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Geology and Hydrogeology > Hydrogeology > Flashcards

Hydrogeology Flashcards

1
Q

How does catchment hydrogeology affect us?

A
  • 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.
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2
Q

What is groundwater?

A
  • 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.
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3
Q

What are the different zones associated with groundwater?

A

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
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4
Q

What is an aquifer?

A
  • 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.
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5
Q

What is the difference between a confined and unconfined aquifer?

A

Unconfined aquifers:

  • Directly flow into other bodies of water.

Confined aquifers:

  • Have no direct contact with any other bodies of water.
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6
Q

How does human land-use effect the water cycle?

A
  • 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.
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7
Q

What is the importance of oxygen?

A

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
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8
Q

How is groundwater replenished and extracted?

A
  • Groundwater is replenished by rain and snow melt through the global water cycle.
  • Groundwater is extracted by wells.
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9
Q

What is the ‘General Water Balance Equation’?

A

P = R + E + ΔS

P = Precipitation (rainfall, snowfall)

R = Runoff (streamflow, overland flow)

E = Evapotranspiration (evaporation, transpiration)

ΔS = Change in stores water

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10
Q

What is the ‘Flow Rate Equation’?

A

Q = V x A

Q = Flow rate

V = Flow velocity

A = Cross-sectional area

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11
Q

What is the ‘Continuity Equation’?

A

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

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12
Q

What is ‘Darcy’s Law’?

A

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)

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13
Q

What is a river?

A

A body of water flowing along a natural channel.

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14
Q

What is a fluvial process?

A

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

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15
Q

What is hydromorphology?

A

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

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16
Q

What are stream orders?

A

A measure of the relative size of streams and rivers.

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17
Q

Which factors affect the rate of weathering?

A
  • Hydrology dynamics
  • Rock type
18
Q

Which factors affect river velocity?

A
  • Gradient
  • Water volume
  • Shape of river channel
  • Friction
19
Q

What is sedimentation?

A

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.

20
Q

What is channel efficiency?

A

The ability of a river to transport bedload and discharge.

21
Q

How does velocity effect sediment load?

A

Low velocity:

  • Low sediment load
  • Sediment is deposited forming point bars

High velocity:

  • High sediment load
  • Sediment is eroded
22
Q

What is a Thalweg?

A
  • 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.
23
Q

How are oxbow lakes formed?

A
  • 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.
24
Q

How do engineered aeration systems influence water quality in reservoirs?

A

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

The two main types of aeration are:

  • Bubble plumes
  • Surface aerators
25
Q

How are dendritic stream patterns formed?

A

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.
26
Q

How are rectangular stream patterns formed?

A

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.
27
Q

How are trellis stream patterns formed?

A

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.
28
Q

How are radial stream patterns formed?

A

If there is a central area of uplift, then drainage becomes radial.

  • Drainage spreads outwards in a radial pattern.
  • Commonly occurs at volcanos.
29
Q

How are rapids formed?

A

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.
30
Q

How are waterfalls formed?

A

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.
31
Q

How are gorges formed?

A

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.
32
Q

How are floodplains formed?

A

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.
33
Q

How are levees formed?

A

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.
34
Q

How are deltas (alluvial fans) formed?

A

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.
35
Q

What are the differences between lakes and reservoirs?

A

Lakes:

  • Natural, water-filled basins surrounded by land.

Reservoirs:

  • Managed natural or artificial storage water bodies used for water supply.
36
Q

What is a Secchi disk?

A

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

37
Q

What is a thermally stratified lake?

A

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.
38
Q

What is a thermocline?

A

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

39
Q

What are trophies states?

A

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).
40
Q

How can geological rocks be aged?

A

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.

Geology and Hydrogeology (9 decks)

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