Click here to go to the USGS website. Here’s an excerpt:
When a drought hits and little or no rain has fallen in a long time, you might expect small streams and even larger rivers to just dry up, right? In many cases, they don’t. Streamflow might lessen to a trickle or so, but water continues to flow. How is that possible? Read on to find out how “base flow”, which is water seeping into the stream from groundwater, helps keep water in streams during droughts.