Power shares

[Nor]

The dam would be made of earth, and plenty of bentonite on the east coast to seal it if necessary.

Land is cheap and already cleared down the East coast from @ young Nicks Head to the coast of southern Wairarapa.

The power house would be located down close to sea level, and off peak power would be used for the pumping..
This could be augmented by some wind turbines built over the lake, rather than over the sea like Denmark does, and/ or higher ground around the lake.

If ground was chosen in a series of valleys, there would be inflow of fresh water and rainfall, same as any other dam as well.

Am I making a case, or just a nut case? lol

It would probably get blocked up with slash in no time, in that location.

[Snoopy]

A question for those who have enough knowledge to reply.

Now that Lake Onslow is not on the agenda, what is the viability of using the ocean as a lake adjacent to the coast, and creating a pumped hydro scheme by pumping water up to a man made lake on an adjacent plateau of say 35 plus metres height, or more if necessary and the site provided it?

I'm aware sea water is more corrosive, but use concrete pipes and races. and liners can be used on steel parts.

I can think of places around NZ, particularly in the North Island to avoid reliance and loading on the Cook Strait cable and SI grid, that would offer a major site, and plenty of scope for smaller ones if local power authorities want to set them up.

Compared to some pumped hydro schemes overseas, one of the 'lakes' is already 'built', and would never run dry, compared even to NZ ones that rely on rainfall or snowmelt.

Going back to the basic physics of this, water can supply power by utilising::

A/ Potential Energy (water falling from a great height) OR
B/ Kinetic Energy (lots of water moving really fast)

Lake Onslow is 700m above sea level and Lake Dunstan is 200m above sea level. So we are looking at a head of 500m for water to fall. The formula for potential energy is 'mgh' (mass x gravitational acceleration x height ). Your proposed 35m high dam walls Getty would house a volume of water that is on average 17.5m high. This is much less of a head than available with Lake Onslow. So to make it as useful as Lake Onslow you would have to compensate by increasing the mass of water available by a factor proportional to the lost height: 500/17.5 = 28.6 times.

Lake Onslow covers an area of 380 hectares. So your equivalent pumped seawater reservoir would have to cover an area of 28.6 x 380 ha = 8580 hectares. To get some idea of that area, the Auckland central business district CBD covers 433 hectares in a triangular area, bounded by the Auckland waterfront on the Waitematā Harbour and the inner-city suburbs of Ponsonby, Newton and Parnell. So you are looking at an area of 20 Auckland Central business districts which would require a truly enormous structure to wall in.

Furthermore unlike the Clutha River which has a natural discharge rate of 614 cubic metres per second, a giant inland insure reservoir from the sea would have an underlying natural flow rate of - zero. All the water would have to be pumped into the reservoir. So there is no net natural kinetic energy, akin to a naturally flowing river, that adds to the kinetic energy that can be recovered from such stored water. (The kinetic energy recovered from such water is only equal (actually a bit less because of frictional losses) to the kinetic energy put into the water as it was pumped into the reservoir).

I think you can see that the construction of such an ''inland sea reservoir" would be an enormous civil engineering task, likely costing multiples more than the dumped Onslow project. And looking at the energy flows you would need to fill it to get a significant output in times of low rain, I don't think the costs involved make sense.

SNOOPY