Cool clear water
New Zealand has huge freshwater resources but growing demand is creating escalating environmental and social impacts such as lower water quality, degraded waterways, increased need for water distribution infrastructure, and increased costs.
With the growing and competing needs of water users – recreational users, urban water supplies, hydro-electricity generators, tourism operators and farmers – it is becoming increasingly important to manage the quality and sustainability of our freshwater catchments and the life that they sustain.
Water demand
With such an abundance of freshwater it's too easy for New Zealanders to be profligate with it. New Zealand's per capita water footprint is estimated (Ministry for the Environment 2007) to be two to three times the global average. (Water footprint is simply the amount of water used and is usually given as per capita figure.)
Water demand and allocation has been rapidly increasing too. The allocation of water (i.e. the water allowed to be used) in New Zealand increased by 50 per cent between 1999 and 2006.
As well as the resource itself, water use requires infrastructure which involves other resources such as land and energy. Infrastructure includes dams and reservoirs, water treatment plants, pumping stations, distribution pipes and aqueducts. Wastewater – greywater and blackwater (sewerage) – also requires a large amount of infrastructure. Increased water demand means increased infrastructure.
Urban runoff and stormwater
In natural catchments surface runoff entering waterways is a relatively rare event, occurring only a few times each year, generally after larger storm events. In these catchments most rainfall soaked into the ground and contributed to groundwater recharge or was recycled into the atmosphere by trees.
Modern drainage systems, which collect runoff from impervious surfaces in urban areas like roofs and roads, ensure that water is efficiently conveyed to waterways through pipe networks, meaning that even small storm events result in increased flows in waterways.
In addition to delivering more pollution from the urban catchment increased stormwater flow can lead to stream erosion, it encourages weed invasion and can alter natural flow regimes which affect flora and fauna.
Agricultural water use
The intensification of land use in New Zealand has led to sharp increases in the development and irrigation of high-producing exotic pastures. Demand for water is also increasing, particularly in areas already short of water. Drier parts of the country have the highest demand: Canterbury and Otago account for three quarters of all water allocated in New Zealand.
Intensification of pastoral land use has led to a noticeable increase in the use of fertilisers as well. Total fertiliser use has doubled and the use of nitrogen fertiliser has increased tenfold in New Zealand in the past two decades. This, combined with increased animal wastes from higher stocking rates, has affected the quality of our surface waterways, groundwater and coastal marine environment in many areas around New Zealand.
Intensified land use also causes increased erosion leading to the silting up of waterways.
Virtual water
Virtual water is the amount of water that is required for the production of food and other goods. The amount of virtual water varies depending on the product, for example a litre of milk requires 1,000 litres of water to produce it whereas a kilogram of tomatoes only contains 185 litres of virtual water and a hamburger contains a whopping 2,400 litres of water.
As a large exporter of meat, wool, milk and other agricultural products New Zealand is large exporter of virtual water. There is a big opportunity for New Zealand to export more virtual water especially when countries like China and Japan do not have enough water.
To minimise impacts at the same time as taking the most effective advantage of our water resources New Zealanders must better manage their water use.
Posted by Michael Lockhart on 13th October, 2009 | Comments | Trackbacks
Tags: General Sustainability
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