BLOG.SED-ENG.COM: Designing Sustainable Stormwater Management Systems (SWMS)

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BLOG.SED-ENG.COM: Designing Sustainable Stormwater Management Systems (SWMS)

Designing Sustainable Stormwater Management Systems (SWMS)

In our last blog, we discussed the basic requirements for determining water quality and quantity for a given project’s stormwater management system (SWMS). We will now continue the storyline to include designing SWMS with sustainability in mind.

Some great examples of low impact development (LID) SWMS are bio-swales, rain gardens, pervious pavement systems, green roofs, and rainwater harvesting systems.

In the past, underground storage SWMS were normally designed when a particular project’s real estate value was at a premium and space was limited. A good example would be an urban city center type project that required a certain commercial density of buildings, parking, and open space to make the project economically feasible and still meet code. An engineer would normally design an underground SWMS to temporarily stage water in the system and slowly bleed it down via percolation in the soil or outfall through a bleeder into an adjacent waterway. The ideal approach would be to design a system that could potentially store water, and then use it for non-potable uses such as irrigation, flushing toilets, or even as make-up water for larger A/C systems. The dilemma often experienced is the fine line and sometimes large costs of storing water for onsite use, but then still plan for the system to function during a back-to-back rainfall event. The key to properly designing an underground storage SWMS is to balance the non-potable water usage with the jurisdiction agency requirements to meet the water quality and quantity criteria.

I know… too much engineering mumbo jumbo. Keep it simple! Let’s say you have a bath tub and you fill it up to the top. Now the tub is full right? What happens if you add more water to the tub? It overflows the tub boundaries. This is the same basic principle with an underground SWMS. Now, what if you filled up the same tub and you add an overflow device into another storage system. Also, what if you pulled the plug in the tub bottom? The water will start leaving the tub at a specific rate. You can apply these same principles in designing an underground SWMS to function the same way. The bleed-down rate (like removing the plug) could be a pump taking water out of the system to be used for irrigation, flushing toilets, or A/C makeup water. The extra storage could be another underground or above-ground system, using the storage in a previous pavement system, or even utilizing storage in a bio-swale.

Just be creative and be prepared to spend a little bit more time with your jurisdictional agency reviewers that will be approving your SWMS system, but it will be worth it in the end. Also, you might even be able to save some utility impact fees with the water you conserved to help pay for a portion of the underground SWMS. There are also other tricks to reducing the size of the required SMWS, but you will need to contact us to learn more. We don’t what to give out all our innovative solutions at once. Check out our next Blog topic on “Pervious Pavement Systems” in Sustainable Engineering & Design, LLC next month blog…