Civil Engineering November 2022 | Vol 30 No 10

Civil Engineering November 2022 57 Water Eng i neer i ng O ngoing flood-related damage to water infrastructure in recent times has added to South Africa’s water quality risks and highlights the need for greater resilience of treatment plants, pipes and drains. Manda Hinsch, a Partner and Principal Environmental Scientist at SRK Consulting, has pointed out that the quality of drinking water erodes when infrastructure is vulnerable to natural disasters. A key challenge comes from the proliferation of algae with increased levels of nutrients in watercourses and dams. “High nutrient levels in rivers and dams – measured by the pres- ence of nitrogen and phosphates –promote the growth of blue-green algae-type, which are not algae at all, but types of bacteria called cyanobacteria. Among the current causes of this eutrophication are the discharge of raw sewage, and runoff from agricultural land, but there is also the destructive impact of floods,” says Hinsch. Variable rainfall patterns and flooding associated with climate change are a growing threat to underground infrastructure like sewage pipes, as well as wastewater treatment works. When these facilities are damaged or under-perform, they discharge more nutrient-rich water into the environment. This compounds existing problems at wastewater plants, such as lack of maintenance, under treatment capacity and the impact of loadshedding. When power to the pumping and other equipment at these plants is interrupted, treatment is affected – and leads to discharging of substandard water quality. “In areas where climate change is leading to higher ambient temperatures, this will further promote the growth of this algae,” she says. Countries like South Africa, with long average daylight, are conducive for algae growth. This combination of factors could undermine the quality of water that arrives in dams that provide communities with drinking water. “Where the problem becomes severe, tertiary treatment is required to remove the effects of the cyanobacteria – before water can be distributed to users,” she says. This treatment adds to the burden of cost among municipalities; indeed, many municipali- ties’ wastewater treatment facilities cannot easily implement this level of treatment as and when it is required. BUILDING RESILIENCE The challenge calls for a greater focus on building the resilience of water-related infrastructure. Hinsch pointed out that pump stations for sewage works are invariably situated in the lowest points and often close to watercourses, for instance. This location makes them particularly vulnerable to incidents of flooding – thereby height- ening the risk of a flood disaster becoming a broader health disaster. Since this type of infrastructure by its nature will be at low elevations, one needs to look at protecting it from failing during severe rainfall events. Where the supply of electricity to these facilities is disrupted by natural disasters – or even just regular loadshedding – there is a case for providing back-up power at these sites, including green energy. Consideration could also be given to the inclusion of balancing dams during the design phase, which could receive the flow of unmanageable sewage volumes and feed it back into the system as capacity returns to normal. Catchment management is key to addressing the problem at source. A key aspect of improved catchment stewardship is to monitor town planning to ensure that the reticulation and treat- ment facilities are designed to cope with plans. Upgrading of the reticulation facilities is often not undertaken in time and results in discharges through manholes and stormwater infrastructure. “An integrated approach to catchment management requires all stakeholders within local council to understand their own role when planning for the growing demands on the system. In many instances the sewage networks were simply not designed for the volume of material that they are expected to handle today, which have an impact on the stormwater which is often being managed by a different department within a council,” says Hinsch. Dam water quality can also be impacted as weather patterns be- come more extreme. With heavy rain alternating more frequently with droughts, there is a likelihood that sedimentation levels in dams will increase. Where ground is exposed after drought, more soil is likely to be washed downstream by intense rainfall. “The treatment of water to potable standards is also being affected when sedimentation levels are high. This makes it more difficult to disinfect the final water which again adds cost to treatment,” she says.  Protect water quality with more resilient infrastructure Variable rainfall patterns and flooding are a growing threat to infrastructure