California Water Geek-Out, Maps Edition

A couple years ago, I made up what I don’t mind saying is a pretty cool Google Maps map outlining where the proceeds of a planned $11 billion California water bond would go (here’s the link). Not to shortchange the amazing capacity of Google Maps, but once you’d played with them for awhile you want to do more. And if you’re adept with code, you can muck around and do something more sophisticated with Google Maps. I am not allergic or adverse to code, but neither am I adept and it would probably take me a while to learn even the basics. But I am impatient and want to find a shortcut.

So, searching around for online mapping tools today, I happened across the National Atlas. There is no such thing as a map that’s not cool (or at least interesting in some way), but the site and basic outline map on the Map Maker page are a little plain vanilla. But then I started to play with it a little: I drilled in on California, then selected some data layers–highways, lakes and rivers, average precipitation. OK–the result was both useful, if I had a use for it, and kind of pretty (precipitation data will do that every time). Then I saw a layer for dams, and added that. Instantaneously, I had a view of the region that both answered and provoked my curiosity (there are at least 1,200 dams under state jurisdiction here–meaning they’re at least 25 feet or store at least 50 acre feet of water). That is a lot of dams, and when you click on individual structures on the map, you realize how few of them you know anything about. I can’t find a way to embed the map here, but here’s the link. Below is a screen shot (click for larger version); every inverted triangle is a dam.


Another layer you could add to the map: A grid that depicts an index of aerial maps. I superimposed the grid to take a look at an aerial photograph of the area of Lake Berryessa, the large elongated body of water at lower center, just west of Interstate 505. The lake (the state’s seventh largest reservoir, with a capacity of 1.6 million acre feet) is formed by Monticello Dam, which impounds a stream called Putah Creek about seven miles as the crow flies west of the town of Winters. I know the dam and the road that passes it from many bike rides from Davis, and one outstanding feature of the little visitors area at the top of the dam is the Glory Hole. It’s a circular intake for the reservoir’s spillway, which empties into Putah Creek.

So, once I found the aerial image (you need to superimpose the aerial photograph grid from the map layers, click on the “Identify” tab above the map, then click again on the spot you want to take a look at; the link to the image is in the “Identify” pop-up window; and as I write this I see how complicated it might seem to the ordinary user), I drilled down to Monticello Dam. Here’s the image (click for a larger version):


See that round thing to the left of the lower edge of the dam? That’s the Glory Hole. What’s remarkable here is that it’s high and dry. It does not overflow every year, but here it looks like it’s unusually exposed. It turns out the picture is dated June 16, 1993, and though the reservoir level had bounced back from the effects of a string of dry years that had shrunk it to just a third of capacity in 1991 and 1992, on this date the lake was little more than half full.

For a contrast, here’s a New Age-y slideshow on the Glory Hole in wet and dry times:

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