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Hydrology > Water Pathways > Flashcards

Water Pathways Flashcards

1
Q

What do water pathways control

A

Denudation processes

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2
Q

What are the denudation processes, starting from the smallest scale

A

Solution
Erosion (particles and aggregates)
Mass movement (landslides)

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3
Q

What are the 2 stages of erosion

A

Detachment and transport

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4
Q

What are the two controls of erosion

A

Erodibility

Erosivity

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5
Q

What is erodibility

A

Properties of soil trying to keep it in one place

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6
Q

What is erosivity

A

Kinetic energy of water flow, whatever is resisting erosion

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7
Q

How to prevent erosion

A

Remediate

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8
Q

Where are the locations f erosion on slopes

A 
Soil pipes 
Gully’s 
Rills 
Rain splash 
Subsurface 
Sheet flow
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9
Q

What is rainsplash erosion

A

What in rainfall hitting ground and dislodging particles and taking them with it in net transfer of material

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10
Q

If raindrop hits the ground at terminal velocity how far can the particles move

A

1m

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11
Q

How does sheetflow erode

A

Focused on a particular point giving you gully erosion

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12
Q

What are direct evidence of rainsplash erosion

A

Soil pillars - what can’t be eroded

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13
Q

What are the two ways rainsplash erosion effects the landscape

A

Detachment of particles wasn’t away from sheet flow and capping of soil which increases sheet flow

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14
Q

How does capping of soil work

A

Lots of rainfall hits the surface of silty materials and the clay particles orientate horizontal and water fant get in

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15
Q

How to protect against rainsplash erosion

A

Mulch tillage

Cover cropping

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16
Q

What is mulch tillage

A

In between crops out dead vegetable matter to protect the soil this cuts off the evaporation from the soil a little bit

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17
Q

What is cover cropping

A

Put another crop in between crops to stop erosion but don’t want this to take up too many water or nutrients

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18
Q

What is surface sheetflow erosio

A

Uniform surface but water tends to move into tiny little channels called micro-rills rather than staying as a sheet. Goes from laminar into channels and becomes turbulent

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19
Q

When does sheet flow by occur

A

Over cement or tarmac

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20
Q

What equation is used to work out sheet flow

A

Reynolds Number (turbulence at depth) is VD/U. Velocity, depth of flow and kinematic viscosity

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21
Q

What is the range of turbulence in Reynolds number

A

100-500

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22
Q

What are the ways to reduce overland flow amount and velocity

A

Increase infiltration
Reducing flow velocity
Reduce net precipitation

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23
Q

How to increase infiltration

A

Organic matter to improve soil structure - slow it down.

Plough surface induration - don’t allow compacted surface.

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24
Q

What is induration due to

A 
Capping
Dessication- hydrophobicitiy 
Burning
Salt precipitates
Salt defloculates
Trampling 
Vehicle compaction
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25
Q

What makes deserts hydrophobic

A

Months of drying means water won’t go in. Setting fire to them also makes it hydrophobic and destroys soil structure

26
Q

How do salt precipitates cause induration

A

If you irritate some water is used by plants and some goes out of the water and it pulls salts in the profile to the surface. Sodium causes sobic souls which destroys the structure making it collapse.

27
Q

How does salt deflocculation occur

A

Clay deflocuates in sobic soils

28
Q

How to reduce flow velocity

A

Terracing - hold back water and slow it down.
Contour bunds - lines of stones across hill slopes to slow the water down.
Mulch tillage - rough vegetable matter resits and slows water.

29
Q

How to reduce net precipitation

A

Afforestation - reduce rainfall that gets to ground.

30
Q

What are the odd circumstances where sub surface erosion occurs

A

Sapping at seepage face

Piping

31
Q

What is sapping at seepage edge

A

If water is going through ground it may come out near the river and as it comes out it accelerates and takes some particles with it

32
Q

What is piping

A

Soil pipes where turbulent flows generate natural tunnels underground - can cause pipe collapse (middle) and pipe emergence (end)

33
Q

Where is the perfect environment for pipes

A

Silty soils don’t have enough cohesion to maintain the integrity of a pipe whereas clays have too much resistance to form a pipe. Silt has perfect structure for them

34
Q

How to protect against piping

A

Very difficult
Afforestation
Controlled drainage

35
Q

How does controlled drainage protect against pipes

A

Try to get some water out of the soil. Put drains in terraces so the water doesn’t fall into any subsurface drainage

36
Q

How does gully erosion form

A

From subsurface flows and surface flows

37
Q

What are the kinds of gully erosions

A

Rill enlargement

Undercutting by scour

38
Q

What is rill enlargement

A

Little channel gets deeper until it can be called a gully

39
Q

What is undercutting by scour

A

Overland flow runs off top of gully and botched under the material will cause collapse. Aided by soil fall and Knickpoint lip erosion

40
Q

How to protect against gully erosion

A

Stop sheet flow

Bunds e.g wire bolsters and log dams

41
Q

How to stop sheet flow and protect gully’s

A

Obstructions above the gully to stop overland flow to stop enlargement

42
Q

What is the case study for water pans

A

Borneo

43
Q

What percentage of precipitation in Borneo is hortonian overland flow

A

1%

44
Q

What is the topography of Borneo

A

V-shaped so limited saturation excess overland flow

45
Q

Why is their enormous drainage density in Borneo

A

It’s a young landscape

46
Q

What does the sharp topography in Borneo mean

A

There’s opportunities for water to come out of the soil before it gets to the river

47
Q

What is the main water pathway in Borneo

A

Subsurface flow

48
Q

What is the exception in Borneo of HOF

A

39% of rainfall over these surfaces

49
Q

How to measure sediment load

A

Measure the rapidity of water to measure the concentration of sediment in water. Take a sample and figure out the mass

50
Q

How much sediment being eroded in Borneo’s roads

A

600 tonnes per km squares of catchment per year. Natural slopes are only 30-40tonnes per year

51
Q

In Borneo where is sediment production higher

A

On tracks

643t/km^2/yr (some only 81). Not predictable

52
Q

Where is most sediment in natural catchments coming from

A

River banks where water is interacting with sediment constantly

53
Q

What erosion do undisturbed catchments in Borneo favour

A

Channel bank erosion

54
Q

What does logging in Borneo lead to

A

Landslides during extreme events as logging adds instability

55
Q

Example of landslide in Borneo

A
  1. 67t in 1 day
56
Q

What is the annual rate of erosion in Borneo

A

1467 tonnes

57
Q

What is the average erosion rate in the uk

A

50 tonnes

58
Q

What is the most extreme erosion rate in New Zealand

A

10,000 tonnes

59
Q

What did the landslide in Borneo lose in one year

A

49% of all sediment lost from Baru

60
Q

What does cut and fill timber haulage roads lead to

A

Landslide impacts seen downstream as they are intrinsically unstable in material

61
Q

What is an important aspect of sustainable forestry

A

Trying to ensure subsurface hydrology not changed by road construction

62
Q

What did Borneo do to try and create sustainable forestry

A

Add drain under road which means water percolates into drainage and changes the properties of the soil to which the small rainfall events caused it all to collapse. Done bc it’s essential to how they might finesse their forestry practices so they don’t generate as much sediment

Hydrology (9 decks)

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