Water on the Earth earth has a limited

Water on the Earth: • earth has a limited supply of water that is constantly being recycled between the land, oceans and atmosphere • Oceans cover 71% of the earth’s surface

The Water Cycle (Hydrologic Cycle) • Earth’s limited supply of water is constantly being recycled between the oceans, atmosphere and land condensation transpiration precipitation evaporation Run off infiltration condensation ocean

Water entering the atmosphere: (powered by the sun’s energy) 1) evaporation surface water changing to water vapor • 2) transpiration process by which living things release water vapor to the atmosphere • 3) evapotranspiration a combination of evaporation and transpiration •

Water vapor in the atmosphere rises, cools and condenses. • condensation the process by which water vapor changes to liquid water -- releases energy

Water returning to the Earth’s surface: precipitation water falling to the Earth’s surface

Water returning to the Earth’s surface: • 1) runoff water on the surface of the Earth moving toward lakes, rivers and oceans • 2) infiltrate sink into the ground through spaces in the soil • Runoff + infiltration = 100% of precipitation

Water below the Earth’s surface groundwater that infiltrates the ground • Gravity pulls water down to the until it reaches the: • zone of saturation the area where the soil is saturated with water (all spaces, cracks and openings in the soil grain and rocks are completely filled with water)

• Where does the zone of saturation end? • impermeable rock layer of solid rock that will not allow water to pass through • Where does the zone of saturation start? • water table the uppermost surface of the saturated zone between the zone of aeration and the zone of saturation • zone of aeration area where the soil does not contain water between particles

• The soil and rock act as a natural filter making ground water a good source of drinking water. • Wells are drilled into the ground to extract ground water for human consumption. If the water is pumped too quickly the well will run dry.

Water Below the Surface

Factors that affect the storage and Movement of Groundwater. • Storage and movement of groundwater is controlled by the characteristics of the soil and rock found near the surface.

Water can infiltrate when there are many openings, or pores between ground particles. Porosity the volume of pores in a material compared with its total volume determine the amount of water the ground can hold Pore Space

factors affecting porosity • o shape - round particles have greater porosity that angular particles • o packing – loosely packed particles have greater porosity than tightly packed particles

• sorting -- well sorted (all particles of the same size) have greater porosity than poorly sorted (mixture of particles sizes)

• particle size does not effect porosity • o large and small particles have the same porosity

permeability • the ability of soil to transmit water, how fast water can pass through a soil Dependent upon • size of the pores • how the pores are connected

Size of the pores: • o large pores created by sand allows water to pass through quickly • o small pores created by clay allows water to pass through slowly

Infiltration is directly related to permeability • increase infiltration, increase permeability • decrease infiltration, decrease permeability

Runoff is inversely related to infiltration and permeability • increase infiltration and permeability, decr runoff • decrease infiltration and permeability, incr runoff

Capillarity • water has the ability to move upward in tiny spaces between soil grains, due to the cohesive nature of the water molecule • capillary water is water available for plants to access with their roots

Rainfall and Stream Flow • Streams and rivers do not respond immediately to rainfall • Streams will respond more quickly if the land is steep, without vegetation or there is paved areas Any factor that decreases infiltration will increase runoff

Watersheds and Drainage Divides • Watershed (drainage basin) the geographic area that drains into a particular stream or other body of water • Drainage divide boundary between two watersheds

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