Fast Question in need of an answer!

[MadLetter]

A river flows into a sea. Can from that sea two new rivers emerge that flow into different directions?

(my river comes from north, the sea nestles near a mountain-ridge, two rivers should emerge, one westward the other eastward. Is this possible?)

[SeerBlue]

Right of the bat I would say that rivers could not originate from a sea and flow outward, being that the location of the sea would be the lowest point in the terrain, and as far as I know water only flows into oceans and sea's, except in cases of things like tidal bores, where the salt water flows back up the fresh water course due to tides....but it really made me think, as sometimes what we think we know is not always true, so I did a google search and could not find any reference of rivers out flowing from a sea. but as there are sea's below "sea level" i could be wrong. The definition of a sea though is a saline lake that lacks a natural outlet

Large fresh water lakes could have outflows though. The great lakes are connected by atleast 5 rivers, and are called inland seas by some, so it is possible to have your seas have outflows. So if your terrain suits an eastward and westward flowing river, it may work.

[Arkkeeper]

Not out of it, that would require both sides of the sea to be exactly the same height, now one river could flow into it on the east and one out the west but not two out on opposite sides. it's okay it's a common thing people attempt to do even though it's nigh impossible and incredibly unrealistic.

Also A sea is not the only lowest point of the land as a out flowing river could be formed from a gorge connected to the sea, after all let's say the sea is a filled up box canyon with very low slopes then a few parts of it continue on like a river canyon except it's not a canyon because the slopes are not sheer drops but gradual descents, but I think you probably still get the idea the point is is that you cant have two rivers outflowing in opposite directions, just like you can't make a river fork into the ocean making a large island right next to the coast, then all of that fork would lose water flow and become ocean, I think a perfect example of this is the Nile where it forks quite a bit but both halves always return to each other before entering the Mediterranean, making a river island.

[MadLetter]

Thanks guys. I will go with one river out then for now. If I get new info, I might make it two if it is viable.

[RobA]

As SeerBlue states, it can only happen with freshwater lakes.

All natural freshwater lakes will eventually only have one outlet. If there is damming (either natural or artificial) then you can have more than one outlet. But unmaintained, erosion will cause one outlet to dominate, and other to dry up as water levels adjust.

-Rob A>

[MadLetter]

Perfect answer, RobA, thanks a lot for it!

Onward to work, then!

(The sea i was talking about is freshwater, coming down from mountains, gathering into a big stream that spands a few hundred miles)

[Arkkeeper]

Beyond perfect. Exactly what I tried to say except with much less words. rep for good answering.

[waldronate]

As others have pointed out, it's not stable to have such an arrangement. However, if your lake or sea is moderately large and positioned correctly then there is the option of having intermittent rivers on each side driven by tides. That particular configuration requires a lake/sea spanning a significant fraction of the globe, a huge influx of water, and isn't geologically stable.

Very narrow straits can also have major tidal currents and if you get two opposite openings into a smallish sea then there will be a rushing river effect twice a day at each end. The straits will open over time, though, due to the erosive power of the moving water. The Mediterranean has such an effect but the channel there is huge.

Any lake or sea is in equilibium between inflow, outflow, and evaporation. Consider what happens if you have a small opening between the ocean and an inland sea. Evaporation in the basin will cause local sea level to drop, making the sea smaller. If the basin is large enough and the openings small enough, then the sea inflow will form "rivers" that go in channels to a hypersaline lake/sea at the bottom of the basin.
This sort of thing has happened to the Mediterranean and Black seas during geologic history. The bottoms of the basins are well below sea level and incredibly hot (dener air at the bottom helps to retain more heat). Freshwater rivers flow from the mountains into the basins to the small sea at the bottom, giving nice oases in the potentially nasty desert. Saltwater rivers flow from the ocean channels to the bottom of the basin, providing no drinkable water. It's certainly not like any conditions we have today (yes, the Afar region of Africa has a basin with saltwater streams trickling from the ocean, but it's not big enough to get the full effect).
This sort of arrangement is not geologically stable, of course, because once the sea breaches the basin walls then the erosive power of a water flow with a few thousand feet of head takes over and your basins tend to fill within a few thousand years (or much quicker if there's a catastrophic breach as happened in the Black sea). It's a great lost civilization story, of course (think Noah).

[NeonKnight]

Theoretically, there is an almost (I say Almost because of certain real issues) of a real world equivalent:

The Dead Sea.

This is not so much a true sea, but rather a a high saline content lake that sits 1,378 feet below sea level. As a result, it could have a river flowing from the real Sea into it, but eventually without some mechanism for the inflow to leave, it would eventually fill.

In a fantasy world this could be accomplished by either extra diemensional rifts, portals, undergound sea etc.

[waldronate]

Theoretically, there is an almost (I say Almost because of certain real issues) of a real world equivalent:

The Dead Sea.

This is not so much a true sea, but rather a a high saline content lake that sits 1,378 feet below sea level. As a result, it could have a river flowing from the real Sea into it, but eventually without some mechanism for the inflow to leave, it would eventually fill.

There have been talks of running canals from the Mediterranean and/or Red Sea to the Dead Sea for years to replenish the lake level. The water would be pumped up over the divide and allowed to flow down to the lake in order to generate power (it'd be up 400 feet, down 1800 feet). The inflow would be adjusted to stabilize the lake at 1930s levels. The lake is currently dropping on the order of 3 feet per year due to diversion of the Jordan river and evaporation in the basin.

The Afar Basin in Africa will become a new ocean branch very soon in geologic time. There are little saltwater streams that trickle into the basin from the ocean, but they are under the terrain for the most part and don't come near to approaching the evaporation level in the area. The basin is in an active rift zone, though, and the barriers will be split soon enough.