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A77 Maybole Bypass, 2020


Beth Doherty

Soil, Silt, Mitigation

Every construction site must plan for silt mitigation and pollution prevention. On construction sites, most pollution incidents are avoidable and the risk of pollution and damage to the water environment can be reduced by careful planning.

Various methods of silt mitigation are used on site to manage water and reduce any potential water pollution incidents. Methods we use include:​

  • Silt fencing​
  • Settlement ponds​
  • Lining of ponds.
  • Check dams.
  • Filtration through natural vegetation​
  • Haybales
  • Flocculants.
  • Over pumping.

On our Maybole Bypass Project we have used silt mitigation methods effectively site wide to ensure protection of the water environment from silt and soil-based site run-off.

An example where we used a conjunction of these methods successfully to protect the water environment on site saw a wetland area on site that discharged into an adjacent burn being utilized. The method of over pumping was first used to divert water from the mainline of the site where it was at risk of entering site drainage and picking up further silt. The water was diverted via the pump towards the wetland area. At the outfall of the pump a sedimat was put in place to catch heavy silt particles. 3 rows of adjacent silt fencing were then installed through the wetland area prior to the discharge point for the water to filter through.

Each row of silt fencing was also supported by strawbales. Once the water had filtered through each of these layers the final layer of mitigation was the natural vegetation in the wetland area. Once the water reached the outfall from site and discharged into the burn it was free of silt. This method allowed us to avoid creating heavily silt-laden water which would be difficult to treat, as well as a potential water pollution incident by directing the water away from discharge and drainage and effectively treating it.