SuDS for SIDS: Permeable or porous pavements, perhaps?

As a Caribbean native, I am fortunate to come from a region which is often associated with beauty (sun, sea and sand); home to a variety of endemic flora and fauna; a destination flocked by millions of tourists annually. Caribbean countries (the West Indies) have been grouped together amongst islands of the Pacific, Mediterranean and South China seas as Small Island Developing States (SIDS). SIDS are recognised as a distinct group of developing countries facing specific social, economic and environmental vulnerabilities at the United Nations Conference on Environment and Development (UNCED), also known as the Earth Summit, held in Rio de Janeiro, Brazil (3-14 June 1992). Despite the numerous positives for SIDS, a few negatives and vulnerabilities exist in SIDS. The scope of this blogpost is limited to only one, however: surface water management, otherwise referred to as drainage.

For numerous decades, the collection and conveyance of stormwater runoff particularly in urban areas across SIDS have been via conventional drainage systems – concrete open box drains, catchpits, culverts, detention ponds (where spaces are available) and so on. Presently, these systems are often stressed because of littering (poor solid waste management) and inadequate maintenance, in addition to the exceedance of design capacities from increased stormwater flows prevalent from either climate change, increased impervious surfaces or a combination of both. The result is often consequential floods on an annual cyclic basis. Urban development and climate change have adversely affected the management of stormwater runoff in SIDS to such an extent that authorities and policy makers have found it significantly challenging to mitigate flooding annually. Existing conventional drainage systems in urban areas of most SIDS have proven to be inadequate. Lack of space often restricts expansion of drainage infrastructure.

What is the solution? Do we continue constructing wider and deeper box drains and culverts? At what cost and economic considerations? Do we continue to deal with stormwater runoff at the downstream end? Perhaps sustainable drainage systems (SuDS) are worth considering for these Caribbean SIDS in more detail.

My research team and I – through University of the West of England, Bristol (UWE Bristol), University of the West Indies (UWI), University of Trinidad and Tobago (UTT), industrial supporters (AECOM), and the International Water Security Network (IWSN) – have made significant strides towards the application of one type of SuDS for SIDS, in particular in the Caribbean region. Research is ongoing regarding the analysis of pilot-scale laboratory permeable pavement prototypes with my PhD student John Monrose. This PhD research project targets the utilisation of permeable pavement systems (PPS) as a long-term, sustainable and resilient urban drainage option for flood risk mitigation and improvement in stormwater runoff quality in SIDS. John’s project also assesses the performance of permeable pavements comprising recycled and/or waste materials. This aspect is being considered to reduce the overall carbon footprint on the construction phase of pavements and to reduce the volume of natural material used in the construction industry. SIDS do not have an abundance of natural material; hence conservation is required.

Permeable pavements and/or porous pavements are engineered to perform as hybrid road and drainage infrastructure. They are pavements with structural requirements typically designed to satisfy lightly trafficked surfaces such as parking lots and pedestrian access whilst performing as source control media whereby a significant amount of water is absorbed at the onset of rainfall. This is significant in reducing peak flows and runoff volumes, improves stormwater runoff quality and encourages groundwater recharge where permitted. Critics will suggest that permeable or porous pavements are difficult to maintain due to clogging. I will argue however, that as with all drainage infrastructure, routine maintenance practices are encouraged and necessary for the promotion of a desirable performance output.