SAEON takes an enduring monitoring legacy forward

Data from the experimental catchment weirs have shown that invasive woody species use more water than indigenous vegetation. These data have been used to justify the Working for Water programme aimed at removing alien species from catchments whilst providing employment and securing water resources (Picture by Rodney February)

A Working on Wetlands team contracted by SAEON remove several hundred tonnes of sediment that has accumulated in the weirs (Picture by Nicky Allsopp)

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Sedimentation and wetland development in one of the Jonkershoek weirs prior to cleaning (Picture by Nicky Allsopp)

- Dr Nicky Allsopp, Manager, and Victoria Goodall, Data Scientist, SAEON Fynbos Node

During the 1930s South Africa pioneered long-term catchment monitoring by establishing one of the first experimental catchment projects worldwide.

In 1935, at the fourth Empire Forestry Conference hosted in South Africa, concerns of farmers were raised that plantation forestry was drying up rivers. Swift action followed with the establishment of a forestry research station that year at Jonkershoek near Stellenbosch, with Dr CL Wicht as research leader.

The first streamflow gauging weirs began monitoring water runoff in 1938. Several weirs were established in first order catchments to measure streamflow. These were based on the “paired catchment” concept that lay behind the Wagon Wheel Gap monitoring project in the USA and the Emmental project in Switzerland.

However, since none of the catchments at Jonkershoek were identical, the approach was that a baseline would first be established for water production by natural catchments. Once this baseline was achieved, plantations would be established in most of the catchments.

It’s a fact: Exotic trees use more water than indigenous vegetation

Today six of the original weirs are still operational at Jonkershoek, five monitoring catchments under plantations and one in a Fynbos catchment. Results from these catchments and others established elsewhere in South Africa confirmed that plantations of exotic trees used more water than indigenous vegetation. These data were used to regularize the forestry industry and ensure practices that ameliorated water use by forestry.

Data from the catchment monitoring programme were used to show that woody invasive species were reducing run-off by 7%, hence depriving a water poor country of a very valuable resource.

For several decades conservationists and concerned citizens had been clearing invasive plants, with little impact. It took a group of scientists convinced of the need for action based on the streamflow evidence and a far-sighted Minister of Water Affairs and Forestry to come up with a solution. In 1995 the Working for Water programme was born, linking poverty alleviation to clearing invasives as a means to secure the water resources South Africa needs for development.

SAEON revives experimental catchment network

Despite the products emerging from the experimental catchment monitoring programme, changing priorities in government led to the closure of most of the gauging weirs. The CSIR at Stellenbosch were able to maintain the Jonkershoek monitoring for a further fourteen years, but eventually were unable to continue with this without funding. SAEON, recognising the continued importance of these data, secured the go-ahead from the Chief Directorate of Water Resource Information Management to continue with the monitoring and revive the experimental catchment network.

Since then the CSIR has been transferring knowledge and know-how to SAEON on how to manage the monitoring. One of the first jobs undertaken was the cleaning of the weirs of sediment accumulated over several years and exacerbated by the 2008 wild fires. Once the weirs are clean they will continue to deliver streamflow data to build on the legacy of data collected over the preceding decades.

Global change opens up new questions

Current environmental concerns around climate change and global change factors have opened up new questions that the data can help answer. These data provide exciting opportunities for time-series analyses and holds promise for improving our understanding of the impacts of climate change on the ecohydrology of catchments.

Questions arising include: Can we develop hydrological models on impacts of climate change on streamflow using the long data record of both streamflow and climate monitoring from the catchments? How do different climate patterns affect the hydrology of the catchments? Can we detect a signal for increasing atmospheric carbon dioxide concentrations influencing streamflow through reduced transpiration? How does atmospheric carbon dioxide influence streamflow under different climate regimes? What are the implications of such changes for longer term planning of water supply to agriculture, industry and people?

To help answer these and other questions, the SAEON Fynbos node has now taken over the responsibility of archiving and disseminating the data from the Jonkershoek experimental catchment weirs as well as other first order catchments around South Africa.

Impressive data records

The streamflow data consist of hourly readings of the water volume flowing over a v-notch weir. The Jonkershoek weirs generate approximately 87 600 observations per decade, which adds up to over half a million observations for each of the six weirs within the catchment system!

Weather monitoring has also been done in the valley with rainfall, temperature and humidity readings being taken at hourly intervals. Jonkershoek has data from 11 different rain gauges within the catchment, which will provide information on the variability of the rainfall. These rainfall readings were mostly started at the same time as the streamflow monitoring, while the temperature and humidity data collection was started in the early 1970s.

The Jonkershoek monitoring provides SAEON with a large database which will be valuable in understanding the changes which have occurred over the past 70 years. The other catchments for which SAEON now has data include Cathedral Peak, Jakkalsrivier, Uitsoek, Westfalia, Moordkuil, Witklip and Zachariashoek.

Although monitoring in these catchments was started later than the Jonkershoek sites and are not currently active, there is still a large number of streamflow and weather observations for these sites and most cover at least three decades. Each of these catchments has between three and 13 streamflow monitoring stations.

SAEON’s responsibility is to archive these valuable data in a stable and safe database format. All of these records will be made available to the public via the SAEON Data Portal (http://data.saeon.ac.za) within the next few months.

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