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My premise is that a bay-like body of water empties into a sea via a waterfall.

Specifications: The sea is roughly the size and shape of the Mediterranean. The tributary body of water is around 20 miles across, and very long (shaped like a huge river). The waterfall is a straight drop of about half a mile (roughly the height of the tallest waterfalls on earth). It is fresh water flowing into salt water. It's not flowing extremely quickly, but the rate of discharge is sufficient to create a continuous curtain of water extending all the way to the bottom.

Things to ignore: Erosion is not an issue. Don't worry about the source of the water either.

Obviously, the waterfall would generate large quantities of mist, much of which would evaporate into the surrounding air. It would also cause turbulence in the sea and an area of diluted salt water. What effects are these factors likely to have on the weather, sea currents, and aquatic life?

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  • $\begingroup$ Temperature? Altitude? Longitute/latitude? $\endgroup$
    – PCSgtL
    Dec 10, 2015 at 14:37
  • $\begingroup$ It's a cool temperate climate, something like southern Canada or northern Europe. $\endgroup$
    – Era
    Dec 10, 2015 at 15:27
  • $\begingroup$ Any mountains near by? $\endgroup$
    – PCSgtL
    Dec 10, 2015 at 15:32
  • $\begingroup$ Yes, the "river" flows south from a high-altitude plateau. The southern edge of the plateau is a range of steep mountains running east-west that forms the northern coast of the sea. There are coastal plains in some areas, but not very large. The cliff of the waterfall is part of the plateau's edge, and there are mountains on either side. $\endgroup$
    – Era
    Dec 10, 2015 at 15:52
  • $\begingroup$ So reversing your description. The Mediterranean like sea is a low elevation. Immediately north is a mountain range of high elevation running east/west. Past the mountains there is a large plane that continues to the North and gradually rises to a higher elevation? If this is accurate, is the highest elevation of the plane higher than the highest elevation of the mountain peaks? $\endgroup$
    – PCSgtL
    Dec 10, 2015 at 16:39

2 Answers 2

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So I have enough understanding to give you one of two options on the weather. That large of a mountain range creates a water shed. It will block storm fronts and cause all the water to be dropped on one side as the moisture is forced up in elevation. (Colder air holds less moisture.) It depends upon witch way the strongest air currents travel in your world.

If they travel from North to south in this area then the weather shall often be cold but mild. Few storms and little rain fall. Farmers in the area depend upon the river for water. Moisture evaporating from the Mediterranean does not fall as rain in the area since there was so little moisture all ready. There is probably a desert on the southern shore for quite a distance. The northern border of the mountains have much precipitation, but most of this occurs as snowfall. Massive drifts may accumulate.

If they travel South to North there are likely many thunder storms and much rain especially in season on the Northern coast. They may experience near torrential downpours for part of the year. The rains will tend to be warm, but there shall often be sleet and hair mixed in. Storms in the rest shall be very similar to the current Mediterranean, just slightly cooler. They won’t be to frequent, but can come out of no wear. The river itself is wide enough body of water that it might help push some of the worst of the storms away. But only slightly.(4 miles at most) Flooding would still be an issue but the worst of the rain might fall a few miles away.

Major air currents flow from both directions. Merge the rainy portions of both answers. Add in frequent and freak tornadoes, especially along the mountain passes and valleys.

In general you shall have the frequency of storms of the Mediterranean, but with much of the temperature of the North Sea and Baltic. This is of course assuming depth of the Mediterranean. (rather shallow). If you chance the deapth storm frequency shall change.

I believe Altera to be wrong about the diverse or tropical life. Winters shall be to cold.

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  • $\begingroup$ Thanks for the very detailed answer. I'm thinking that winds travel northward, creating the Monsoon-like conditions you mentioned on the northern coast. Being relatively flat, the coastal plains would have numerous smaller, meandering rivers flowing from the mountains to the north, with massive annual floods. What kind of ecosystem might this produce? $\endgroup$
    – Era
    Dec 10, 2015 at 18:53
  • $\begingroup$ The eco system could be another question. Your looking at systems with deep root structures that wont be washed away. Or Quickly growing things that sprout after the floods. Or much marshland/swamp to help disperse and absorb the watershed. Leaning towards the marshland myself but that would require a greater depth of coast-land. $\endgroup$
    – PCSgtL
    Dec 10, 2015 at 20:11
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Edit:This answer assumed a warm local climate, as the question is now for a cool local climate it is invalid.

I agree that there would be a large amount of mist, which would allow people to see where the falls were from far away (You could probably hear them from a large distance too), the nice thing about the mist is at night it should allow moonbows to be seen. The spray is good for the surrounding environment, it would allow a rainforest to form around the waterfall, expect there to be rare plants and animals (perhaps even some that are only found in that rainforest).

The falls would separate the river from the sea, so very different species would be found in the two. The birds that hunt the fish might even specialise to only eat from the river or the sea bellow. The nutrients in the river (from the rainforest and from further up the river) will attract (sea) fish to the waterfall, possibly seasonally. Which will of course attract predators. Those that can survive the fresh water (which would have to deal with increased amounts of sediment as well the lower salinity) might try and escape the predators by swimming into the diluted water.

If there is a current that is relatively near the surface it may be 'pushed' deeper by the less dense fresh water which will spread put into the sea. The effect this could have depends where on the planet the falls are and where all the ocean currents are. The falls would have take a long time to form so things could have slowly adapted to the change.

If there are humans on this planet expect there to be lots of tourism to see the waterfall, with boat trips above and bellow it.

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