Public Information Statement
Issued by NWS Sioux Falls, SD

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NOUS43 KFSD 092143

Public Information Statement
National Weather Service Sioux Falls SD
445 PM CDT Mon Apr 9 2018

...Flood Stage is being changed for the Big Sioux River Above
Hawarden IA river gauge (HWDI4)...

To:       Family of Services /FOS/ Subscribers, NOAA Weather Wire
          Service /NWWS/ Subscribers, Emergency Managers Weather
          Information Network /EMWIN/ Subscribers, NOAAPORT
          Subscribers and Partners, and NWS Employees

From:     Mike Gillispie
          Sr. Service Hydrologist
          WFO Sioux Falls, SD

Subject:  Change to Flood Stage Elevation for the Big Sioux River
          Above Hawarden IA (HWDI4) River Gauge

After coordination with local, county, state, and federal officials
in the Hawarden, Iowa area following the recent high river levels,
it has been determined that the Flood Stage (FS) elevation for HWDI4
is set too low compared to where flooding begins to have impacts in
the area. Therefore, on Wednesday, April 11, 2018, the elevation
defining FS for HWDI4 will be changed from 19.0 feet to 20.5 feet.

The 19.0 feet FS was initially established following a move of the
river forecast point from a manual gauge in Hawarden (HAWI4) to a
new automated gauge upstream of Hawarden (HWDI4), and was estimated
by comparisons of elevations between the two gauges. The lack of
flooding since the change in gauges prevented an observed
correlation of river stage levels to impacts from river flooding
until March 2018. It has now been established that significant
flooding impacts in the area do not begin until stages reach 20.5
feet at the HWDI4 gauge.

All future river forecasts, statements, watches, and warnings will
reference the FS as being 20.5 feet. No other changes to moderate or
major flood levels or impacts will be affected by this change.

If you have any questions or comments regarding this change, please

     Mike Gillispie
     Sr. Service Hydrologist
     National Weather Service Forecast Office
     26 Weather Lane
     Sioux Falls, SD 57104

     Phone: (605) 330-4247


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