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

Question

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

Answer 1

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).