Monday, January 25, 2016


Lake Sumner.

Not many of us have been there, possibly most would not even know where it is.

Plenty of us have an image that fresh water in this bountiful country is under serious threat due to the massive growth in irrigation.

The East coast of the South Island has gazillions of acres of flat to rolling arable land that has for ever suffered summer dry that inhibits productive activity.

Three areas, Marlborough, Canterbury between the Waiau and the Waimakariri or maybe that should read the Rakaia  and North Otago have serious times of water insufficiency from the rivers that cross the opportunity land and therefore irrigation has constraints.

Travelling on SH 1 there are a regular crossings of rivers that in a dry summer can appear clearly challenged for flows even to some that actually have no visible flow, eg the Selwyn at Dunsandal.
The Conway, the Ure (Waima), The Kowhai and the Kahautra at Kaikoura, The Ashley, The Waipara are just a few that have a SH1 bridge that seems to be a massive over capacity for the mid summer flows that are in some years disappear completely below the shingle bed.

As a child the Pahau a tributary of the Hurunui  became a  series of ponds growing algae and slime,  an even smaller creek a couple of kilometres south was very appropriately named "Dry Creek".
With the advent of the Amuri Plains irrigation scheme in the 1970s, the last major border dyke effort with serious subsidies, transformed those two water ways  into robust flowing streams.
As more efficient distribution systems replace the "wild flooding of border dykes where the areas near the head race were over watered to achieve a bare minimum at the nether ends, supplementation of ground water from irrigation is manifesting in significantly reducing  visible flows in both the Pahau and the now quaintly misnamed Dry Creek.

Amongst those of us who see green grass as infinitely more pleasing to the eye, never more starkly obvious when travelling through the McKenzie Basin where vast areas that in my youth carried a handsome sward of thriving tussock but following depredations from rabbits was turned into a depressing scene of hyracium and  stunted briar, have been transformed into highly productive pasture land using a small proportion of the vast water storage of the upper Waitaki hydro scheme, see storage as a huge resource to benefit our nation.

Damming is not a viable option for the braided river systems that prevail in the East coast due to massive shingle movements that are part and parcel but there exist options to augment low summer flows with control dams in head waters as demonstrated by the Opua dam near Fairlie

The Hurunui is a true alpine river as are the Waiau, Waimakariri, Rakaia, Rangatata and the significantly modified Waitaki but with a major difference where the head waters of the North branch has a series of natural lakes, formed  I assume from seismic events. The biggest of these is Sumner with a surface area of 3000 acres and a flood range of levels that varies by over two meters.
A proposal to weir the outlet to hold the spring level at high flood level had a storage capacity of 26 million cumecs which would provide 26 days of minimum flow at 15 cumecs but of course it would only need a fraction of that as there is already a minimum base flow that needs augmentation
 A further supplementary storage could be formed on the South Branch to capture the winter rains of vast areas of foothill country with limited gravel flows.

Sounds simple and with the undoubted demonstrated benefits to farms, fish, communities and flows from the Opua scheme albeit somewhat challenged last year as a first in was it twenty years, the question is why not.

Well you see there was an immediate protest from a very small coterie of melons who selfishly see the bits of NZ that only very few can or wish to access as theirs as of right, immediately made an inappropriate fuss and the  major beneficiary by squillions, Ngai tahu withdrew their support.
Ngai tahu is the mob of bludgers and tax avoiders who inherited the 25 thousand acres that the depression era Balmoral Forest grew on and have proposals to turn that considerable area into pasture for more Dairy Cows.
Living as they do in their entitled world, the tribal leadership believe they will get priority for whatever water they desire so on that basis decided to support an economically stupid scheme to create a lake on the little Hurunui tributary, The Waitohi.
No one has been able to provide any logical argument as to why drowning many acres of downland when a high country lake would do the storage thing, makes any sense.

At present the Special people and the Melons are in the ascendant and until next time sense breaks out, Lake Sumner will remain the wasted resource it clearly is.
That could well be next time the planets align and that is a very long time away.

1 comment:

The Veteran said...

I can remember what nowadays would be called Adventure Training along the western side of Lake Sumner in the early 1960s armed with an almost new 7.62 SLR and very tasty the venison too. Venison & eggs and fried potatoes for bkfst, coffee and biscuit for lunch and venison & jacket potatoes & tinned peas for dinner. That was when I first imbibed 'ski' (beer was too heavy to lug in and any meaningful amount) ... gueez, the lake was cold for the obligatory daily swim.