Permeable Pavements

Introduction

No longer do we need to consider what effect greenhouse gases may have on our climate, Climate change has become a reality; those who have suffered the consequences of recent flooding events can bear witness to the destruction to property and livelihood caused by extreme rainfall events in recent times. Recent research suggests that by the year 2020 there will have been a yearly increase in rainfall of 15 – 20% on historical values. Clearly there can be no overnight solution to these flooding problems, but as part of the overall drive towards more sustainable construction techniques, concrete block permeable pavements have been introduced into the UK and Ireland in the last 5 years. Originally devised in Germany 25 years ago, they are now used worldwide as a method of controlling storm water/flood prevention without the high cost of setting land aside to install detention ponds and soakaways.
The basic concept is a very simple one. Instead of pavement areas having a sealed surface, the block paving surface is designed to allow water to percolate freely through the joints, where it is filtered in the stone layers beneath, before being allowed to soakaway into the ground or held and slowly and gently released into the storm drainage system.
Today, where optimising land use is vital, and where local drainage systems have been barely able to handle existing storm water flows, Concrete Block Permeable pavements offer the designer and developer a viable and cost effective alternative to existing storm drainage systems.

The problem

During the past number of years, there has been a marked increase in the incidences of extreme weather conditions across the world and in particular in these islands. A recent report from the Environment Agency states “Floods are now nearly twice as frequent as they were one hundred years ago - today’s extreme flood is tomorrow’s norm”. As links within the construction industry chain, we all need to reconsider the methods we have been using as to whether these are contributing to the problems, one area of immediate concern being storm drainage.

The cause

For many years now we have been designing and constructing more and more efficient methods of evacuating water from hard surfaces. So efficient have our drainage systems become, that storm water from many hard surfaces is released to watercourses within minutes of falling. Whereas in rural areas only 5% of rainfall finds its way directly to watercourses and 95% simply infiltrates into the ground it has been calculated that 95% of water falling in urban areas makes its way directly to storm drainage systems. Couple this with the fact of ever increasing urbanization, therefore an automatic increase in total area of impermeable surface exposed to rainfall, and the reduction in permeable area of soil, and therefore increased areas needing drainage. Conventional systems simply convey rainwater away from urban areas to a watercourse via a network of solid pipes rather than deal with the run-off at source. Conventional wisdom dictates that all these watercourses should constantly be cleaned of growth speeding water flow to the main watercourses where joined by flows from other sources, a surge effect is generated leading to overloaded rivers and consequential flooding.

The consequence.

Compared to the Natural processes occurring in undeveloped land large volumes of water are generated within much shorter time periods creating sudden deluges and dangerous flash flooding. Add to this then the cocktail of pollutants generated in today’s society being flushed directly into the drainage system, and it is clear there has had to be a radical rethink of how we deal with storm water discharge.
Serious consequences of this overall situation include erosion of riverbanks, localized flooding, pollution of wildlife habitats, contamination of water supplies and local drought conditions leading to low water levels in catchment areas due to poor recharge of ground water.