Month: March 2009

So Igor and I piled in his jaunty hybrid and drove out to Antioch last night to talk watershed. The scout involved with the tree-planting came too so he could listen to our overview and catch up to date. Igor spoke first about the way watersheds work and it was a great opportunity to think about our creek and how we have treated it.

One of his main points is that creeks need room to live a normal creek life. They need to meander, to move their banks, deposit sediment, and build up resources. When healthy creeks encounter high flows the water is absorbed by the floodplain and things return quickly back to normal.

Very early on we decided creeks were property lines, and we didn’t want them changing on us. Imagine if we used clouds for property lines? We confined creeks with sheetpile and cement to keep our feet and acres. However, creeks that can’t “meander” simply cut deeper into the earth, so we end up with faster, harsher high flows that are threatening to property. One thing he said last night that I had never heard was that confined channels, whether its concrete or sheetpile, have a life expectancy of about 60 years. It’s not like you build them once and all your problems are solved. In fact many of our impermeable surface creeks in California have reached the end of their life span, and require significant maintenance.

I found this description from Toby Hemenway a while back and was fascinated by the implications of how we changed our waterways when we decimated the beaver population. Add to this that a downcut stream has a lower water table, so tree roots can’t reach it and the vegetation along the bank dies off.

You know what a stream looks like. It has a pair of steep banks that have been scoured by shifting currents, exposing streaks and lenses of rock and old sediment. At the bottom of this gully—ten to fifty feet down—the water rushes past, and you can hear the click of tumbling rocks as they are jostled downstream. The swift waters etch soil from first one bank, then the other as the stream twists restlessly in its bed. In flood season, the water runs fast and brown with a burden of soil carried ceaselessly from headwaters to the sea. At flood, instead of the soft click of rocks, you can hear the crack and thump of great boulders being hauled oceanward. In the dryness of late summer, however, a stream is an algae-choked trickle, skirted by a few tepid puddles among the exposed cobbles and sand of its bed. These are the sights and sounds of a contemporary stream.

You don’t know what a stream looks like. A natural North American stream is not a single, deeply eroded gully, but a series of broad pools, as many as fifteen per mile, stitched together by short stretches of shallow, braided channels. The banks drop no more than a foot or two to water, and often there are no true banks, only a soft gradation from lush meadow to marsh to slow open water. If soil washes down from the steep headwaters in flood season, it is stopped and gathered in the chain of ponds, where it spreads a fertile layer over the earth. In spring the marshes edging the ponds enlarge to hold floodwaters. In late summer they shrink slightly, leaving at their margins a meadow that offers tender browse to wildlife. An untouched river valley usually holds more water than land, spanned by a series of large ponds that step downhill in a shimmering chain. The ponds are ringed by broad expanses of wetland and meadow that swarm with wildlife.

The entire article is a great look at the way our beaver-huntin’-habit changed the face of America in ways we never considered. It also reminded me of the fact that our beavers now have increasingly harder jobs of keeping up creeks formed by years of downcutting.

Good thing they aren’t slackers.