Yosemite Valley spring runoff and flooding / Yosemite snow pack

This page has statistics, links and news releases about Yosemite valley flooding, spring runoff and snow pack/ snow water content for various years.

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.php

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Below: at a bridge over the Merced river in Yosemite Valley, the line on the sign in the upper right of this winter photo shows the water depth during the January 1997 Yosemite valley flood:

line on sign was water depth during Yosemite flood:

That sign is gone now, but was replaced by a metal sculpture worth looking for. At Yosemite valley free shuttle bus stop #6, Yosemite falls, looking across the road you can see a path leading to a bridge over the river. When you first step up on to the bridge, on the left hand side, there is a metal sculpture showing the depths of the water various years Yosemite Valley has flooded. It is amazing to stand on the bridge and see when Yosemite valley became a lake. Yes, the entire bridge has been under water at times.

metal sculpture with various years on it

See details and more pictures at Yosemite floods display on Superintendent’s Bridge.

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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 CA– USE 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 HO– USEKEEPING 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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When it starts to flood, as in this February 2017 photo, a seasonal temporary creek in Upper Pines campground totally floods some campsites:

Yosesmite campsite with a pond under and around the picnic table and bear box

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More What Happens during Yosemite Valley Flooding? from news releases:

From January 2017 flooding:

Jan. 7 “Yosemite Valley is now closed due to forecast high river flows in the next 48 hours. Residents have been evacuated, all entry and exit is prohibited. . .

“The latest river forecast is calling for a peak at 18.4 feet in Yosemite Valley on Sunday at 4 pm.”

Jan. 8

“The latest river forecast is calling for a peak at 11.8 feet (1.8 feet above flood stage) in Yosemite Valley tonight at 10 pm. Flood waters are expected to recede to a level below flood stage by 6 am on Monday, January 9” . . .

“Yosemite Valley residents may return home on Monday, January 9. Gates will be opened at 10 am. Closure remains in effect for visitors until further notice.”

Jan. 9

“The Merced River peaked at 12.68 feet overnight and was at 11.8 feet at 9 am. The South Fork Merced River peaked just under 10 feet. The latest river forecast is calling for river stage to get below 10 feet (flood stage) around 1 pm, however, this forecast doesn’t account for the effects of the El Capitan Moraine, which slows outflow from Yosemite Valley. . .”

“The sewer system is near capacity right now due to floodwater infiltration. This should resolve as flood waters recede. We are waiting for this to occur before allowing additional people into Yosemite Valley, since more people in the Valley will cause the sewer system to exceed its capacity. . .There are no known issues with flooding at residences, however, we are continuing assessments. Flooding did occur at the concession security office and garage area due to overflow from Indian Creek. . . Rivers and creeks are running high and fast. Use extreme caution around any flowing water.”

From February 9, 2017:

“The current river forecast for the Merced River is calling for a peak of 9.5 feet at 5 am on Friday morning. While this is lower than the nearly 11-foot peak last night, there’s some uncertainty with the river forecast. If the snow level remains high, the river could peak at over 13 feet.

Given the uncertainty, employees who commute to Yosemite Valley should not plan on arriving to the Valley prior to 9 am. Please work with your supervisor to identify an alternative work location or work schedule for tomorrow. Conditions will be reassessed in the early morning and a new update will come out on Friday morning around 7 am.

Yosemite Valley residents are encouraged to reduce their water usage during the peak flow of this storm in order to reduce impacts on the water and wastewater utility system. Residents are also encouraged to avoid driving around the Valley tomorrow morning as a safety precaution.”

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From a park webpage, in anticipation of Spring crowds and needed roadwork, patience is advised:

Valley Roads and Parking, Spring 2017

Heavy winter rains and snow are affecting on-going road improvement projects in
Yosemite Valley, resulting in road closures and detours. Visitors arriving this spring in
personal vehicles and buses may encounter delays, congestion, and detours. One-
way roads may become two way, and vice versa; pay attention to road signs. Road
segments may close to prevent gridlock when areas of the park become congested.
Printed and online maps may not reflect current road conditions.

With anticipated high-flowing waterfalls, late openings for Tuolumne Meadows and
Glacier Point due to snow, and the Mariposa Grove closed for restoration, expect
crowded conditions in Yosemite Valley this spring.
Being prepared for significant
traffic, especially on weekends and holidays, will help result in a more enjoyable visit
to Yosemite National Park.”

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And a report after April, 2018 flooding, again when the valley was closed to visitors,

Yosemite Valley Flood Narrative

On April 7th, Yosemite Valley experienced the 8th largest flood recorded at Pohono Bridge since 1917, the largest flood in 21 years. The Merced River peaked at Pohono Bridge at 6:15pm at 13.73 feet, flowing at 12,200 cubic feet per second (cfs). Upstream at the gage at Happy Isles, the Merced River peaked at 3:45pm at 10.09 feet, flowing at 8,000 cfs, which was the 6th largest on record at this gage since 1916. During the river’s peak, more than 60% of the river’s flow entered Yosemite Valley at Happy Isles, with the rest coming mainly from the numerous tributaries flowing into the valley. At Pohono Bridge, flood conditions occurred for nearly 30 hours, rising above 10 feet on April 7 at 08:00am and dropping below 10 feet on April 8 at 1:45pm. Floodwater inundated roads at numerous places, water depths ranged 2 – 4 feet at Chapel Meadow, Wosky Pond, Sentinel Cross, and El Cap Cross.

The flood resulted from an unusual Spring atmospheric river of warm precipitation falling on a saturated snowpack and saturated soils. With the snowline higher than 12,000 feet, most of the precipitation falling in the Tuolumne and Merced River watersheds fell as rain. This combination of preexisting conditions and high snowline led to rapid runoff from most of the watershed area, generating flooding with only 2 – 4 inches of precipitation. This scenario differs from typical winter storms when the snowline is lower and a much smaller area of the watershed is contributing runoff.

Interestingly, during rain-through-snow events it is generally thought that rain contributes most of the runoff, while smaller amounts of runoff are contributed by melted snow. However, during this storm, snow sensors in Yosemite measured larger amounts of snowmelt, in some places possibly doubling the amount of runoff. The amount of rain during the event ranged 2 – 4 inches, while snowmelt ranged 0.7 – 4.3 inches of liquid water. During the afternoon of April 7, winter rangers in Tuolumne Meadows observed the Tuolumne River melting out rapidly, which was last observed during the historic flood of 1997. We are still investigating why such a large amount of snowmelt occurred. (H. Forrester)

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

May 1, 2019 snow survey results
The water content of the snowpack in the Tuolumne drainage is 149% of average; in the Merced drainage it is 160% of average.

April 1 Snow Survey Results
The water content of the snowpack in the Tuolumne drainage is 176% of average; in the Merced drainage it is 153% of average. The storms this year were colder than in recent years, with a deep snowpack at lower elevations. At 7,000 feet, for instance there is approximately 8 feet of snow.

March 1, 2019 Snow Survey Results
The water content of the snowpack in the Tuolumne drainage is 147% of average; in the Merced drainage it is 151% of average.

February 1, 2019 Snow Survey Results
The water content of the snowpack in the Tuolumne drainage is 110% of average; in the Merced drainage it is 93% of average.

May 1, 2018 Snow Survey Results The water content of the snowpack in the Tuolumne drainage is 40% of average; in the Merced drainage it is 39% of average.

As of April 25, 2018 there was no report yet in the Yosemite Daily Report of the April 1, 2018 snow survey results, but this was at http://cdec.water.ca.gov/cgi-progs/reports/COURSES.201804

Tuolumne River Basin
157 Dana Meadows 9,800 26-MAR 76.5 20.0 26% 30.1 66%
158 Rafferty Meadows 9,400 28-MAR 75.0 23.0 31% 32.5 71%
159 Bond Pass 9,300 27-MAR 111.5 29.5 26% 43.7 68%
368 New Grace Meadow 8,900 31-MAR 109.5 42.0 38% 46.6 90%
161 Tuolumne Meadows 8,600 25-MAR 44.5 13.5 30% 22.3 61%
162 Horse Meadow 8,400 27-MAR 100.0 32.5 32% 45.8 71%
163 Wilma Lake 8,000 31-MAR 85.5 35.0 41% 42.9 82%
165 Sachse Springs 7,900 29-MAR 48.5 19.5 40% 36.7 53%
164 Spotted Fawn 7,800 29-MAR 75.0 30.0 40% 44.8 67%
166 Huckleberry Lake 7,800 28-MAR 77.0 30.5 40% 40.4 75%
167 Paradise Meadow 7,650 30-MAR 58.5 23.0 39% 38.6 60%
348 Kerrick Corral 7,000 31-MAR 34.0 14.5 43% 23.0 63%
169 Vernon Lake 6,700 29-MAR 31.0 13.0 42% 21.6 60%
173 Lower Kibbie 6,700 30-MAR 29.5 12.5 42% 24.2 52%
168 Upper Kibbie Ridge 6,700 30-MAR 21.0 10.0 48% 17.8 56%
171 Beehive Meadow 6,500 29-MAR 34.0 16.0 47% 22.2 72%
172 Bell Meadow 6,500 31-MAR 23.0 10.5 46% 14.8 71%
Basin Average Pct. of April 1: 67%

Merced River Basin
176 Snow Flat 8,700 29-MAR 82.0 31.5 38% 44.2 71%
177 Ostrander Lake 8,200 29-MAR 56.0 24.0 43% 33.6 71%
178 Tenaya Lake 8,150 31-MAR 44.0 17.5 40% 31.8 55%
179 Gin Flat (Course) 7,000 30-MAR 40.0 17.0 42% 31.1 55%
180 Peregoy Meadows 7,000 30-MAR 33.5 14.0 42% 27.7 51%
Basin Average Pct. of April 1: 61%

March 1, 2018 Snow Survey Results
The water content of the snowpack in both the Tuolumne drainage and the Merced drainage is is 20% of average. Nineteen out of twenty snow courses were sampled before the recent storm.

February 1, 2018 Snow Survey The water content of the snowpack in the Tuolumne drainage is 25% of average; in the Merced drainage it is 16% of average.

May 1, 2017 snow surveys. The water content of the snowpack in the Merced drainage is 201% of average. The water content of the snowpack in the Tuolumne drainage is estimated at 167-180% of average. The snow pack is heavily weighted toward the higher elevations, with many courses over 200% of their May 1 average.

April 1, 2017 snow surveys. The water content of the snowpack in the Tuolumne drainage is 177% of average; in the Merced drainage it is 168% of average. The snow pack is heavily weighted toward the higher elevations. Below 7,500′ the snow is deep but not exceptional; 143% of average across the park. Above 8,500′ the water content of the snowpack is the highest on record. The snow on the high elevation courses is 10-14 feet deep and contains 5-7 feet of water.

March 1, 2017 snow surveys. The water content of the snowpack in the Tuolumne drainage is 208% of average; in the Merced drainage it is 177% of average. Several courses established new records for both depth and water content. The snowiest course in the park is Grace Meadow, with 16 1/2 feet of snow and over 7 feet of water content.

May 1, 2016 The water content of the snowpack in the Tuolumne drainage is 57% of average; in the Merced drainage it is 63% of average.

April 1, 2016 snow surveys showed water content of the snowpack in the Tuolumne drainage at 89% of average; in the Merced drainage at 91% of average. According to the park “The April 1 survey is considered the benchmark for the year; the water content of the snowpack typically peaks near this date.”

March 1, 2016 snow surveys showed water content of the snowpack in the Tuolumne drainage at 101% of average; in the Merced drainage at 89% of average.

Feb. 1, 2016 snow surveys showed water content for the Merced river drainage at 105% of average and the Tuolumne drainage at 132% of average.

May 1, 2015 snow surveys showed water content for the Merced river drainage at 0% of average and the Tuolumne drainage at 3% of average.

April 1, 2015 snow surveys showed water content for the Merced river drainage at 2% of average and the Tuolumne drainage at 7% of average.

March 1, 2015 snow surveys showed water content for the Merced river drainage at 12% of average and the Tuolumne drainage at 16% of average.

Feb. 1, 2015 snow surveys showed water content for the Merced river drainage at 21% of average and the Tuolumne drainage at 22% of average.

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.

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

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

April 1, 2009 The Tuolumne drainage has 92% of average water content and the Merced drainage has 93% of average.

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.

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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 Oct. 31 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

Tioga road snow plow NPS photo:

Watch a video of plowing (it is potentially dangerous, they have an ambulance on site)
https://www.nps.gov/media/video/view.htm?id=F99C47BC-DA5D-5DB6-9B080585218403F4

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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.”

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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

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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

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The start of a hike to Mirror Lake, the trail along the cliffs, (across the parking lot from the Majestic (Ahwahnee) hotel) in some months, you can see and feel mist from the Royal Arch Cascades. When the valley is nearing flooding, or sometimes just in heavy rain, this section of trail can become an unsafe creek/river!
(Photos below from February 2017 – the white is not snow, it is rushing water.)

multiple creeks flowing across a normally dry trail

water flowing in a trail during rainstorm

Compare the photo above to April 2017:

a trail with a little water flowing across it

————- – – – – May 16, 2005 Flood – – – – – —————-

From the Yosemite Daily Report: (2005) “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.

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

flooded Sentinel meadow Yosemite May 16 2005 NPS photo: meadow Yosemite falls June 2005: Yosemite Falls and snowy meadow feb 4 2008:

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”

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Find a chart of mid-May to mid-June peak spring flows and many other stats:

http://www.nps.gov/yose/learn/nature/flooding.htm

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

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

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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.

NPS May 15 2004 from Taft Point:

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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

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Video of the floods of 1996 and 1997:

https://www.nps.gov/media/video/view.htm?id=EA81A54A-CB4D-410C-6BCB1393E86F108A

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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”

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How much water has been flowing in Yosemite valley 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.

The U.S. Geological Survey maintains stream gages along the Merced River in two locations in Yosemite Valley. The info for today and/or this year, with the median daily streamflow based on over 80 years of record (the little triangles you will see on the chart) is at:

USGS Yosemite Valley stream gages

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see also:

Yosemite rock falls

How much water will there be in the Yosemite waterfalls?

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