Permeable pavements could help mitigate flood disasters

Researchers in Australia have proposed use of designing permeable pavements to specifically suit local rainfall and soil conditions and reduce flood impacts.

Permeable pavements are used on many driveways, carparks and roads (excluding main arterial roads and motorways) and typically consist of permeable pavers laid on an upper bedding layer of between 2-6 millimetres of gravel under which lies a base course layer above natural soil.

They are designed to allow rainfall to infiltrate through their surface, storing water in the base course for later reuse, and reducing urban flooding by up to 50 per cent. However, their success is variable, depending on rainfall intensity, soil type and pavement thickness.

UniSA engineers collected data from 107 towns and cities across Australia, designing an optimal permeable pavement system based on a five per cent probability of excess rainfall and a storm duration of 30 minutes.

They built an algorithm to determine the dominant soil types (clay, silt, sand or gravel) for each locality, which infiltrate water at different rates. Sand and gravel are highly permeable, for instance, whereas clay soil has a low permeability.

UniSA Professor in Geotechnical Engineering, Mizanur Rahman, says the design proposal is based on pavements storing 70 per cent of the water in the base course layer, with only 30 per cent released as stormwater runoff.

At least one third of Australian towns and cities fall in low to moderate rainfall areas, requiring no more than a 100mm base course layer on most of their road surfaces. However, the north-east of the country has both clayey soils and intense rainfall, requiring much thicker permeable pavements to reduce the stormwater runoff.

Many councils across Australia are already installing permeable footpaths, significantly reducing stormwater runoff to the roads, as well as storing water to support roadside watering of trees.

The study is published in the journal Sustainability