Physical Geography 102
Runoff occurs both on the surface and below the surface.
Precipitation falls on the ground - some of this soaks in - Percolation or infiltration.
Groundwater is specifically defined as the part of the subsurface water that fully saturates the pore space in bedrock, regoltih or soil.
Four terms are used to define the different subsurface zone.
1) Ground Surface - above this surface the water is considered surface water.
2) Vadose Zone.
3) Water Table.
4) Phreatic Zone.
This is also called the Zone of Aeration.
Characterized by unsaturated soil and sediment, soil moisture.
Percolation is controlled gravity - movement is primarily downward.
Composition and structure of the soil will control actual direction of flow.
This is the top of the zone of saturation.
The water table is roughly shaped like the ground surface above - raised under hill or high areas - lower in valleys.
Lakes and streams are surface expressions of the water table - the water table exposed on the surface.
Water table level varies seasonally.
This is the zone of saturation - pore space is completely filled by water.
Once water is in the phreatic zone, gravity still controls the direction of flow to some extent.
Water flow in high water table areas is downward - while it is upward in areas under lakes and streams.
What causes this flow?
Ground Water Flow
Two factors control groundwater flow.
1) Porosity - the proportion of void space within the earth material.
2) Permeability - measure of the interconnectedness of the pore space.
In order for water to be able to flow as ground water the earth material must be both permeable and porous.
0.63% of world's water supply is groundwater.
Many areas rely on this as a source of fresh water.
Any time humans are involved in the use or extraction of a resource - problems arise.
Water Table Depletion - lowering of the WT due to withdrawal from pumping.
Infiltration of pollutants
1) Septic Systems
2) Garbage dumps
3) Industrial waste
4) Pesticides, herbicides and fertilizers
5) Acid rain
6) Saltwater encroachment