Restoring a wetland on the property of a Free State colliery holds the promise of benefiting not just the mine but the broader environment, including biodiversity and surface water resources in the area.
According to Dr Simon Lorentz, principal hydrologist at SRK Consulting, the mine requested advice on remediating a wetland that had dried out – mainly due to a large trench previously excavated through the wetland.
“Once you dig a ditch in a wetland, the water drains into that space and quickly flows away,” said Dr Lorentz. “This drops the wetland’s water table and the ground dries out.”
He noted that wetlands are very sensitive to water levels, requiring that water percolates right through to the surface level. Without sufficient moisture in the peat soil of this wetland area, the ground has begun to burn frequently. While this is possibly due to the veld fires in the area, the ground may also spontaneously combust due to its high content of hydrocarbons. Besides rehabilitation of flow pathways within the wetland, the proposed solution will include controlled and monitored discharges from the mine into the area that was previously a wetland, thereby contributing to the rehydration of the soil.
“If we can get this water to spread out again like it used to – rather than discharging down the slope through the ditch – we will bring all the benefits of the wetland back into play,” he said. “This includes creating an improved habitat for greater biodiversity, and cleaner water flowing into the nearby river system.”
According to Avril Owens, SRK Consulting principal scientist, an immediate benefit for the mine is to reduce its health and safety risks arising from fires on the property.
“The significance of a project like this, however, is that we can use nature to address the issue in an entirely sustainable and non-intrusive way,” said Owens. She highlighted that most projects involve a ‘hard engineering’ response where structures and technology are applied in a highly structured and controlled way to serve their purpose.
“This case presents an opportunity for us to tackle the project quite differently,” she said. “Here, we will essentially be allowing nature back in so that it can do its work. In many ways, it turns conventional engineering on its head.”
There are a number of challenges to consider, though, including the roads that disconnect some parts of the wetland from others. Culvert beds beneath ground-level roads also have the effect of lowering the water table – and thus draining the wetland. Innovative solutions will be required to address this. Owens emphasised the importance of the country’s current environmental regulations in balancing the requirements of development and environmental sustainability. She pointed out that if proper studies had been conducted at the time, these roads through the wetland area would have been designed differently.
“Our plan will take into account all the activities taking place in the area, which impact both currently and historically on the functioning of the wetland,” she said. “The project will engineer, in a ‘soft’ way, the necessary flow and interconnectedness that will allow the wetland to revive – while still accommodating the mining, quarrying and other activities in the area.”
This is not to suggest that the task will be simple. There are multiple aspects to consider, requiring an integrated range of specialised expertise. The project team includes the involvement of a hydrologist for studying surface water contributions, and a vadose-zone hydrologist to focus on the soil water between the surface and the aquifer.
A soil scientist specialising in hydropedology is also important, helping understand how water moves from the surrounding hillslopes into the wetland. This is vital in predicting how much water will be coming into the wetland and in the development of strategies to spread it effectively. Lorentz has been engaged in vadose zone hydrology and hydropedological studies for over 25 years, and experience in various geologies is delivering valuable results as a discipline.
Differential GPS surveying has been applied to generate a detailed topography of the wetland, resulting in accurate vertical data to augment contour maps. A civil engineer will be engaged for the most effective ways of retarding the rapid loss of water by spaced trench-filling impediments. This may involve designing suitable environment friendly rock weirs or using the limited on-site material in the most conducive way. The geochemistry of the soils will also need to be analysed, to know how they will react to the mine’s discharge.
The legal aspects of the project are substantial, including the necessary permissions from the Department of Water and Sanitation (DWS) and potentially the Department of Environment, Forestry and Fisheries (DEFF).
“Once there is a plan of what construction and other changes need to be made in the wetland, this needs to be taken to the relevant departments,” said Owens. “Rehabilitating of wetlands is an activity requiring authorisation from DWS.”
She said this project has the potential to demonstrate the broader benefits of working with nature to address developmental challenges relating to water.
“We can develop in a sustainable way, but we need to re-think our approach often so that we integrate our urban and industrial structures with nature,” she said.
Dr Lorentz took a similar view, highlighting how functional wetlands are a valuable reflection of the health of the natural environment.
“Modern society’s demand for water has clearly led to many interventions in the water cycle, as we control the flow of water for our own needs,” he said. “Wetlands can provide a useful indicator of where such interventions have gone too far.”
South Africa certainly has much work to do in this regard. The 2011 National Biodiversity Assessment revealed that 65% of our wetland types are under threat, with 48% critically endangered, 12% endangered and 5% vulnerable. The report notes that only 11% of wetland ecosystem types are well protected, and that 71% are not protected at all.
This project may therefore have significance well beyond its benefits to immediate stakeholders. It is likely to be another important contribution to best practice in the field of wetland remediation.