Cotuit Rain Garden



Innovative green infrastructure sits unobtrusively within the parking lot of the Cotuit Town Dock at Oyster Place Road in Cotuit, just mere feet from Cotuit Bay. A long rain garden, otherwise known as bio-retention, was installed along the north side of the parking lot there in April 2016.

A rain garden is an alternative to a conventional storm sewer, and is designed to intercept and treat stormwater runoff. Stormwater contains pathogens and nutrients such as nitrogen and phosphorus, metals and hydrocarbons. The runoff water will now be filtered through the rain garden that is planted with indigenous plants, with the runoff treated before it reaches Cotuit Bay.

This particular Cotuit project was designed as a pilot project to publicly showcase how a retrofitted drainage system can mitigate the impacts of pathogens and nutrients in stormwater that negatively affect an ecosystem.

The retrofitted stormwater drainage system at Cotuit Town Dock can accommodate runoff from 35,000 square feet of paved surfaces that drain into the area. The widespread implementation of this type of green infrastructure could potentially reduce by up to 25% the amount of nitrogen loads into the larger Three Bay estuary system. The Massachusetts Estuaries Project reports that the Three Bays system that includes West, North, and Cotuit Bays, exceeds a critical threshold for nitrogen, which is harmful to water quality, human health, and toxic for wildlife including fish and shellfish, and plant life.

Section 208 of the Clean Water Act requires states and local governments to develop plans to mitigate the impacts of wastewater, improve water quality, and eliminate point source discharges of pollutants. The so-called 208 Plan for Cape Cod focuses on a new watershed-based approach to ecosystem restoration and was developed and drafted by the Cape Cod Commission. Governor Charlie Baker certified the plan in June 2015, and the Environmental Protection Agency signed off on the same plan in September 2015.

Barnstable Clean Water Coalition played an integral role in implementing the Cape Cod 208 Plan in its mission area that includes West Bay, North Bay and Cotuit Bay, including all coves and connecting freshwater rivers and ponds.
All plants found in this rain garden are native to the area and are able to withstand extreme types of weather. They are also resistant to the occasional submergence in salt water during storm events. The garden cycles the water throughout the root zones twice, and provides a longer retention period for the water, which results in cleaner water entering our precious bays.

During and after each significant rain event, water samples from the garden are taken and analyzed. Pollutants we test for include nitrogen, phosphorus, fecal matter, total suspended solids, and oil and grease.

The installation also includes a solar-powered irrigation system that recycles the infiltrated stormwater through the plant community and its root zones where microbes provide biochemical processing of the pollutants. The solar-powered irrigation system typically distributes the water for two minutes during a ten-minute span or for 24 minutes every hour. During colder months, the pump is used less frequently.

A similar project is under design at the Cotuit Library. This project will incorporate an educational component associated with the library. This will be a two-tiered rain garden with a Wi-Fi-enabled water pump that will coordinate its functions with weather reports.