IRRIGATION IS GOOD FOR THE ENVIRONMENT…?
……. says Federated Farmers, Irrigation NZ, Dairy NZ, MPI and all those whose financial interests are founded upon such schemes. This new revelation is also being accompanied by the proposition that irrigation schemes are as much for cropping as for dairy. Given the $750 million worth of subsidies to the irrigation industry, jobs for the boys are also at stake.
So, at the risk of stating the very obvious, here’s a summary of research into why putting a massive concrete wall across a river is most certainly not good for the environment:
1. Regulating river flows might seem a good thing in terms of those stable flows translating into a stable ecosystem, but it doesn’t work like that. The Opuha Dam is a case in point – of greater importance is not regularity of flow but volume…minimum flows have historically been well below the level needed to support a health aquatic ecosystem so it’s uniformity is completely irrelevant. Secondly, regulated flows are the principal cause of algal blooms, especially didymo, as there’s no force or friction to scour the river bed on which such algae sticks. Thirdly, variable flows move the river bed about keeping it porous; the Opuha River has a heavily armoured (tightly packed) bed which is no good for invertebrates (trout food) or for trout to cut spawning redds.
2. The assertion that the lakes behind dams offer recreational opportunity is a substitution of existing recreational facilities. So jet boats supersede kayaks and river fishing cedes to lake fishing. The latter however, is only viable where the formed lake has a large shallow edge, or littoral zone, where most of the aquatic biodiversity is concentrated. Proposed dams such as the Lee Valley in Nelson or the Ruataniwha in Hawkes Bay will be characterised by steep sides and deep edges – pretty poor life-supporting cross-sections. The Maitai Dam in Nelson is a typical example of an anoxic lake – a water body that’s deep, has steep sides and has little or no mixing between water layers (thermoclines) causing low concentration of oxygen in lower water levels – the level where the water is released downstream and back into the river. Indeed the Cawthron Institute laid some of the blame on the Maitai River’s lack of life on the anoxic water leaving the dam.
A sudden flushing of silt can destroy river life instantaneously; the horrendous problems with the siltation of the Waiau River in Hawkes Bay as a result of Eastland Group’s dam gates failure is a case in point.
The regulated and periodic flushing of sediment causes it to accumulate downstream and in some cases closes the river mouth where the sediment comes out of suspension as it loses velocity to form a wall of silt and debris.
4. Decaying organic matter from flooded hillsides and bush is largely anaerobic, releasing environmentally harmful gases such as methane and sulphur-based compounds. Given methane has around 20 times the global warming capacity of carbon dioxide, it’s difficult to see why this byproduct of flooding a valley can be touted as good for the environment.
5. Irrigation is, without exception, about intensification. Whether it be grapes, milk or apples, it enables more bang per hectare, provided it is accompanied by a corresponding higher use of plant food – fertiliser, effluent or both. This increases nitrogen, phosphorus and potassium (NPK) loadings on soils which in turn eventually seeps back into rivers, lakes and groundwater. When the irrigation is for dairying, it increases pathogenic presence in freshwater by the same mechanism. The Hinds zone in Canterbury is a victim of E.coli poisoning as evidenced by Dr Alison Dewes and the Canterbury District Health Board Medical Officer, Alistair Humphrey. Canterbury has the highest rate of E.coli-caused diseases in the world!
6. Given that net river flows are always reduced by dams (i.e. consumed water is physically taken out of the river and not returned) this contributes to increased water temperature – generally, the lower the flow, the slower the flow and the greater surface area to volume ratio. Thus more water is exposed to the heat of sunshine and thermal mass of semi-submerged rocks.
7. Fish passage is impeded. Of the 28 hydro-electric power schemes in NZ, 17 have fish passage provision but only six of these are designed to assist in salmonid migration. This doesn’t mean they work, of course. For example, the Branch River Hydro Scheme in Marlborough has failed to work despite 35 years of TrustPower’s attempts at modifications. It is basically a high velocity water chute through which nothing could pass or survive. One of DOC’s conditions for supporting the proposed Ruataniwha dam in Hawke’s Bay is that it should incorporate a native fish ladder but not a trout one!
8. The purported economic regeneration of rural towns by irrigation schemes is transitory at best. A Spanish company is the preferred contractor for the Ruataniwha scheme and the North Canterbury town of Culverden is hardly an economic miracle as a result of the Amuri Irrigation Scheme. Schools and shops remain closed and locals need to travel further for essential services resulting in more cars and more carbon fuel consumption.
Once again, it’s time for those who benefit from subsidised irrigation schemes to stop insulting our intelligence by posing as environmental guardians, and having some deep concern for our heartland, and instead to be honest – it’s about their remuneration, period.
For any anglers concerned at all about the claims for irrigation – aka ‘erosion protection’ – and loss of trout habitat, whatever – if you want to learn more the 2006 book “The Water Thieves” by Sam Mahon is compulsory reading. Reviewed as follows:
The Water Thieves is a marvellous and engaging account concerning our most valuable natural resource. Sam Mahon, galvanized into action by rumours that the Hurunui River is under threat, agrees against his better instincts, to become involved in local politics.
Mahon embarks on a crusade that rivals the best of Shakespearean comedy: he’s comically disarming yet often a blistering social satirist. His energy for sustaining the good fight is prodigious, his techniques for gaining media and political attention are hilarious, bloody-minded and bold. From pyrotechnics to mock funerals, from stabbingly witty speeches to asking men in power to drink polluted river water, Mahon demonstrates all the qualities of a firebrand.