Tuesday, January 10, 2017

Liveblogging the Deluge: Perspectives on the Biggest Storm in a Decade, Part Four

Check out some newly "discovered" footage from the floods of 1997!
We've been following developments on the Stanislaus, Merced, and Tuolumne Rivers as the biggest atmospheric storm in a decade or more has been sweeping through California. Many references have been made to the record-setting floods of 1997, and I was reminded that I was actually around back then. I even had a thing called a "VHS video camera" that recorded images on, of all things, magnetic tape. How so very quaint! I finally remembered the tapes, and even more importantly remembered that I had the tapes recorded to a DVD a couple of years ago to assist someone's research on the 1997 floods. I dug it out and isolated my videos of the Tuolumne River in Waterford, CA, and Dry Creek in Waterford and Modesto (it was not very dry at the time).

Some important numbers can be compared to the events transpiring right now. Don Pedro Reservoir is a huge dam upstream of Waterford and Modesto. It has a capacity of 2.04 million acre-feet. In 1997 it was relatively full, but not out of sync with the seasonal guidelines (about 1,690,000 acre-feet, around 83% of capacity; that's the level of the reservoir today, January 9). The storm of 1997 was not normal, however, and awareness was growing that the dam might fill and start flowing in an unconstrained manner. Operators ramped up flows on the river downstream to near-flood level at 9,000 cubic feet per second, and realized eventually that they were going to have to make a difficult choice. They were going to have to flood out a number of homes and ranches in order to make room in the reservoir for the even bigger flood to come. Several feet of warm rain fell on a near-record snowpack, and soon river flows well over 100,000 cubic feet per second were entering the reservoir. The lake level rose at an astounding rate of a foot per hour, and in less than two days, the level rose to 830 feet, overtopped the dam weir and floodgate.

For several hours, the Tuolumne River below the dam was flowing at 60,000 cubic feet per second, the highest such flow ever recorded. This was a disaster for several hundred homes downstream, but had the dam not been there, and had the operators not made the choice to produce an artificial flood, there would have been a flood in Modesto that was twice as large.

To compare to the flood going on right now in 2017, inflow to Don Pedro has been ranging as high as 38,000 cfs, and the controlled outflows have been as high as 10,000 cfs. The lake has reached an elevation of almost 802 feet, but the main part of the storm has passed, so I don't expect major problems on the Tuolumne River (but of course predictions are just that, predictions). Keep your attention on the news until this storm is over with).

And so that is the background to the video above. I was filming what I could from the various bridges before some of them were closed. I had to take a circuitous route to get to town that day to get video of Dry Creek in the La Loma Park area, which was completely inundated. I couldn't even stop, and had to take the video from a moving car (Mrs. Geotripper assisted with the driving in case you were wondering).

So here it is in all the glory of hand-held amateur film-making. Be thankful that it isn't happening again, at least not here (but give a lot of thought to those who are struggling with high water farther north in the Great Valley and along the Truckee River in Nevada).

UPDATE (1/10/17, 12:20 PM): It looks like the inflow at Don Pedro reached 44,905 cubic feet per second yesterday. Lake level reached 802.6 feet, about 1,698,000 acre-feet.

UPDATE (1/10/17, 4:40 PM): Don Pedro Lake level reached 804.9 feet, about 1,723,000 acre-feet. That's about 84.5% full.
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