Clearing vegetation from waterways to reduce flooding. Have we learned nothing?

A few days ago, Victorian Water Minister and National Party member, Peter Walsh told that a parlimentary enquiry had been set up to look into the haphazard management  of Victoria’s waterways, and  was quoted in The Age as saying:

“A lot of people were brainwashed into thinking that it was never ever going to  rain again because of the discussion around climate change.  If  you look at quite a few of the areas where there was flooding issues last year,  there had been vegetation grow up into stream ways and flood ways that then held  up the water.”

Fortunately, there has been an outcry over his comments, with condemnation from The Age editorial of 7 March, Jamie Pittock from ANU on The Conversation, while also contradicting a recent submission to an enquiry being held by the NSW Department of Premier and Cabinet.  Not to mention that it flies in the face of everything we know about aquatic plants and river health!

Aquatic plants are absolutely essential to the health of rivers: they stabilise sediments, provide a diversity of habitat to animals and other plants, act as food for herbivorous fish, birds and macroinvertebrats, and when dead as a material for decomposers, and contribute oxygen to the water itself.  They were also once an important source of food for Aborigines and were used by them to make spears and nets for catching fish.

Indeed, aquatic plants or macrophytes as they are typically known, have been as hard hit as any part of riverine ecosystems around the world; not least in Australia.  There is considerable evidence to show that many of our rivers supported much more extensive macrophyte beds than currently exist, but that probably because of river management, especially river regulation, past removal of snags (woody debris) and habitat destruction generally, they have been badly affected.  Loss of macrophytes tends to mobilise sediments and in turn makes it much harder for plants to re-establish.  Once plants are lost, it is very hard for them to come back. 

Trees and understorey plants along the riparian zone (along the banks of rivers) are also critically important for river health, providing sediment stability, the source of much of the carbon which fuels riverine food webs, acting as a buffer for contaminants and indeed, slowing down the entry of rainfall into rivers in the first place.

Of course, not all aquatic plants are beneficial to our waterways.  There are several nuisance introduced plants, like arrowhead, which can infest and block waterways.  And native and introduced cumbungi or Typha can encroach at times and cause problems. But invariably, as with most of these things, the problems are related to poor management and are a symptom rather than the ultimate cause. 

If anything, we should be promoting the rehabilitation of aquatic plants in our rivers, as critically important components of these ecosystems.  Advocating their removal to mitigate floods, is certainly a backward step.

This entry was posted in Macrophytes, River conservation, River ecology, River ecosystems and tagged , , , , . Bookmark the permalink.

One Response to Clearing vegetation from waterways to reduce flooding. Have we learned nothing?

  1. Aquatic plants are of course a necessity for aquatic life of any type. They are also the driving force in the process of hydrosere, which converts wetlands to drylands. When aquatic weeds clog a river or lake enough to block water flow they cause flooding. Look at what water hyacinth did recently in China and the Philippines. Look at what Typha is doing to Lake Chad. The silt that the weeds deposit cut the waterways off from the aquifers, to the detriment of both. Weed infestation is one of the driving forces in climate degradation. They are dessication machines.

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