Flooding Problem Fixed

From: Saul Gross
To: Fred Beckman

Fred

Thanks for the thorough explanation

I'm sure the folks on Belle Isle will be pleased to know they have one less issue to worry about.

Cheers

Commissioner Gross
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From: "Beckmann, Fred"

Commissioner,

The problem of bay water and/or stormwater flowing out onto the street from the stormwater manhole on the east side of the Venetian Causeway at Belle Isle has been solved.

Below is a recap of the issue and the implemented solution:

When CIP initially observed the recirculation of water at the east manhole Control Structure 3 (CS-3) at high tide, it commenced a comprehensive investigation of the stormwater system, with the design Engineer of Record (EOR). The new stormwater system is comprised of a pump station, three (3) wells, numerous stormwater structures, and 24" stormwater piping throughout Belle Isle. As and interim measure, to alleviate the storm and bay water recirculation, tidal backflow prevention valves were installed by the City at each of the three (3) outfalls located at the east and west ends of Belle Isle, and at Farrey Lane.

Initially, the EOR attributed the recirculation of storm and bay water at CS-3 to the restricted flow to the bay, created by the new 24-inch pipe, that was reduced to the existing 8-inch outfall pipe at CS-3, and potential barnacle build-up inside the existing outfall pipe. At the request of the EOR, the City, a). conducted an inspection and verification of the actual clear inside diameter of the existing pipe at the east outfall, and provided the data required for calculations; b). installed pressure gauges and flow meters at each well to monitor the pressure and the flows, and to verify that the wells were receiving the intended design flows.

Readings were taken at each well, and it was determined that the wells were not receiving the required design flows. A comprehensive technical memoranda was issued buy the EOR indicated that there was insufficient head pressure at the wells. Inadequate head pressure allowed all the storm and bay water in the system to by-pass the wells to the CS-3, where it flowed onto the Causeway.

The EOR was directed by the City to provide a corrective measure, while meeting the initial stormwater design intent. A device was designed to be placed inside the CS-3. This device would reduce the 24-inch diameter pipe to a 7-inch diameter opening at the CS-3, thereby creating the necessary head pressure required to force storm and bay water into the three (3) wells, and eliminate the recirculation at CS-3. Additionally, new hydraulic calculations were submitted to the City Engineer for approval. As a result, it was agreed that the pump station would be operated with one pump, while utilizing the second pump as an alternate. The pump floats were also adjusted as part of the design modifications.

The fabrication and installation of the device, including modifications to the stormwater system were completed in December 2008. Final tests were conducted on January 15th; the results proved that there was no recirculation of storm or bay water at CS-3.

Please let me know if you need anything else.

MIAMIBEACH

Fred H. Beckmann, P.E., INTERIM CIP DIRECTOR

OFFICE OF CAPITAL IMPROVEMENT PROJECTS
777 17th Street, Miami Beach, FL 33139
Tel: 305.673.7071 / Fax: 786.394.5472 / www.miamibeachfl.gov

We are committed to providing excellent public service and safety to all who live, work and play in our vibrant, tropical, historic community.

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From: Saul Gross
Sent: Wednesday, January 21, 2009 8:31 PM
To: Middaugh, Bob
Subject: Engineered valve to stop back flow of bay at high tide

Bob

I had understood from Fred that the City had retained an engineering firm to design and construct an engineered valve to stop back flow from the bay into storm water drainage out falls during high tide.

Can you update me as to the status of this project which affects many of the City's neighborhoods. The issue came up this evening at the Belle Isle HOA meeting.

Thanks

Commissioner Gross