Hello Everyone,
Good winter rainfall has seen regional dam levels rising. According to a report issued by the City of Cape Town on Monday 17 July 2023, five of the six major dams in the Western Cape are exceeding capacity. These include the Berg River, Steenbras Lower, Steenberg Upper, Theewaterskloof, Voelvlei and Wemmershoek dams. Theewaterskloof Dam, which accounts for more than 50% of the province’s total dam capacity, is at 102% of capacity, and these six dams, combined, amount to 99% of total storage. Last year this time, combined water storage for the Western Cape stood at 74%.
While water level at Die Oog has risen significantly from a mere puddle in April 2023, it is still a long way from capacity as Die Oog does not have stream input to complement localised rainfall.
The fact that water levels have not risen as much at Die Oog as the provincial dams is possibly a sign that the natural spring has not recharged. We believe that the historical subsurface spring supporting Die Oog became plugged or disconnected during the 1-in-400-year drought between 2015 and 2019. Increasing borehole use has, most likely, also impacted underground water flow towards Die Oog.
Dredging work in June
A major project just as the winter rains were setting in was the closing of Die Oog for a week early in June 2023. The council brought a dredging excavator in to remove debris and sludge. Our initial request was to bring in an amphibious excavator to deepen the pond so that water can hopefully be retained in Die Oog for longer during the dry summer months.
An assessment was done by the Cape Town City Council’s biodiversity and water department. They committed to removing invasive Typha capensis and Tradescantia zebrina (Wandering jew). A terrestrial excavator was provided, and dredging work was focused around the banks of Die Oog for as far as the boom could safely reach.
The team also removed sediment build-up around the island so that the water can once more flow around the island to the sanctuary area.
Sludge that was dug up was left in piles to drain on the banks of Die Oog and was later removed.
Unfortunately, it was a bit of a muddy mess once the excavator left the site, but the banks should recover soon.
Water chemistry
The council has made water chemistry and quality data available on their website.
The two charts below show how water quality at Die Oog deteriorated into 2023 showing increased pH, un-ionized ammonia and chlorophyll levels. This is in response to low water levels and overgrowth of invasive aquatic plants.
Water chemistry parameters are coloured to show when levels are ideal for aquatic life (cooler colours) and reaching toxic/non-ideal levels (red).
Un-ionised Ammonia is shown as bars here with values shown on the primary y-axis. Un-ionised Ammonia is calculated using the measured soluble ammonia, temperature, pH and conductivity values. The target water quality range is < 0,007 mg/l. Temperature and pH are shown as line curves relating to the secondary y-axis.
Decreasing water quality justifies action by the council and Friends of Die Oog to dredge and clear overgrowth early in June 2023.
Water Quality (Health and safety)
A longstanding problem involves sewerage lines in Lake View Road. Incidents of blockages in the main sewer line have been reported incidentally for over a decade. The severity of these blockages increased during the latter half of 2022, and overflows into neighbouring gardens and the grounds of Die Oog were reported to the council. This matter was temporarily addressed at the end of 2022 when the council relined the sewer pipes.
The problem unfortunately occurred again following heavy rains at the end of May this year. The issue was reported to the council on 6th June 2023, and the council responded by unblocking the sewer after 2 days.
Samples from Die Oog during this time are concerning as they peak to record (and dangerous) levels of Escherichia coli exceeding 1 million (CFU | MPN/100ml).
We are pushing for a longer-term solution as there is clearly an underlying problem with the sewer lines along Lake View road.
The chart does not extend to reflect this number in the scale as it is so large that we would lose the historical variability of this critical health indicator. The chart is complemented by a table below with advised ranges for management risk and implications.
This information is provided by the City of Cape Town.
Salvinia molesta (Kariba weed) growth
Unfortunately, the combination of removing existing invasive plant species, coupled with the overflow of sewage into the sanctuary of Die Oog, resulted in another invasive floating weed taking over. In just 3 weeks, a species commonly known as the Kariba weed (Salvinia molesta) rapidly spread across the surface of Die Oog, and it now completely covers the water surface.
Salvinia molesta is an aquatic fern, native to south-eastern Brazil. It is a free-floating plant that does not attach to the soil, but instead remains buoyant on the surface of a body of water. On windy days, it is pushed towards one side of Die Oog, only to recover the surface of the pond on calm days.
Ideal growth conditions involve still water ponds or marshes, a pH of 6 – 7.7, water temperature of 20–30 °C, and nutrient-rich waters such as those found polluted by wastewater.
Its ability to grow and cover a vast area makes it a threat to biodiversity. The plant’s growth clogs waterways and blocks sunlight needed by other aquatic plants and algae to carry out photosynthesis, thereby deoxygenating the water. As it dies and decays, decomposition uses up the oxygen in the water as well. This can kill any plants, insects and other fauna trapped beneath its growth and a breeding ground for mosquitoes.
Large infestations covering a wide area may also pose a problem to migratory birds, as they may not be able to recognise an infested waterway when flying overhead.
On a more positive note, S. molesta has been used to extract both nutrients and pollutants from the water. Proven studies have shown that it can remove over 40% of fecal coliform from the water.
Extracts of giant salvinia have also shown promising signs of inhibiting growth of human cancer cells without destroying nearby healthy ones.
The council is aware of this issue, and they will be meeting with Friends of Die Oog for a site visit this month. The meeting will address actions to remove this invasive weed, and possible options to maintain water levels at Die Oog.
I-Naturalist Challenge
We thank the biodiversity officers from the City’s Recreation and Parks Board for sharing their knowledge to educate and inspire local residents who came to Die Oog to participate in the 2023 City Nature Challenge on Sunday 30 April 2023. It was a beautiful day, regardless of the Die Oog being almost completely dry at that time.
Cape Town, once again, rose to the challenge with 52 518 observations. A total of 3 847 species were documented from 1 284 observers. Cape Town therefore leads in the southern Africa stage and achieved 2nd place globally, where La Paz, Bolivia took the lead.
Thank you to everyone who contributed. Our biodiversity carries so much value and is globally recognized.
2 years ago, a team from the Biodiversity and Ecological department of the City of Cape Town initiated a pilot project to reintroduce Peninsula Granite fynbos into the fynbos garden at Die Oog. The active restoration project involved the collection of seeds from selected locations (including Die Oog) around the southern suburbs during the summer months of 2020. The seeds were stored and smoked at the SANBI Millennium Seed Bank, where they were later subjected to controlled x-ray analysis to determine viability for germination. The team distributed viable specimens at Die Oog on the 14th May 2020.
The 2023 i-Naturalist event allowed for an opportunity to visit the site and a juvenile seedling was identified, providing hope that the seeds will germinate and mature with time.
For more information you can click on the link provided here: Saving Critically Endangered Peninsula Granite Fynbos from extinction and rising from the ashes, species that rely on wildfires for seed dispersion and germination.
Waiting for the Western Leopard Toads: It’s that time of year again
Good rains in 2021 led to the return of the Western Leopard Toads who migrate to Die Oog as a breeding site. During the week of 18-20 July 2023 toads were heard calling at some of the Clovelly golf course wetlands, so we might expect them to make their way towards Die Oog sometime during the coming weeks. Please drive with care on the roads around these wetland areas, especially at night when they are most active.
Friend of Die Oog Cards
Our custom-made cards, which were beautifully designed and painted by Michelle Liebenberg to support the endemic fauna residing at Die Oog, were sold out during the AGM early in March. We have since sold another bulk order and replenished our stock. Please contact us should you wish to purchase some notelets (R60 for a pack of 3 designs). Proceeds are split between the artist and FODO towards maintenance and care for Die Oog.
Security and maintenance
An important aspect of our role as Friends of Die Oog (FODO) is to engage with the city council and relevant organizations like WESSA for the overall maintenance and improvement of our beautiful City.
Positive work by the council includes the clearing of plant overgrowth in and around the dam and the creation of fire breaks between Die Oog, the wetland area, and surrounding residential areas.
The electronic locking mechanism of the access gate is unfortunately an ongoing problem for FODO. We are very grateful to Mark Shaw who has spent many hours troubleshooting and working on repairing it. We rely on a gardener who comes once a week for ongoing maintenance at die Oog. If you see Ebby at die Oog (usually on a Wednesday), feel free to thank him for his dedication. We also thank the committee members who ensure that he is instructed on his weekly tasks, that he receives tea and lunch and that he is paid at the end of the day.
PLEASE NOTE: Gate times are daily from 6:30am to 6:30pm.
Many hands make light work
As agreed at the AGM, we have increased the annual family membership fee to R100 from the start of the new financial year, February 2023. Thank you for the renewals and generous donations that came in after our AGM.
We rely heavily on subscriptions and donations, and with rising costs, we are starting to deplete our funds. We will send out reminders to any members that have not paid a subscription this year.
Currently we have 67 members, and we would like to bolster the numbers as broader support will help our community tremendously. Please extend our invite to join ‘Friends of die Oog’ to neighbours, family and friends.
Any additional membership amounts and donations go a far way to help us cover the rising costs of maintenance and ensure that we are able to keep our gardener employed on a regular basis.
Please click on this link for membership renewal or donations. You are also welcome to email us at admin@dieoog.org.za if you have any questions.
From all of us on the Friends of Die Oog committee, may you and your loved ones have a blessed year ahead.
Best Regards,
Keryn Tsimitakopoulos
Co-chair for Friends of Die Oog
Leave A Comment