks and valleys that match the shape of the valleys that match the shape of the land above. Groundwater tends to land above. Groundwater tends to flow slowly from the peaks to the flow slowly from the peaks to the valleys.valleys.

• AquiferAquifer - body or rock or sediment that - body or rock or sediment that stores groundwater and allows the flow stores groundwater and allows the flow of groundwaterof groundwater

• Water table forms the upper boundary Water table forms the upper boundary of an aquifer, and most aquifers consist of an aquifer, and most aquifers consist of materials such as rock, sand, and of materials such as rock, sand, and gravel that have a lot of spaces where gravel that have a lot of spaces where water can accumulate.water can accumulate.

• Groundwater can also dissolve rock Groundwater can also dissolve rock formations, filling vast caves with water, formations, filling vast caves with water, creating underground lakes.creating underground lakes.

• Porosity -Porosity -% of the total volume of a % of the total volume of a rock or sediment that consists of open rock or sediment that consists of open spacesspaces..

• Water in an aquifer is stored in the pore spaces Water in an aquifer is stored in the pore spaces and flows form one pore space to another.and flows form one pore space to another.

• The more porous a rock is, the more water it The more porous a rock is, the more water it can hold.can hold.

• Permeability Permeability is the ability of a rock or is the ability of a rock or sediment to let fluids pass through it open sediment to let fluids pass through it open spaces or pores.spaces or pores.

• Materials such as gravel that allow the flow of Materials such as gravel that allow the flow of water are permeable. Materials such as clay or water are permeable. Materials such as clay or granite that stop the flow of water are granite that stop the flow of water are impermeable.impermeable.

• The most productive aquifers usually form in The most productive aquifers usually form in permeable materials, such as sandstone, permeable materials, such as sandstone, limestone, or layers of sand and gravel.limestone, or layers of sand and gravel.

• Recharge ZoneRecharge Zone is an area in which water is an area in which water travels downward to become part of an travels downward to become part of an aquifer. aquifer. • Recharge zones are environmentally sensitive Recharge zones are environmentally sensitive areas because any pollution in the recharge areas because any pollution in the recharge zone can also enter the aquifer.zone can also enter the aquifer.• The size of an aquifer’s recharge zone is The size of an aquifer’s recharge zone is affected by the permeability of the surface affected by the permeability of the surface above the aquifer. above the aquifer.

• Structures such as buildings and parking lots Structures such as buildings and parking lots can act as impermeable layers and reduce the can act as impermeable layers and reduce the amount of water entering an aquifer.amount of water entering an aquifer.

• Communities should carefully manage Communities should carefully manage recharge zones, because surface water can recharge zones, because surface water can take a very long time to refill an aquifer, even take a very long time to refill an aquifer, even tens of thousands of years.tens of thousands of years.

The Recharge ZoneThe Recharge ZoneChapter 11

• We dig wells because ground water may be a We dig wells because ground water may be a more reliable source of water than surface more reliable source of water than surface water and because water is filtered and water and because water is filtered and purified as it travels underground.purified as it travels underground.

• The height of the water table changes The height of the water table changes seasonally, so wells are drilled to extend seasonally, so wells are drilled to extend below the water table. below the water table.

• If the water tables falls below the bottom of If the water tables falls below the bottom of the well during a drought, the well will dry the well during a drought, the well will dry up. In addition, if groundwater is removed up. In addition, if groundwater is removed faster than it is recharged, the water table faster than it is recharged, the water table may fall below the bottom of a wellmay fall below the bottom of a well