What's wrong with a concrete drain? In short: almost everything.
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Probably the only desirable purpose of a drain is to protect structures such as houses, bridges, roads and buildings. Otherwise, drains convert a natural waterway into an ugly artificial environment.
According to this thinking, the job of a watercourse is to remove water, and a stream becomes a drain/pipe.
It's a solution to a problem that ignores the ecosystem services that a healthy watercourse provides for free.
Like soil, rivers and their riparian zones are important carbon sinks. It is estimated that a degraded river stores less than 2 per cent of the carbon of a healthy one. Drains are very poor at capturing nutrients which are lost to the local environment. They can become concentrated in the receiving waterbody (such as a lake) where they can trigger problems such as algal blooms.
This kind of engineering damages the attractive public spaces that are valued by communities.
To construct a drain, bulldozers clear away vegetation. Trees, shrubs, reeds and sedges are removed along with aquatic insects, fish and birds. Rocks, pools, riffles, and any obstruction that might impede the flow of water are flattened and edges are straightened.
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The usual reason for the construction of drains is to mitigate flooding. While there are places where this is necessary, it's frequently a dubious argument because a drain accelerates the movement of water from one place to another, which can actually make flooding worse.
This makes them very different to natural streams which contain deep pools or backwaters that take time to fill. Often they are surrounded by wetlands which also absorb much of the flow.
Natural stream features mitigate the pulse of water following rainfall which is exacerbated by hard surfaces such as roads, roofs, footpaths etc, that dominate our urban environments.
All this begs the question of what to do about the huge network of drains that have been built in urban environments.
While it's simply impossible to restore them all to anything like their original condition, there are many excellent examples that show what can be done.
One of the biggest barriers to this is that they are generally expensive to restore, and therefore should be supported by strong community engagement.
Then there are aspects requiring expertise, such as how to best improve the hydrology and ecology within the available budget.
And, as with all things, prevention is better than the cure. New developments should capture and use rain where it falls and ensure there is enough infiltration to top up groundwater.
Paying careful attention to natural water systems during the early stages of development offers a lasting benefit to communities and the environment.
- Leon Metzling is a freshwater ecologist.
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