Topic 8: Water Cycle and ClimateTopic 8: Water Cycle and Climate

What is the water cycle?What is the water cycle?

~The water cycle is also called the ~The water cycle is also called the hydrologic cycle. It is a model used to hydrologic cycle. It is a model used to illustrate the movement and the phase illustrate the movement and the phase changes of water at and near the Earth's changes of water at and near the Earth's surface.surface.

~It is fueled by the sun.~It is fueled by the sun.

What happens when precipitation falls on What happens when precipitation falls on the ground?the ground?

~It can be stored or retained on the ~It can be stored or retained on the surface as ice or snow (water retention).surface as ice or snow (water retention).

~It can infiltrate or seep (sink into) the ~It can infiltrate or seep (sink into) the Earth’s surface.Earth’s surface.

~It can flow over the Earth’s surface ~It can flow over the Earth’s surface as runoff.as runoff.

~It can be evaporated or transpired ~It can be evaporated or transpired (both of these together is called (both of these together is called evapotranspiration).evapotranspiration).

Factors Affecting InfiltrationFactors Affecting Infiltration** Remember: Infiltration means to sink into. **** Remember: Infiltration means to sink into. **

Ex: Watering a plantEx: Watering a plant

• Slope of the LandSlope of the Land • SortingSorting

• Degree of SaturationDegree of Saturation • ShapeShape

• PorosityPorosity • CapillarityCapillarity

• PermeabilityPermeability • VegetationVegetation

• PackingPacking • Land UseLand Use

Slope of the LandSlope of the Land

The steeper the slope (gradient), the lessThe steeper the slope (gradient), the less

the infiltration or seepagethe infiltration or seepage

--- inverse or indirect relationship--- inverse or indirect relationship

Degree of SaturationDegree of Saturation

The more saturated the loose EarthThe more saturated the loose Earth

materials are, the less the infiltrationmaterials are, the less the infiltration

--- inverse or indirect relationship--- inverse or indirect relationship Water infiltrates into the ground until it meets the interface between the zone of saturation and the zone of aeration

This interface is the WATER TABLE

The depth of the water table below the surface varies with the amount of infiltration

Subsurface water below the water table is called GROUND WATER

PorosityPorosity

Porosity is the percentage of open space (pores Porosity is the percentage of open space (pores and cracks) in a material compared to its total and cracks) in a material compared to its total volumevolume

Generally: the greater the porosity, the Generally: the greater the porosity, the greater the amount of infiltration that can occurgreater the amount of infiltration that can occur

---Direct Relationship---Direct Relationship

Dependent upon shapeDependent upon shape

ShapeShape

Well rounded particles have a greater porosity.Well rounded particles have a greater porosity.

Round particles = more pore space, higher porosity, and more infiltration

Angular particles = less pore space, less porosity, and less infiltration

PackingPacking

The closer the particles are packed The closer the particles are packed together, the lower the porositytogether, the lower the porosity

Therefore if you have a lower porosity, Therefore if you have a lower porosity, infiltration will also be lower.infiltration will also be lower.

SortingSorting If all the particles in a material are about the same size, If all the particles in a material are about the same size,

they are said to be they are said to be sortedsorted

If the particles are of mixed sizes, they are said to be If the particles are of mixed sizes, they are said to be unsortedunsorted

Unsorted = lower porosity because the smaller particles fill in the pore space

Sorted = higher porosity or pore space

PermeabilityPermeability

The ability of a material to allow fluids such The ability of a material to allow fluids such as water to pass through it. Larger particles as water to pass through it. Larger particles will increase permeability, because pore will increase permeability, because pore space is larger.space is larger.

**Impermeability may be due to tight packing **Impermeability may be due to tight packing or cementing of particles, which seals off the or cementing of particles, which seals off the pores from one another.pores from one another.

ex: ice in the winterex: ice in the winter

CapillarityCapillarity

The process by which water is drawn into The process by which water is drawn into openings due to the attractive force between openings due to the attractive force between water molecules and the surrounding earth water molecules and the surrounding earth materials. As the particles decrease, materials. As the particles decrease, capillarity increases. capillarity increases.

When water moves upward against gravity, it When water moves upward against gravity, it is called capillary action.is called capillary action.

ex: How plants take water from the soilex: How plants take water from the soil

VegetationVegetation

Grasses, trees and other plant types capture Grasses, trees and other plant types capture falling precipitation on leaves and branches, falling precipitation on leaves and branches, keeping that water from being absorbed into the keeping that water from being absorbed into the EarthEarth

If any water gets through the vegetation, the If any water gets through the vegetation, the velocity of the water will be reduced and this will velocity of the water will be reduced and this will give the ground more time to absorb the watergive the ground more time to absorb the water

Ground without vegetation usually has high runoff Ground without vegetation usually has high runoff and low infiltration ratesand low infiltration rates

Land UseLand Use

Roads, parking lots, and buildings create Roads, parking lots, and buildings create surfaces that are not longer permeable.surfaces that are not longer permeable.

These impermeable surfaces often channel These impermeable surfaces often channel runoff.runoff.

Farming, cutting down trees and grazing Farming, cutting down trees and grazing animals will reduce vegetation and animals will reduce vegetation and therefore decrease permeability.therefore decrease permeability.

Factors Affecting Runoff and Stream Factors Affecting Runoff and Stream DischargeDischarge

Runoff can occur when:Runoff can occur when:1)1) The rate of precipitation exceeds the permeability rateThe rate of precipitation exceeds the permeability rate2)2) The pore space of loose material or rock is saturated The pore space of loose material or rock is saturated

with waterwith water3)3) The slope of the surface is too great to allow infiltrationThe slope of the surface is too great to allow infiltration4)4) The water on the surface has not evaporatedThe water on the surface has not evaporated

**The greater the runoff, the greater the amount of stream **The greater the runoff, the greater the amount of stream discharge (volume of water flowing past a certain spot discharge (volume of water flowing past a certain spot in a stream in a specific amount of time.)**in a stream in a specific amount of time.)**

UNITS FOR STREAM DISCHARGE = UNITS FOR STREAM DISCHARGE = meters/secmeters/sec

**Flooding occurs when a stream overflows its normal **Flooding occurs when a stream overflows its normal channel**channel**