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I am trying to wrap my head around the geography of a settlement in my world.

The settlement is situated along the coast, along a river roughly 500m wide with temperate mixed forests surrounding it, which I hazard to guess is relatively common.

The difficulty comes with the freshwater springs to which the settlement has access to. There is a spring near the river meeting the ocean, perhaps stemming from a hill or mountain.

What is the closest I can realistically have my spring to the ocean?

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    $\begingroup$ They have a five hundred meters wide river flowing through the city. That's more fresh water than they can use. $\endgroup$
    – AlexP
    Jun 26, 2019 at 11:55
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    $\begingroup$ I've seen freshwater springs among the dunes just above the storm line of the beach, and freshwater wells barely 0.5 km inland, just a couple meters above sea level. However, nice big aquifer flowing toward the sea there - draw too much from wells too close, and you'll get saltwater intrusion.. $\endgroup$
    – user535733
    Jun 26, 2019 at 12:42
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    $\begingroup$ Yous settlement is on the river's mouth? Depending on river flow and intensity of tides, water in the river may likely be drinkable. $\endgroup$
    – Alexander
    Jun 26, 2019 at 16:23
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    $\begingroup$ At Easter Island, they literally found fresh water springs flowing directly into the ocean: cnn.com/travel/article/easter-island-statues-location-scli-intl/… $\endgroup$
    – Adam Miller
    Jun 26, 2019 at 20:14
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    $\begingroup$ The biggest issue you could have is that the spring must put out sufficient water flow to prevent back flow from the ocean (or river). This is something we see in the N Florida springs around my house - when the river(s) flood or get high water due to lots of rain in Georgia, etc. the tannic river water rises, which can cause enough pressure that the spring water doesn't go up and out, and in extreme cases can cause river water (or ocean in your case) to back flow into the springs. On a coast, the tides may have a strong effect on this. $\endgroup$
    – ivanivan
    Jun 27, 2019 at 15:35

3 Answers 3

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What is the closest I can realistically have my spring to the ocean?

0 meters

When, as a kid, I went to the sea during summer, it was common knowledge that, in some places along the coast, there were springs pouring fresh water directly into the sea.

One could tell it by both the sudden drop in temperature, especially with calm waters preventing mixing (the surface was chilly, while the bottom was warmer) and by the different appearance of the waters due to the different density. While I could see for quite a distance with my bare eyes open underwater, when I went into the spring zone the water looked kind of foggy and seeing through it was much harder.

In the generation before mine such places, in particular where the water was shallow, where used by shepherd to supply their herd with drinking water, which was otherwise impossible to find in the surrounding Mediterranean shrub.

The geology of the place where I grew up is made mostly by limestone surface layers, with clay like layers underneath. The interface between limestone and clay is where water accumulates and flows. There was no visible spring, rather a diffuse percolation through the rocky coast.

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  • $\begingroup$ What kind of formations are around the springs? Do they stem from holes in the ground or from elevations? Are the coasts sandy, gravelly or cliff-like? $\endgroup$
    – A Lambent Eye
    Jun 26, 2019 at 11:21
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    $\begingroup$ I'll second this, at Kai Iwi Beach near Whanganui there are freshwater springs that come right up through the beach at low tide, at high tide you can see them discolouring the water off shore. $\endgroup$
    – Ash
    Jun 26, 2019 at 15:41
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    $\begingroup$ @BilboBaggins, considering a city cannot be underwater in this scenario, if the spring is then it is further away than if it was at level 0. $\endgroup$
    – L.Dutch ♦
    Jun 26, 2019 at 16:07
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    $\begingroup$ Doesn't have to be cold, either. en.wikipedia.org/wiki/Hot_Water_Beach has a spring between high and low tide level at 64°C (147°F). $\endgroup$
    – Rupert Morrish
    Jun 26, 2019 at 23:38
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    $\begingroup$ Therma beach, on Kos, Greece, also has a hot spring jetting directly into the sea. There is a pool round it which people sit in. Europeans sit round the edge of the pool, and Russians sit right by the spring! $\endgroup$
    – Tom Anderson
    Jun 27, 2019 at 15:13
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  1. They have a five hundred meters wide river flowing through the city. That's more fresh water than they can use.

    The entire country of Egypt lives off a large river flowing through the country.

  2. Istanbul (formely Constantinople, formely Byzantium) is a very large city sitting astride the Bosphorus, a salt water strait connecting the Black Sea and the Marmara. There are numerous wells and springs and small fresh water courses emptying in the sea, some of them captured since two and a half millennia ago. Not to menium aqueducts and huge cisterns for storing water, built by the Roman emperors back in the days of the glory that was Rome.

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    $\begingroup$ Of that I am aware, the spring has further significance other than as a source of drinking water. $\endgroup$
    – A Lambent Eye
    Jun 26, 2019 at 15:08
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Freshwater springs can appear at any distance to the sea, even under the sea.

The easiest explanation for springs next to or under the sea is karst. It is formed from soluble rocks (often limestone), which are full of cracks, crevices and caverns. Rain water, and even whole rivers can disappear underground and continue flowing through underground cracks and caverns. They can resurface at any point, usually at lower elevations, and often where the soluble karstic rocks meet less soluble rocks underneath them. If there are less soluble rocks underneath, the water doesn't flow down anymore, but sideways, and surfaces as a spring (though there are also other ways for springs to form).

I mentioned that you can have freshwater springs even under the sea. Undersea karst springs are pretty common in the Mediterranean, along karst coasts. In Croatian they are called vrulja. For a freshwater spring to appear under the sea, the hydrostatic pressure of the fresh water has to be high enough to counter the sea water pressure so the fresh water from karst caverns can flow out into the sea, rather the other way around (seawater flowing into the caverns). High hydrostatic pressure of fresh water usually happens if there are karst mountains (or at least hills) right next to the sea. If the coast doesn't have high enough elevation, there can be temporary vruljas, where fresh water is forced out only under certain conditions (like during a rainy season), or if the elevation is very low, the fresh water may never be able to create a spring under the sea.

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