Public Information Statement
Issued by NWS Anchorage, AK

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NOAK48 PAFC 171012
PNSAFC
AKZ101-111-121-131-145-171-181015-

Public Information Statement
National Weather Service Anchorage AK
212 AM AKDT Fri Mar 17 2017

...Datum and flood threshold changes on several streams and
rivers around Southcentral Alaska...

On or around April 17 2017 the National Weather Service (NWS)
Forecast Office in Anchorage Alaska and the Alaska-Pacific River
Forecast Center (APRFC) will be adding or modifying the existing
flood thresholds at several area rivers.

Of particular note, the flood thresholds at the river gage on the
Matanuska River near Palmer will be changing from a stage (water
level height)-based threshold to a discharge (amount of water
flowing through the river)-based threshold. For more information
please visit: www.weather.gov/afc/MatanuskaRiver

A summary of all changes is found below:

Flood Category         Old Value             New Value

Lowe River above Horsetail Falls near Valdez (Site: LHFA2)
Action Stage            None                 11.0 FT
Minor Flood             None                 14.0 FT
Moderate Flood          None                 15.0 FT

Solomon Gulch Creek near Valdez (Site: SGLA2)
Action Stage            8.0 FT               16.0 FT
Minor Flood             8.5 FT               16.5 FT
Moderate Flood          9.0 FT               17.0 FT

Yentna River near Lake Creek (Site:YLKA2)
Action Stage           19.0 FT               Unchanged
Minor Flood            20.5 FT               Unchanged
Moderate Flood         21.5 FT               22.0 FT
Major Flood            23.0 FT               24.0 FT

Iliamna River near Pedro Bay (Site: ILRA2)
Action Stage           71.0 FT               64.0 FT
Minor Flood            72.5 FT               71.0 FT
Moderate Flood         75.0 FT               Unchanged

Matanuska River near Palmer (Site: MATA2)
Action Stage            9.0 FT               15,000 CFS flow
Minor Flood             9.5 FT               30,000 CFS flow
Moderate Flood         10.8 FT               35,000 CFS flow

These new and revised flood stages will be referenced in flood
warnings, flood statements, and flood advisories. These changes
are part of a recent re-evaluation of flooding impacts at these
locations which included coordination with local emergency
managers.

In addition, on or around April 17 2017 the published datum for
several sites will be changing to match the datum used by the
United States Geological Survey (USGS - who owns and maintains
these gages). The water levels reported by these gages will NOT
change, and flood stages will NOT change unless noted above. This
change simply brings NWS into full agreement with the official
USGS information.

Site                     Old Datum            New Datum
CHRA2 - Chester Creek     16.00 (NGVD29)         16.02 (NGVD29)
KNKA2 - Knik River        30.20 (NGVD29)         33.57 (NAVD88)
MATA2 - Matanuska River  170.90 (NGVD29)        185.24 (NAVD88)
MONA2 - Montana Creek    245.00 (NGVD29)        250.00 (NAVD88)
SXRA2 - Kenai River       35.34 (NGVD29)         40.40 (NAVD88)

Comments and questions about these changes should be directed to:

Andrew Dixon
Senior Service Hydrologist
NWS Anchorage
Andrew.Dixon at NOAA.GOV



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