ARMORFLEX: Solution To An Environmental Problem

8 April 2004




echnicrete's Armorflex erosion-control system has made a major contribution to environmental protection in an eastern Free State town, simultaneously safeguarding against local flooding, preventing erosion and protecting an ecologically valuable natural wetland.

A +R5-million project to upgrade storm-water drainage has involved the laying of 4 500m² of Armorflex concrete drainage blocks lining a channel in a residential area near Ladybrand which is prone to damaging flooding. The blocks are specially engineered to retain soils, withstand high water flow velocity and create an environment for the flourishing of natural vegetation.

Consulting to the Mansopa Municipality of Ladybrand, Engineers Stewart Scott International identified an urgent need for improved drainage control along a vlei between the township of Brightside and a newer extension in Ladybrand to the east. Frequent flooding was occurring, especially in the residential area, and a gravel road downstream had deteriorated due to poor drainage in the area of the nearby wetland.

Investigating the existing drainage infrastructure, engineers found a 400m-long channel with a concrete base and grouted stone sides running into an unlined earth channel which had become silted up and overgrown with vegetation. Litter in the channel added to the problem. Water from the channel finally emptied upstream of the wetland, leaving discharge from the wetland to flood across an important road.

The central feature of the consulting engineers' solution was the construction of a new lined channel 1,8kms long which would greatly improve drainage by replacing the heavily silted earth channel. A weir, culverts, the raising of roads and construction of embankments also formed part of the engineering solution.

Three design options were put to the municipality. All specified the use of Armorflex as the channel lining. However, the most economically and technically attractive solution would have affected the wetland, something the Department of Environmental Affairs and Tourism (DEA) had strictly vetoed. The most environmentally attractive, because it avoided the wetland, was also marginally the most costly. It was the option finally chosen.

"The normal water level of the wetland maintains a trickle downstream in the vlei," says Flip Geyer of Stewart & Scott. "It was a requirement of the DEA that the normal water level remained much the same after construction of the channel."

Armorflex-Ladybrand 2

Armorflex had been specified for the channel lining for a number of reasons. These included that it was better able to accommodate anticipated movement of the clay foundations than rigid concrete; its open-cell design allowed vegetation to grow through it; and its method of construction was labour-intensive, providing employment to the local community.

Len Mizen, Technicrete Regional Manager, added: "Recent heavy rains have demonstrated that Armorflex has succeeded brilliantly in doing what it was supposed to do, which basically was to prevent erosion and protect the wetlands by spreading drainage over a wide area instead of concentrating it into one outfall."

The project was jointly funded by the Consolidated Municipal Infrastructure Programme (CMIP) and the Motao District Municipality. Main contractors were Sefutho Construction, a local black empowerment company. The work-force was recruited entirely from local skilled and unskilled residents of Matsayeng township and Ladybrand, and training was given by Technicrete staff in the laying of the Armorflex blocks.

Engineering solution

As an engineering solution to erosion-control and drainage problems, Armorflex is one of the most widely used systems in South Africa - on coastal shorelines, defending property against wave-attack, and on inland waterways, countering the damaging effects of heavy currents and flood-waters. Its secret lies in its design - a matrix of open compressed concrete blocks and projections which readily mould themselves to the contours of the ground, settle without fracturing, retain soils and relieve hydrostatic pressure. An added bonus - which makes the system highly popular with environmentalists - is that it encourages the growth of natural vegetation, usually making the Armorflex become invisible.