An idea discussed in >>>/biz/1106359 led to the idea in pic related, which I'll describe in detail since I am terrible with a pen.
The idea is to dig a lake which mostly lies only a few cm below sea level (it would curve downwards towards the middle), so that water evaporates rapidly, with the intention of increasing local rainfall.
This lake would be connected to the ocean by an overground channel and an underground tunnel. As water evaporates, the overground channel replaces it with seawater, and the salt left behind by evaporating water would cause water at the bottom to become very saline and thus sink through the tunnel to return to the ocean.
What's the point of the tunnel? As long as there's a connection between the pond and ocean tides are going to keep the salt levels in the pond at the same level as the ocean.
>>950965
Are you sure? One would need a two way flow in one river that way.
>>950962
There's nothing wrong with it at a fundamental level, but in practice it may be difficult to achieve adequate circulation with density/hydrostatic pressure alone. If the flat in question was located right on the coast then sure, but over scores of km to get to an arid inland location in need of hydration, a few cm isn't going to cut it. Free-flowing aqueducts generally have gradients of 1 in 5000 or steeper.
Also, basins that are below sea level (where such a proposal would obviously be located) are always separated from the ocean by elevated terrain (otherwise they would already be flooded), so digging an open channel over ground would require some serious digging. Modern aqueducts generally use pumping/turbine stations to lift/lower the water over the terrain instead, and in mountainous areas employ pressurized pipelines instead of open channels. In practice, your proposal would need to employ a similar arrangement to be viable.
>>950971
The river leading to the basin would be deeper than a few cm to allow a good flow, even if the lake would be only a few cm.
As for terrain issues, if I have an effective means of digging a long and narrow tunnel (I have one in mind) then rather than an overground channel I just make a tunnel higher up, meaning that my last issue remaining it to lower the land for the lake.
I take it that a lot of explosives would be required to just do it by making a crater?
>>950973
>The river leading to the basin would be deeper than a few cm to allow a good flow, even if the lake would be only a few cm.
I'm not talking about depth, I'm talking about gradient - that is, elevation below sea level. If your lake is just 100 km from shore and you by some miracle have terrain flat enough to dig a channel with no pumps (or the ability to dig 100 km of tunnel through any sort of Earth regardless of geology), you'd still need your lake to be at least 20 meters below sea level for it to flow naturally.
Realistically, though, that's just not going to happen, and unless your lake is right at the coast you're going to need pumps from a practical standpoint.
>>950978
A big problem with digging big tunnels is that the bigger you make your mining vehicle, the more you can dig, but the more tunnel you have to dig so you don't go any faster.
While it's inefficient to dig by evaporating rock and pumping away the vapour, technically it is possible to make a small mining vehicle which does that with great power by connecting it up to something supplying that thermal power.
>>950980
could i remove the earth with say, a shovel?
i was thinking about using a shovel and removing the dirt with a few buckets on a pulley wire.
>>950985
You could, but the problem with a shovel is that the maximum digging power it can reach is limited by size, and digging speed is power/size-of-tunnel, so of course you have a hard barrier.
Even Superman can only dig so fast with a shovel before the shovel melts, whereas using a gigantic parabolic dish to make a beam of intense sunlight that instantly vapourises rock can make a tunnel as narrow or wide as you like, still retaining the same tunnelling power.
>>950978
Does that mean that a canal to create the Saharan Sea is impossible, because the gradient of the water in the canal would slant down lower than the deepest point of the Saharan Sea?
>>951287
The Qattara Depression is within 100-300 km from the Mediterranean coast, and has an average elevation of 60 m below sea level and a minimum elevation of -133 m. Assuming you COULD manifest the resources to cut through the surrounding terrain, the gradient is steep enough for a well-constructed aqueduct/canal, though it certainly wouldn't fill the depression to within a few cm of sea level. More likely it would remain at least 20 meters below sea level or lower.
>>951469
How does that even work though? Is it that surface tension overcomes force of flow at that gradient?
Because in that case, it sounds like literally any disturbance in the water would cause it to flow little smidgens at a time.
>>950962
all you are doing is increasing the surface area of the lake. remove the dirt between the saline outflow and the inflow, and you have a bigger lake.
>>951471
Well, that's necessary to have a deep river efficiently flow into a shallow lake, but what does it have to do with making the lake bigger?
>>950962
yah, this has been discussed at length. for like 100 years. old idea.
http://press.anu.edu.au//anzsog/auc/mobile_devices/ch06s04.html
>Advocacy on the part of politicians and enthusiasts of the idea of bringing water from the north of Australia to the inland, and of the related idea of permanently filling Lake Eyre by fresh or sea water, dates back to the 1870s and 1880s. Interest in such massive hydraulic projects appears to have been originally inspired by contemporary French proposals to using seawater to flood inland depressions in the Sahara desert. The proposal to build a canal from the Upper Spencer Gulf to flood Lake Eyre with seawater was seriously considered by South Australian Parliament in 1883 and was raised again in 1905, but was rejected on the basis of impracticality and cost.
>>951486
>In this same period, a young engineer named Jack Bradfield was working for the New South Wales Government Engineer for Water Conservation, Hugh McKinney, on a proposal to build a network of locks and weirs along the Barwon and Darling Rivers.
also, inspired by a french plan for the sahara
https://en.wikipedia.org/wiki/Sahara_Sea
also, planned by the nazis later on was a plan to dam the Mediterranean sea.
