There are numerous locations around the globe where the Earth's surface is below sea level. My careful analysis suggests that almost all of these are underwater. Just occasionally, you can find locations that are below sea level and are not underwater. Some of this is the Dutch, defying the natural order, but other anomalies exist. One example is the Salton sea. This depression in a dry bit of California was hilariously filled with water by accidentally diverting one of the world's great rivers into it. For a number of reasons it has since begun to dry out and presently sits as a nasty salty thing with little future.
Several people have suggested filling depressions with seawater. <link> The filling is always the easy part, however the annoying tendancy of water, and not salt, to evaporate means that this system just leaves you with a shallower depression with more salt than before. The key is exchange. Pumping can do this, but it's expensive and the volumes are large. So we need to get some, preferably selected, water back out.
The main problem at the moment is that to get water out, you have to pump it UPHILL 230ft or so to sea level. This is hard work. It would be much easier if the lake were AT sea level. So let's do that. Now, according to one of the Salton sea advocacy websites, the sea looses 360,000 gallons per year to evaporation. This is trivial hosepipe territory to get a net filling effect*. The obvious way to fill the sea is to dig a canal from there to the gulf of California. This is very much shorter than the current map suggests. The canal only need traverse the sections above sea level<link> between the Salton and the Gulf. There is only a little section to the west of Mexicali needed to join up the Salton sea and Laguna Salada, then another section from there to the Colorado river estuary. Total is only around 80- 150 miles of canal.
During construction, consideration to flow through the body of water should be included, a way to preferentially shepherd the influx toward the far side of each body of water. This could be extremely simple, polythene sheet suspended from buoys with a little weight could create a pseudo channel within the water. So, now the Laguna Salada is filling with sea water. With some gates, this should be easily controllable at such a rate as to motivate but not inundate those building the Salton-Salada canal section. Once full, the new inland sea at Laguna Salada will displace... noone, no major towns at least.
Once high enough, water from the Laguna Salada may start to enter the Salton-Salada canal. Here things get a little messy. The Imperial valley is populated. El Centro, Brawley and a couple of others, gone. Around 160,000 people total. The dumb ones will have to be told to move, the clever ones will be buying land at around sea-level elevation nearby.
Eventually we'll have a full Salton basin and a full Laguna Salada. We have to build in a mechanism of water exchange. Luckily, the energetics of moving water a vertical distance of 0 are pretty good. The energetics of letting water flow downhill are even better. This is where tides come in. The tides in the gulf vary between about 1ft to 13ft above mean sea level. If we set our inland sea level about 3-5ft above sea level we can have a net inflow of water at high tide and a net outflow at low tide. An online calculator suggests a 10 mile canal with a 10ft head, 80ft wide should be able to flow about 10million gallons during the 3hrs of high tide. There are two per day.
To prevent exchanging the same water near the canal repeatedly, control of in and out flow is necessary. Even something as simple as directing incoming water to the right and allowing outflow from the left could set up a beneficial circulation. Or, as mentioned a floating canal could be used to direct fresher water to the far side of the lake, pushing the saltier stuff back toward the entrance/exit. Perhaps the clever thing to do would be to install platforms for artificial reefs a few 100ft off the shoreline, clean water could be directed between the shore and the reef along the periphery.
In and outflow could be managed along the same canals since the tides are separated by time. Frequency of events need not match between the two inland seas. The Salton-Salada link can have much lower capacity. Since it can open at the same time as the Laguna Salada-ocean link and stay open long after it has closed. Careful management of differential openings could be used to effectively flush the content using annual tidal maxima/minima.
The complainers in the valley should remember that this will all happen anyway... eventually...
*obviously this will be very slow and will hit a new equilibrium very soon. I'm illustrating a point about scale.-- bs0u0155, Nov 07 2016 Australian Sea The_20Australian_20sea [bs0u0155, Nov 07 2016] Red is below sea level http://weather.unis...ap.php?32.0,115.0,1 [bs0u0155, Nov 07 2016] // sits as a nasty salty thing with little future. //
Sorry, is this Hilary Clinton, or the Salton Sea ?
// annoying tenancy of water //
Oh, we know about that. It pays its rent late, has noisy parties, and then doesn't clean the place before leaving.
Now ...
Build two large parallel pipes from the sea to the basin. The oceanic ends need to be submerged; the basin ones a little above the existing water level. Build reversible pumping stations in the pipes, probably at the basin end; they could possibly be solar powered.
Pump water through both pipes towards the basin, such that the syphon effect then draws more water through without pumping. Once the syphon flow is established, bypass the pumps and let the levels equilibrate.
Eventually, the syphons will stop.
Put the pumps back inline, one incoming, one outgoing. The incoming side will need more flow to compensate for evaporation. The lake will have the same salinity as sea water, and the energy required will be lower as both ends of the pipes are submerged; no requirement to "lift" any water.
When the "Big One" hits California tho, all bets are off.-- 8th of 7, Nov 07 2016 //The main problem at the moment is that to get water out, you have to pump it UPHILL 230ft or so to sea level. This is hard work. //
No no. The solution is simply to dig another hole, near the Salton Sea, and let the water run into that of its own free will. Of course, the new hole will eventually fill up, but all you have to do then is to dig another, even deeper hole. This could be done under the existing Salton Sea, to reduce land usage. Repeat as necessary.-- MaxwellBuchanan, Nov 07 2016 Hence the phrase beloved of the Democrats, "If you're in a hole, keep digging".-- 8th of 7, Nov 07 2016 random, halfbakery