ENVIRONMENTAL ENGINEERING
Installation of a wood chip blanket on an attenuation pond embankment in Gauteng
Designing and building bio-engineered structures Gabion baskets and gabion mattresses are among the oldest and most proven environmentally engineered structures. At times, however, the strategic use of plants and geotextiles can work equally well on their own, or in combination, says Louis Cheyne, managing director, Gabion Baskets. By Alastair Currie
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hile serving effectively as mass gravity retaining wall structures, gabion baskets and gabion mattresses are also ideal for slope and riverbank stabilisation. Their main purpose here is erosion control – an especially important intervention given increasing stormwater runoff within urban centres. Previous land use, as well as deforestation, fires, droughts and the drying out of wetlands are also all major causes of erosion in both urban and rural areas. This is compounded by the invasion of alien species, like black wattle, which displace indigenous plants that were naturally suited to anchoring soils via their water-wise roots. “Over the years, there’s been increasing appreciation for the role that plants play
as nature’s bio-engineers. While we’ve traditionally focused on supplying solutions for ‘hard’ engineering designs, we are seeing a growing interest in the ‘soft’ side of environmental engineering. Here, the use of plants can complement, enhance or even replace conventional techniques. Either way, today’s emphasis is on green designs that blend in and coexist with their surroundings,” says Cheyne.
and lizards. The soil contained in the gabions for this purpose is held in place by geotextiles to prevent fines loss. The use of tickey creepers is also ideal for growing up and over gabion structures. “Essentially, there are endless variations of soft and/or hard interventions,” says Cheyne, adding that environmental engineering specialist Gabion Baskets provides installation training for industry. This includes SMME and community-based projects.
River Willow anchor system: a hybrid approach A classic example of a system that combines hard and soft approaches is the employment of shrubs to either green or help anchor retaining systems. Globally, the use
Permeability The one major advantage of gabion baskets is that they are formed using double-twisted galvanised wire mesh filled with rocks that are permeable to a greater, or lesser, degree, according to the design. This means they are also perfect for establishing plants, as well as forming a habitat for fauna like insects
This environmentally engineered solution combines a range of interventions that include gabion weirs, and a geocell-lined channel planted with vegetation. Soil blankets on the channel banks have been seeded with plants for further erosion protection (Credit: HansKingSRS)
Young tree cuttings planted to grow through and above the gabion retaining wall
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IMIESA May 2021
