Erosion control, stabilisation, revegetation, landscaping, rehabilitation – what, why and how?
A key principle of ESC and construction site management is to reduce the area and time which soils are exposed to erosion. This is possibly the most important principle and underlying goal to reduce erosion at source and therefore reduce our need and reliance for temporary sediment and drainage measures and the ongoing maintenance of such. Like most things it is a relatively easy concept to grasp but can be rather difficult to achieve.
What is erosion control?
The terms stabilisation, revegetation, rehabilitation, landscaping are all related to erosion control and most simply the duration which the erosion control is intended to be effective at protecting the soil surface and minimising erosion.
Short term erosion control may be required during the construction phase to manage high risk areas of the site or supplement sediment control measures which may only capture coarse sediments. Common instances where short term erosion control are required include works in and adjacent to waterways, disturbed but inactive areas due to project staging or delays, stockpiles, small catchment areas where typical sediment controls may not be effective or accessible, and many more. Typical options for short term erosion control include soil binders/polymers (note there are many different products in this category suitable for a number of different scenarios and it is encouraged to adopt a product with proven performance), erosion control blankets (i.e. geotextile, jute, etc), plastic sheeting, site won mulch, and a range of hydraulically applied proprietary products.
Revegetation, rehabilitation and landscaping are common terms related to long term erosion control. A vast range of options, techniques and application styles are available to suit almost any long term erosion control scenario, however each will typically combine a degree of immediate ground cover, a range of vegetation species and soil conditioners aimed at not only establishing suitable growing conditions in the short term but providing a long term sustainable ground cover.
Why is erosion control essential?
Erosion control provides an effective means of covering up exposed soil surfaces and is therefore highly efficient at preventing/minimising erosion resulting from raindrop impact, splash erosion and sheet erosion. Any amount of ground cover will provide some benefit, however a figure of 70-90% is commonly referred to within guidelines and specifications as the minimum acceptable percentage in order to consider a catchment stable and therefore remove, reduce or convert any sediment control measures which were previously being relied upon to manage the potential for sediment discharge from site.
Assessing the percentage of ground cover should be systematic and undertaken across representative locations onsite, and consider the proportion of cover offer when looking vertically down at the ground surface. Achieving 100% ground-cover in one area will not offset very poor ground-cover in another area. In other words, it is not appropriate to suggest 70% ground cover has been achieved as a total, if only the roads and verges are stabilised (all be it 100% ground cover), but other portions of the site are at 0% ground cover. This is best expressed with the point of diminishing return demonstrated in the Figure below.
Figure 1 – C factor vs Ground cover (Source: NSW Blue Book).
(Note – C factor is considered to be directly proportional to soil loss)
How is erosion control undertaken?
There are many underlying factors which will need to be considered in determining the best option/s for your erosion control needs onsite. Some of the more obvious ones include:
Duration which erosion control is required (i.e. is it only short term or is bulk earthworks nearing completion and a long term stabilisation solution is required)?
Soil conditions onsite must be considered. Understanding the physical and chemical properties of soils is essential and requires soil testing to be undertaken.
Availability of resources (noting this may also include water)
Experience of local suppliers
Cost (noting the cheapest solution in terms of upfront capital cost may present significantly hire operational and maintenance costs ongoing)
Experience shows that regardless of what specific erosion control product/s are adopted, it is often the preparation (or lack of) which will dictate the success (or costly failure) of your erosion control efforts. Preparation is a wide ranging concept which includes understanding your site conditions, in particular soil characteristics (i.e. dispersion potential, texture, pH, salinity, reactiveness and permeability to name a few) as well as climatic conditions. Input by experienced and reputable industry professionals, who are familiar with the work area and specific conditions onsite should be sought prior to commencing any erosion control efforts (and ideally prior to commencing construction). Most instances of failed erosion control observed onsite could be avoided by undertaking some fairly basic steps, however unless you are experienced in this area these steps are not always obvious and won’t necessarily be the same as the previous project you have worked on.