Could there be a plausible way to have a freshwater river that sources water from a saltwater ocean? By plausible I mean by means of everyday, scientifically-sound, boring-ass reasons, so no magic.
I am not a scientist, and do not know anything about rivers. Please help.
I think one of the defining features of rivers is that they flow down to sea level right? So I don't think so. But maybe if you have a salty inland sea at high altitude and the river flows down from there?
idk about fresh sourced from salt, but Brackish water (in between) can occur in different ways including even subterranean connection to an ocean
https://en.wikipedia.org/wiki/Brackish_water#Brackish_water_habitats
https://en.wikipedia.org/wiki/Anchialine_pool
https://en.wikipedia.org/wiki/Cenote#Freshwater/seawater_interface
I've heard of springs where salty water comes out of the ground and flows into a creek or river
If your river source is at sea level, where does it go from there? A system of caves that provide filtration to desalinate the water and then it...just goes deeper. Yeah idk I don't think this one works
Maybe some sort of geyser/volcanic pressure hits these subterranean reservoirs and forces it upwards into a bubbling creek?
From my understanding you would just get a brackish marsh or an inland saline sea.
However ... theoretically there could be so many mangrove trees along the inflow that the water is desalinated.
There could even be a cool scenario where a country cuts down a path through the mangroves to open up a trade route or military supply line and inadvertently salinates the inland freshwater sea.
This is actually an explanation I thought about; perhaps there's some sort of plant life that sucks up a lot of sodium and hangs around river-inlets? A mangrove tree is a great idea!
Desalination plants esentially push water through a membrane at high preassure. The salt(with a lot of watter) stays in the filter(is trown away) and fresh water cones from the other side.
A preassure diferential is esentialy the (heigth 1x density 1 - heigth2x densuty2 )x a constant.
Since fresh watter is ligther than salt water if we build a straw long enough then the preassure diferential will be enough to push the heavier salt water into the fresh water filled straw.
I did the math a while ago, the straw has to be about 75 km long. For the moment lets ignore that at those depths we are probably not dealing with water any more so the membrane does not work. Lets supose it does.
This contraption still violates the laws of termodynamics. So where is the mistake? My best guess is that the filtering action should push the straw down until it is at sea level. And you need to constantly apply work to keep it in place but i am not sure.
In a fantasy setting you could pribably apply that work by using tidees or bouyant forces or something.
