Monday, June 14, 2010

High Water in Yosemite III

We continue our journey through Yosemite Valley during the peak runoff last week (part I here, and part II here), when the Merced River exceeded 7,000 cubic feet per second, and reached flood stage. Numerous meadows and trails were underwater, and it was a wonderful thing to see! Above is the view from in front of the chapel at Old Yosemite Village. The slope on the right is the lower part of the Three Brothers, with the Cathedral Rocks in the distance.
And above we have a flooded portion of the meadow at the base of El Capitan. Once again, we are looking at the incredible Cathedral Rocks with the Cathedral Spires on the left.

The gaging station that measures the discharge of the Merced River is just upstream of Pohono Bridge. The problem with bridges is that we tend to put them at the narrow parts of river channels. When the floods come, the bridges can cause a bottleneck effect, having all kinds of implications upstream and downstream. Some of the bridges have been redesigned in recent years to allow the river to flow in a more natural pattern and to stabilize bank erosion.

As noted in the previous posts, floods are not a particular problem for the natural ecosystems of the valley. The ecosystem developed under a seasonal pattern of flooding and drought. The floods can be a minor inconvenience to hikers on the valley floor, as in the picture above where the riverside trail is flooded.

Trees that grow too close to the river will have their roots inundated. If the flood lasts for any period of time, the trees will suffocate and die. Usually the high water backs off within a few days. Today, a week after my trip, the river is flowing at 3,160 cubic feet per second, half of what it was a week ago, but still about 50% above normal for the middle of June.

Update: Martha at Martha's Musings was in Yosemite at the same time. See some nice pictures here.
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