My plan,
1 Place a Medium sized Hydro Electric Dam at the West Exit Providing Power to Manawatu to accompany the Wind Farms - Lake level set at 5 metres below the current Rail and Road.
2. Have a walkway across the Dam to augment the existing Gorge Trail.
3. Provide road access for the following recreational uses (remembering the Manawatu does not have these resources)
A. Rowing
B Canoeing
C. White Water Kayaking (Below Sluice Gates) and flat water racing
D. Jetski Racing
E. Waterskiing
F. Kiteboarding
G. Sailing
H. Waka Ama Racing.
Other benefits.
1. Flood control for lower regions and diminishing any dangerous floods in Palmerston North.
2. Provide Water Irrigation to farms in times of Drought.
The following picture is indicative only.
You would still have slip problems which would have to be mitigated. Any slips entering the lake would cause problems and if the slip was large enough would generate a tsunami that would have the potential to overtop the dam creating a significant hazard below the dam, as well as inundating land at the Woodville end of the lake.
ReplyDeleteThese could be geologically engineered for, however it would be expensive. Having said that, the sides of the Cromwell Gorge had to have serious stabilisation work carried out during the construction of the Clyde Dam. This was because of the weakness of the schist rock and it's low strength during seismic events. It is possible that similar techniques and methodologies used to stabilise slopes in the Kaikoura region after the recent earthquake sequences could be utilised. The question is who would be willing to pay the the costs for such mitigation?
My contention is yes there are similar issues. As I see it, the heavy traffic (re trucks) are not causing loosening of rack faces from vibration. As I also see it there would be a small lake as the catchment back to Balance has to be considered.
ReplyDeleteThank you for your comments.
Meant to add, How many slips have occured since the road was closed?
DeleteDo not know because I don't follow it.
DeleteNo probs about the comments Zaps.
ReplyDeleteYes, I would think that the reduced traffic and reduction of subsequent vibration may be positive in reducing incidences of slope failures within the gorge.
The next point to consider is that the lake will take time to settle. It has to reach its equillibrium which is where it stops slopping around; much like after you finish filling a bath and leaving it to settle before you get into it. This is important because it impacts upon the final shoreline and from memory, after they last raised Lake Pukaki it took 15 years before it reached its equillibrium. I no longer have my notes on that so can't refer to them. You can estimate and model where the final shoreline will be, but in the end nature and the lake eventually decide.
Why this is important is because what I do remember about Lake Pukaki, was that the state highway had to be moved up the hill and the new shoreline was estimated by the MOW engineers at a certain elevation so they just moved the highway up hill a bit. However during the 15 years that the lake took to reach its equillibrium, wave action was forever eroding the beach and base below the road and the road itself. There is an active wave climate on Lake Pukaki due to its fetch being in a high wind environment. So being engineers they placed rocks on the beach to stop the erosion. No problems,the wave action just kept undercutting the rocks they kept putting on the beach. Moral of the story go speak to coastal scientist who would've saved them $1 million a year by telling them to place the rocks where the depth of water equals 1/2 the wave length, which reduces the wave energy significantly by the time it reaches the beach.
In my time my father was a lead advocate for Save Manapouri. 30m was quite a water level and many foreshore trees fell under.
ReplyDeleteI have one major issue with this proposal, how far back up the catchment will the lake go? Especially if the river level rises 15 - 20 metres in the Gorge. Zaps
Ah Manapouri, one of my most favourite places. The original proposal was a lake rise of 100 ft (30m) and that was fought quite vociferously, which was a good thing, and in the end the lake level wasn't raised. It's level is controlled by control gates at the mouth of the Upper Waiau River where it drains Lake Te Anau.
ReplyDeleteA lake created by a dam will move through a catchment to the contour that is equal to the level of water depth plus the contour height of the river water level at the base of the dam. So if the river where the dam is built is at an elevation of 100m and the lake is to be 20m depth, then the lake level will be at the 120m elevation contour, wherever that is across the terrain - just like a pond.