Yesterday two anglers were astonished and curious how, after the rain had passed on, the river suddenly rose and coloured up to an angry dirty pumice texture? The Tongariro River flow graph was as follows:
This “spike” to 45 cumecs is not weather related. The gradual increase to 37 cumecs is natural. The reducing flow back to 31 cumecs is natural. But the sudden dirty water flow is not a natural phenomena. It is most likely the power company tripped their dam in the upper river to remove all the build-up of debris, sand, pumice, ash, etc. They have to close off the tunnel and canal that redirect much of the flow across to Lake Rotoaira to prevent the pumice from scouring the turbines at the Tokaanu Power Station.
The anglers were understandably annoyed and asked why they cannot do that at night between 12 and 5 am when fishing is prohibited. Seems fair?
In anticipation that our explanation of the spike is pure supposition, we referred to TRM’s files of old reports for a more complete explanation and precedent 3 years ago:
How local hobbits dangerously increase Tongariro river flows?
Anglers were concerned on Tuesday when, on a beautiful fine spring day, the Tauranga Taupo River rose rapidly and trapped an angler unable to cross back to the southern bank – car park – side. How can this happen? That is explainable and understandable.
But then yesterday, on Wednesday evening, after two days of fine weather, the Tongariro flow suddenly increased from 39 cumecs to 56 cumecs just on dusk – see the spike above. That is not weather related. That is extremely dangerous to anglers and totally irresponsible as it is controlled by Genesis – the power company controlling the flow. TRM have repeatedly warned Genesis over the last 12 years that eventually someone will get drowned, but the power company remain blameless and in denial.
TRM will try to explain…
Anglers are always naturally curious about the weather and likely effects on river fishing.
It is a well established tradition that the Tongariro River and other tributaries to Lake Taupo fish best after floods – as the tide recedes. Every “fresh” – as they are known – encourages a fresh run trout to commence their spawning runs which encourages more anglers to try their luck, and who then try to wade deep across the river to get to the magic spot X. As it is no longer raining they somehow expect the river level to lower. But not on the TT – Tauranga Taupo…
What is not understood is that the Tongariro flow pattern does not naturally follow the rainfall pattern.
The above graph illustrates the rainfall in Turangi for the last 3 months. (The last two days of fine spring weather have been so welcome. On Wednesday the town buzzed with the noise of motor mowers at last being able to deal with spring grass growth for about the first time since May. Recently it has been too soggy to mow.)
So why is the rainfall graph so different from the river flow graph below?.
Surely, logic dictates they should follow a similar pattern?
As illustrated above the rain pattern in Turangi over the last three months has been very regular every few days preventing the swampy ground from drying out thoroughly.
But what Tongariro River anglers have been asking is why does the rainfall pattern not follow through to a similar river flow pattern over the same three month period?
The first difficult consideration for anglers to adjust to is that this is Hobbitt country where weird weather behaviour is normal and usual practical logic does not apply. Once you get your head around that then the rest is easy.
Evidence? Above on left is the entrance to a tunnel deep under the Kaimanawa Range leading to the caves of Mordor. Below is a peep through the doors into the road leading down to the mysterious dungeon. That is as close as you will get to identify who is to blame.
(1) The main reason on the Tongariro River is that the hydro power company – Genesis – controls the river through two dams and an underground power station.
They divert much of the flow from the Poutu Dam into the canal across to Lake Rotoaira, to spin the turbines at the Tokaanu Power Station. Their power requirements do not necessarily follow the rainfall pattern. It is all about the production of $$$.
So often we have noticed the river graph rise or fall steeply as they play around with their dams to get rid of sediment build-up, etc. or for no apparent reason as indicated yesterday, suddenly increase the flow by over 50%. That adds to the confusion.
There is no consideration of how their electric power manipulations leading to the dumping of silt down river might affect the access for trout fishermen. Sadly, in the past, anglers just have to live with it.
(2) A second reason is that the rainfall up on the plateau and in the Kaimanawa Range does not follow the rainfall pattern in Turangi. It has a wetter micro-climate all of its own. It can be fine in Turangi and hailing up on the plateau. Anglers understand that.
(3) The third reason is more difficult to explain and even more difficult to understand – that even on beautiful fine days the river can rise due to snow melt. It has taken SWMBO 12 years to work that out… This particularly refers to the TT – Tauranga Taupo River images on right.
There are no dams affecting the flow on the TT and it has a much wider catchment so it should be more predictable following the rainfall. But often it isn’t.
Particularly after dirty colder winter weather from the southern quarter there is often a huge dump of snow on the Kaimanawa Ranges at a higher elevation which melts rapidly as soon as the warmer weather arrives.
Example 1: Tuesday on Tauranga Taupo River
On Tuesday in fine sunny weather an experienced angler – we will call him Ray – safely crossed the Tauranga Taupo River, but on his return he discovered he was unable to wade safely. He ended up stranded and contacted the police who alerted the local Search & Rescue team which eventually saved him just before nightfall by entering and retreating up river on the northern side (where the quarry used to operate). Ray spent Wednesday recuperating from his ordeal.
This happened on a perfectly fine day when the river flow increased quickly from snow melt to make his return crossing impossible and too dangerous. So you have been warned… OK? If you still have difficulty understanding that then blame the hobbits.
Example 2: Wednesday on Tongariro River
This is a far worse situation that anglers have seen too often which as nothing to do with the weather – where some bloke (or blokess?) sitting 230 km away up north in Huntly peering at a wall of monitors decides for whatever reason (usually to increase $$$ by spinning turbines) to suddenly increase the flow as illustrated above – from 39 to 56 cumecs – an increase of almost 50% which occurred after dark. We repeat, this was after two days of fine weather. Any danger to fishermen would be the last thing on their mind, but it should be!
Every evening on the Tongariro anglers go fly fishing. They have done so for the last 100 years. To anglers, that is known as the “magic hour”. For fly fishos, it is a religious experience. Books have been written about it. Often they need to wade across to their favourite pool – such as down river to fish the Log Pool or in town to fish the Island Pool. The Log Pool crossing is a diagonal down-stream wade across fast riffles over slippery gravel. But on the return last night after dark the current quietly increased by over 50% and made the return trip up-river almost impossible. That is more than an accident waiting to happen – it is inevitable that eventually someone could drown.
That is the dangerous situation that Tongariro anglers have been so concerned about for so long, when someone will eventually get caught out, unable to return and perish. But despite many previous warnings, Genesis, the power company, continues to be in denial – as proven again by their sudden increase in the flow on Wednesday evening just on dusk. As they will claim they are innocent (?) anglers can only blame the hobbits down in their tunnel under the Kaimanawas.
The warning notices on the river bank are useless insurance as there is no way that anglers crossing over the Tongariro bypasses in the dark could be aware of any sudden increase in the flow and would have been in peril if they had tried to return later, in the dark on Wednesday night.
TRM Recommendation: It is so dangerous that we have to warn anglers again and again not to cross over anywhere to fish after dark, but of course they always do as that is the magic hour for fly fishermen. So we request at least take a buddy and use wading poles and make sure you wear adequate warm waterproof clothing to be prepared to survive in sub zero temperatures all night. It might sound like a grim over-reaction but we have seen far too many close calls over the years.
If/when the worst scenario eventually happens you know who will be to blame and anglers will be rightly ‘gunning’ for them.