I was recently working on a detention system design project that provided stormwater control for airfield improvements, and all was going according to plan. The new detention system had to be deep, storing multiple acre-feet of stormwater at a depth of nearly 15 feet underground due to the airport environ and site constraints. We evaluated alternatives to balance capital costs and long-term maintenance. After various iterations of the flow control design for the system, we found a way to reduce the detention storage needs by incorporating a variable outlet control device. This would result in a lower capital cost while providing comparable maintenance requirements to a system without the variable outlet control. But during final design, we hit a roadblock: we were not able to verify product availability of the variable outlet control devices. Now what?
We had a tough decision to make. Should we revert to a full-size underground detention system that relies on standard flow controls, or do we go back to the drawing board on another modeling and analysis process? Reverting to a full-sized detention system could add an estimated million dollars to the project cost. On the other hand, modeling and analyzing a significantly different flow control concept would require significant effort with potentially paltry gains. Whatever the solution, it needed to be quick as we needed to finalize the design for bidding within critical funding timeframes.
We chose to be daring, trust our instincts, and look to other innovative solutions for flow control to minimize detention requirements. We considered different passive control valves and we ran new hydraulic models. The physical design, installation layout, and head-discharge curve data considered were vastly different from the original solution. Nonetheless, we were able to hit the sweet spot with the right number of valves at the right size to achieve our goals.
Ultimately, taking the risk and going for the new, innovative solution paid off. The final solution yields a smaller detention system and is straight-forward and effective. The new valve options are more resilient, more affordable, and are simpler to install than the original design. The overall system will have a lower capital cost and comparable maintenance requirements to standard underground detention systems. This would not have been the case had we played it safe and utilized standard flow controls. Sometimes, to deliver the best possible solution, you have to take a chance on new approaches.
