Andreas Späth

Reviving our city rivers

2015-03-10 13:23

Andreas Wilson-Späth

Most of us living in cities don’t tend to see rivers very often. Not because they’re not there, but because we don’t really notice them much. Many have been buried in underground pipes for decades. When they are visible, too often, they seem little more than canalised trickles encased in concrete or, worse, exposed garbage traps.

In the past, streams in urban settings were frequently considered a nuisance. If they weren’t in the way of new developments, they were looked at as seasonal flooding hazards.

Around the world, as cities have grown, they’ve had major impacts on streams within their boundaries, causing them to become increasingly degraded ecologically. The phenomenon is so widespread, scientists have given it a name: urban stream syndrome. Our city rivers are sick.

 Some of the more widespread symptoms include:

- An increase in the frequency of high flow events and floods during episodes of high rainfall when compared to streams in undeveloped areas.

- Increased concentrations of nutrients and polluting chemicals in stream water and sediment as well as the aquatic organisms that live in them.

- An increase in the numbers of a few tolerant plant and animal species, but an overall drop in biodiversity.

The main reasons for this decline in the health of urban streams are fairly well established. As cities expand and more and more areas are covered by buildings, roads and other impervious surfaces that don’t allow rainwater to soak into the ground, the amount of runoff (water that flows along the surface of the ground rather than infiltrating it) increases. As naturally low-lying areas in a landscape, streams are the places this extra runoff will flow towards, picking up all manner of contaminants – dust, rubbish, polluting chemicals – along the way and adding them to the river water.

In addition, when cities’ sewer systems leak or overflow, they add contaminants to natural streams, as do effluents from wastewater treatment plants and industry. In some instances, long-lived pollutants from earlier land use practices, such as mining, manufacturing and agriculture, may contribute to the continuing decline of an urban river’s ecological wellbeing.

The good news is that in recent years, researchers have developed a number of innovative ways to restore, resuscitate and conserve streams that flow through urban landscapes and many city governments have put a considerable amount of energy, resources and money into bringing them back to a semblance of their natural state.

Measures may include increasing the area of city surface that rainwater can filter into easily and quickly, stabilisation of river banks, improved stormwater management, better strategies for managing a stream’s catchment area and planting appropriate new vegetation in and alongside stream and canals.

The desired results include improved habitat for indigenous plant and animal species, better water quality and overall ecosystem services from city streams and wetlands, and attractive greenbelt areas that offer fantastic spaces and impetus for city dwellers to enjoy the outdoors.

It’s not cheap, nor is it always an outright success, but from Seoul to Los Angeles, urban river restoration is increasingly seen as an important option to improve the physical and ecological state of previously degraded streams.

One great local example of ongoing efforts to improve the status of an urban stream is the Liesbeek River in Cape Town, which has its source above Kirstenbosch National Botanical Garden and joins the Black River near the old South African Astronomical Observatory to form the Salt River which flows into Table Bay at Paarden Eiland.

The Friends of the Liesbeek, a volunteer organisation founded in 1991, have been particularly active in creating public awareness about the importance of the river. In collaboration with the City of Cape Town, extensive sections of the stream have been substantially rehabilitated and represent not only an increasingly healthy ecosystem, but also a beautiful recreational facility for locals.

Which is why during the 2015 Watershed Festival, an event I’m helping to organise, a number of fun events will take place along the Liesbeek’s banks with the aim of raising public consciousness about the value of our many freshwater ecosystems.

Starting this Saturday and continuing until the 24th of March, the festival includes a fun run and a family walk, as well as a free outdoor film screening and a film festival. See you there!

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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