Mass movement, climate change and water delivery: Implications for monitoring programmes

Professor Tim O’Connor, SAEON’s Observation Science Specialist (left) explains the history of the Cathedral Peak catchment experiments to the NRF’s top management, highlighting the value of this site for answering climate change questions relevant today.   The opportunities that these catchment experiments provide need to be profiled at the highest levels so that an informed appreciation of the value of these and other long-running projects guides appropriate resource allocation to maintain them into the future.   From left: Professor Tim O’Connor; Johan Pauw, SAEON Managing Director; Dr Albert van Jaarsveld, NRF President and CEO; Bishen Singh, NRF Executive Director: Finance; and Dr Gatsha Mazithulela, former NRF Vice President for National Facilities. Click to enlarge With Mikes Pass cleared, the NRF executives were able to visit the weirs that SAEON’s Grasslands, Wetlands and Forests Node staff members are planning to revamp to observe the logistical challenges as well as the potential of the sites. Click to enlarge While Mikes Pass has now been cleared of debris from the landslides that took place in January, it is clear that it will only be a matter of time before there are more slides unless a clear stabilisation strategy is put in place. Without attention sections of the pass could be completely lost, compromising the chance for long-term access. The landsllides on Mikes Pass completely blocked the road low down on the pass, and it is a long way to get to the top. Examining the problems are, from left: Danne Joubert (SAEON), Basanda Nondlazi (SAEON) and Darryn Hilton (Ezemvelo KZN Wildlife). Click to enlarge So far and no further!

Landslides, several of them! This was one of the challenges facing SAEON’s newly established Grasslands, Wetlands and Forests Node when it started in January this year.

The landslides, which took place after what was described by Ezemvelo KZN Wildlife (EKZNW) managers as “a series of unusual and extreme weather events”, blocked the way up to one of the node’s key study areas.

The uKhahlamba Drakensberg Park World Heritage Site is of vital importance to South Africans as it provides several ecosystem services, not least of which is water production. The importance of the site as a source of water for the country was recognised by the early 20th century. Visionary scientists were therefore concerned about the impact of different potential land uses on the quality and quantity of water stemming from this and other catchments.

Situated in the Cathedral Peak-Didima Gorge area, Mikes Pass provides access to a series of sub-catchments where, in response to these concerns, the Department of Forestry established significant infrastructure in the form of gauging weirs in the 1940s to study the long-term impact of different land uses on stream flow. The long-term data emanating from these catchments have provided an invaluable understanding of the impacts of afforestation with alien vegetation on stream flow. This has consequently provided a basis for some of the forestry legislation guidelines and the evidence necessary to establish the Working for Water Programme.

Climate change impact on water delivery

While the weirs and monitoring systems put in place over 50 years ago were aimed at answering very specific questions around stream flow, water quality and land management, the infrastructure provides a valuable opportunity to answer another very critical question relevant to South African today: What impact will climate change have on water delivery?

Minor changes in rainfall can lead to significant changes in water delivery and the hydrological cycle. These relationships are seldom linear. Given the importance of water to South Africa’s economic growth potential, understanding the impacts of climate change on water delivery is a focus area within SAEON’s long-term monitoring framework. To study this, however, one requires relatively pristine first order catchments such as some of those in the Cathedral Peak study area. Further downriver there is simply too much interference from different land uses and other anthropogenic impacts to disentangle the purely climate related changes in stream flow from everything else.

Historic data records

Choosing sites that have historic data records of stream flow and weather provides an advantage because it means we get a fairly good head start in trying to look at natural variability versus anthropogenically driven climate change. With similar histories, Jonkershoek in the Western Cape and Cathedral Peak in KwaZulu-Natal were the two natural choices for SAEON to pursue this monitoring theme.

SAEON’s Fynbos Node has succeeded in reinstating several of the Jonkershoek catchment weirs. It was with resources the Fynbos Node had secured, and with their guidance, that one of the first tasks that the Grasslands, Wetlands and Forests Node had to tackle was to get four of the Cathedral Peak weirs up and running again after they had been left unmaintained for over a decade. This was planned in conjunction with EKZNW, the host organisation for the Grasslands, Wetlands and Forests Node and the custodians of the uKhahlamba Drakensberg Park World Heritage Site.

There was only one problem. We were a very far way down the pass and our access to the weirs was completely blocked off by landslides. Short of hiring a pony squad, which we seriously considered at one point, there was no way we could get to and from the sites other than walking a very long way. With the amount of work that was needed to clean out the weirs and get them operational, this was not going to be an option.

Standing on a rather precarious edge of the road which looked like it could give way any second, I stood looking at the pile of soil and impossibly large boulders strewn across the pass with Darryn Hilton, the EKZNW officer in charge. We considered the options. At a reasonable cost we could get the pass cleared, and create jobs in doing so, as an interim measure. Stabilising it would be a different story altogether, requiring a massive investment.

Knowing that this landscape is considered to be fairly erosion prone, I raised questions about how often this was going to happen and whether a large investment would be worth it. It emerged that, according to the EKZNW managers, slides of this nature seemed to have followed a very unusual set of conditions, the precursor being an extended period of above-average rainfall (over a month or two), followed by a particularly continual and heavy “extreme” rainfall event spanning several days. Some of the slides supposedly triggered by this weather event were associated with human infrastructure (e.g. Mikes Pass), but others had occurred at the same time in pristine areas.

Risk and vulnerability

Apparently the weather patterns leading up to the slides had not been experienced in the area in over 25 years. Climate change predictions of more extreme weather events in this area have led to the suggestion that these slides may become a more common occurrence. Part of our role as scientists is to gather evidence to test perceptions and predictions when relevant.

Several questions arose: To what extent are landslides associated with climatic events, and given the prediction of more intense extreme weather patterns, can the frequency and occurrence of landslides be expected to change with climate change? What would the consequences of such events be for water delivery, vegetation dynamics and alien plant expansion? In terms of risk and infrastructure management, what would the implications be for managers on the ground (and SAEON teams trying to get to the gauging weirs)?

Learning platform

After discussions with EKZNW staff, it was agreed that SAEON could facilitate a workshop on this topic. The primary aim of the workshop was to provide a learning platform for SAEON and EKZNW staff with experts in the field who generously agreed to come and share their knowledge with us. Eighteen people attended the workshop in June – six were expert scientists, three represented SAEON and nine represented EKZNW, six of whom were managers.

The scientists presented information on a range of fields - from the historical formation of the uKhahlamba Drakensberg Site (from 300 million years ago to present), to how the geomorphological processes are playing out currently. Resonating strongly with concerns voiced by managers at the workshop, risk analysis was also addressed by the scientists, providing managers with some hope that we could, to some extent, be proactive in anticipating risk areas and planning infrastructure more appropriately.

Within the framework of geological time scales, trying to understand historical patterns to help predict possible future scenarios, the role that wetlands can play as historical archives was also highlighted. And finally the soil/air interface was addressed. A range of specialised yet interlinking topics were covered, which prompted considerable debate.

Key outcomes

It was concluded that climate and land slide events were interlinked, but that there were knowledge gaps regarding specific sets of triggers which require particular research. One of the variables required to enable such work is detailed weather data. SAEON’s potential role in facilitating the collection of more spatially detailed weather data in the uKhahlamba Drakensberg Site was highlighted. A conceptual framework for such monitoring was defined and potential sites identified and agreed upon by all involved. Having managers and relevant staff from EKZNW involved in this discussion proved invaluable. SAEON aims to take the outcomes forward in collaboration with EKZNW, with implementation within the next two years.

In terms of using landslides as a monitoring tool to determine climate change signatures and impacts, workshop participants agreed that the issue was more complex but warranted investigation. This would partly involve trying to assess the frequency, locations, timing and type of historic landslides (retrospective analysis) as well as monitoring the new landslides in relation to weather.

EKZNW managers undertook to include field patrol observations of such events in their monthly monitoring returns. SAEON, in conjunction with experts in the field, was tasked with developing a more systematic statistical annual monitoring programme to be implemented in collaboration with EKZNW and academic institutions. Specific priority research areas were identified to look at additional consequences of landslide events on a range of processes. For details on what was discussed, contact sue_at_saeon.ac.za.

Mikes Pass has now been cleared thanks to funds sourced by SAEON from the Working for Water programme and we can start on a range of stream flow and vegetation monitoring programmes planned for the area. The long-term stabilisation of the pass remains a challenge, however.

Additional spin-off

An additional spin-off from the gathering was that one of the expert participants, Professor Heinz Beckendal serves on the International Erosion Control Association (IECA) Board. Once a year, this group holds a workshop for “public good” looking at a particular case study. The idea of conducting a case study for Mikes Pass to provide expert international input and recommendations on the long-term stabilisation and management of the pass seemed too good to be true. Fortunately both IECA and EKZNW supported this concept, and SAEON is currently arranging this workshop. High-level political support may, however, be needed to secure the resources to implement the recommendations.

A comment by two of the scientists was that the workshop had provided them with an opportunity to share information and creatively explore ideas, identifying potential points of collaboration and synergy. What the scientists also found exciting was the chance to interact with the people responsible for managing the land and exploring ways in which their work as scientists can have greater relevance to the people on the ground.

SAEON would like to thank Dr Greg Botha, Professor Heinz Beckendal, Rebekah Singh, Jemma Finch, Devlyn Hardwick and Dr Denise Magda for generously sharing their knowledge with SAEON and EKZNW representatives. We look forward to fruitful collaborations with you.