Dr Daniel Collins is a hydrologist at NIWA. He formed the Waiology blog to bring together commentary on New Zealand's freshwater systems. The blog features commentary from numerous contributors.

How deep was Wednesday’s snowfall? The people weigh in - Waiology

Jun 08, 2012

By Daniel Collins The snowstorm that covered much of the South Island with a white veil on Wednesday cut power to over a thousand homes and closed many schools and businesses. But in the midst of the disruption was a rare opportunity to do some important science: to measure the amount and density of the snow that fell at low elevations. To get as much of this data as possible we asked for your help, and the results are now in. 42 people, at last count, sent in measurements, from Dunedin to Rangiora; a few more data are to be added. Here is a Google Map of the measurements we’ve received. Ross Woods has helpfully compiled the largest measured depth at each location submitted. Sampling is obviously biased towards Christchurch, because that’s where our social and scientist … Read More

Citizen science: How deep is the snow at your place? - Waiology

Jun 06, 2012

By Daniel Collins and Ross Woods Measurements of snowfall at low elevations around New Zealand are few and far between, and yet the data would be really helpful in understanding how snowfall occurs and quantifying snow-related risks. After all, the large majority of New Zealand’s population and infrastructure reside closer to the coast than the mountains. And so we’d like your help. If you live at an elevation below 400 m, measure the snow depth after it snows. And if you’re extra keen, measure the snow water equivalent too. Here are the instructions: Safety first. Do not make any measurements if it puts you or anyone else at risk. Data are valuable, but not that valuable. Measure the snow depth. Choose a location. Choose somewhere typical; don’t just focus on deep snow or snow drifts. Put a ruler vertically … Read More

How much water does it take to produce one litre of milk? - Waiology

May 24, 2012

The single biggest consumer of water in New Zealand is the dairy industry. As of 2010, farmers are permitted to take about 4707 million m3 of water per year from New Zealand’s rivers and aquifers to irrigate pasture, most of which is for dairying. This is 44% of all consumptive uses (excluding the Manapouri hydropower scheme), and 68% of this water is allocated in Canterbury alone (21% in Otago). Not all of this water is ultimately taken, though, and for various reasons. One is because irrigators typically ask for more water than they may need in average conditions as a form of insurance in dry times. What is actually taken is more like 50% of that allocated. In Canterbury during 2010-11, for example, 52% of the allocated groundwater was used and 50% of allocated surface water, each based … Read More

Canterbury water use, 2010/11 - Waiology

Apr 10, 2012

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 … Read More

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

Apr 03, 2012

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. Now 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’ … Read More

Canterbury Lysimeter Network: Measuring the hydrologic inputs to aquifers - Waiology

Jan 30, 2012

By MS Srinivasan Irrigated agriculture is growing in Canterbury. This growth has resulted in a greater rush for accessing water resources — surface and ground waters – across the region. Since these water resources are finite, limits on their takes are imposed to conserve them and make them available for other uses. However, setting limits on groundwater has remained a challenge. There are more unknowns than knowns. Does groundwater recharge occur uniformly over a year? Does irrigation add to recharge? How much groundwater could be allocated for irrigation sustainably? To answer these questions, we need to take a closer look at how much water is draining through the ground and recharging the aquifers, as Paul White discussed two weeks ago. In Canterbury, where there is substantial abstraction from groundwater and where groundwater-fed streams and rivers are vitally … Read More

Kinky relationships among Canterbury’s springs - Waiology

Jan 23, 2012

By Daniel Collins As Ross mentioned some time ago, one of the frontiers of hydrological research at present is the interface between surface water and groundwater. On the one hand, we need to understand how aquifers are recharged from the surface; on the other, how aquifers in turn discharge water back to the surface. This is important to water resource managers so that they can determine how water use at one location may affect water availability and aquatic ecosystems elsewhere. One question, particularly relevant to both Canterbury and Hawke’s Bay, is how fluctuations in groundwater levels affect spring flow near the coast. This is actually part of a larger research programme we have looking at the environmental effects of water use. As part of this research I have been examining streamflow and groundwater data around Lake Ellesmere/Te … Read More

Rainfall recharge to groundwater - Waiology

Jan 17, 2012

Guest post by Paul White, Senior Groundwater Scientist at GNS Science. Groundwaters are very important water resources in many New Zealand regions — important because they are used for water supplies (urban and rural) and because they supply flow to many springs, streams, rivers and wetlands. The two major inflows to groundwater are from rainfall and from surface water. We need to know the rates of recharge to groundwater so we can manage groundwater use. For example, groundwater use must be significantly less than groundwater recharge to ensure that groundwater wells and springs do not go dry. Groundwater recharge from rainfall is the subject of this post which will cover some concepts, how it is estimated, measured, uncertainty and some relevant New Zealand water management polices. Groundwater recharge from rainfall occurs as rainfall trickles through the … Read More

Edmond Halley, an underappreciated hydrologist - Waiology

Jan 09, 2012

By Daniel Collins I remember in 1986 going to the Beverly-Begg Observatory, in Dunedin, to see Halley’s Comet. At the time, I was a young kid fascinated with astronomy. I had discovered a book on the topic the previous year while on holiday in Central Otago, and soon joined an astronomy club. Through the club, I built a basic telescope (with a lot of help) and dreamed of becoming an astronaut. But this dream was short-lived and that career never eventuated. Instead, I became a hydrologist. Edmond Halley (1656-1742), after whom the comet is named, is best known for his role in astronomy. But of his 107 or so published papers, only 36% were on the topic. 34% of them were on geophysics, a few of which covered the water cycle and in turn helped usher in a … Read More