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Mike Joy, freshwater ecologist
This detailed analysis of the environmental effects of large irrigation dams, available here, strongly supports the Wise Water Use message. Penned by Mike Joy, freshwater ecologist, the article exposes the claim that “dams are good for the environment” as being pure myth, and not backed by science.
For instance, flushing flows, often used to sell the environmental benefit of dams to the public, are found to only be effective for 5 to 10 kilometres, because releasing water from a single point loses the power of a natural flood event which incorporates water from a river’s many tributaries.
Similarly, release of water to maintain minimum flows does not preserve a river’s ecological health because ecological communities require natural floods and variable flows to survive.
The sting in the tail for ratepayers – seldom announced by dam promoters – is that the water for environmental flows is billed to councils at commercial rates. The HB Regional Council agreed to pay $43 million over 35 years for water for flushing flows from its own dam, Ruataniwha v.1, while the promoters of Ruataniwha v.2 are currently proposing that ratepayers pick up the tab to the tune of an estimated $6 million per year, equating to a 17% rate rise.
Other myths that are busted include:
Dilution of contaminants in our waterways by supplementing natural flows is not a solution;
The increased levels of nitrogen in our waterways due to the intensive farming that dams enable actually worsens pollution problems;
Promises that water will be released for environment purposes are questioned – irrigation may become the priority in times of drought and water shortages;
Promoting dams as a solution to climate change is nonsensical, when they further promote the same water-intensive farming practices which have caused rivers to dry out.
Intensive dairying comes under the spotlight. Unsurprising, it is found that large irrigation dams facilitate dairy conversion – 36% of water from Ruataniwha v.1 would have gone to dairy or dairy support, placing increasing pressure on our land and waterways. One dairy cow produces faecal waste equivalent to 14 humans – it’s perhaps no coincidence that Aotearoa New Zealand has the highest per-capita frequency of water-borne diseases among OECD countries.
Unquestionably, Aotearoa New Zealand has an issue with over-reliance on our limited water resource for irrigation – 78 % of the weekly consumptive allocation of freshwater
(excluding hydro) is used for irrigation, mainly for pasture (this figure is 90% in Canterbury).
Solutions are also offered. In short, we should be investing in farming practices that are drought resistant and adaptable to regional changes in climate.
Large irrigation dams which remove more water from rivers and catchments will only amplify low river flows and drought conditions. Time to look seriously at how we can promote the logical and cost-effective alternative: Wise Water Use.
Source article located on 'Freshwater for Life' website, on 2 June 2022
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