Water Pathways Flashcards
What do water pathways control
Denudation processes
What are the denudation processes, starting from the smallest scale
Solution
Erosion (particles and aggregates)
Mass movement (landslides)
What are the 2 stages of erosion
Detachment and transport
What are the two controls of erosion
Erodibility
Erosivity
What is erodibility
Properties of soil trying to keep it in one place
What is erosivity
Kinetic energy of water flow, whatever is resisting erosion
How to prevent erosion
Remediate
Where are the locations f erosion on slopes
Soil pipes Gully’s Rills Rain splash Subsurface Sheet flow
What is rainsplash erosion
What in rainfall hitting ground and dislodging particles and taking them with it in net transfer of material
If raindrop hits the ground at terminal velocity how far can the particles move
1m
How does sheetflow erode
Focused on a particular point giving you gully erosion
What are direct evidence of rainsplash erosion
Soil pillars - what can’t be eroded
What are the two ways rainsplash erosion effects the landscape
Detachment of particles wasn’t away from sheet flow and capping of soil which increases sheet flow
How does capping of soil work
Lots of rainfall hits the surface of silty materials and the clay particles orientate horizontal and water fant get in
How to protect against rainsplash erosion
Mulch tillage
Cover cropping
What is mulch tillage
In between crops out dead vegetable matter to protect the soil this cuts off the evaporation from the soil a little bit
What is cover cropping
Put another crop in between crops to stop erosion but don’t want this to take up too many water or nutrients
What is surface sheetflow erosio
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
When does sheet flow by occur
Over cement or tarmac
What equation is used to work out sheet flow
Reynolds Number (turbulence at depth) is VD/U. Velocity, depth of flow and kinematic viscosity
What is the range of turbulence in Reynolds number
100-500
What are the ways to reduce overland flow amount and velocity
Increase infiltration
Reducing flow velocity
Reduce net precipitation
How to increase infiltration
Organic matter to improve soil structure - slow it down.
Plough surface induration - don’t allow compacted surface.
What is induration due to
Capping Dessication- hydrophobicitiy Burning Salt precipitates Salt defloculates Trampling Vehicle compaction
What makes deserts hydrophobic
Months of drying means water won’t go in. Setting fire to them also makes it hydrophobic and destroys soil structure
How do salt precipitates cause induration
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.
How does salt deflocculation occur
Clay deflocuates in sobic soils
How to reduce flow velocity
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.
How to reduce net precipitation
Afforestation - reduce rainfall that gets to ground.
What are the odd circumstances where sub surface erosion occurs
Sapping at seepage face
Piping
What is sapping at seepage edge
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
What is piping
Soil pipes where turbulent flows generate natural tunnels underground - can cause pipe collapse (middle) and pipe emergence (end)
Where is the perfect environment for pipes
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
How to protect against piping
Very difficult
Afforestation
Controlled drainage
How does controlled drainage protect against pipes
Try to get some water out of the soil. Put drains in terraces so the water doesn’t fall into any subsurface drainage
How does gully erosion form
From subsurface flows and surface flows
What are the kinds of gully erosions
Rill enlargement
Undercutting by scour
What is rill enlargement
Little channel gets deeper until it can be called a gully
What is undercutting by scour
Overland flow runs off top of gully and botched under the material will cause collapse. Aided by soil fall and Knickpoint lip erosion
How to protect against gully erosion
Stop sheet flow
Bunds e.g wire bolsters and log dams
How to stop sheet flow and protect gully’s
Obstructions above the gully to stop overland flow to stop enlargement
What is the case study for water pans
Borneo
What percentage of precipitation in Borneo is hortonian overland flow
1%
What is the topography of Borneo
V-shaped so limited saturation excess overland flow
Why is their enormous drainage density in Borneo
It’s a young landscape
What does the sharp topography in Borneo mean
There’s opportunities for water to come out of the soil before it gets to the river
What is the main water pathway in Borneo
Subsurface flow
What is the exception in Borneo of HOF
39% of rainfall over these surfaces
How to measure sediment load
Measure the rapidity of water to measure the concentration of sediment in water. Take a sample and figure out the mass
How much sediment being eroded in Borneo’s roads
600 tonnes per km squares of catchment per year. Natural slopes are only 30-40tonnes per year
In Borneo where is sediment production higher
On tracks
643t/km^2/yr (some only 81). Not predictable
Where is most sediment in natural catchments coming from
River banks where water is interacting with sediment constantly
What erosion do undisturbed catchments in Borneo favour
Channel bank erosion
What does logging in Borneo lead to
Landslides during extreme events as logging adds instability
Example of landslide in Borneo
- 67t in 1 day
What is the annual rate of erosion in Borneo
1467 tonnes
What is the average erosion rate in the uk
50 tonnes
What is the most extreme erosion rate in New Zealand
10,000 tonnes
What did the landslide in Borneo lose in one year
49% of all sediment lost from Baru
What does cut and fill timber haulage roads lead to
Landslide impacts seen downstream as they are intrinsically unstable in material
What is an important aspect of sustainable forestry
Trying to ensure subsurface hydrology not changed by road construction
What did Borneo do to try and create sustainable forestry
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
