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Archive April 2012

Canterbury water use, 2010/11 Waiology Apr 10

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Guest post by James Tricker, Principle Extension Services Officer, Environment Canterbury

There are increasing expectations, both within the Canterbury community and also within a national context, that the relation between water allocation and water use is more strongly understood. The Environment Canterbury Water Use Report presents the information gathered on consented water use in Canterbury between 1 July 2010 and 30 June 2011.

The Canterbury Water Management Strategy sets targets for improved water efficiency and irrigation, as well as targets for better environmental and cultural outcomes resulting from more water in rivers and better water quality. Agriculture and horticulture are the primary uses for water in Canterbury, accounting for around 90% of consented water use.

Within the Canterbury region there were 5,179 consents to take groundwater in the study period. The groundwater allocation for all of these consents amounted to 39,222,849 cubic metres per day, and was taken from 7,022 wells, of which 33.7% were equipped with water measuring devices. The surface water allocation within the region was taken at 1,337 surface water abstraction points, of which 19.7% were equipped with water measuring systems.

Water takes with an abstraction rate of 20 litres per second or more are required to be equipped to measure and report on water use by 10 November 2012. By the end of the 2010/11 water year, of all takes in Canterbury 20 litres per second or more, 43.1% of the groundwater wells were metered and 23.7% of surface water abstraction points were metered. If all water takes, with an abstraction rate 20 litres per second or more, are equipped to measure and report on water use by 10 November 2012, this will account for 97.4% of all daily allocated groundwater, and 99.3% of all daily allocated surface water.

These data showed that 52.4% of the allocated groundwater was used during the 2010/11 water year, although this figure is based on 11.4% of the groundwater takes in the region.

The allocated groundwater volume in the Canterbury region and the proportion of water allocation that was unmetered, metered, and provided information on water use for 2010/11

The allocated groundwater volume in the Canterbury region and the proportion of water allocation that was unmetered, metered, and provided information on water use for 2010/11

The data also show that 49.8% of the allocated surface water was used during the 2010/11 water year, although this figure is based on 7.1% of the surface water takes in the region. Of the 264 metered surface water takes, 95 provided use data that could be used in this report.

The allocated surface water volume in the Canterbury region and the proportion of metered surface water abstraction points (SWAP) that provided information on water use

The allocated surface water volume in the Canterbury region and the proportion of metered surface water abstraction points (SWAP) that provided information on water use

These data highlight the need for consent holders to install water measuring systems and to ensure they are working properly. Having reliable and widespread information about actual use will allow Environment Canterbury to better manage and allocate the huge freshwater resource.

Within the Water Use Report there is an update for each of the Canterbury Water Management Strategy zones on the progress towards installing water measuring devices and actual water use. It is anticipated that this information will be used by the zone committees as they formulate programmes and ultimately will be reflected in river and catchment plans, and Environment Canterbury’s regional land and water management plan.

For more information see:
http://ecan.govt.nz/advice/your-water/water-metering/Pages/water-use-report.aspx

Clutha River/Mata-Au re-imagined as a public transport system Waiology Apr 03

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By Daniel Collins

Some time ago I came across these maps of US rivers systems depicted as subway routes. They’re nice illustrations of rivers as a connected system of transport corridors, with populated areas as stops along the way. Instead of viewing a map with blue lines in the background and cities brought to the fore, the roles are reversed. They combine hydrology with graphic artistry.

CluthaRiverSystemNow I’ve concocted my own version of these maps using the Clutha River/Mata-Au. This is New Zealand’s 2nd longest river, after the Waikato, but the largest by flow at the coast. The topology of the ‘transport’ network pictured is largely the same as the real river network, with only the larger rivers depicted. I used some artistic license in choosing which rivers to include and how faithfully to follow the rivers’ courses. Population centers and geographical features along the way are represented as stops. Each longitudinal river system is coloured the same, representing specific subway or train lines; the darker they are, typically the greater the flow.

But rivers don’t just move water. They also move eroded rock or sediment, nutrients, pollution, and fish. In the case of fish, this movement is two-way. About 50% of New Zealand’s native fish are diadromous, meaning they migrate between river and sea.

How much of this stuff moves along the rivers depends a lot on the flow. Where there is abundant sediment, its movement downstream is roughly proportional to the river’s flow rate to the power of an exponent greater than one (i.e., Qsediment ~ Qwaterb, where b > 1), which means that the conveyance of sediment down rivers mainly occurs during high flows and floods. The same applies to phosphorus, which typically binds to soil particles to get anywhere. Nitrogen, on the other hand, is more readily dissolved and doesn’t need high flows so much. If all flow stops, so does the transport system; no sediment downstream and no migrating fish. (In fact, not many fish at all, unless they burrow into the ground or climb over to more hospitable locations.) In a way, this all means that the train timetables differ from passenger to passenger, but at least for the Clutha basin you can expect trains to be running non-stop.

If people ask nicely, I’ll make a similar map for the Waikato, but with New Zealand’s size, shape and population distribution there aren’t many options for good system maps.

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