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Monday, December 3, 2012

High water events on valley trails

Silicon Valley has a bunch of water features if you know where to look. You might not realize it if all you ever do is drive around, but there are creeks, streams and rivers scattered all throughout. After all, rainfall which lands on the right side of those hills has to drain out to somewhere, and that somewhere is the bay. The closer you get to the bay, the larger these things get.

After a number of nasty floods over the years, levee systems were put in place. These tend to be fairly massive things with dirt, gravel, or even paved trails on top which have historically been used by the county water district maintenance trucks. They've also become great paths for running or biking.

There is a catch, though. All of these trails tend to dip under the roads they encounter, and in doing so, come rather close to the water line. Most of the year, this is no big deal, but now and then it can be troublesome. The official line from various agencies in the county is to not use these undercrossings during high water events.

Here's what the Guadalupe River looks like at Montague Expressway most of the time:

Relatively low water

It's muddy but passable. That's the situation this afternoon, more or less. The river itself is staying in the low area between the trail undercrossings on either side.

I always wondered how bad it could get. Now I have some idea. This is what that same spot looked like just 24 hours earlier:

High water

In other words, when they say high water event, they really do mean high water event. It's not like an inch or two. All it took was a good downpour on Sunday morning, and that was the situation by the afternoon. I made a couple of special trips to get those pictures in preparation for this post.

The USGS has a measuring system about a mile upstream from this crossing, and this is what it captured (look at "Dec 02 2012"):

USGS stream gage

It looks like I took my second picture around the time it crested.

If that's what one good morning rain can do, I don't want to see what happens when it starts and keeps going for a couple of days. That sort of thing has "bad day" written all over it.

Finally, as a bonus for people using browsers which can handle Ogg Theora video, I shot some video near that spot, including some crazy waterworks from a pump outlet which was submerged. This is something of an experiment to see if I melt down my web server by serving videos to anyone who clicks.

[View video]