This chapter describes a tool box of erosion and sediment control measures, including vegetative ones. It also provides detailed information on debris traps, a structure designed to trap larger slash after harvesting.
Investing in adequate erosion and sediment controls at the time of construction makes good business sense. They increase the life of a road or landing, and associated fill slopes, by reducing repairs and maintenance costs. Without good water control structures, the road formation and pavement can rapidly deteriorate, leading to significant safety, environmental and economic consequences. A key factor is identifying ways to decrease both the amount and speed of stormwater to reduce erosion and loss of sediment.
Plan the location of erosion and sediment control structures as part of the overall road or landing engineering design. Likewise, plan the location and design of debris traps as part of the harvest planning process. For all jobs, as part of the overall construction specification (prescription), provide the contractor with details of the structural design requirements and location. For more complex work, spend time on-site with the earthworks’ contractor.
The release of sediment into a watercourse has been identified as being a significant factor in the degradation of river and coastal habitat. The NES-PF regulations have specific requirements for sediment and stormwater control measures and debris traps. These are located throughout the regulations, so make sure these are understood. The control of erosion, along with minimising the release of sediment into waterways, is a critical component of forest engineering. Activities which do not meet the permitted activity regulations will need consents. It is suggested that the location, design and construction of the more significant structures, such as major fill areas, sediment retention ponds and debris traps, are documented and photographed.
Another important aspect is to check that the newly constructed structures are working correctly during rainfall, and as designed. If not, enlarge them, add more, or find other solutions to make them effective.
Road maintenance is discussed in Chapter 9. This chapter also includes detailed information on the maintenance of erosion, sediment and slash control structures. See the FOA Forest Practice Guides and the NZ Forest Road Engineering Manual Operators Guide for further information on this topic.