Public Information Statement
Issued by NWS

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NOAK47 PAJK 041255
PNSAJK
AKZ025-092345-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE JUNEAU AK
500 AM AKDT MON MAY 4 2015

...MENDENHALL RIVER LEVEL READINGS ARE BEING DISCONTINUED...

THE NATIONAL WEATHER SERVICE IS DISCONTINUING OBSERVATIONS AND
FORECASTS OF THE MENDENHALL RIVER STAGE AND FLOW AT THE MENDENHALL
LOOP BRIDGE LOCATION IN JUNEAU. FLOOD INFORMATION ALONG THE
MENDENHALL SYSTEM WILL NOW BE BASED ON THE AUTOMATED MENDENHALL
LAKE GAUGE.

ALL FLOOD STAGE... FLOW MEASUREMENTS... AND IMPACT STATEMENTS FOR
THE MENDENHALL RIVER HAVE BEEN CONVERTED AND UPDATED USING THE
MENDENHALL LAKE READINGS AND ARE AVAILABLE ON THE NWS ADVANCED
HYDROLOGIC PREDICTION SERVICE /AHPS/ WEB PAGE:

HTTP://WATER.WEATHER.GOV/AHPS2/HYDROGRAPH.PHP?WFO=PAJK&GAGE=MNDA2

DURING NORMAL FLOW FROM MENDENHALL LAKE TO MENDENHALL RIVER THERE
IS A STRONG CORRELATION BETWEEN THE WATER LEVEL IN THE LAKE AND
THE WATER LEVEL IN THE RIVER AT MENDENHALL LOOP BRIDGE.
HOWEVER...DURING THE RECORD MENDENHALL RIVER FLOOD ON JULY 12,
2014 THAT RELATIONSHIP PROVED UNRELIABLE. ALTHOUGH THE FORECAST
STAGES FOR THE LAKE LEVEL PROVED TO BE VERY ACCURATE DURING THE
EVENT, THE FORECAST STAGES FOR THE MENDENHALL LOOP BRIDGE LOCATION
WERE NOT AS ACCURATE. WHEN THE MENDENHALL LAKE GAUGE READING
EXCEEDED 8.0 FEET...SOME NEIGHBORHOODS AND THE DREDGE LAKES AREA
UPSTREAM FROM THE BRIDGE EXPERIENCED FLOODING. AT HIGHER FLOWS
THE BRIDGE PILINGS AFFECTED THE OPEN CHANNEL HYDRAULICS AND
CREATED A BACKWATER EFFECT. THE BRIDGE ALSO CAUSED VERY HIGH
STANDING WAVES TO FORM DURING HIGH FLOWS MAKING IT DIFFICULT TO
ACCURATELY MEASURE THE RIVER LEVEL MANUALLY FROM THE BRIDGE.

TYING FLOOD IMPACTS ALONG THE MENDENHALL RIVER TO HIGH WATER
LEVELS AT THE MENDENHALL LAKE GAUGE WILL PROVIDE MORE ACCURATE
INFORMATION FOR RESIDENTS ALONG THE RIVER. THE LAKE GAUGE IS
MAINTAINED THE UNITED STATES GEOLOGICAL SURVEY /USGS/.

PLEASE REFER TO THE NWS ADVANCED HYDROLOGIC PREDICTION SERVICE
/AHPS/ WEB PAGE ABOVE FOR MENDENHALL LAKE
OBSERVATIONS...PREDICTIONS...HISTORICAL READINGS... AND IMPACTS
AROUND THE LAKE AND RIVER AT VARIOUS LAKE WATER LEVELS.


$$

NWS JUNEAU
END










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