LTC 028-2013 Extreme Tides and City Response MIAMIBEACH I V E D
OFFICE OF THE CITY MANAGER 2013 JAN 3 1 AM 11 : 1 2
028 -2013 LETTER TO COMMISSION , C�:
CITY CLERK'S �IF�= :
TO: Mayor Matti Herrera Bower and Members of the City Commission
FROM: Kathie G. Brooks, Interim City Manager
l
DATE: January 30 2013
SUBJECT: Extreme Tides and City Response
The purpose of this LTC is to provide you with information on the extent of flooding during
extreme seasonal tides and the efforts of the City to minimize its impacts.
BACKGROUND
Tides are primarily driven by the gravitational pull of the moon and sun. When the moon and
sun are aligned during the moon's new and full phases, their gravitational pulls combine to
produce higher tides called spring tides. The moon's gravitational pull is also greater when the
moon is at its closest point to the earth, its perigee, which produces higher tides called perigean
tides. These two astronomical events occur simultaneously several times per year and produce
extreme tides called perigean spring tides or king tides.
Ocean storms and currents affect the tides by pushing water to the coast. Last October and
November, Hurricane Sandy, followed by additional storms in middle of the Atlantic Ocean,
coincided with perigean spring tides to produce exceptionally high tides.
Typical high tides in the City average about 0.3 feet. The perigean spring tides reach elevations
around 1.6 feet. Last October and November, these high tides reached as high as 2.2 feet. (All
elevations are based upon NAVD88, which is a vertical datum.)
The National Weather Service, a branch of the National Oceanographic and,Atmospheric
Administration (NOAA), predicts tidal elevations at its tidal stations. At a conference call with
staff from NOAA, it was explained that these latest extreme tides were between 0.5 and 1.5 feet
higher than the predicted tides because of the storms. NOAA staff further indicated that it was
rather difficult to predict more than one week in advance when the tides will be higher than
predicted. However, the City is providing, more detailed topographic data to NOAA so that it can
provide more specific flooding forecasts to the City.
FUTURE HIGH TIDES
The City will experience perigean spring tides again in April 2013 and November 2013. At this
time, .the NOAA predicted tides will not be as high as those experienced last October and
November. However, the City will be working with staff from NOAA in the week leading up to the
expected tides to more accurately forecast the high tides and to be better able to mitigate their
impacts.
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Extreme Tides and City Response
January 30, 2013
Page 2 of 2
MITIGATION EFFORTS
Certain areas within the City begin to flood when the tide reaches an elevation of 0.5 feet. In
some locations, there is nuisance flooding like ponding and birdbaths at the edge of the street.
Other locations experience more severe flooding. These include:
0 North Bay Road centered on 52 Street and-just north of 59 Street
• 5 th Street intersections from West Avenue to Jefferson Avenue
• West Avenue from 6 th Street to 9 th Street
• 10 Street and Alton Road
• 14 Street and Alton Road
• Coconut Lane on Palm Island
• Sunset Harbour neighborhood .
Staff has mapped the locations of tidal flooding in GIS (viewable on -line) and is developing
short-term and longer term plans to reduce its impacts. The Florida Department of
Transportation (FDOT) is also beginning work on three pump stations — at 5 th Street and West
Avenue, 10 Street and Alton Road, and 14 Street and Alton Road — in April 2013. This will
relieve some of the worst flood -prone areas. The City is also planning to install check valves at
other locations with low elevations. (Attached is a spreadsheet, showing locations prone to
flooding along with long -term and short-term mitigation efforts.)
Short-term mitigation efforts may include closing travel and parking lanes, installing temporary
inflatable seals in drainage piping, and installing temporary pumping systems. Over the longer
term,_ improvements proposed in the recent Stormwater 'Management Master Plan will also
alleviate the extreme tidal flooding. Already, the City also has several projects in construction
including capacity. improvements to two pump stations in Sunset Harbour with the retrofit of a
third pump station being advertised in the coming days. Star Island is also under construction,
and a joint participation agreement is being negotiated with FDOT to provide for improvements
to 59 Street and North Bay Road. FDOT will be beginning construction of three pump stations
along the Alton Road corridor this April with the pumps located at the intersections of 5 th Street
and West Avenue, 10 Street and Alton Road, and 14 Street and Alton Road. Included in this
project has. been a discussion with FDOT about the need to prevent tidal and stormwater
flooding on West Avenue during the Alton Road project as it will be the primary detour.
Should you have any questions or comments, please do not hesitate to contact me.
Attachment
Drainage Improvements. Spreadsheet
KGB /,"//JJF/RWS
F: \WORK \$ALL \(1) EMPLOYEE FOLDERS \Rick Salthck \LTC's \LTC for Extreme Tides.docx
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