Week 9: Groundwater Flashcards
What percentage of the world’s freshwater is groundwater?
~22%
How is groundwater formed?
By infiltration of rainwater through soils, unconsolidated surface materials, and cracks and openings in bedrock.
What are aquifers?
Zones of accumulation of groundwater. A body of highly permeable rock or sediment that stores large quantities of water that is sufficient to supply water wells
What is Porosity?
The percentage of the total volume of a soil, sediment or rock that is taken up by pores
- Depends on size and shape of grains and how they’re packed together
- Soils and loose sand and gravel have highest porosity
- For rocks, sandstones and sedimentary rocks have highest porosity whereas igneous/metamorphic have lowest
What is Permeability?
The ease with which a fluid will pass through the material
Does good porosity mean good permeability?
No, if a rock has high porosity but the passage ways for water movement are small and tortuous, then the rock will have low permeability
Compare porosity with permeability
High porosity means the material will hold a lot of water, whereas High permeability means that water can be easily pumped out of the aquifer
What is the water table?
It separates the saturated zone from the unsaturated zone in the ground
What is the Unsaturated Zone?
Zone of Aeration that lies close to the ground surface and is unsaturated with respect to water (contains water and air)
What is the Saturated zone?
The opposite of Unsaturated where pores are all filled with water
What is Recharge?
The infiltration of water into the subsurface materials by infiltration of rain and snow.
What is an influent stream?
A stream that recharges ground water and lies above the water table
What is discharge?
The exit of groundwater to the surface
What are Effluent Streams?
Where groundwater discharges to the stream
What is an unconfined aquifer?
A body of material that has more or less uniform permeability to the surface in both recharge and discharge areas. The level of the water reservoir is the same as the height of the water table.
What is a confined aquifer?
A permeable unit that is bound above and below by impermeable layers that restrict the flow of water.
What are the impermeable beds in a confined aquifer called?
Aquicludes
What is water flow in a confined aquifer known as?
Artesian flow - occurs under pressure
What is the pressure at any point in an aquifer equal to?
The weight of the overlying water in the aquifer
What are artesian wells?
Where a well is drilled into a confined aquifer at a point where the elevation of the ground surface is lower than the elevation of the water table in the recharge area - causing water to flow out spontaneously
For a reservoir to be in balance, the rate of ________ and ___________ must be equal.
the rate of recharge and discharge
What is a cone of depression?
A depression in the water table around a well that is caused by excessive pumping
What is Darcy’s Law?
States that the volume of water flowing in a certain time is proportional to the vertical drop divided by the flow distance
Q = KA(h/I)
where: k = hydraulic conductivity, l = flow distance, A = cs area, and h = vertical drop
What is the hydraulic graident?
h/l
the vertical drop/ distance travelled
