Gabion Weirs – Waterberg 24 April

Waterberg Golf Estate.

Gabion Baskets were approached recently to assist in the design of water attenuation structures for a river course in a new golf eco-estate to be built near Alma in the Limpopo province. Alma is about 10km from Bela Bela (Warmbaths). The site is to be developed into a 18 hole golf course and eco-estate with game and eco-lodges in the next 5 years. The initial works being done now were part of an insurance claim from floods that damaged some gabion structures and unprotected water couses earlier in the year.

Gabions and mattresses had already been used on site (built last year) and due to poor design and implementation there had been some failure and excessive soil erosion caused by large amounts of rainfall earlier in the year. More extensive soil erosion protection structures were also required.

I visited site with Reg Laskey from Littlecreek Civils in February and we undertook the preliminary design proposals and pricing to complete the works on site. Reg started on site in early March, initially programmed for three months, the works are now to be completed in two months (by the end of April). We were also asked to work with Mr. Helmut Keller a hydraulic design engineer with SKC engineers in Pretoria, who had done the design water flows and had been of technical assistance to the client previously. We met with Helmut and he recommended some modifications to our designs to allow for further protection of the watercourse.

The gabions on site amounted to 1000m3 of galvanised materials with extra mattress works for repairing and repacking existing mattresses not laid correctly, providing for removal of damaged mesh and repacking and replacing of extra rock within the mattress compartments. Contractors often try to level off the mattress tops with smaller flat rock to achieve a flat level surface on the top of the mattresses. This allows strong water flows to remove the finer rock fragments up through the mesh openings and the partial emptying of the mattresses. We found that some oversized rock placed in the mattresses had also been used and this had to be removed and replaced in position. Normally rock of 100mm min. size to 2/3 of mattress depth maximum size is required for this purpose.

Labor related;- 14 trained and 9 untrained laborers were on site for the duration of the works. Reg used the unskilled labor mainly for collecting, passing and filling of the baskets. The skilled installers were used to erect the baskets, lace them, brace and close them and also for the nice/correct packing on the external front faces, this being the most important task to ensure great looking gabions. On-site rock was mostly used to fill the baskets to allow for reduced costs and the blending in of the rock color with the local soil on site.

Repacking of the River (Reno) mattresses that were not correctly installed and replacing their lids. In many cases no cut-offs were installed on the upstream ends of the mattress protections. We designed gabion weirs at specific points along the river course to reduce water velocities and encourage accretion of finer river bed materials upstream of each structure. The water hydraulic energy was now focused at specific points where adequate mattress protection was designed for and placed. River mattresses were placed where there existed the possibility of soil erosion upstream or downstream of weirs and within the gabion stilling basins. A 20-30Mpa concrete 100mm thick capping was placed on all weir crests and the first two metres of the stilling basins downstream, to prevent debris damaging mesh lids during flash flood situations.

Experienced gabion teams were used for the installations and a neat and tidy project was completed in a short space of time relatively economically and environmentally friendly when compared with any other solution. The client (Matkovitch and Hayes) a landscaping and golf course erection company were very happy with the works and like using gabions on their golf course projects due to the environmental benefits of the system. They were also working on a site:- Nondela in the Natal Drakensburg where we have supplied W.B.H.O. Construction with many gabion materials up untill now.

We have shown some project photos below, kindly contact us for any further information you may need.

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