Week 11: Erosion and Sediment Control Flashcards
What are the three processes in erosion?
- Detachment (erosive forces > cohesive forces)
- Transport (water or wind)
- Deposition (sedimentation)
What are the different types of erosion?
- Splash erosion
- Sheet erosion
- Rill erosion
- Gully erosion
- Tunnel erosion
- Channel erosion within streams
- Wind erosion
What are the factors influencing erosion?
- Weather
- Topography
- Soil characteristics
- Ground cover
- Duration of soil exposure
How might soil type affect erodibility?
- Texture/particle sizes
- Organic matter content
- Structure
- Soil permeability and porosity
- Soil moisture
What are the environmental impacts of erosion?
- Soil loss
- Impact on aquatic ecosystems (habitat loss, water quality decline, smothering of plants, insects and fish)
(Also, recreational impacts.)
What are the principles of erosion and sediment control?
(I.e., what are our main objectives?)
- Minimise disturbance
- Construction in stages
- Protect slopes
- Protect waterways
- Stabilise exposed areas quickly
- Consider weather
- Install perimeter controls and diversions
- Use sediment control tools
- Mix & match your tools
- Adjust the plan as needed
- Monitor and adjust tools
Describe the principle: minimise disturbance.
- Leave vegetation/ground cover where possible
- Fit development around sensitive areas
- Design to suit topography (rather than doing significant earthworks)
- Staging + rapid stabilistation of soils to minimise exposed areas
Describe the principles: do the construction in stages.
- Avoid bulk earthworks across whole site
- Break project into stages
- Expose only area that you are working on
- Progressively stabilise exposed areas as you go
- Allow for staging in project programme
Describe the principle: protect slopes
On slopes, topsoil/hydroseeding may not be enough. May need additional:
- Texturing slopes
- Compost
- Polymers
- Straw mulch
- Other protective surface covers
Diversion of clean runoff at the top of slopes is good too.
Describe the prinicple: protect waterways.
- Identify waterways and drainage areas
- Ephemeral streams and/or drainage areas also require protection
- Avoid earthworks in or adjacent to these areas
- Avoid stockpiling soil near drainage areas
- Where does the water go?
Describe the principle: stabilise exposed areas quickly.
- Stabilise soils as soon as earthworks are complete
- Stabilisation can be achieved using vegetation, compost, mulch, grassing, polymers, geotextiles, sealing of roads etc.
- Consider the time required for grass/vegetation to grow vs. weather window.
Describe the principle: consider the weather
- Consider weather in the programme
- Some parts of NZ only allow earthworks during summer to avoid heavy rainfall
- In Canterbury: hot dry winds (NW)
- Specific high-risk activities must be undertaken in fine weather
- Allow time for stabilisation & consider impact of weather on grass growth
Describe the principle: install perimeter controls and diversions.
- Divert runoff away from active earthworks areas, stockpiles and exposed areas
- Separate dirty & clean runoff
- Clean water diversions
- Perimeter bunds
Describe the principle: use sediment control tools.
Provide treatment of sediment-laden runoff before it is discharged to the receiving environment. Some tools are:
- Sediment retention ponds
- Decanting earth bunds
- Silt fences
- Silt socks
- Stormwater inlet protection
- Coagulants and flocculants
How to prepare an ESCP:
(Erosion and Sediment Control Plan)
- Site scoping
- Construction programme
- Identify tools & techniques
- Inspections plan
- Monitoring plan
- Emergency procedures
- Live document
