Water, Sewage & Effluent November December 2018 | Page 30

The Bruma Lake wetland and retention dam had to be filled in when, what was supposed
to be an environmental improvement, turned into a smelly eyesore and a health hazard.
looked at the role that wetlands can
play in urban drainage.
I have teased municipal officials
and academics in Cape Town about
their enthusiasm for environmental
approaches. I have suggested that
their ‘day zero’ water crisis reflected
the European approach of promoting
more careful use of water rather
than more water supply. I tell them
that their desire to use ‘natural
infrastructure’ — wetlands are
always mentioned — rather than hard
storage, treatment, and transmission
infrastructure, is further evidence
that they do not understand the
challenges of ensuring water security
for growing African cities in a very
variable climate.
So, when Aa’isha Dollie, a UCT
civil engineering honours student,
asked to see me about these issues,
I could hardly refuse. She was in
Johannesburg to look at several
cases. These included the Jackson
Park community in Diepsloot
that has suffered from extensive
flooding, which saw one young girl
drowned; other settlements along
the Jukskei River that are often
flooded; and a private residential
development where a wetland is
being rehabilitated.
In Diepsloot, the problem is that
there is no stormwater drainage. When
it rains, water simply runs downhill
through the informal settlement,
damaging homes and endangering
people. This is not an isolated problem:
around 25% of Gauteng’s residents live
in places without adequate, or any,
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stormwater drainage, and this is the
province’s biggest and most immediate
water security challenge.
A ‘water-sensitive’ approach might
propose open drainage channels big
enough to slow the flow and allow
some stormwater to soak into the
ground. Was there enough land to
allow such a solution, I asked? Might
conventional stormwater drains not
be better to get the water safely out
of the crowded settlement and into
the Jukskei River? Which would be
cheaper and most effective? And
what needs to be done about the
houses in the low-lying area below
that are regularly flooded?
Elsewhere along the Jukskei,
flooding is also the most immediate
water management problem. Every
time there is a storm over central
Johannesburg, residents downstream
along the riverbank in Alexandra are at
risk. Should there be more investment
in flood protection there, or should
engineers encourage the authorities to
develop alternative housing on vacant
land nearby?
Then there was the wetland case.
A private developer has invested
in reclaiming a wetland as part of
a new upmarket residential project
— an environmental improvement
which is now a key selling point
but should also help to reduce
flooding downstream. How much
did that cost; could those funds
have been more productively used
to address the wider challenges
using conventional technologies?
And while the developer is currently
Water Sewage & Effluent November/December 2018
maintaining the wetland, will that
continue into the future?
Dollie’s brief was to review attempts
to implement elements of water-
sensitive urban design, consider their
pros and cons and the challenges
that would have to be addressed if
this approach were to be more widely
adopted. There were concerns about
how they might work in practice,
she agreed. Open channels need
to be regularly maintained — that
needs organisation and money.
Wetlands face similar challenges. An
experimental constructed wetland
along Cape Town’s Liesbeek River
has failed for lack of maintenance
and because of the poor quality of
the incoming stormwater. Similarly,
in Johannesburg, the Bruma Lake
wetland and retention dam had to be
filled in when, what was supposed to
be an environmental improvement,
turned into a smelly eyesore.
Alternative solutions
Engineers should always seek the most
cost-effective option to meet their
client’s objectives throughout their
life cycles. So, in our discussion, we
kept coming back to the challenge of
choosing alternative solutions. Dollie
assured me that ‘traditional’ stormwater
management practices are still taught
in UCT’s engineering curriculum. While
her project focuses on alternative
approaches, she knows how to
calculate concentration times and to
dimension pipe and canal networks.
That is important. Public health
might have been one reason to
drain swamps, but now that malaria
no longer plagues rich countries,
the driver is more often economic.
Reclaiming land from well-located
swamps is a great way to turn a
quick real estate profit. Building
environmentally friendly artificial
wetlands can be an additional
selling point. But private developers
often fail to consider the impact on
downstream communities who may
be either vulnerable to floods or to the
biodiversity, unless they are forced to.
They also have a habit of disappearing
when operational problems emerge,
as happened with Johannesburg’s
Bruma Lake.
So, the challenge for tomorrow’s
engineers will continue to be to identify
cost-effective technical solutions
that meet their society’s long-term
objectives, with water security high on
that list. At the least, there will be no
lack of work for them to do. But they
are learning to think about wetlands as
they do it. u
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