LTC 144-2007 Status of Prairie Ave Drainage Improvements
2001 Jtl~3 25 PM I I ~ 52
~f'1C ! ! CITY CL~~~~~'S OFF 1Cf:
OFFICE OF THE CITY MANAGER
NO. LTC # 144-2007 LETTER TO COMMISSION
TO: Mayor David Dermer and Members of the City Commission
FROM: Jorge M. Gonzalez, City Manager -~~~ ___ '~
DATE: June 22, 2007
SUBJECT: Status of Prairie Avenue Drainage Improvements
The purpose of this letter is to inform you about the status of the City's review of drainage
improvements along Prairie Avenue, required due to the construction of the Miami Beach High
School.
Background
The Public Works Department has had numerous discussions regarding the drainage design
along Prairie Avenue with the Miami Beach Senior High School, TYLIN International/HJ Ross
and Zyscovich Inc.
In these meetings, City staff's message to the consultant has been consistent throughout. The
School Board must provide a "functional and sustainable design" to address the flooding
concerns along Prairie Avenue.
The City's specific design criteria requires that the stormwater system for Prairie Avenue must
be able withstand and release the rainfall intensity of a Syr/24hr storm event. The Syr/24hr
storm event criteria is consistent with the South Florida Water Management District
requirements for flood protection of local roads, as well as the adopted level of service for
drainage in local streets as incorporated in the City's Comprehensive Plan.
The rationale fora "functional and sustainable design" pivots around the fact that the raising of
the School Board's property has triggered a displacement in the historic basin storage and a
subsequent alteration in the historic runoff patterns (flood plain encroachment) of the original
runoff basin. The natural course existing prior to the School's construction for the storage
conveyance and discharge of stormwater runoff has been altered without mitigation.
It is staff's opinion that the design as presented does not provide sufficient proof that would
indicate the design is both "functional and sustainable".
Design Requirements
In order to properly contain and discharge the rainfall generated by a Syr/24hr event, the
design calculations would need to show that the swale can collect, treat, convey and
discharge the volume of water that is generated by this event. If the design fails, flooding in the
Prairie Avenue neighborhood would be anticipated.
The design submitted to the City for review has a swale system that discharges into a pipe
collection system that is connected directly to a Collins Canal outfall. Although the swale
appears to have enough capacity to store the rainfall generated within Prairie Avenue, the
design does not provide sufficient proof that a direct connection to Collins Canal will be able to
discharge during high tide. If the system is unable to discharge, then it runs the risk of backing
up and overtopping the swale, therefore leaving standing water in the swale for over 30 hours
which may become a safety and health hazard to both residents and students.
Presently the City has disapproved the plans and calculations issued by TYLIN
International/HJ Ross submitted on May 24, 2007. The basis of this disapproval is that the
Engineer of Record has not met the aforementioned design requirement.
Conclusion
City staff continues to work with the School Board's Engineer to assist the project in moving as
expeditiously as possible. In the meantime, the City is cognizant of the existing flooding
conditions which have taken place during construction, and the nuisance and impacts this has
caused to the residents living along Prairie Avenue.
In the absence of a prompt response by the School Board representatives, The City has
undertaken an emergency response system to immediately alleviate flooding during rainfall
events, until such time a functional and sustainable system is approved and such system
becomes fully operational. The City effort was under taken to alleviate the impacts on
residents while the City and School Board resolve final responsibility.
Please feel free to contact me if you have any further questions or concerns.
~~
J / FHB/FV
F:\work\$ALL\(1) EMPLOYEE FOLDERS\FERNANDO VAZOUEZ\LTC\Prairie Ave Update.doc