1. Groundwater & Infiltration

2. Water Cycle and Groundwater
What is the water cycle?
~The water cycle is also called the hydrologic cycle. It is a model used to illustrate the movement and the phase changes of water at and near the Earth's surface.
~It is fueled by the sun.

3. Aim: What happens to rain water after it reaches the ground?

4. Steps of the water cycle:
Evaporation- Liquid to gas (water to water vapor)
Transpiration- Liquid to gas- evaporation from plants
Condensation- Gas to Liquid (water vapor to water)
Precipitation- any form of water leaving a cloud (rain, snow, sleet, hail)
Infiltration: Rain water seeps into the ground to form ground water. Water that infiltrates the ground is pulled down by gravity.
Runoff- water that does not go into ground will flow in nearby bodies of water

5. When water reaches the ground
50% evaporates again
18 % trickles down into the ground
32% runs off the surface of the land into rivers and lakes

6. What happens when precipitation falls on the ground?
~It can be stored or retained on the surface as ice or snow (water retention).
~It can infiltrate or seep (sink into) the Earth’s surface.
~It can flow over the Earth’s surface as runoff.
~It can be evaporated or transpired (both of these together is called evapotranspiration).

7. ESRT, p1- Properties of Water

8. Aquifer: Underground area that contains and carries water
Groundwater zones
Zone of Saturation: Area where, all spaces cracks and other openings in the soil and rock grains become filled with water.
Impermeable Bedrock- Zone of solid bedrock where water cannot pass through.
Water Table: The uppermost surface of the saturated zone. The water table will rise and sink depending on the season.
Zone of Aeration/Unsaturated Zone: Area
Above the water table. The pores are filled with air.
Impermeable bedrock

9. If you increase the amount of rain
(recharge) the water table will rise.

10. The Water Table (cont.)

11. Factors Affecting Infiltration
** Remember: Infiltration means to sink into. **
Ex: Watering a plant
Slope of the Land
Sorting
Degree of Saturation
Shape
Porosity
Capillarity
Permeability
Vegetation
Packing
Land Use

12. Slope of the Land The steeper the slope (gradient), the less
the infiltration or seepage
--- inverse or indirect relationship

13. Degree of Saturation The more saturated the loose Earth
materials are, the less the infiltration
--- 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

14. Porosity
Porosity is the percentage of open space (pores and cracks) in a material compared to its total volume
Generally: the greater the porosity, the greater the amount of infiltration that can occur
---Direct Relationship
Dependent upon shape

15. Shape 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

16. Packing
The closer the particles are packed together, the lower the porosity
Therefore if you have a lower porosity, infiltration will also be lower.

17. Sorting Sorted = higher porosity or pore space
If all the particles in a material are about the same size, they are said to be sorted
If the particles are of mixed sizes, they are said to be unsorted
Sorted = higher porosity or pore space
Unsorted = lower porosity because the smaller particles fill in the pore space

18. Permeability
The ability of a material to allow fluids such as water to pass through it. Larger particles will increase permeability, because pore space is larger.
**Impermeability may be due to tight packing or cementing of particles, which seals off the pores from one another.
ex: ice in the winter

19. Porosity and Permeability
Zone of Aeration
Water Table
Saturated Zone
Poor

20. Permeability depends on:
Shape
Packing
Sorting
High
Rounded
Loose
Sorted
Low
Angular/flat
Tight
unsorted
Permeability

21. Porosity depends on: Porosity Shape Packing Sorting High Rounded Loose
Sorted
Low
Angular/Flat
Tightly packed
unsorted
Permeability

22. Capillarity
The process by which water is drawn into openings due to the attractive force between water molecules and the surrounding earth materials. As the size of the particles decrease, capillarity increases.
When water moves upward against gravity, it is called capillary action.
ex: How plants take water from the soil

23. Vegetation
Grasses, trees and other plant types capture falling precipitation on leaves and branches, keeping that water from being absorbed into the Earth
If any water gets through the vegetation, the velocity of the water will be reduced and this will give the ground more time to absorb the water
Ground without vegetation usually has high runoff and low infiltration rates

24. Land Use
Roads, parking lots, and buildings create surfaces that are not longer permeable.
These impermeable surfaces often channel runoff.
Farming, cutting down trees and grazing animals will reduce vegetation and therefore decrease permeability.

25. Factors Affecting Runoff and Stream Discharge
Runoff can occur when:
The rate of precipitation exceeds the permeability rate
The pore space of loose material or rock is saturated with water
The slope of the surface is too great to allow infiltration
The water on the surface has not evaporated
**The greater the runoff, the greater the amount of stream discharge (volume of water flowing past a certain spot in a stream in a specific amount of time.)**
UNITS FOR STREAM DISCHARGE = meters/sec
**Flooding occurs when a stream overflows its normal channel**

26. A cone of depression- forms when water is pumped out faster than it can be replenished. This can cause a well to run dry.

27. Effects of Pumping Wells
Gaining
Stream
Pumping wells
Accelerate flow
Reverse flow
Cause water table drawdown
Form cones of depression
Water Table
Drawdown
Low well
Dry Spring
Cone of
Depression
Gaining
Stream
Low well
Low river
Pumping well

28. Effects of Pumping Wells
Dry well
Continued water-table drawdown
May dry up springs and wells
May reverse flow of rivers (and may contaminate aquifer)
May dry up rivers and wetlands
Losing
Stream
Dry well
Dry well
Dry river