A Jolly Jollie – snow sampling in the Jollie catchment, Mt Cook

Definition:

Jolly: adjective. a field trip where work is done, but the enjoyment of being in the area outweighs any hardships.

A hard days travel through remote and unsympathetic country, wintery conditions, repetitive work, long hours, must be good at digging holes and not mind being in a small team likely to be made up of hairy smelly men. Voluntary. Will involve views to die for and heli-skiing!

For me it was a no brainer, for sure I would drive to Mt Cook to be part of the team of scientists laying siege to the Jollie Catchment in the annual snow survey. The National Institute of Water and Atmosphere (NIWA), over 4 consecutive years has undertaken the Jollie Snow Experiment (J-SEx), collecting hundreds of snow depth and density samples over a single day at the time of maximum snow storage.

With the boys, on the ridge. Ready for a Jolly Jollie. Photo by Jason Blair

With the boys, on the ridge. Ready for a Jolly Jollie. Photo by Jason Blair

In hydrological models, snow has traditionally been treated simply as ‘snow’. Anyone who has spent any time in the mountains knows full well that all snow is not created equally. Firstly snow does not layer onto the mountains like Christmas cake icing in perfect uniform thickness. Rather it billows around under the force of the storm, accumulating in some areas and being stripped in others perhaps like trying to ice a head of broccoli while someone holds a hair dryer next to it. Strangely I’ve never tried to do this, but I’m sure you would end up with variable icing cover. Secondly as any skiers will know, some snow is like icing powder, some like porridge and some like sheet ice, all which have very different densities. Therefore from a water storage point of view, snow is variable.

Satellite images that gather snow data for hydrological models have the ability to measure more than just the presence of snow. As the Inuit peoples of the Arctic know, snow is not just white. The Inuit people have many different words for what we simply call snow. Satellite images have the ability to measure more parameters but to ensure accuracy this requires ground truth points. In other words, if I can tell the satellite that the “pixel” I am standing on is x, and the pixel that Fred is standing on is y, and the pixel that Charlie is standing on is z, it can then work out the values for all the pixels between me and the boys. This is called extrapolating the data, and is a powerful remote sensing tool for obtaining data for large areas that could never be covered by foot. In fact, remote sensing has changed the way people do modern earth science.

No description required. Photo by Jason Blair

No description required. Photo by Jason Blair

The Jollie catchment is a contributor to Lake Pukaki, one of New Zealand’s major hydroelectricity dams, and it is a relatively small and simple catchment with a water flow gauge on the stream. There is good satellite coverage but little was understood about snow depth and density and the environmental drivers of this. In order to understand what the satellite can measure, ground data has to collected, and this is where the siege comes in. One day, and as many people as possible to take as many samples as possible. And the quickest way to get people around the mountains – helicopter to the top, ski to the bottom. Simple.

Helicopter with GPR strapped underneath. Photo by Jason Blair

Helicopter with GPR strapped underneath. Photo by Jason Blair

So in teams of 4 were dropped in by helicopter along the ridges bounding the catchment. We all skied down into the valley, stopping every 100m in elevation to take snow samples. Now don’t get me wrong, a bit of hard labor was done at every 100m, but it was between beautifully carved fresh turns.

Digging. Photo by Jason Blair

Digging. Photo by Jason Blair

We did a bit of digging! At each location we dug a snow pit, either to the base, or until the snow became isothermic (so the pits were all at least 2m deep). Down the snow pit we measured the temperature, the permeability, noted the depth of all the layers, and took snow density measurements every 10cm. While two people were doing this the other two did a snow depth transect, probing the depth of the snow every meter along the contour for 100m.

Snow pack analysis. Photo by Jason Blair

Snow pack analysis. Photo by Jason Blair

As well as the ground teams, a Ground Penetrating Radar (GPR) was strapped underneath the helicopter. This was able to measure the depth of the snow, and was verified by the ground measurements. The airborne GPR was successfully tested and into the future will be used over ground sampling as a greater area can be covered increasing the spatial resolution for catchment wide sampling for snow storage estimates.

Snow depth probing

Snow depth probing

Jolly good!

 

 

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