3.4 The human impact Flashcards
How does construction decrease stability of slopes?
Construction:
- can compromise stability of slopes when there is a change in the topography
- stress on hillslope may be added due to construction; e.g weight of housing
- slopes may be undercut in order to build, causes instability
- Groundwater affected due to sewage systems
- water erosion can affect internal strength of a slop, hydraulic engineering (dams) can cause surrounding slope to become saturated if not properly managed, triggering mudslides
How does tourism decrease stability of slopes?
- prevalent in alps (mountains)
- can Create stress on hillslopes
- erosion of the slop is dramatically increased due to the trampling of vegetation, skis, heavy machinery, walking etc
- also in alpine areas where seasonal melting is common, dramatic increase of water can often trigger mass movements processes such as mudslides when the slope has been degraded
How does agriculture decrease stability of slopes?
- soil can be compacted through heavy machinery/animals
- leaves slopes vulnerable to many issues, e.g soil erosion, changes in water flows and reduced vegetation cover
- reduction of vegetation cover due to overgrazing/trampling causes degradation of soil
- vegetation, vital to soil’s structure so without landslides and other movements more likely
- increased rates of soil erosion due to less vegetation
- hillslopes left exposed to the elements, causing erosion/weathering
How does forestry lead to decreased slope stability?
- deforestation
- soil strength enhanced by tree roots, when they cut down strength compromised
- deforestation decreases interception of precipitation causing more water to flow over hillslope and infiltrate into it
- less water taken up by tree roots, increasing saturation of soil further
- clearcutting leaves hillslope vulnerable, especially to wind
- forest roads often constructed for use of transporting timber, disrupts water flow and can create channels for run-off, which can be highly erosive
What human activities decrease slope stability?
mining
construction
tourism
agriculture
forestry
How does mining lead to decreased slope stability?
- removes support from the slope, (underlying or lateral support)- causes instability
- bring large amount of waste, often left on slope
- adds stress onto slope, due to weight
What human strategies can be used to increase stability on slopes?
afforestation
netting
pinning
grading
How does afforestation increase slop stability?
- process of planting trees in an area without trees
- roots from trees increase internal strength of soil, meaning slope can take more stress before it fails
- more trees reduce the Saturation of the soil both from intercepting precipitation and taking up water from roots
- reduces risk of mass movement triggered by high soil saturation levels and decreased erosion caused by water which also compromises internal strength of a slope
- however vegetation can may allow soil moisture to build up too much and make landslides more likely
Pros:
- aesthetically pleasing/encourage biodiversity
- regulate water in the slope
Cons:
- time consuming to take effect
- could compete with existing land-use
- can be expensive to set up as land needs preparing/maintenance regularly
How does netting increase slope stability?
- netting/mesh placed over a slope to stabilise it
- contains any falling debris or rock to beneath the netting, limits hazard
- prevents falls as there is little room for anything to fall
Pros:
- covers wide area and can cope with different angles
- can be long-lasting
- cost effective
Cons:
- not aesthetically pleasing
- impact on wildlife who can become tangled in netting
How does pinning increase slope stability?
- pinning, nailing and bolting slopes increases strength of slope
- soil nailing is where the Steel rods are drilled into the soil
- the steel rods can carry weight, increasing the stability of the slope/reducing risk of mass movement
- rock bolting where bolts are drilled into rock slopes in a *specific pattern** which transfers the load from the weaker exterior to the stronger interior of the slope
- ‘knits’ rock together making it stronger
Pros:
- secure the rocks
- cheaper than other methods
- good for specific areas/problems
Cons:
- corrode over time = maintenance required
- cannot withstand extreme earth movements so not good in tectonic areas
How does grading increase slope stability?
- where the geometry of slope may be changed by removing material from slope and the slope may be re-graded to a lower angle through a combination of slope reduction and infilling at the foot of the slope
Pros:
- simple/cheap method
Cons:
- requires lots of space
- depends on land use, if there are already buildings there it is not appropriate
What are the hydrogeological strategies to reduce mass movements?
- groundwater level is lowered or water content of the slope material is reduced
- shallow drainage trenches may be cut into the slope when the potential slope movement is a shallow landslide affecting the ground to a depth of only 5-6 metres
- when there is a deeper slope movement, Deep drainage has to be introduced, often in addition to shallow trenches
What were the key facts of the Aberfan disaster?
1966
south wales
116 children dead, 28 adults
tip fell 9:14 am, last day before half term
reached speeds of 30-40 mph
What were the causes of the Aberfan disaster?
Human
- man made tips (coal waste)
- coal waste kay on top of mountain spring so dangerously fluid
- 3 yrs before written to council about danger of tips but ignored (and petition) < evaluation
Physical:
- torrential rainfall turned slurry liquid
What were the impacts of the Aberfan disaster?
Social:
- 116 children, 28 adults dead
- survivors guilt for many
- PTSD
- grief for parents of children
- ‘lost generation’
- anger towards council
Economic:
- destroyed Pantglas junior school
- destroyed 18 houses
- £1.5 million
What were the immediate responses to aberfan disaster?
- miners/other people digging by hand in search of children
- some children pulled out alive - most werent
- took queen 8 days to visit (controversial)
- make shift mortary set up in the villages Bethania Chapel on 21st October
- 400 volunteers assisted with cleaning/dressing of the corpes
What were the long term responses of the Aberfan disaster?
- national coal board claimed unaware of spring and blamed the weather
- no prosecution and no one lost their jobs on the national coal board
- NCB attempted to dodge responsibility/insensitive towards victims families
- £1.75 million funds raised by charity for victims however gov took 150k to fund removal of tips and only repaid in 1997 (no account for inflation)
- victims offered therapy by the crown
- school replaced with memorial garden
What were the key facts of the Vaiont dam disaster?
1963
- 70 miles from Venice
- 44 billion gallons water dam
- 200 metre wide slab of rock created 100 m high wave
- sent waves over 30mph to local village Erto
- 2043 dead
What were the cause of the Vaiont dam disaster?
Human:
- decision to build dam in an area with known geological instability
- dam was built on a steep slope, making it more susceptible to landslides
- dams height/shape didn’t properly account for the pressure exerted by the reservoir making it more vulnerable
-several raisings/lowering of the dam
Physical:
- period of heavy rainfall
- rocks were dipping down towards the bottom of valley creating natural slip planes
-also fault line creating slip planes
- valley had been scene of a previous landslide and much of rock unstable
- reservoir led to increase in groundwater pore pressure as water table rose in the rocks
What were the impacts of the Vaiont dam disaster?
Social:
- 2,043 fatalities
- many homes/villages destroyed, displacing numerous families
Economic:
- $200 million
- loss of infrastructure: cost of rebuilding substantial
- local economy effected: businesses disrupted/destroyed
Environmental:
- caused destruction of natural habitats, including forests and wildlife
- release of water and debris into the valley and river system led to water pollution/contamination
- biodiversity significantly disrupted (animals killed/habitats destroyed)
-
What were the responses to the Vaiont dam disaster?
Immediate:
- focused on search and rescue efforts to save as many lives as possible
- emergency services evacuated people from the affected areas- medical assistance to injured
- temporary shelters and relief centres set up
Long term:
- improved dam safety: conducting thorough geological surveys and studies to better understand stability of dam sites
- enhanced engineering techniques/technologies to strengthen dam structure and improve their ability to withstand potential risks
- monitoring systems put in place to continuously assess dam performance and detect any signs of instability
- support provided to affected communities
What causes landslides in Hong Kong?
June 1966 - rainstorms triggered landslides:
64 killed
2500 homeless,
8000 evacuated
- 1650mm rainfall in 15 days. causing 700 landslides
- vegetation partly to blame, as smaller slips were held back, causing larger washouts to occur instead
- triggered by excavation, building works and traffic
What are the attempts to reduce mass movement in Hong Kong?
-
Prediction & Monitoring: Geotechnical Engineering office: 700 workers manage and improve safety systems
- use of slope monitoring systems = no major deaths since 1982 -
Hazard mapping and slope registration: Catalogue of Slopes: records updated, maintained and disclosed for 57,000 manmade slopes, Helps planners and constructors assess risk and install precautions
- reduced fatalities by over 90% in 1970s -
Preparedness/Public awareness
- Fines: HK$50,000 and 1 year in prison if private owners do not comply with slope safety protocols
- regular community drills/school awareness: over 80% in high risk areas know what to do when warning -
Prevention: Drainage systems: help to remove excess water from heavy rainfall that leads to slips. Some confusion exists over responsibility, so some poorly maintained.
- Manmade slopes: main method of slope stabilisation. over 4,500 high-risk Slopes graded to reduce risk, drains built to intercept/direct water away. Impermeable hard covers added to protect slopes from infiltration and erosive effects of water.
What are the greening techniques used to manage landslide in Hong Kong?
Greening techniques:
- Mulching: provides protective cover that vegetation can grow through, to hold it in place. Highly adhesive capacity on steep slopes, resistance to rain erosion, retains water, long lasting fertilisers, adaptable to rough surfaces
- Long rooted grass: hard cover with drilled holes - fertilisers and soil added to hole and grasses planted in.
Environmentally friendly, fast, easy cost effective installation, low maintenance and works on steep slopes
- Fibre reinforced: polyester fibres mixed into soil to resist tension and hold soil stronger.
Low maintenance, self sustained, erosion prevented, restoration of natural habitats, visual improvement of slope and addition of plant species
