On the of 25th of November a seminar was held at the University of Pretoria on the implementation, operation and management of Sustainable Drainage Systems (SuDS) / Water Sensitive Design (WSD). It formed part of a series of country-wide seminars hosted by the Water Research Commission, UCT Urban Water Management research unit, City of Johannesburg, City of Tshwane, City of Cape Town, eThekwini Municipality, and SAICE Amathole.
The introduction by Professor Neil Armitage included a brief overview of the conventional method of manging water in cities and how this needs to change to create cities that are Resilient, Liveable and Sustainable. Dr Kirsty Carden also shared on the water crises and how important education and stakeholder engagement is in order to change behaviour and achieve the goals of Water Sensitive Design (WSD).
The aim of Water Sensitive Design is to transform South African settlement into settlements that “mitigate water scarcity, improve water quality, thereby protecting ecosystems, through the development of water sensitive urban areas (for all) that are sustainable, resilient and adaptable to change, while simultaneously being a place where people want to live” (http://wsud.co.za/ - two important resources can be downloaded from this website, see images below)
Conventional engineering dealt with water as a waste substance to be collected and removed as quickly as possible. WSD proposes that water be managed as a precious resource through infrastructure that utilises stormwater in a way that transforms spaces into multifunctional assets with numerous benefits. The philosophy behind WSD is to keep the water in the city through establishing Blue/Green corridors which have multiple advantages to the city including: increase in biodiversity, climate control, water and flood management, human well being, increase in property value, recreation opportunities, tourism as well as the added benefit of storing carbon.
Professor William (Bill) Hunt from North Carolina State University is an expert in this field and he shared insightful information on how WSD systems work and best practice for their construction and maintenance. Practices currently being utilised worldwide include: dry ponds, wet-ponds, wet-pond with floating island, stormwater wetlands, bio-retention cells, level spreader, swales, bio-retention and swale (also termed “Regenerative Stormwater Conveyance”), permeable paving, green roof, underground device, and street trees. An innovative system using a steel grid to create a well that is installed below street trees was shown. The tree root ball grows downwards into the grid filled with a growing medium instead of lifting paving in search of surface water because of compacted soil below. A landscape architect would be able to assist in choosing the best species for street trees in this application because tree size, root growth and water requirements are all factors to consider in selecting a tree that will survive.
Professor Hunt also explained how the State of North Carolina has enforced legislation which compels new developments to reach certain hydrologic goals. Certain sites qualify as “Low Impact Developments” and these need to manage stormwater in such a way that the run-off levels are the same as the pre-developed site. Several case studies were explained and the results were not always as expected: for example a wetland filtration system with three ponds had the largest amount of filtration happening in the first pond and not much more in the second and third pond. Which suggests that it may be better to only have a system with one pond instead of three. These studies prove be very beneficial in providing the knowledge of how to build the most effective and cost efficient systems and clearly there is still much to learn.