Quantcast

High water observations

178465950

By

On Sunday, following the edicts of a decades-long tradition, I slid my whitewater kayak into the flow of Sonoma Creek near Glen Ellen and headed down stream to see what a weekend of rain had created. The creek was the size of a small river, moving like a freight train at a volume I would guess exceeded 3,000 cubic feet per second. This is not, by the way, an activity the uninitiated should even consider, especially during high water. I’ve been running rivers for years, I know Sonoma Creek’s charms and its hazards fairly intimately, but with all that, the power of Sunday’s flow caught me somewhat by surprise and dictated course corrections I hadn’t planned on having to make. And it revealed a potentially deadly hazard I only avoided because I had carefully scouted a safe take-out site in advance.

What I saw on that trip was instructive about the overall health of our principal watershed and the impact we who live in it have had over the years.

The two most obvious discoveries involved the color and volume of the water, which was milk-chocolate brown. That’s not unusual for high-water events, but more and more common with the inexorable increase in soil erosion caused, at least in part, by the expansion of vineyards and their encroachment into the riparian corridor of the creek. Cultivated farmland, once it’s saturated, inevitably surrenders soil to water runoff, and vineyards – like fields of corn and hay – significantly reduce the capacity of the land to hold back and absorb rainfall. Simultaneously, because Sonoma Valley agriculture commonly requires irrigation, growers pull water out of both the creek itself and from the underlying aquifer to which the creek is connected.

The result of all this is increased extremes of high and low water, with flow further reduced during dry times because watershed retention is lower, and dramatically increased during heavy rains because the denuded landscape can’t hold water back.

It’s not clear what the actual figure was, but a good guess suggests that Sonoma Creek was flowing at something well under 5 cubic feet per second before the Pineapple Express roared through, which means it could have increased in volume by something approaching 1,000 percent.

The result of such sudden flow on vulnerable streambeds can be dramatic and permanent, especially where the flow encounters irregularities like curves and cut banks. And that’s what happened on Sonoma Creek where, just downstream from my chosen take-out, the entire right side of the 15-foot-high bank was washed out, bringing a massive oak tree down and across the full width of the swollen creek.

Among the consequences of this boom and bust cycle could be the destruction of salmon redds, where and if they remain viable, downcutting of the main streambed to the point that tributaries become unreachable to spawning salmon, and increasing havoc from periodic floods as the watershed’s holding capacity shrinks.

On top of that, as climate change takes increasing hold of our meteorological cycles, these hydrological extremes can be expected to increase.

None of this is intended to villainize vineyards – subdivisions would be much worse for the watershed – but it suggests the need to better understand all impacts on the principal artery of our Valley.

  • The Village Idiot

    Duh.