Yosemite valley has become a lake due to flooding many times in history and you can visualize the depth standing on Superintendent’s Bridge, which has a display that you can stand next to, showing the depth of the water during 5 major Yosemite valley floods.
The water overflowed the bridge to these heights as measured from the bridge deck:
Dec. 11, 1937 2.7 feet
Nov. 18, 1950 3.9 feet
Dec. 23, 1955 4.1 feet
Dec. 23, 1964 3.8 feet
Jan. 2, 1997 5.3 feet
(If this display were to be removed, you can still visualize the depth of the water by seeing that a person 5 feet tall would be, in effect, under water during the 1997 flood.)
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Below, a NPS photo of the bridge being rebuilt after the 1997 flood:
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When you walk up the stairs onto to the bridge from the north, the metal sculpture is on the left hand side.
Cook’s Meadow hike (or walk) , has various maps and descriptions of routes to find Superintendent’s Bridge from the visitor center, free shuttle bus stops, from the path from Swinging Bridge and the parking lot along southside drive just before the chapel.
As you walk from the far side of the parking lot at shuttle stop #11, you may see a sign showing the depth of the water at that location during the 1997 flood:
Video of the floods of 1996 and 1997:
https://www.nps.gov/media/video/view.htm?id=EA81A54A-CB4D-410C-6BCB1393E86F108A
Below: the line on a sign (that has since been removed), next to Superintendents Bridge in the upper right of this photo shows the water depth during the January 1997 Yosemite valley flood:
Press releases and details about recent Yosemite valley floods, including April 7, 2018 (the largest flood in 21 years), January 7-9, 2017 and May 16, 2005, are at: Yosemite Valley spring runoff and flooding / Yosemite snow pack
How much water will there be in the Yosemite waterfalls?
How much water has been flowing the last few days?
To see the water flow at Happy Isles where the section of the Merced River that fills Vernal and Nevada falls enters the valley, click on this webcam link:
http://ca.water.usgs.gov/webcams/happyisles/
You can also find a Weekly Video & Image Archive.
How cold is the water in the Merced River in Yosemite valley right now? Scroll down at:
https://waterdata.usgs.gov/nwis/uv/?site_no=11264500
This park service photo above, of flooding during the 1997 flood, is from:
https://www.nps.gov/yose/learn/management/1997-flood-recovery.htm
and here are more photos from the park service of the damage:
at Housekeeping camp
at employee housing in what was called Camp Six and is now the day use parking and round-about
and another at Camp Six:
see a larger version of this Park Service map of the extent of flooding in east Yosemite Valley during the January 1997 flood
