When settlers first touched the shores of North America, there were an estimated 60 to 400 million beavers. Think about that, over two million beavers in every state, which means they were in every creek and lake and stream they could reach. Their fur was so desirable and their habits so easy to predict that by the early 1900’s hunting had dropped the population as low as 100,000. In many parts of North America there were no beavers at all.
That’s a dramatic change, but lets think for a moment about what life was like when all these furry wetlands engineers scurried around the continent. They terraced every meandering creek with dams, caught the water and held it for drier times, and slowed down periods of high flow. In fact the arid western territories weren’t so arid when there were beavers to control the water. The creeks were shallower and changed their banks more often, moving the rich deposit from one side to the other. The soil along the banks made rich habitat for trees to grow healthy and green. Just like in Egypt along the Nile, the rich sediment allowed for hugely productive crops. I have even heard that our pioneers could never have been as successful if beavers had not conditioned the soil for them.
We may not really think about it, but creeks are changing things. The move their path, they meander, they develop. As America grew more populated, we stopped allowing our creeks to change. Creeks were borders, boundaries and markers. That was someone’s land they were meandering onto or away from. We may have continued to let our cattle roam but we started to put our creeks in fences. Riprap, concrete walls, steel piling. We narrowed the options for our creeks, and nearly exterminated their caretakers.
So what happened? Creeks are changing things. If the can’t meander from side to side, that doesn’t mean they don’t evolve. Since they can’t go out they go down. Undercutting began across the continent. Our channels grew deeper and faster and the exposed soil thinner and harder to support vegetation. When I walked our Alhambra Creek with the fluvial geomorphologist Laurel Collins, she pointed out several examples of undercutting in our bed. Development gave the creek no where to go but down, and that means that the flow gets steeper and faster in hard weather, hence the flooding we see every few winters.
When a creek undercuts it is harder to store water, harder to replenish soil and grow crops. Drier areas begin to suffer and wetter areas get overwhelmed. Animals that depend on the creek are also affected, and the game you might have hunted to put food on your table moves farther to find water as well. I started thinking more seriously about this when I read Eric Collier’s book “Three Against the Wilderness” about re-introducing beavers in Canada. He wrote in particular about a complicated waterway that fed several farms. Without beavers to keep the water in a series of dams, the entire area was subject to draught. He hoped anxiously that when they returned they would be able to keep the water during high flow and eek it out through the summer months.
This confused me because our dams wash out so easily during high flow. A little review has shown that any time we receive more than a half inch of rain over 24 hours we’ve had a full or partial washout. So how did these Canadian beavers manage their magic? Are our beavers just slackers, or not as talented at dam maintenance?
No. The answer came from a conversation with Igor Skaredoff who attended the beaver conference in Oregon where they are reintroducing beavers to increase the salmon population. They noticed the dam washout problem as well and decided that beavers need a little structural help to keep the water back. They provide reinforcement to dams, and a foundation starter. Why? Because the landscape has changed since the 1900’s and the writing of Eric Collier’s book. Undercutting has made streams faster and deeper, and beavers, hard workers though they are, can’t keep up.
As in so many ways, mankind has made their work harder. Now that streams are deeper and faster there is less rich soil deposit, and that means less treescape, and less habitat for beavers to feed. At the very time when humans need their dam building to eek out water in drought and minimize water during high flow, our creeks are less able to take care of their needs, and less hospitable to their efforts.
American history is inextricably linked to the beaver. We may as well figure out how to get along.
