Yosemite Valley spring runoff and flooding / Yosemite snow pack

See also: How much water will there be in the Yosemite waterfalls?

Read John Muir on 'Winter Storms and Spring Floods' from the book The Yosemite at:

http://www.abovecalifornia.com/lib/JohnMuir/Yosemite/index.shtml

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What happens when Yosemite valley begins to flood?

from a California Emergency Digital Information Service warning email, June 16, 2011 and June 23, 2011:

WARM TEMPERATURES WILL CONTINUE TO CAUSE SNOWMELT TODAY AND THE MERCED RIVER AT POHONO BRIDGE WILL REACH FLOOD STAGE AGAIN LATE TONIGHT... * AT 8:00 AM THURSDAY THE STAGE WAS 10.2 FEET. * FORECAST TO RECEDE TO 9.2 FEET THURSDAY AFTERNOON THEN RISE TO 10.0 FEET AROUND 3 AM FRIDAY. * FORECAST TO RECEDE TO NEAR 9.0 FT FRIDAY EVENING THEN FORECAST TO FLUCTUATE NEAR 9.5 FT THRU SATURDAY MORNING. * FLOOD STAGE 10.0 FT * ...

NEAR 10.5 FEET, WATER TOPS THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW. OVERFLOW FROM WOSKI POND FLOODS ACCESS ROAD(NORTHSIDE DRIVE) LEADING OUT OF THE WEST ENTRANCE OF THE PARK. *

NEAR 10.0 FEET, WESTERN PORTION OF NORTH PINES CAMPGROUND... LOCATED AT THE EAST END OF YOSEMITE VALLEY BETWEEN THE CONFLUENCE OF THE MERCED RIVER AND TENAYA CREEK... BEGINS TO FLOOD. WATER RISES TO THE BASE OF THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW.

NEAR 9.5 FEET PORTION OF LOWER PINES CAMPRGOUND BECOMES FLOODED. LIMITED SITE-SPECIFIC EVACUATIONS BEGIN AT HOUSEKEEPING CAMP LOCATED ALONG THE SOUTH-FACING BANK OF THE MERCED RIVER (UPSTREAM FROM SENTINEL BRIDGE AND DOWNSTREAM FROM STONEMAN BRIDGE).

NEAR 9 FEET, CHAPEL MEADOW (SOUTH SIDE OF RIVER) AND COOKS MEADOW (NORTH SIDE OF RIVER) BEGINS TO EXPERIENCE OVERFLOW.

NEAR 6.5 FEET RIVER IS CLOSED TO RAFTERS AND FLOTATION."

One year we were lucky enough to be camping during very high water flow and visitors were warned that they needed to be prepared to evacuate on four hours notice, quite probably in the middle of the night. The park closed to incoming people and only visitors who were already there got to witness the magnificent waterfalls.

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May 1, 2014 snow surveys showed water content for the Merced river drainage at 15% of average and the Tuolumne drainage at 25% of average.

April 1, 2014 snow surveys showed water content for the Merced river drainage at 28% of average and the Tuolumne drainage at 33% of average.

April 1, 2013 snow surveys showed water content for the Merced river drainage at 53% of average and the Tuolumne drainage at 52% of average.

March 1, 2013 snow surveys showed water content for the Merced river drainage at 68% of average and the Tuolumne drainage at 70% of average.

May 1, 2012 snow surveys showed water content for the Merced river drainage at 36% of average and the Tuolumne drainage at 26% of average.

April 1, 2012 snow surveys showed water content for the Merced river drainage at 47% of average and the Tuolumne drainage at 43% of average.

Feb.1, 2012 snow surveys showed water content for the Merced river drainage at 29% of average and the Tuolumne drainage at 32% of average.

May 1, 2011 snow surveys showed water content for the Merced river drainage at 199% of average and the Tuolumne drainage at 184% of average.

April 1, 2011 snow surveys showed water content for the Merced river drainage at 172% of average and the Tuolumne drainage at 178% of average.

Feb. 1, 2011 snow surveys showed water content for the Merced river drainage at 142% of average and the Tuolumne drainage at 149% of average.

Feb. 1, 2010 snow surveys showed water content for the Merced river drainage at 107% of average and the Tuolumne drainage at 117% of average.

March 1, 2010 snow surveys showed water content for the Merced river drainage at 102% of average and the Tuolumne drainage at 111% of average.

May 1, 2010 saw the Tuolumne drainage at 141% of normal and the Merced drainage at 134% of normal.

June 7, 2010 the Merced River had it's highest recorded flow on that date from 93 years of records.

April 1, 2009 Yosemite snow survey results

The Tuolumne Drainage has 92% of average water content and the Merced drainage has 93% of average. Individual course results:

The March 1, 2009 snow surveys reported "90% of average water content for the Tuolumne drainage and 84% of average for the Merced drainage."

The February 2008 snow surveys found the "Tuolumne drainage at 133% of average and the Merced drainage at 125% of average ... -most of the lower elevation courses in the Tuolumne drainage are already well above 100% of their April 1 average. The snowiest course this month was Wilma Lake, with 9 1/2 feet of snow and 36" of water. (M. Fincher - 2/8/08)"

The March 1, 2007 snow surveys found that snow (water content) is at 63% of average in the Tuolumne River basin and 66% of average in the Merced River basin.

The amount of snowpack and the temperature in April and May, will affect when the Tioga road up to and beyond Tuolumne meadows is plowed and open. This varies since 1990 from May 12 to June 30, with a late opening in 1988 on July 1. In 2003 it opened on May 14, in 2002 it opened May 22, in 2001 on May 12 and in 2000 on May 18. This has a corresponding effect on when the high country campgrounds and High Sierra Camps can open.

Tioga road opening (anywhere from April 29 to June 30) and closing (from Nov. 8 to Dec. 11) dates are at: http://www.nps.gov/yose/planyourvisit/tiogaopen.htm

below: a NPS photo of the Tioga road in early May, 2005

From a May, 2006 Yosemite daily report, the peak time of day for flooding in Yosemite valley:

"The Merced River has a distinct daily peak at about 1am every day and a daily low at about 1pm every day, and it is almost always either rising or falling during spring runoff if you are watching it over the course of a few hours."

In a May 15, 2006 Daily Report, the order in which parts of Yosemite valley flood as the river rises:

"HISTORICALLY...WHEN FORECAST OR OBSERVED STAGE AT POHONO BRIDGE REACHES 10.0 FEET...WESTERN PORTION OF NORTH PINES CAMPGROUND... LOCATED AT THE EAST END OF YOSEMITE VALLEY BETWEEN THE CONFLUENCE OF THE MERCED RIVER AND TENAYA CREEK...BEGINS TO FLOOD. WATER RISES TO THE BASE OF THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW.

WHEN FORECAST OR OBSERVED STAGE AT POHONO BRIDGE REACHES 10.5 FEET... WATER TOPS THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW. OVERFLOW FROM WOSKI POND FLOODS ACCESS ROAD(NORTHSIDE DRIVE) LEADING OUT OF THE WEST ENTRANCE OF THE PARK."

Spring Runoff 2006, from a March 1 Yosemite Daily Report

Monday's high water on the Merced was one of the highest flows for this time of year ever recorded. Flows at Pohono Bridge topped 4400 cubic feet per second (cfs) with a stage of 8.3 feet, just 1.7 feet shy of flood stage. Was this the beginning of spring runoff or just an odd meteorological event? Keep up with the latest river and weather conditions in Yosemite by using the following online resources:

Real-time flow at Happy Isles and Pohono Bridge USGS Gaging Stations:

http://cdec.water.ca.gov/river/mercedStages.html

See also the river forecast for the Merced River at Pohono Bridge at http://www.cnrfc.noaa.gov/graphicalRVF.php?id=POHC1

Real-time weather and snowpack information is available for many stations in Yosemite:

Tioga Pass: http://cdec2.water.ca.gov/cgi-progs/queryFx?s=tes&d=now&span=12hours

Dana Meadows: http://cdec.water.ca.gov/cgi-progs/queryFx?s=dan&d=now&span=12hours

Tuolumne Meadows: http://cdec2.water.ca.gov/cgi-progs/queryFx?s=tum&d=now&span=12hours

Tenaya Lake: http://cdec2.water.ca.gov/cgi-progs/queryFx?s=tny&d=now&span=12hours

Gin Flat: http://cdec.water.ca.gov/cgi-progs/queryFx?GIN

Crane Flat (Doghouse Meadow):

http://cdec2.water.ca.gov/cgi-progs/queryFx?DGH

Yosemite Valley: http://cdec2.water.ca.gov/cgi-progs/queryFx?YYV

Ostrander Lake: http://cdec2.water.ca.gov/cgi-progs/queryFx?s=str&d=now&span=12hours

Wawona: http://cdec2.water.ca.gov/cgi-progs/queryFx?YOW

Lower Kibbie Ridge:

http://cdec2.water.ca.gov/cgi-progs/queryFx?s=kib&d=now&span=12hours

Paradise Meadow:

http://cdec.water.ca.gov/cgi-progs/queryFx?s=pds&d=now&span=12hours

(2005) According to the Yosemite Daily Report: Park personnel have completed the April 1 snow surveys. This is the benchmark survey for the year, with the results used to determine water allocations for the year. Both the Merced and Tuolumne drainages have 163% of average water content. The lower elevation courses are disproportionately deep this year. 2005 is the 7th wettest season on record for the park (for 4/1). The top six years: 1983, 1969, 1952, 1995, 1978, and 1993. While it is tempting to predict an opening date for the Tioga Road based on this data, potential prognosticators should be aware that, historically, the 4/1 snowpack and the Tioga Road opening date are not well correlated. The opening date is better correlated to spring temperatures. 1978, 1993, and 1998 had snowpacks with water content similar to this year. In 78 and 93, the road opened June 3. In 98, average temperatures for April, May, and June were 6-9 degrees lower than in 78 and 93 and the road opened on July 1.

The May 1, 2005 snow survey had the pack at 179% of average, about halfway between the 1983 record snowpack and the long-term average.

Current and previous rain/snowfall statistics for California can be found at:

http://cdec.water.ca.gov/snow_rain.html

Warm spring weather and rain caused some of this 2005 snowpack to flood Yosemite valley again on May 16, 2005 and close all roads into and out of the valley for a short time. On May 17, high water levels peaked at about 11 feet, 6 inches in Yosemite Valley at about 5:00 PM.

In the NPS photo of flooded Sentinel Meadow taken May 16, 2005, you can just make out the sunken edge of the boardwalk across the meadow between the two posts on the fence and can just see Yosemite Falls thru the low clouds in the background. Next to it is the same place in June, 2005 and again in February 2008

NPS photos of high water posted May 16, 2005 are at:

http://www.nps.gov/yose/news/highwater/

For weeks after this the roads flooded again and again. About one third of the units at Housekeeping camp were damaged.

The National Weather Service issued and reissued this warning:

...A FLOOD WARNING REMAINS IN EFFECT FOR THE MERCED RIVER AT POHONO BRIDGE...

SNOWMELT HAS PRODUCED ADDITIONAL RISES TO FLOOD STAGE THIS EVENING ALONG THE UPPER MERCED RIVER AT POHONO BRIDGE. ADDITIONAL RISES ARE EXPECTED OVERNIGHT.

HISTORICALLY...WHEN FORECAST OR OBSERVED STAGE AT POHONO BRIDGE REACHES 10.0 FEET...WESTERN PORTION OF NORTH PINE CAMPGROUND...LOCATED AT THE EAST END OF YOSEMITE VALLEY BETWEEN THE CONFLUENCE OF THE MERCED RIVER AND TENAYA CREEK BEGINS TO FLOOD. WATER RISES TO THE BASE OF THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW.

WHEN FORECAST OR OBSERVED STAGE AT POHONO BRIDGE REACHES 10.5 FEET...WATER TOPS THE SWINGING BRIDGE DOWNSTREAM FROM CHAPEL MEADOW. OVERFLOW FROM WOSKI POND FLOODS ACCESS ROAD (NORTHSIDE DRIVE) LEADING OUT OF THE WEST ENTRANCE OF THE PARK."

The Park Service said: "Flooding is a natural process in Yosemite National Park. High snow levels this winter, combined with unsettled spring weather patterns, indicate that flooding may occur. Visitors are advised to check the web site www.nps.gov/yose , or call 209/372-0200 for current weather conditions"

Pictures of the early 2005 flooding are at:

http://www.nps.gov/yose/news/highwater/

April, 2004 Snow Survey Results from Yosemite

"With the record breaking warm temperatures in March, there is a lot of interest in how the snow pack survived. The April 1st courses are generally thought to be the most representative of the year's snow pack. Here are the results for the Yosemite’s Tuolumne and Merced drainages. The high densities are normally not seen until May, and may trigger a faster run-off this spring. Remember that the depth and water content averages were well above average last month, so this does not necessarily indicate a dry year. The following figures are the real time amount of snow left on the ground (“stored water”) as of April 1, 2004." Read all the details at: http://www.nps.gov/yose/enews/200404/snow.htm

The Merced river drainage is the water for the Little Yosemite Valley waterfalls, such as Vernal, Nevada and Bunnell Cascade.

As of April 1, 2004 the Merced Drainage had 84%,

Tuolumne Drainage had 83%

as opposed to Merced Feb. 1, 2004, 105%; March 1, 116%

and Tuolumne Feb. 1, 2004, 116%; March 1, 125%

State average April 1 was 82%.

We had some very warm weather in April, so snowpack for the Merced River drainage as of May 1, 2004 is only 43% of normal for this time of year. Tuolumne River drainage is at 52% of normal.

In the NPS photo below, taken from Taft Point on May 15, 2004, we can see lots of water flow from Yosemite Falls, but we can also see that the cliffs, hills of the Yosemite Falls drainage are practically free of snowpack.

Yosemite valley flooding, 2003

From the Daily Report of Thursday, June 5, 2003

Recent Flooding

If you've visited the Valley recently you've undoubtedly noticed the booming spring runoff. How booming is it? Hydrologists quantify flood events, even if they're only annual spring "floods", in probabilities. For example, a 100-year flood has a 1-in-100 chance of happening each year (to call it "a flood that happens only once every 100 years" is technically incorrect . . . just as flipping a coin 10 times you could get all heads, we could have two 100-year floods in back-to-back years, its just very unlikely). Similarly, we have a 1-in-10, or 10%, chance of seeing at least a 10-year flood in 2004.

The Merced River in the Valley peaked this year on May 29th at 1:45 AM, with 4,550 cubic feet of water flowing past Happy Isles every second. These numbers come from the USGS Happy Isles gauging station, one of the oldest in the US with 88 years of data. Calculations based on this long-running dataset show that this year's spring runoff is a 6-year flood event. The last time we had a flood greater than this was the roughly 89-year flood in 1997. The '97 flood was a winter rain-on-snow event . . . the last time that we had spring runoff exceeding 2003's was on May 16th, 1996, when the Merced at Happy Isles peaked at 5,900 cubic feet per second. Below are the

top 20 floods recorded at Happy Isles:

Recurrence Interval in years     Date     Instantaneous Peak in cubic feet per second

89     1/2/97     10100*

45     12/23/55     9860*

30     11/18/50     9260*

22     12/23/64     9240*

18     12/11/37     8400*

15     5/16/96     5900

13     5/29/83     5450

11     7/9/95     5220

10     2/1/63     5200*

9     6/3/69     4980

8     4/11/82     4880

7     6/2/75     4650

7     6/30/67     4640

6     5/29/03     4550

6     5/31/73     4240

6     6/9/78     4190

5     6/16/98     4150

5     1/13/80     4040*

5     5/31/86     4040

4     5/28/19     3800

PEAK YOSEMITE VALLEY WATERFALL FLOW

for 2003 was at the end of May.

In the Yosemite National Park Daily Report of Friday, May 30, 2003 we read

"What a spectacular year!! This is the day or weekend to get out and check it out!

Per the hydrologists at the California Department of Water Resources, the snowpack generally is melting at a rate of 1" or more a day (Tuolumne staff says they are losing up to 1.5 inches/day). Although more than 1/2 of the April 1 average pack is gone, the remaining central Sierra snowpacks are still well above average for this time of year. Snowmelt run-off has peaked in Northern California and the Tahoe/Truckee river basins, and is peaking in the Central and Southern Sierra rivers in the next few days (I think USGS is predicting today or tomorrow).

At Happy Isles, the gage depth at 8:00 this morning was 7.66', and the prediction for today at the Happy Isles gauging station is for the water to peak at 2 a.m. at 4,460 CFS (cubic feet second!) with a low at 4:00 pm at about 2,600 CFS. To put the year into perspective, at 8:00 this morning, the flow was 4,110 CSF, and the 85 year mean is 1,413 CFS . (Boyers)"

During the last week of May there was some flooding in the campgrounds. "The upper end of Yosemite Valley is in the midst of a minor, approximately 5- to 10- year flood"

Below: the line on the sign next to Sentinel Bridge in the upper right of this winter photo shows the water depth during the January 1997 Yosemite valley flood:

see also:

http://cdec.water.ca.gov/snow/current/snow/pillowplots/TuolumneMerced.html

Yosemite rock falls

Webcam of Yosemite Falls http://www.yosemiteconservancy.org/webcams