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It’s no secret that reducing the size of stormwater management ponds can ultimately lead to environmental benefits and reduced right-of-way and construction costs. The secret is how can public agencies reduce the size of ponds while still meeting all regulatory requirements? Buoyant flow control devices (BFDs) are innovative tools that can be used to minimize the amount of storage volume that is required in stormwater ponds by maximizing the outflow rate. The devices operate on the constant head principle and have the ability to produce a constant flow rate regardless of the depth of water in the pond. These new devices have been used in Washington and other states throughout the northwest and have recently been permitted for both public- and private-sector projects in Florida. The speakers will present an analysis conducted to demonstrate the volume of savings made possible in a stormwater management facility by using a Thirsty Duck BFD. Hydrologic and hydraulic models of existing stormwater ponds were analyzed based on their geometry and performance with a standard outlet control structure and with a BFD. The models were then compared to determine the pond volume required when utilizing the BFD versus a standard outlet control structure. RS&H began the analysis by selecting three permitted stormwater ponds in Florida. These ponds were selected from projects in three different water management districts: one in St. Johns River Water Management District (SJRWMD), one in South Florida Water Management District (SFWMD), and one in Southwest Florida Water Management District (SWFWMD). One of the ponds included a multi-stage weir and met the Florida Department of Transportation’s Critical Duration Storm requirements, as defined in Chapter 14-86 of the Florida Administrative Code. Two different analyses were performed. The first analysis, Analysis A, used a BFD designed to match the permitted discharge rates for the proposed ponds. The second analysis, Analysis B, used a BFD designed to meet the existing conditions, as required by the water management districts and other agencies. Analysis A demonstrates the pond volume and area savings that would have been possible had a BFD been used in the permitted pond, as opposed to a traditional outlet control structure. Analysis B demonstrates the pond volume and area savings made possible had the original pond been completely re-designed with a BFD outlet control structure. The analysis demonstrates that the Thirsty Duck BFD can reduce the required pond volume and area by an average of 36% while meeting the permitted pond’s design parameters (Analysis A). The Thirsty Duck BFD can also reduce the required pond volume and area by an average of 44% while meeting the existing conditions and all stormwater requirements (Analysis B).
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9400 River Crossing Blvd. Suite 102New Port Richey, FL 34655(727) 376-2400 telephone(727) 376-2411 facsimilewww.Thirsty-Duck.com
Makes Ponds Smaller!
Buoyant Flow Control● Flow restriction moves with water
surface elevation (constant head)
● Constant Head = Constant Flow
● Two device types: ER (Early Riser) Series is a buoyant tube within a stationary tube. (Use for flows>3.0 cfs)
TD (Thirsty Duck) Series is a floating orifice attached to an expanding conduit (the “bellows”). (Use for flows< 3.0 cfs)
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ER Series
TD Series
Traditional Outlet Control DeviceStorage Volume=Inflow-Outflow
Thirsty Duck BFDStorage Volume=Inflow-Outflow
Benefits and Advantages• Minimize total detention storage volume
(Savings up to 50%)• Maximize land usage
(Additional impervious surface, Higher CN or C)• Minimize volume of underground vaults or chambers
(Expensive storage-$$$)• Maximize water quality treatment volume
(Less volume needed for flood attenuation)• Lower peak design stages
(Solve flooding problems)(Reduce import fill requirements)
• Construction cost savings(Reduced excavation, grading, slope stabilization, fencing)
What is the ER Series?
ER Series is a tube within a tube.
Inner tube is buoyantOuter tube is stationary
•For dual flow restriction, water passes through the buoyant tubeAND the annular space between the tubes.
•For single flow restriction, water passes through the annular space ONLY.•Tubes can have round or rectangular shaped cross sections•Tubes of varying cross section produce constant flow rate. Tubes of constant cross section produce varying flow rate.
ER-200 Series (single restriction)
ER-200 Series (dual restriction)
What is the TD Series?• TD Series is a buoyant body housing an orifice• Buoyant module is connected to an expanding conduit (“the bellows”)• Bellows fabricated from high strength, welded polyurethane with stainless steel reinforcing rings in each pleat• Bellows available up to 14” diameter (3.0 cfs max. discharge)• The “Duck Body” rests in its “Nest” when it’s not floating• Uses standard flange to connect to outfall system• Device is self-skimming. Water enters the body from its underside.
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TD Series
Little Road-Pond IIIA, Pasco County, FL
Lakewood Ranch Toyota, Manatee County, FL
Bellingham International Airport, Bellingham, WA
Rating Curve (Free Discharge Condition)
Submerged Interstitial Opening
Rating Curve (High Tailwater Condition)
How can we help?• Three company principals are FL licensed, experienced drainage engineers.
• Provide design details, hydraulic analysis and technical support• Assist with agency permitting and coordination• Live demonstration – Test station located in Oldsmar, FL• Basic data to get us started:
•Pond Bottom Elevation•Water Quality Elevation•Proposed TOB/DHW Elevation•Allowable peak discharge rate•Tailwater Elevation
