Week 9: Groundwater

Question 1

What percentage of the world’s freshwater is groundwater?

Answer 1

~22%

Question 2

How is groundwater formed?

Answer 2

By infiltration of rainwater through soils, unconsolidated surface materials, and cracks and openings in bedrock.

Question 3

What are aquifers?

Answer 3

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

Question 4

What is Porosity?

Answer 4

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

Question 5

What is Permeability?

Answer 5

The ease with which a fluid will pass through the material

Question 6

Does good porosity mean good permeability?

Answer 6

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

Question 7

Compare porosity with permeability

Answer 7

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

Question 8

What is the water table?

Answer 8

It separates the saturated zone from the unsaturated zone in the ground

Question 9

What is the Unsaturated Zone?

Answer 9

Zone of Aeration that lies close to the ground surface and is unsaturated with respect to water (contains water and air)

Question 10

What is the Saturated zone?

Answer 10

The opposite of Unsaturated where pores are all filled with water

Question 11

What is Recharge?

Answer 11

The infiltration of water into the subsurface materials by infiltration of rain and snow.

Question 12

What is an influent stream?

Answer 12

A stream that recharges ground water and lies above the water table

Question 13

What is discharge?

Answer 13

The exit of groundwater to the surface

Question 14

What are Effluent Streams?

Answer 14

Where groundwater discharges to the stream

Question 15

What is an unconfined aquifer?

Answer 15

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.

Question 16

What is a confined aquifer?

Answer 16

A permeable unit that is bound above and below by impermeable layers that restrict the flow of water.

Question 17

What are the impermeable beds in a confined aquifer called?

Answer 17

Aquicludes

Question 18

What is water flow in a confined aquifer known as?

Answer 18

Artesian flow - occurs under pressure

Question 19

What is the pressure at any point in an aquifer equal to?

Answer 19

The weight of the overlying water in the aquifer

Question 20

What are artesian wells?

Answer 20

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

Question 21

For a reservoir to be in balance, the rate of ________ and ___________ must be equal.

Answer 21

the rate of recharge and discharge

Question 22

What is a cone of depression?

Answer 22

A depression in the water table around a well that is caused by excessive pumping

Question 23

What is Darcy’s Law?

Answer 23

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

Question 24

What is the hydraulic graident?

Answer 24

h/l

the vertical drop/ distance travelled