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
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To find the Superintendent’s Bridge, take the free Yosemite National Park valley shuttle bus to stop #6. From there, looking across the road at a cross walk near the bus stop, you can see a meandering path leading to a pedestrian bridge over the river (Superintendent’s Bridge).
When you first step up the stairs onto to the bridge from the north, the metal sculpture is on the left hand side.
The section of a shuttle bus map below shows stop #6 at the top center and a dotted red line showing the path to the bridge to the south. The bridge is just below the letter “M” in the words Yosemite Lodge.
You can also find the bridge on your drive into the valley by going directly across Southside Drive from the Chapel and walking a path to the bridge. (Again, see the section of shuttle bus map above and follow the dotted red line from the Chapel going north.
The bridge is in the upper left hand side of this photo taken from the Chapel area:
A third way to find the bridge is to go to free shuttle bus stop #11 (Sentinel Bridge), go through the parking lot to a path / trail some times of the year with large puddles (dotted black line in the mini-map above), roughly parallel to the Merced river, and take a left hand turn to a section of pathway (again, the red dotted line) towards the bridge.
Below, a NPS photo of the bridge being rebuilt after the 1997 flood:
Take a look at the lower section of the figure-8-ish Cook’s Meadow loop, and you can spot where Superintendent’s Bridge crosses the Merced River.
Video of the floods of 1996 and 1997:
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:
A 360 degree view from the bridge is at https://www.google.com/streetview/#us-parks-trails-and-beaches/yosemite-national-park
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 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:
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: