Flood and Climate Resilience - Improved Detention Design

Phillip Taylor, Hydro International Ltd., ME, USA


On-site management of stormwater runoff volume is often one of the most challenging and expensive aspects of site stormwater design. Increased development and changes in development density, combined with more frequent and intense rainfall events, are resulting in significant flooding, with associated costs in the billions of dollars for damage. Many regulators are seeking to adjust design storms to higher volume scenarios, and combined with increasingly restrictive regulations limiting discharge rates, stormwater detention systems are becoming larger and harder to manage within the site design process.

Importantly, after decades of relying on detention system design, the frequency of flooding has not decreased and, in many places, is actually increasing. This necessitates adapting our thinking, modeling methods, and "go-to" practices to be more robust and resilient.

Traditional outlet control structures typically employ technology that has been used for thousands of years, including round orifice controls, rectangular weirs, and "V" notch weirs, each in various configurations to manage the outflow hydrograph. However, these traditional flow controls suffer from inflexibility. Designers can only control the flow using the outlet size and head pressure, unable to leverage water velocity or other available fluid dynamic properties to manipulate the outflow discharge curve. This limitation often results in detention systems being over or undersized or having excessively long drain down times depending on the final configuration.

While a fully automated, predictive computer-controlled outlet gate would represent the ideal outlet control solution, these systems are expensive, require power, necessitate regular inspection, and demand high levels of operator involvement. Additionally, security and reliability risks must be considered.

Fortunately, another option exists: the vortex flow control valve. Invented in the 1960s and extensively utilized in the wastewater industry, the vortex valve is still not widely known for its application in stormwater flow control. It offers numerous advantages over traditional controls, including:

• Customizable head discharge curves: This allows for more precise control over the outflow hydrograph.

• Larger outlets: These are less prone to blocking, reducing maintenance needs.

• Optimized detention volume: This can lead to cost savings and increased climate resilience.

• Fully passive operation: No moving parts means minimal maintenance is required.

The presentation will introduce the vortex valve, explaining its operation, design, and integration with industry-standard software such as HydroCAD, HydroFlow, and other common hydraulic models. Case studies of successful projects will showcase how vortex flow control devices optimized inflow-outflow hydrograph relationships throughout the US, enabling designers to create more robust, often smaller detention systems while saving their clients significant money

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