Hard rain brings Yosemite’s waterfalls to life. Warm rain on snow can cause especially rapid runoff, and severe flooding. Yosemite Valley dodged a bullet last week when the increase in Merced River flow was relatively moderate.
Further south, residents in the Kern River canyon were not so lucky – more below.
Yosemite National Park remains closed, but photos Tueeulala (left) and Wapama Falls were captured through the mist. (unknown source)
Rain and melting low elevation snow feed numerous intermittent waterfalls on the north wall at Hetch Hetchy.
Rainfall amounts were similar March 9th and 10th throughout the southern Sierra, sharply increasing runoff everywhere. But slightly different temperatures at similar elevations in Yosemite Valley, at Hetch Hetchy, and on the Kern River led to very different results.
- In Yosemite Valley, the average temperature was 35 degrees. The Merced River at Happy Isles (just down from Vernal Falls) increased fivefold from 140 cubic feet per second (CFS) on March 9 to 724 CFS on March 10.
- At 39 degrees, Hetch Hetchy was a bit warmer. Falls Creek at Hetch Hetchy (Wapama Falls) increased tenfold, from 57 cubic feet per second on March 9 to 579 CFS on March 10.
- Temperatures on the Kern River were higher – averaging 42 degrees. Flows at Kernville increased more than 34-fold, from 561 CFS on March 9 to an average of more than 19,185 CFS on March 10 (flows exceeded the rating table maximum of 41,400 CFS between 10 am and 6 pm). Homes were destroyed, but sensible residents got out of the river’s way. See video below.
Most of the time, flows on the Kern are smaller than those on the Merced. Many of us recall the devastating 1997 New Year’s Day flood in Yosemite Valley when flows reached 24,600 CFS. Had weather been a few degrees warmer last week, the flooding Yosemite Valley might have been more damaging than it was in 1997.
Let’s keep our fingers crossed that the large storm forecast for this week doesn’t flood Yosemite, the Kern River canyon or, for that matter, anywhere.