How do rivers last so long in dry weather?

Question

I got caught in a downpour while climbing a mountain and was amazed to see, as I climbed down, the tiny trickles of water combine to form mini-streams, the dry rocks I had climbed up now hosted sizable waterfalls, and the path which I had followed to the mountain had become a small river. But it got me wondering about my question, which is the reverse of this. Why, after a long period of dry weather, are many rivers still flowing? I live near a river and it seems that it takes over a week of dry weather before there's any noticeable drop in its level. How does it not simply run out of water? Is it simply that it takes very a long time for the water at its source and the sources of all its tributaries to reach the point I'm observing from? It seems there's a constant supply of water when I would have expected the network of rivers to start draining, and the drying up starting from the source the moment the rain stopped.

Answer 1

Hello,

Each creek, stream, river and water tributary is within a watershed. And you pointed out you were hiking at a certain elevation. Water flows downhill due to gravity. And the visible water (visible streams, rivers, creeks) are not the only sources of water that flow downhill. There are underground channels of water (groundwater) that can add to the downstream water. And if you were to map a watershed, the different channels flow down typically to a collection area (river, lake or large stream) before they flow to their main channel (large river, lake or ocean).

In regard to the question why don't the rivers dry up, it is because there are other sources feeding into them that you aren't observing or aware of. Again, watersheds cover a very wide area and typically follow gravity to flow downhill to a collecting channel.

Hope this helps answer your question. Best, Lisa H.