What’s the difference between a healthy stream and an unhealthy stream, and why does it matter?
It may seem hard to tell if a river or stream is healthy. I always thought that if there was running water it was a stream, and that was that. But now that I’ve spent a lot of time in beaver-restored sections of the Salinas River, the difference is like night and day.
The healthy, beaver-filled areas have a crisscross of ponds and woody structures throughout, lush vegetation, and much more water overall. There are side channels dug by the beavers in many directions. Islands of sediment form and vanish with the flow of the river, and the whole area is just absolutely buzzing with life.
In short, healthy rivers and streams are messy.
A healthy, messy river meanders, recharging groundwater, lessening the intensity of floods, and creating a large area of wetland that won’t burn even in the most intense wildfires. The wetlands beavers create are among the most biologically productive ecosystems in the world, supporting hundreds of species: birds, fish, amphibians, reptiles, insects and other mammals.
Unhealthy rivers and streams are what most of us are used to in California. Land uses that extend right up to the bank create incised streams, which typically only have one channel for the water to flow. Because the water is forced to flow in a narrow channel, it flows much faster and ends up digging out the channel bottom. Over time, the channels get deeper and deeper until roots cannot reach the water they were once connected to. Most rain water that does fall rushes to the ocean with no chance of spreading onto the land – leaving a dry, dead, highly flammable riverbed and floodplain that is a fire hazard instead of a lush, green fire break.
The good news is that if we give the incised streams some room, they can be restored to their healthy state and bring us the fire protection and water storage benefits that we really need.
Beavers are the experts when it comes to stream restoration, but humans can help too! All we need to do is mimic beavers by using natural materials to add structure and complexity to our incised streams. The structures slow the water flow and catch sediment, so over time with continually adding complexity, the river bottom builds back up and the stream becomes healthy once again.