Hydrogeology

Question 1

How does catchment hydrogeology affect us?

Answer 1

• It effects water quality within the environment.
• If the ground is permeable, the water will infiltrate down through the ground and into aquifers.
• This all effects the quality of our drinking water.

Question 2

What is groundwater?

Answer 2

• Groundwater is water which fills the spaces between soil particles and fractured rock beneath the Earth’s surface.
• Groundwater soaks into the ground, and flows through it, before seeping back out enriches in minerals.

Question 3

What are the different zones associated with groundwater?

Answer 3

Saturated zone:

• A region where pores and fractures of the ground are saturated with water.

Unsaturated zone:

• The region of sediment above the water table.

Water table:

• The upper surface of the saturation zone.
• The height of this is effected by:

1. Groundwater extraction
2. Seasonal rainfall
3. Catchment mining
4. Runoff variations

Question 4

What is an aquifer?

Answer 4

• An aquifer is an underground layer of water-bearing rock of unconsolidated material.
• Water in aquifers is brought up to the surface naturally via springs or lakes.

Question 5

What is the difference between a confined and unconfined aquifer?

Answer 5

Unconfined aquifers:

• Directly flow into other bodies of water.

Confined aquifers:

• Have no direct contact with any other bodies of water.

Question 6

How does human land-use effect the water cycle?

Answer 6

• Mining: Leading to soil erosion and heavy metal pollution.
• Forest conversion: Leading to changes in water flow and increased soil erosion.
• Agriculture: Leading to pesticide pollution and soil erosion.
• Human settlements: Modify the river channel and increase the risk of flood damage.
• Overall, these decrease water quality which is eventually used as drinking water.

Question 7

What is the importance of oxygen?

Answer 7

Oxygen governs both water quality and how rocks weather.

Oxygen depletion leads to:

• Decreased ecosystem health
• Oceanic dead zones
• Fish kills
• Decreased drinking water quality
• Algal blooms

Question 8

How is groundwater replenished and extracted?

Answer 8

• Groundwater is replenished by rain and snow melt through the global water cycle.
• Groundwater is extracted by wells.

Question 9

What is the ‘General Water Balance Equation’?

Answer 9

P = R + E + ΔS

P = Precipitation (rainfall, snowfall)

R = Runoff (streamflow, overland flow)

E = Evapotranspiration (evaporation, transpiration)

ΔS = Change in stores water

Question 10

What is the ‘Flow Rate Equation’?

Answer 10

Q = V x A

Q = Flow rate

V = Flow velocity

A = Cross-sectional area

Question 11

What is the ‘Continuity Equation’?

Answer 11

When a fluid is in motion, it’s mass must always be conserved. Therefore, the rate at which mass enters a system must equal the rate at which mass leaves a system.

Q₁ = Q₂

so, V₁A₁ = V₂A₂

Question 12

What is ‘Darcy’s Law’?

Answer 12

Describes the fluid flow through a porous medium (such as an aquifer).

Q = k x i x A

Q = Flow rate

k = Permeability

i = Hydraulic gradient

A = Cross-sectional area (perpendicular to flow)

i = (h₂ - h₁) / (L₂ - L₁)

Question 13

What is a river?

Answer 13

A body of water flowing along a natural channel.

Question 14

What is a fluvial process?

Answer 14

A process which is associated with rivers and streams, and the deposits and landforms created by them.

Question 15

What is hydromorphology?

Answer 15

Hydrological and geomorphical processes which affect the attributes of rivers/lakes/estuaries etc.

Question 16

What are stream orders?

Answer 16

A measure of the relative size of streams and rivers.

Question 17

Which factors affect the rate of weathering?

Answer 17

• Hydrology dynamics
• Rock type

Question 18

Which factors affect river velocity?

Answer 18

• Gradient
• Water volume
• Shape of river channel
• Friction

Question 19

What is sedimentation?

Answer 19

Occurs when eroded material which is being transported by water settles out of the water column and onto the surface, as the water flow slows.

Question 20

What is channel efficiency?

Answer 20

The ability of a river to transport bedload and discharge.

Question 21

How does velocity effect sediment load?

Answer 21

Low velocity:

• Low sediment load
• Sediment is deposited forming point bars

High velocity:

• High sediment load
• Sediment is eroded

Question 22

What is a Thalweg?

Answer 22

• A thalweg is a line drawn to join the deepest points along the length of a river.
• It is usually the line of fastest flow in a river.

Question 23

How are oxbow lakes formed?

Answer 23

• Crescent-shaped lakes form on a river when a meander is cut through and abandoned.
• The outer bank eroded so rapidly that the river cuts through the neck of a meander, allowing the river to flow through a straighter path in the channel.
• The oxbow lake then dries up and water flow stops.

Question 24

How do engineered aeration systems influence water quality in reservoirs?

Answer 24

Aeration is used to improve water quality by increasing the oxygen mixing levels.

The two main types of aeration are:

• Bubble plumes
• Surface aerators

Question 25

How are dendritic stream patterns formed?

Answer 25

On uniform ground, river networks form dendritic (tree-like) patterns, cutting valleys into the uniform geologic materials. * Tributaries meet at low angles and branch in random patterns. * They form on roughly planar surfaces or erodible rocks/sediment.

Question 26

How are rectangular stream patterns formed?

Answer 26

If the geology has large-scale fracturing, the river channels will follow the fractures, producing rectilinear patterns. * Straight tributaries meet straight trunk streams, with the bends produced being approximately right-angled. * They form on faulted bedrock.

Question 27

How are trellis stream patterns formed?

Answer 27

In strongly folded rock, drainage is in predominantly one direction, or becomes trellised. * Short tributaries meet long trunk stems. * They form on folded or tilted sedimentary rocks with different erosion rates.

Question 28

How are radial stream patterns formed?

Answer 28

If there is a central area of uplift, then drainage becomes radial. * Drainage spreads outwards in a radial pattern. * Commonly occurs at volcanos.

Question 29

How are rapids formed?

Answer 29

Formed when a river cuts downwards rapidly in a localised section of the river. * Distinctly steep gradient. * Due to channel roughness, flow is turbulent and known as white water.

Question 30

How are waterfalls formed?

Answer 30

Waterfalls form when river channels cross a fault line where tectonic processes have lifted or folded the rock. * When softer, less resistant rock is eroded quickly, a step in the river is formed, which eventually produces a waterfall. * Due to the force of water, a deep plunge pool often forms at the base of the waterfall.

Question 31

How are gorges formed?

Answer 31

A gorge is a deep and narrow ricer valley with steep sides. * A gorge is formed overtime as a waterfall becomes higher and retreats upstream. * As the waterfall retreats, a deep gorge forms down the length of the river.

Question 32

How are floodplains formed?

Answer 32

Low lying plains on each side of a river that has repeatedly overflowed its banks and flooded the surrounding areas. * Once flooding has subsided, alluvium is deposited on the floodplain. * Larger settles materials at the river banks create embankments called levees.

Question 33

How are levees formed?

Answer 33

Levees are raised banks on the side of a river channel, produced from material settling on the river bank during a flood. * This can help to prevent future flooding. * They build up over-time as flooding occurs periodically over the years.

Question 34

How are deltas (alluvial fans) formed?

Answer 34

All of the sediment carried in a river is deposited as it flows into a large body of water due to the flow rate slowing drastically. * They form at the mouth of a rivers, or inland on the approach to lakes. * Sometimes, a delta can be dynamic: 1. A mature stream develops a classic stream profile. 2. A change in base levels through faulting changes the profile. 3. Erosion moves the material towards sea level where sediment is deposited. 4. The previous delta is then mostly abandoned and eventually the original stream profile is restored and sediment is again deposited at the delta.

Question 35

What are the differences between lakes and reservoirs?

Answer 35

Lakes: * Natural, water-filled basins surrounded by land. Reservoirs: * Managed natural or artificial storage water bodies used for water supply.

Question 36

What is a Secchi disk?

Answer 36

A disk used to measure the light level at different depths as a measure of water quality.

Question 37

What is a thermally stratified lake?

Answer 37

A lake which has been separated into layers due to temperature: * Eplimnion: Top layer of a lake which is directly exposed to sun and wind. * Metalimnion: Middle layer. * Hypolimnion: Bottom layer.

Question 38

What is a thermocline?

Answer 38

The depth at which there is a sudden drop in temperature.

Question 39

What are trophies states?

Answer 39

A useful categorisation of how healthy a lake is. * **Oligotrophic**: Low primary productivity due to low nutrients (HIGH QUALITY). * **Mesotrophic**: Intermediate level of productivity. * **Eutrophic**: High biological productivity due to excessive nutrients. * **Hypereutrophic**: Very nutrient-rich lakes characterised by frequent and severe algal blooms (LOW QUALITY).

Question 40

How can geological rocks be aged?

Answer 40

Relative age dating: * Based on a sequence of sedimentary layers, with newer rock atop the older ones. * This allows you to compare the date of one rock to that of another. Absolute age dating: * Based on the decay of chemical radioisotopes. * Measurement of different radioactive species give chronology information about the rock.