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.

Landscapes shaped by water - Waiology

Oct 30, 2014

By Daniel Collins New Zealand is both a pluvial and fluvial country. A lot of water falls on, moves through, and runs off the landscape to the surrounding seas. At each step along the way water can play a role in shaping the landscape, whether by resisting or facilitating erosion or by providing environments where eroded sediment is deposited. The resulting landscape becomes a collage of many different erosional and depositional fingerprints. Here’s how they work. Erosion by water begins as soon as raindrops hit the earth. The impact of innumerable droplets on exposed soil will tend to mobilise and catapult soil particles into the air. While this is a random process, over time the particles will gradually move downslope because they are afforded more time to travel. This is one of the various reasons why hilltops tend to … Read More

Southern Alps groundwater sheds light on the Alpine Fault - Waiology

Oct 28, 2014

By Simon Cox During the spring months of 2014, international attention will be drawn to the Alpine Fault along the western side of the Southern Alps, as the Deep Fault Drilling Project (DFDP) enters its second phase. Scientists from around the world aim to complete a 1.5 km drill hole near Whataroa, recover fault rocks for testing, and install a downhole laboratory that can measure fluid temperature and pressure, stress and listen for tiny earthquakes within the fault at depth. The first phase (DFDP-1) was completed in February 2011 with the successful construction of two shallow boreholes intersecting the fault at Waitangitaona River (Gaunt Ck). It was found then that the Alpine Fault acts as a low-permeability barrier to fluid flow, has a 0.53 MPa fluid-pressure difference across it, and the local geothermal gradient reaches 62.6°C/km downwards into the … Read More

Thirsty trees and water yields: Vegetation, water and a changing climate - Waiology

Oct 23, 2014

By Cate Macinnis-Ng Future climate projections predict that some parts of New Zealand will become drier with droughts being more severe and frequent. This is particularly true for the north and eastern parts of the country. We know that soil moisture availability will decline due to reductions in rainfall and increased evaporative demand will lead to faster transfer of water back to the atmosphere. However, we do not yet fully understand the impact of climate change on water balances of vegetated catchments. In forested areas, a large proportion of rainfall (up to 90% or more) is lost back to the atmosphere as evapotranspiration, the sum of loss of water through plants (transpiration) and evaporation of water from bare soil. Transpiration is the dominant component of evapotranspiration. The amount of water remaining after evapotranspiration (often known as the water … Read More

Tussocks – a fundamental component of New Zealand’s water cycle - Waiology

Oct 20, 2014

By Alice Trevelyan, Sarah Mager and Peter Wilson The significance of fog deposition to increased water yield has been contested for many years, especially across the Otago region. Determining the importance of the role of tussock grasslands in the hydrological system is becoming increasingly important, especially over the summer periods when the demand for water for irrigation, recreation and domestic use is at its peak.  Retaining tussock headwaters for fog capture may protect rivers from potentially running dry in the lower reaches during summer. Protecting our waterways from the headwater down is a fundamental part of catchment management. Therefore, understanding the function of tussocks throughout the hydrological cycle is essential for catchment management, both at the regional and national scale. Snow tussocks have been advocated as a significant component of the water balance. Consequently, from a catchment management perspective it … Read More

A pluvial and fluvial country - Waiology

Oct 14, 2014

By Daniel Collins As Sir Geoffrey Palmer once remarked, New Zealand is a pluvial[1] country. It rains a lot. On average, 2.3 metres of water falls across New Zealand each year, or 610,000 million m3 in volumetric terms (about 10 times the volume of Lake Taupo). This is more than most countries, but not all. Values vary from source to source, but according to FAO data[2] the wettest country is Sao Tome and Principe (3.2 m/year), the driest is Egypt (51 mm/year), and our trans-Tasman neighbours receive 534 mm/year. But these long-term, national averages hide a lot of variability. In recent years, NZ’s annual rainfall has varied from 2 to 2.6 m. What is larger still are the differences among regions: Otago is NZ’s driest region with an average of 1.4 m/year, and the West Coast the wettest with … Read More

Weather and water in New Zealand – where do our storms come from? - Waiology

Oct 13, 2014

By James Renwick New Zealand sits astride the middle latitudes in western Pacific Ocean, exposed to wind and weather from all quarters. Yet we do not usually receive our rain and storms from all quarters. Because the flow of the winds is normally from the west, most of the rain New Zealand experiences arrives from somewhere to the west or the southwest of us. Combine that with our mountainous topography (which acts as a barrier to the westerly winds) and you have a recipe for lots of rain in western regions and relatively dry conditions in the east. The strength of the Southern Hemisphere storm track, estimated as the amount of day-to-day variability in the winds several kilometres above the surface of the earth. The darker colours indicate more variability and more vigorous storms.The great Southern Oceans are the … Read More

The natural history of New Zealand’s freshwaters: Series introduction - Waiology

Oct 09, 2014

By Daniel Collins Freshwater issues are among the most important environmental issues facing New Zealanders and receive frequent news coverage. Degraded water quality and its link to dairying in particular is a case in point. Examining the policy and the policy-relevant science are important in order to resolve these issues, and are frequent topics here at Waiology (including last year’s series on water quality) but sometimes it’s also important to take a step back. To satisfy our innate curiosity with the world around us and to improve our management and use of it, it is good to ask what it is about our freshwater environment that makes it interesting, useful, or unique. This is a question of natural history. How much water do we have and where does it come from? How does water shape the … Read More

Full citizen science flood map for Christchurch, March 2014 - Waiology

Sep 04, 2014

By Daniel Collins As a follow-up to Waiology’s article in June, here is a full map for the flooding of Christchurch on 5 March 2014. The map is derived from photos sent in by the public which were generally taken within a few hours of peak inundation. The blue colours represent the depth of water above the ground surface – the darker the deeper. Flood levels are extrapolated around the photo locations using ground levels taken from LiDAR and field survey measurements. Because the analysis hinges on the public’s photos taken at different times of the day, the map can only approximate the depth of flooding across the city, because either we did not receive photos in a particular area or the photos were taken when water levels were not at their highest. It is natural for some people … Read More

NIWA revising national flood statistics - Waiology

Jul 16, 2014

By Daniel Collins As we have seen in Northland in recent days and in Christchurch in March, severe floods pose a significant threat to rural and urban lives and livelihoods. One person drowned in the Waitangi River on Saturday, and the cost of the flooding will likely be in the millions. As a point of comparison, the Southland floods of 1984 cost insurers $140 million (inflation-adjusted to 2014). Protecting against flood hazards is a vital part of local government responsibilities, as mandated under the Resource Management Act 1991 and the Soil Conservation and Rivers Control Act 1941. It is also important for land owners to know what level of flood hazard they are exposed to as they decide how to develop their property. To calculate this flood hazard we turn to historical records of river flow. Read More

Reviews coming in on new policy for freshwater management - Waiology

Jul 11, 2014

By Daniel Collins The Government recently released the National Policy Statement for Freshwater Management (2014). The policy provides the most comprehensive instructions to regional councils yet on how our freshwaters – rivers, lakes, wetlands, and aquifers – are to be managed. Amendments made in the new policy include numerical thresholds and bottom-lines for a range of water quality attributes in order to meet human and ecosystem health objectives (referred to as the National Objectives Framework, NOF). This was a key recommendation of the Land and Water Forum. Reception of the new policy has been mixed, with freshwater scientists and stakeholders alike seeing improvements and shortcomings. To read the various comments to date, see the Government press release, the Science Media Centre’s collation of scientist comments, and the press releases from Dairy NZ, the Environment … Read More