Ever have one of those days when elusive things you’ve been chasing around at top speeds just suddenly fall in your lap? Lisa Owens-Viani is a science writer who works for the San Francisco Bay Estuary Project. She approached us months ago for Martinez beaver photos which went into their recently released report, and decided as an after thought to send me two pages of a federal report generated in the late 90’s.
The title of the report is “Stream Corridor Restoration” and the whole thing is available online. It is the result of laborious work by 15 federal agencies including the EPA, National Park Service, US Geologic Society, and the Army Corp of Engineers. The report is about how to repair damaged streams and restore ecosystems. Guess what chapter 8 recommends for controlling waterflow, reducing erosion, and increasing bird and wildlife?
You guessed!
Beaver dams on headwater streams can positively influence riparian function in many ways, as summarized by Olson and Hubert (1994) (Figure 8.18). They improve water quality by trapping sediments behind dams and by reducing stream velocity, thereby reducing bank erosion (Parker 1986). Beaver ponds can alter water chemistry by changing adsorption rates for nitrogen and phosphorus (Maret 1985) and by trapping coliform bacteria (Skinner et al. 1984). The flow regime within a watershed can also be influenced by beaver. Beaver ponds create a spongelike effect by increasing the area where soil and water meet (Figure 8.19). Headwaters retain more water from spring runoff and major storm events, which is released more slowly, resulting in a higher water table and extended summer flows. This increase in water availability, both surface and subsurface, usually increases the width of the riparian zone and, consequently, favors wildlife communities that depend on that vegetation. (8-26)
Where was this report when I was slogging through the environmental section of the subcommittee work? Thanks Lisa for sending it our way. Beaver dams can control water release upstream so that downstream has more regulated flow and less impact for hard rains. Maybe instead of worrying that beaver offspring might go upstream we should be worrying that they might NOT!
I got an email a year ago from our New Zealand Supporter William Hughes-Games suggesting that what we needed was beaver colonies every few miles up the creek to control water release. I initially dismissed this as eco-crazy talk, but after reading more about it I can see that he was right. Beaver ponds catch water, control release, and manage reserves. More about this and a recommendation for a great late summer read will follow. I plan to do some major pouring through this report in the weeks to come, especially about the riparian border recommended for creeks in natural and urban settings.
And speaking of OUR riparian border, the beavers successfully finished toppling a cottonwood tree last night. We saw it hanging by a thread yesterday and talked with Bob Cellini of city staff. He agreed it should be left for the beavers and figured they would fell it the right direction. This morning it is laying neatly in the creek. Our beavers appear to like Cottonwood for dam building, so expect to see some exciting work on the “third” dam tonight. Come check it out!
