eli5: Why does there continue to be water in a river, even though it doesn’t rain all the time in the upper parts?

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eli5: Why does there continue to be water in a river, even though it doesn’t rain all the time in the upper parts?

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It’s called base flow.

Basically there’s a bunch of water underground. It seeps into the rivers. So, usually it’s a combination of the water cycle and base flow. But when the water cycle is interrupted (drought), the base flow is still running.

So you get lower water levels, but still running.

It can be from a lake and flows to the ocean. Of course, without rain, the lake will start to dry up slowly. So long as it rains sometimes, the water will stay until the lake fills up with silt or sand.

Edited

Many rivers are fed by lakes or snowmelt which will slowly release water over time even if there’s no rain at that particular time. These days, more and more rivers have artificial reservoirs that achieve this by creating a man-made lake with a controlled release volume.

I think about this every time i see a creek in the summer, it seems so mysterious. But notice that creeks and rivers are always cut into the ground. They are lower than the soil above, and sometimes just that few feet is enough for ground water to seep into the creeks and streams and feed them.

But that doesn’t meant it never stops. In dry summers lots of waterways do dry up.

Whenever it rains water flows into the ground, and from the ground it seeps into groundwater flows and that water makes it into rivers.

That groundwater reservoir is generally big enough to keep rivers fed even if there is a big drought. A drought will reduce the flow somewhat, but not enough to dry out the riverbed (well, unless you’re in a desert or savannah, where riverbeds will frequently dry up).

Generally people don’t think about this, but city planners and builders think about it all the time (because if you don’t take it into account you’ll have problem with mold, collapsing streets, houses cracking, seasonal floods, sewage backflow etc).