One of the most common problems that beaver cause again and again everywhere they set up shop is blocked culverts. To them, a culvert just looks like a leak in an otherwise fully functioning dam which they generously fix it for us and are probably surprised when we aren’t very grateful for their services. This week I had a chat with a retired watershed steward from Washington State who told me that a change a few years back required for fish passage had mostly fixed this problem. Seems for all new roads and restored roads with a culvert underneath the culvert needs to be as wide OR WIDER than the stream itself. Since the culvert isn’t the most narrow part of the water to dam up the beavers usually choose elsewhere.
• Width equal to or greater than the average channel bed width at the elevation the culvert meets the streambed. Make the culvert the same width as the channel to maximize both water flow and fish passage.
This of course assumes that we’re talking about an actual streambed and not a drainage ditch or overflow. (One of those, prove you’re really a stream, deals). California actually has similar regulations provided that the stream can then show that its a regular passage for anadromous fish). There are a series of design methods which generally call for minimum culvert width to be equal to, or greater than the active channel width. CalTrans is required to meet the guidelines for any anadromous fish bearing stream when repairing or replacing stream crossings. Which, if you think about it, must be hard to prove that fish go through a stream once you built something that keeps fish from going through a stream.
Which makes me think anew about the misnaming of Alhambra Creek as a “draining culvert” a “levy” or a “canal”. Obviously naming has serious consequences and a rose by any other name WOULD NOT smell as sweet.
Pay special attention to the ‘naming issue’ when you watch this clip.
