Pavement versus Rainwater
We all know the serious effects that hard paving areas have on the natural passage of rainwater:

  • It catches the rainwater, concentrates it and sends it elsewhere;
  • It causes excess runoffs of great energy;
  • The runoff water picks up hydrocarbons (oil and tyre rub-off) off the roads and transports it to waterways;
  • Groundwater is depleted by the denial of natural rainwater to the roots of trees in and around the paving area and
  • Anoxic conditions that prevail under impervious paving.

We know the damage that may be caused by concentrated runoff if it is not properly managed. We know how much it costs to build elaborate storm water systems – massive pipe networks, gulley’s, catch pits and outlet structures. We know the cost of and space required by attenuation dams and structures. We know the waste involved in paying to have water taken away from tree roots and then paying again for irrigation.

Do we even know the cost of pollution to waterways caused by or exaggerated by large impervious paving plazas as is found in urban areas?

The Problem
At the root of the problem is the interference by man in preventing the ground from absorbing rainwater as it naturally would. In nature the ground accepts, stores, filters and purifies rainwater. Only the excess caused by above average rainfall will run on the surface. With urbanisation, more and more roofs and paving are being built, covering ever more of the land surface.  Less and less space is left to function in its natural way.

The extent of the problem in built-up areas is huge. In countries that use road vehicles as a primary means of transport like South Africa (and the USA), pavements occupy twice the surface area of buildings. Of all the physical features of cities it is the most influential. Pavements dominate the quality of urban environments. It is responsible for essentially two thirds of the excess runoff with all of its consequences as mentioned above (ref 1).

Permeable Paving
Permeable paving, as opposed to ordinary paving, allows the free passage of rainwater through the paving into the ground. It also allows air to pass through the provided voids. This ensures that the ground breathes naturally by thermal action, supplying oxygen to roots and beneficial aerobic bacteria.

Grand Parade, Cape Town: Only the lower portion of the large parking area was paved with permeable paving. The picture was taken during a bout of rain. The difference between the wet and dry surfaces is obvious.

Picture: CMA, Blocks By Inca Concrete

Permeable paving is known in different forms: Chipped stone, grass blocks and open-pattern paving. Less well known are plastic geo-cells and Permeable Concrete Block Paving.

Permeable Concrete Block Paving is a constructed surface suitable for all forms of traffic. It makes use of Special Concrete Paving Blocks that allow the penetration of water but is functionally similar to conventional block paving. The paving foundation, i.e. the base and sub-base courses, are constructed in a porous manner that facilitates water collected from the surface. This water may be allowed to infiltrate the natural ground straight away, or if the permeability of the soil is poor, the constructed road foundation can be used as a flood absorption reservoir. Only the excess water is drained away to swales, ponds or watercourses. Permeable paving systems are used in the arid parts of Australia for collecting and storing of rainwater. It is then used locally for irrigation or in water features.

Permeable Concrete Block Paving has been around throughout the UK, Europe, especially Germany and other parts of the world for decades and is well proven. There is a wealth of information and experience available so that design and implementation is no longer experimental but a specifiable practice.

Permeable paving, beyond conventional stormwater management, is the next important advance towards achieving a pristine and working urban habitat.


Vanstone's Offer:
Interlocking type concrete block pavers are by far the best performers for load bearing capacity. Vanstone's Aqualock Pavers are specially designed to have strong interlock together with openings to let the water through.

Vanstone now offers three new Permeable Concrete Block Pavers: The Aqualock Pavers in 60mm and 80mm thick and the Aqua Random Pavers that are 50mm thick.

(1: Bruce K. Ferguson: Porous Pavements, CRC Press 2005)

Read Also:
Important Civil Engineering Aspects

> View Vanstone's "Aqua Range" of Permeable Concrete Block Pavers