Erosion and sediment control devices 

Several systems and methods have been used to try to contain the soil at the source and keep it from eroding and generating sediment that eventually finds itself into lakes, streams and rivers which affects water quality. These several systems and methods include straw and hay bales, silt fences, rock check dams, fiber rolls, sand bags, earth berm and diversion ditches, straw and coconut wattles, gravel berms and filter socks, compost berms, brush barrier, vegetated strips, mulch berm, sediment traps, sand bag barriers and triangular silt dikes. The list of erosion and sediment control devices is very exhaustive and for the purpose of our discussion we will focus on just a few selected examples which will be understood from what devices are in the context of erosion and sediment control solutions. Of these few selected examples we will highlight different types of devices and their applications in comparison to cutting edge polymer technologies that combine what separate devices would cumulatively achieve if used together. 

Common devices

Erosion and sediment control represents a combined offensive and defensive approach to site runoff through erosion prevention and sediment control respectively. Erosion prevention is an attempt to stabilize slopes, disturbed areas and other surfaces susceptible to erosion and prevent detachment of soil particles from the ground surface. Sediment control on the other hand, involves the capture and containment of eroded sediment and other pollutants being transported in runoff water. In general, erosion control products are less installation dependent but more geotextile index properties reliant. Contrastingly, performance of sediment control devices is very installation-dependent and often not dependent on material index tests. So predominantly, sediment control is the one that utilizes devices, and these devices are normally installed along the outer edge of sites to prevent sediment from escaping the site which is termed perimeter controls or barriers. Other devices that are installed are meant to reduce concentrated flow conditions to slow the rate of runoff flow and to filter suspended solids are known as check dams. Temporary perimeter sediment control devices that will be intricately evaluated as part of best management practices include silt fences, bales, berms, wattles, socks and gabions. 

Silt fence

The most commonly installed perimeter control device are geotextile silt fence which is a woven polypropylene geotextile supported by wooden or metal stakes. They are difficult to construct and maintain and their use is for short term maintenance only and the downside to their made of nonbiodegradable materials. Although some filtration occurs with new installations, geotextiles clog rapidly, and the primary mode of sediment removal becomes flow retardation and subsequent sedimentation of suspended solids. Silt fences performance is very installation dependent. There are two installation techniques, static slicing and trench-based with the former requiring insertion of a narrow custom-shaped blade into the ground whilst silt fence fabric is simultaneously pulled into the opening that is created. The latter requires digging of a trench and place fabric in the trench and then bury it followed by compaction. 

Berms and bales

Straw bales are linear sediment barriers designed to intercept and slow the flow of water and filter sediment-laden sheet flow runoff. They allow sediment to settle from runoff before water leaves a disturbed area. Their bulkiness and being heavy when wet is one disadvantage which is also coupled with their susceptibility to leaks forming at the bale connections. There are often implemented as a short term erosion control solution and are utilized best at the base of a slope or down-slope of disturbed soil. They can also be placed around stockpiles to remove solids by retention and sedimentation. Bales readily degrade in the field and may require replacement in as little as three months. Berms are linear piles of material used to retain and filter sediment-laden runoff water. The materials used to make berms include soil, stone, mulch or compost. Soil, mulch and compost berms may require some compaction and larger berms are less susceptible to erosion, offer greater filtration capabilities and are less likely to clog. For better confinement of materials, berms may be covered with geotextile and berms formed from brush debris created during site clearance are termed brush barriers. 

Fibrous logs

Fibrous rolls or logs are tube shaped erosion control devices that are filled with straw, rice husks, flax, coconut fiber or composting material that is wrapped in netting. This netting can be made up of biodegradable material such as jute, coir or non-biodegradable polypropylene. Their best application is on contours along slopes where they reduce water velocity on the slope, protecting against sheet flow and concentrated water flow. Wattles also reduce sediment loss by trapping water long enough for the sediment to settle out and they should be partially buried and staked. Filter socks are essentially contained berm and are normally filled with compost, mulch or stone. Their performance depends on filter material and connection with the ground surface. Removal of sediment as well as pollutants is possible with compost filter socks. Vegetative gabions begin as rectangular containers fabricated from a triple-twisted hexagonal mesh of heavily galvanized steel wire. Empty gabions are placed in position wired to adjoining gabions, filled with stones and then folded shut and wired at the ends and sides. The technique is appropriate for the base of a slope where a low wall may be necessary to stabilize the toes of the slope and reduce its steepness. 

Stop erosion – the first step!

All the given erosion and sediment control devices involve some form of labour-intensive process for installation and the risks associated with installation could affect their efficacy. The limitations include the need for other labour-intensive procedures such as compaction. The physical nature of the erosion and sediment control devices usually faces limitations related to failure to stop erosion and sediment at the source but rather focus on capturing it beyond and along the way to the sink. In all honesty, the erosion and sediment control devices perform as temporary measures which are faced with many technical limitations which create much more room for shortcomings. Instead, more innovative solutions which limit erosive forces at the source, penetrate and bind erodible particles, create a crust to protect the underlying layers, keep the surface intact and stable from the possible motion of particles with post-life environmental biodegradability whilst offering durability and cost savings is available at Global Road Technology. The erosion and sediment control flagship product GRT Enviro-Binder is a simple, effective and easy to apply erosion and sediment control solution which shows superior performance to erosion control devices. 

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REFERENCES 

Dugan Jr, L.I. 2015. Gabion Erosion and Sediment Control Device. US Patent US 9,057, 168 B1.

Fay, L., Akin, M., and Xianming, S. 2012. Cost-Effective and Sustainable Road Slope Stabilization and Erosion Control. The National Academies Press. 1-70. 

Hangul, A.R. 2017. In Service Performance Evaluation of Erosion Prevention Sediment Control Devices. University of Tennessee Master’s Thesis. 

Troxel, C.F. 2013. Life Cycle Analysis of Sediment Control Devices. MSc thesis Georgia Institute of Technology.