Environmental Services

CLIMATE CHANGE, A HILLTOP DAM AND FIXING THE MISTAKES OF THE PAST

CLIMATE CHANGE, A HILLTOP DAM AND FIXING THE MISTAKES OF THE PAST

Client: 
Paul Cluver Wines
This case study post shows how climate change is already impacting farmers’ water storage decisions and how these decisions can have broader environmental impacts. The frank and open discussion with the landowner has value for us all and highlights our need to look critically at past decisions in the light of our current environmental awareness and increasing environmental pressures.

BACKGROUND

A key limiting factor in agriculture is the availability of water as you can only farm as much land as you have water to irrigate. As is the case with most of the Elgin Valley, the macro planning regarding water extraction, movement and storage was done in the 1960’s and 70’s.  Such was the case with a hilltop storage dam planned in the early 70’s on the farm De Rust belonging to the Cluver family. At the time, the benefits of hilltop storage where considered to be significant electricity savings on irrigation pumping, provided the supply could be piped by gravity from an in-stream weir.

In the early 1990’s the De Rust management team decided to proceed with the construction of the proposed hilltop storage dam on the lower slopes of the Groenlandberg mountain. However shortly after construction started, several compounding factors led the management team to change their mind and construction was stopped. The factors influencing their revised decision included:

·       Early indications of changing rainfall patterns which would mean that the water source would no longer provide sufficient, regular, year-round stream flow to fill the dam;

·       The high construction costs of a hilltop dam per m3 of storage capacity due to the scale of the excavation works and

·       The below average financial performance of the business at the time.

The scar left by the initial excavation work has however remained a constant reminder to Dr Cluver, the landowner, of an environmental impact that, in hindsight, could have been avoided.

One of the impacts of climate change in the Western Cape is fewer, heavier rainfalls. It is therefore more effective to capture and store the resultant infrequent, high-volume stream flow in dams that are built in valley-bottoms. De Rust had an existing in-stream storage dam on the farm and it made more sense to increase the storage capacity of this existing dam.  This would also result in a reduced impact on biodiversity by avoiding the construction works at both the hilltop dam site and the supply pipeline and weir. New rural electricity tariff structures also allow for cost-effective off-peak pumping.  This allows the farm to fill smaller hilltop irrigation dams from the main storage dam during off-peak periods and then gravity feed the irrigation systems across the farm.  A related consideration is the ever-reducing costs of solar installations to provide electricity for pumping.

With the above considerations in mind and capitalising on the low dam levels in 2016, the De Rust management team made the decision to increase the capacity of their existing in-stream storage dam.

This meant that they would have machinery on site in early 2017 and the decision was taken to use this opportunity to complete the construction of a scaled down version of the original hilltop dam which involved the completion of two smaller, balanced irrigation dams.  At the same time, the machines would be used to restore the old vegetation scar by transporting surplus top soil from the enlargement of the lower in-stream dam to cover the scar. Once covered with top soil the restoration site would be surface seeded using seed-containing leaf litter from adjacent areas of the same vegetation type.  Dr Cluver had previously conducted a pilot restoration project on a small section of the old scar and his intervention had proven remarkably successful in terms of the restored species composition. It was therefore felt that a similar approach would be effective for the larger-scale restoration of the remaining impacted areas.  To provide advice and assistance on this restoration project, Dr Cluver contacted NCC Environmental Services.  

DESIGNING A CUSTOMISED SOLUTION

Restoration work is different from rehabilitation in that it seeks to restore the ecosystem to its pre-existing condition and associated functioning as opposed to superficially repairing it. This is more complex and specialised undertaking however, whilst being the ethically preferred option, it is not always possible due to the extent of the damage or the nature of the underlying ecological systems. After an initial site assessment, NCC determined that ‘restoration’ was indeed possible on this site and thereafter set about designing the implementation processes to bring this about.

IMPLEMENTATION

After an assessment of the available topsoil stockpiled during the enlargement of the in-stream storage dam, selected topsoil was transported to the hilltop site and spread over the scar. This process is an attempt to replicate the original soil horizons and providing a more suitable growing medium. This topsoil also contained many years of stored seed as well as bulbs and other essential microorganisms needed to kick start the ecological processes at the restoration site. Prior to the spreading of topsoil, the surface crust of the exposed clay was disturbed to better integrate the new topsoil layer.

Suitable seed-donor sites for the surface seeding were then identified by taking into consideration soil and vegetation characteristics including species, assemblages and composition. Due to recent fires, the seed donor site was not directly adjacent to the restoration site, but all seed was sourced from mature stands of the same vegetation type, within a 2km distance and at the same altitude and aspect.

NCC’s horticulturalist, Sean Altern, then trained the De Rust alien clearing team in the principles and practical techniques of sustainable fynbos seed and mulch harvesting.  Sean took the team in-field and together they harvested the first loads of protea heads and seed containing leaf mulch.

The carefully gathered seed mix was then spread over the receptor site in a random fashion, allowing for the natural germination of the correct variety of species, with intact genetic integrity. Restoration is a time-consuming process requiring many seasons to achieve the intended outcome and this process may be repeated for a few more years. During the five years after seeding, ongoing monitoring is conducted to assess the growth and composition of indigenous species as well as address any issues that might arise such as top-soil erosion and the germination of invasive alien plant species.

LESSONS LEARNED

NCC is proud to be a part of this project helping De Rust to maintain their reputation as farm that applies sound environmental management and conservation principles to their farming operations.  As Dr Cluver so openly sums it up, “With this project, there was a degree of wanting to repent for the sins of the past. As one gets older, one becomes increasingly aware of the regrets one has in life, most of these regrets relate to things you didn’t do, but sometimes, as in this case, they relate to something you did. Knowing what I know today, I would not have embarked on the hilltop dam project. However, in my defence, man’s relationship to the environment is evolving and today we understand much more about our responsibility as custodians of the environment.  When I started farming, we were at a point in history when growth, development and advancement were the ultimate goals with little or no consideration given for the environment or the future. Today we see a completely different story. The awareness of our dependency on ecological systems and processes is increasing and with it comes increasing levels of concern for the sustainability of our socio-economic systems and the indeed our survival as a species.”

ACHIEVING REAL GROWTH

Through this project, NCC has most certainly been able to live up to our balanced vision of real growth of people, planet and business. We will publish some follow-up blog posts in due course to show the restoration progress over time – please stay tuned. We applaud the team at De Rust because it’s not about making a mistake, everybody makes mistakes at some point, it’s about what we do after we make a mistake that counts. 

NCC ENVIRONMENTAL SERVICES PROJECT TEAM:

Justin Miller - Project Manager
Sean Altern - Project Lead
Robin Jangle - Botanical Consultant
Andrew Purnell – Sustainable Agriculture Consultant