One of the most sophisticated aspects of the design behind Mill District is a detail most people will never see or notice: The neighborhood’s stormwater management system.
According to Drew Norton, principal of Sherwood Design Engineers out of San Francisco, Mill District has stormwater treatment technology that no other real estate development is using, anywhere in the world. Sherwood Design Engineers is a civil engineering firm that applies innovation and elegant design to the creation and implementation of sustainable infrastructure.
“This project is incorporating things nobody has ever incorporated before,” he said.
First on the list of innovative sustainable design: the use of Mill District’s iconic Redwood Grove, which naturally filters runoff from all the Canopy buildings through the ground before passing the water into the Russian River ecosystem. The park also is flanked by rain gardens—landscaped areas designed to allow water to flow through them on its way to the creeks.
Another standout aspect of the design of Mill District: Silva cells, catchment basins that lie beneath the sidewalk.
The way these work – giant underground chambers collect runoff and store it for use another time. Street side trees also have their root balls in the Silva cells, meaning the trees get watered daily, no matter what.
Norton said Mill District’s array of Silva cells represents the largest installation in Northern California.
“The Silva cell system was a unique solution that was appropriate for this project and also required a strong working relationship with the city to get them to accept something unique,” he said.
Norton added that during all the atmospheric rivers of the last two months, stormwater runoff systems were able to receive the large amounts of water without any flooding or downstream effects while functioning at a level that was above what was expected, even during open construction activities.
More good news is on the way. As Norton puts it, the entirety of this green infrastructure will treat approximately 1.6 million gallons of stormwater on an average rain year. This includes approximately 700,000 gallons of stormwater that enters the underground Silva Cell system and infiltrate and recharge the aquifer. Ultimately this is water that is diverted from being an immediate impact to Foss Creek and thus the Russian River, reducing flooding and improving water quality.
In short, Mill District stormwater management is a win for everyone involved. Sustainability is at its best when it’s sensible, too.