CMA PUBLISHES CRB HYDRAULIC APPLICATIONS PROJECT REVIEW:

CMA director, John Cairns, says the use of concrete retaining blocks in hydraulic applications can be divided into three distinct areas, attenuation ponds, river bank protection and coastal protection.

“The need to protect river banks and other water courses dates back to the earliest civilizations and many methods of protection have been developed down the years. Several natural materials used in the past are still used today, together with modern materials and engineering principles.

“River banks suffer random and in some instances regular flooding and the results can be devastating. Beaches on the other hand are subjected to wave action, which is more predictable and regular, although changing currents and heavy seas can also be devastating, laying waste to buildings and other beach-front structures. Controlling the flowrate of stormwater discharge of new property developments has become a JRA requirement and attentuation ponds are being used to achieve that objective.

“The success of CRB retaining walls was demonstrated conclusively in March last year when turbulent seas and extraordinarily high tides, which wreaked havoc on large stretches of beach on the north and south coasts of KwaZulu-Natal, resulted in only slight damage to those sections of the coast protected with sea walls constructed with retaining wall blocks supplied by a CMA member.

“South Africa’s rainfall patterns, particularly those of the interior, where storms and then dry spells between them are commonplace, generate hydraulic instability. Engineers need to adopt a wholelistic approach to river bank protection, taking complete catchment areas into account, because unless they do, any river bank work is likely to lead to failure.
 
“Two factors are of particular importance in hydraulic protection. First, irrespective of the materials and form of construction, beaches and river banks form part of the natural environment and effective design must embrace sound environmental as well as engineering practice. Secondly, the development of an adequate design requires a clear understanding of factors effecting the stability of the existing bank/beach, as well as those factors which are likely to affect the stability of the protective wall,” says Cairns

Despite being relatively new to this type of application, concrete retaining blocks are now at the forefront of erosion protection, coastal protection, river training and general hydraulic structures, especially where traditional reinforced concrete is unsightly.

CRB blocks look more natural, due to a patterned yet uneven face and a facility to harbour vegetation. Moreover, their versatility lends them to some very attractive layouts. On larger projects, best results are gained from a multi-disciplinary approach, incorporating the skills of professionals in the fields of hydraulics, soil mechanics, landscape architecture, horticulture and wildlife.

Copies of the brochure are obtainable at no charge from the CMA. Contact Pam on (011) 805-6742 or on main.cma@gmail.com .

Beachfront CRB retaining walls such as this one at Umhlanga in KwaZulu-Natal, successfully withstood the damaging effects of the exceptionally heavy seas which pounded the KZN coastline during March 2007. 

A typical example of an attenuation pond, this one having been constructed at Chilli Lane, a shopping centre in Sunninghill, Sandton.