The storm was short and intense but the sky stayed gray long after the rain stopped. Walking outside, I saw little waterfalls cascading down the previously dry gullies that dotted the landscape. The stream – which hours before had been a grassy depression – was filling with water, turning what was a dry creek bed into a full, free-flowing stream.
This was last July at my in-laws in eastern Colorado. In this semi-arid region (dry, but not quite a desert) all but the largest rivers are empty most of the time, waiting for the next storm to send water tumbling down their channels.
How do rivers keep flowing even when it is not raining? Where is that water coming from? California recently suffered from a severe drought (although that has changed lately) but most of their rivers didn’t just dry up. These streams kept flowing because of groundwater. Groundwater acts like a battery. It gets charged when it rains and then slowly releases that water into streams and rivers, providing a continuous “power” source.