Groundwater notes
Groundwater is the water that exists in subsurface voids.
The upper limit of the saturated zone is the water table.
Extending upward from the water table is a narrow zone called the capillary fringe.
Gaining streams pull groundwater through the stream bed.
Elevation of the water table is higher than the surface level of the stream
When in reverse, this is known as a losing stream.
Factors that influence ground water movement:
Porosity: percentage of total volume of rock/sediment that consists of pore spaces.
Permeability: the ability of a rock to transmit fluid.
Aquitards are impermeable layers that hinder or prevent water movement
Aquifers are permeable rock strata or sediment that transmit groundwater freely.
A perched water table is when an aquitard is situated above the main water table.
Recharge areas are places where groundwater is replenished.
Discharge areas are places where groundwater flows back to the surface.
The slope of water tables is the hydraulic gradient.
Groundwater flow systems can be local or regional.
A drawdown happens when the water table is lowered. This results in a cone of depression in the water table. It increases the hydraulic gradient near a well, which causes discharge towards the openings.
Artesian systems occur where groundwater under pressure rises above the level of the aquifer. Pressure forces water to rise in artesian systems.
When pressure surface is below ground, the well is a nonflowing artesian well.
When pressure surface is above ground, water rises to the surface as the well is a flowing artesian well.
Springs occur where the water table intersects Earth’s surface, resulting in a natural flow of groundwater. They often occur where aquitards block downward movement and force groundwater to move laterally.
A hot spring is when water is 6-9 degrees Celsius warmer than the mean annual air temperature. They can be formed when:
Groundwater is heated by magma bodies
Groundwater is heated by the geothermal gradient at depth, which then rises to the surface.
Geysers are intermittent hot springs in which columns of water are ejected. They’re created where underground chambers exist within hot igneous rocks.
Caverns are the most known landform created by groundwater.
Stalactites form on the ceiling of the cavern where water seeps through cracks above.
Stalagmites form on the floor of the cavern from water dripping onto the floor.
Karst topography occurs where the landscape has been dramatically shaped by groundwater.