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Water levels for the Merced in Yosemite Valley.

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Water levels for the Merced in Yosemite Valley.
May 31, 2010 09:10AM
Does anyone know if the water level marker at Sentinel bridge reflects closely the water level guage at Pohono bridge? In other words if the guage at Pohono shows 9 ft. will the gauge at Sentinel reflect about 9 ft. also, or is Sentinel a different measuring system?

thanks,

Tom
avatar Re: Water levels for the Merced in Yosemite Valley.
May 31, 2010 09:58AM
The flow rate in cubic feet per second is the measure that matters. Depth will vary widely from place to place due to the width of the stream bed varying widely.



Old Dude
Re: Water levels for the Merced in Yosemite Valley.
May 31, 2010 10:16AM
Any idea on how the Pohono Bridge guage relates to the Sentinel bridge gauge? That is if Pohono shows 9 ft. what would Sentinel show at the approximate same time frame?
avatar Re: Water levels for the Merced in Yosemite Valley.
May 31, 2010 10:26AM
I would say that each depth gauge shows the depth at the location of that gauge with no correlation to any other depth gauge. A narrow stream bed would actually show a greater depth increase per increase of flow rate than would a wider stream bed depth gauge. The flow rates would correlate though.

If the stream bed at both bridges had the exact same cross section then the gauges would correlate.



Old Dude
Re: Water levels for the Merced in Yosemite Valley.
May 31, 2010 12:56PM
As a general rule, twice as much water passes through the Pohono Gaging station as the Happy Isles station. Well maybe not a rule but a policy or a guideline. For example the Happy Isles station recorded just over 1300 cfs early this morning, and at Pohono the flow was a bit more than 2800 cfs. So between Happy Isles and Pohono Bridge the flow increased by about 1500 cfs. This additional water came primarily from Tenaya Creek, Yosemite Creek (Yosemite Falls), Sentinel Cr., Ribbon Cr., Bridalveil Cr.,and a few other minor streams. The Majority of this came from Tenaya, Yosemite, and Bridalveil Creeks. Since Yosemite and Bridalveil are downstream from Sentinel Bridge The flow would be Happy Isles plus Tenaya Cr. plus just a little more for water running off the fen at Happy Isles, Royal Arch Cascade, Staircase Falls, and Indian Creek.

Here's an educated guess of the streamflow at Sentinel Bridge.

Happy Isles 1300 cfs
Happy Isles Fen 50 cfs
Tenaya Cr. 600 cfs
Royal Arch Cascade 50 cfs
Staircase Falls 50 cfs
Indian Creek 70 cfs

Total at Sentinel Bridge 2120 cfs
Re: Water levels for the Merced in Yosemite Valley.
May 31, 2010 08:36PM
Thank you. Very educational and very helpful.
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