eli5: Why does there continue to be water in a river, even though it doesn’t rain all the time in the upper parts?
In: 29
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.
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).
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.
THe ground acts like a big, porous sponge, soaking up water when it rains, storing it and releasing it gradually at lower levels.
There are problems in some cities where all the ground is paved or roofed over. All the rain goes into the drainage system straight away, resulting in flash flooding in some parts.
A lake, stream, or river isn’t a free standing body of water, it’s just the visible part of the MUCH larger water table. In all but arid areas there is groundwater some distance below the surface.
People have mentioned the water in the ground already, so I’d just like to point out that trees are a huge part of this. Trees can store literally tens of thousands of gallons inside them, which they slowly release over time through multiple different processes. This is a huge part of why when you cut down all the trees, flooding becomes much more common and rivers become a lot less healthy. The trees aren’t there to store and purify it anymore.
I hate to be the one saying this and I know I can’t be the only one thinking this; once we accept what human kind is doing to this planet we call home, we must accept that ultimately all these wars that have been fought and are currently being fought will be nothing when all of humanity is going to war over the limited amount of fresh clean drinking water we have left. With the ever growing population of the world we are going to reach a tipping point very quickly. Sure, we’ve all had hunger pains but can you imagine the desperation of someone who is thirsty? 3 weeks without food and the human body starts going through some gnarly changes, 3 days without water your going to be very desperate.
Never underestimate the desperation of someone when their life depends on it. Can you imagine millions of people days of way from dying of thirst?? How about Billions? If humanity doesn’t get its stuff together we are less than 200 years away from extinction.
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