Cisterns and Native Landscaping Practice
A 4,000 gallon cistern located inside the warehouse of the WSSI office collects runoff from the building’s main roof. It is sized to retain the equivalent of one quarter-inch of water from the roof. The water stored by the cistern is used to flush all onsite toilets, conserving about 48,000 gallons of potable water annually. Based on the rainfall characteristics of the area and assumptions about the rate of water use in the building, the cistern is expected to be empty about 3 days each year.
The rainwater coming off the roof is not treated as it enters the indoor cistern. Any particulates in the water settle out to the bottom of the tank and are cleaned out manually. Screens are used to prevent sediment or other floating particles from entering the pump or tank outlet. Any water pumped from the cistern is not suitable for drinking and has its own clearly marked pipe network separate from the building’s potable water supply.
More Information on WSSI’s Indoor Cistern
The runoff from the main roof and the green roof (approximately 28,000 square feet total), as well as any overflow from the indoor cistern, flows through underground piping to the 8,000 gallon outdoor cistern. One half-inch of water from the roof (the "first flush") is captured in the cistern to irrigate the site landscaping, and any excess flows through the underdrain network to the rain garden. In extreme storm events when the cistern cannot drain to the rain garden quickly enough, water is also released into the gravel bed detention area via an emergency overflow pipe.
The cistern irrigates the site using drip irrigation and is fitted with a level sensor that switches the irrigation pump on and off to achieve the most efficient water reuse. Since most of the landscaping consists of native meadow species that grow 2’-3’ tall, standard 12" pop-up spray heads were not a viable irrigation method. Instead, the cistern pumps water through a drip irrigation system consisting of a network of flexible tubing all around the site. The underside of each tube is perforated with tiny holes that allow the water to drip out slowly to soak the ground. Spray irrigation, in contrast, must use a much larger amount of water to soak the ground due to evaporation and misdirected spray.
More Information on WSSI’s Outdoor Cistern
Native landscaping offers several advantages over non-native landscaping and sod. Native plants are much more acclimated to local weather patterns and wet/dry cycles, so they require less watering to remain healthy. Native landscaping also provides indigenous animal species with habitat and food, both of which can be lost when meadow is replaced by lawn. Since being built, WSSI's site has been visited by turkeys, foxes, hawks, cardinals, blue jays, hummingbirds, and other wildlife.
WSSI's native landscaping surrounds many of the parking areas and extends all the way to the building beneath the green roof, where a 4’ native meadow buffer (adjacent to the building) and an 18” sod buffer (adjacent to the pavement) separate the building from the parking lot. The sod buffer allows the tall meadow plants to fall over in the autumn without occupying the drive aisle, and also gives the building a cleaner, more conventional look.
More Information on WSSI’s Native Landscaping