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.

What causes didymo blooms (“rock snot”) in NZ rivers? - Waiology

Dec 19, 2012

By Cathy Kilroy Ever since the alga Didymosphenia geminata was discovered growing prolifically in a South Island river, scientists have puzzled over how “blooms” (unusually large algal growths) of this alga can form. Rivers below lakes and dams in the South Island have been especially severely affected. Massive, persistent mats of didymo in these rivers have changed their character, reduced their appeal for angling, and have sometimes caused problems such as clogging irrigation intakes. So far didymo has not been detected in any North Island river. Didymo in the upper Ohau River. Didymo cells and stalks.D. geminata (commonly known as didymo, or “rock snot”) is a stalked diatom. Cells colonise rivers by attaching to rocks or other surfaces and then growing out into the water column on stalks. The stalks are exuded from the cells and are made … Read More

Phreatogammarus fragilis: The fragile well shrimp - Waiology

Dec 06, 2012

By Daniel Collins Phreatogammarus fragilis is an endemic New Zealand crustacean that lives in aquifers. It is an amphipod (a relative of the sand hopper), and is one of the largest (commonly up to 25 mm excl. antennae) and strongest swimming of NZ’s stygofaunal* crustaceans. Because it is so rarely observed, it does not have a common name; the best translations are ‘fragile well shrimp’ or ‘fragile groundwater lobster’, ‘fragile’ probably because its appendages broke off when early specimens were being identified and preserved. The individual below is a 12 mm-long female with a brood pouch beneath the abdomen. It is white and translucent because there is no point in investing in pigments if it’s too dark to see or if there’s no risk of sunburn. This individual was caught in a trap in a 6 m-deep well beside the … Read More

Map: Projected effects of climate change on New Zealand freshwaters - Waiology

Nov 27, 2012

By Daniel Collins Maps are helpful tools in communicating and understanding the potential implications of climate change. We have national maps of projected changes in temperature that show faster warming in the north, and in precipitation that show more rain in the south and west and less in the north and east. We also have national maps of projected changes in drought, that show much of the country is likely to experience more severe droughts. Now, I am able to give you a map of the potential freshwater changes across New Zealand. This includes changes in snow, ice, river flow, groundwater, aquatic ecology, geomorphology, and water use/management. This is an important step in synthesising and understanding climate change impacts, drawn from existing case studies across the country. Projections are pin-pointed on the map below; in some cases they … Read More

Waiology moving from water cycle to freshwater sciences - Waiology

Nov 26, 2012

By Daniel Collins After over a year serving New Zealand as a source of information and discussion on hydrology and the water cycle, I am pleased to announce that Waiology is expanding its scope to freshwater sciences and allied disciplines more generally. This includes all things hydrological, as before, but also aquatic ecology and chemistry, fluvial geomorphology, hydraulic engineering, and related policy and management. Waiology will continue to serve as a conduit among scientists, professionals and the public, and guest posts will continue to appear from time to time. The pool of contributions will now grow, and no doubt the relevance to both science and the country. The reason for the evolution is simple. Research and management of freshwater is better if working across disciplinary boundaries. Our challenges are not about the quantity of water alone, nor quality or hazards, … Read More

Water allocation and limit-setting in a changing climate - Waiology

Nov 20, 2012

By Daniel Collins Last week, the Land and Water Forum released its third and final report on water management in New Zealand. It is a substantial piece of collaborative work with 67 recommendations. Number 29 is that allocation limits be set by taking into account “any flow and water level fluctuations caused by seasonal or other climate variations”. While this primarily refers to natural variability, such as the Interdecadal Pacific Oscillation, it’s also important to consider climate change. And along the same lines, last year’s National Policy Statement for Freshwater Management stated the need to account for the “foreseeable impacts” of climate change. This is an important issue, as climate change is expected to bring about a raft of changes to New Zealand’s freshwaters (more details on that soon). Among these changes are reductions or increases in … Read More

Canterbury does not have 70% of New Zealand’s freshwater, it has 12% - Waiology

Oct 29, 2012

By Daniel Collins In the Christchurch Press today there is an article about the race to irrigate Canterbury. In it is the following statement: “Canterbury had 70 per cent of New Zealand’s fresh water resource, and 34 per cent of its hydro-generation capacity.” Unfortunately the 70% is an error that has appeared in the past and it is timely to make a correction and provide some other statistics that describe water resources in Canterbury more generally. Canterbury has about 12% of New Zealand’s freshwater. This number is obtained from a Statistics NZ report, written by NIWA, on the water stock accounts of New Zealand. To check for yourself, download the two Excel files from the Statistics NZ website, calculate the annual average of “Outflow to sea and net abstraction” for both Canterbury and the country as a … Read More

The rise and fall of the Heathcote River - Waiology

Aug 17, 2012

By Daniel Collins It would have been hard to miss the deluge that washed over the country this past week. Otago and Canterbury were particularly affected, with flood damage in Waitaki District estimated at about $1 million. Minor flooding also occurred around Christchurch, with the lower reaches of the Avon, Heathcote and Styx Rivers overflowing their banks. To put these high Christchurch flows into context, on late Tuesday afternoon I drove out to two flow gauging sites on the Heathcote River, one at Ferniehurst St (managed by Christchurch City Council) and one downstream at Buxton Tce (managed by Environment Canterbury and Christchurch City Council) and filmed the flows. See the footage below (top = Ferniehurst; bottom = Buxton). In many places, the water levels reached just shy of the top of the bank or beyond; … Read More

The big hydrological OE in New Zealand - Waiology

Aug 10, 2012

Guest post By Jasper Hoeve, visiting student from the University of Twente, Netherlands I am a third year Civil Engineering student at the University of Twente, the Netherlands. As part of our studies, we have to do an internship at a company relevant to our field. I thought this was a good excuse to travel to the other side of the world. My family did not share my enthusiasm but I went anyway. NIWA invited me for a 10 week long internship to develop and apply a methodology for high river flow estimation under El Niño Southern Oscillation (ENSO), Interdecadal Pacific Oscillation (IPO) and climate change under the supervision of Roddy Henderson. After some research on the internet I found out that NIWA is actually a rather big company. I was expecting that a company of this size would have … Read More

Climate change and NZ’s freshwaters: NIWA presentation, Friday - Waiology

Jul 26, 2012

By Daniel Collins For those of you in or around Ōtautahi/Christchurch, I will be giving a presentation on climate change and the future of New Zealand’s freshwaters on Friday (tomorrow), 3:30 pm, at NIWA’s Kyle St site. I’ll talk about what we know and what we don’t know about the potential implications for the freshwater system, including water quantity and quality, ecology, and management. I’ll also discuss the more pressing avenues and what adaptation options different stakeholders may adopt. Ka kite ano! … Read More

Predicting river flows in ungauged catchments, from New Zealand to the world - Waiology

Jul 13, 2012

By Ross Woods Our knowledge of the water cycle is imperfect – for example we don’t have data for all rivers across the landscape, and yet so often we want river flow information for resource and hazard management purposes. In the absence of direct data, then, we turn to models and seek to make hydrological predictions in these ungauged river basins. Predictions in Ungauged Basins (PUB) is an IAHS initiative operating throughout the decade of 2003-2012, established with the primary aim of reducing uncertainty in hydrological predictions. It is a ‘grass-roots’ science movement intended to engage the interest of hydrologists around the world, and has grown to encompass an enormous variety of approaches and settings. You can read about the full scope of PUB activities on the web site. One of the major current activities is the publication … Read More