Lawn to Rain Garden Project

A family in Lagunitas knew that their lawn required an unsustainable amount of water and energy for upkeep. They were ready to let it go. Living in the Lagunitas Watershed on a low hill just above a small creek that is home to endangered coho salmon creek, they were very interested in doing what they could on their property to help reduce harmful stormwater runoff. In addition, they had major issues of erosion on their own property, where a majority of the rainwater runoff from their 3,500 square foot roof was draining with force directly into the foundation.

They decided to install a rain garden (see photo set below) that would direct runoff from the roof to an earthen infiltration basin that would temporarily hold water from up to a 6" storm event, and allow it to slowly percolate into the ground. They opted to build a fallen tree into the rain garden design as a symbol of the woody debris needed in streams to create safe havens for baby salmon fry to thrive and grow in.

A workshop was scheduled, with SPAWN Conservation Director, Paola Bouley facilitating, and in four short hours, sixteen people transformed a dying lawn to a beautiful and functional rain garden that collects thousands of gallons of rainwater each year and allows it to soak into the soils and replenish groundwater. 

Together they calculated the number of gallons of water that would come off of the roof in a 6" storm event, and translated that to the number of cubic feet of water the new basin would need to hold. Then the work began:  A shallow, gently sloping channel was dug from the "headwaters" where the rainwater runoff exited from a main downspout. A galvanized steel basin was repurposed as a design element, drilled with holes around the sides and filled with river rock. It was then placed below the downspout to absorb some of the force and impact of the great volume of water coming off of the roof and allow it to flow more gently "downstream" to the rain garden.  Pond liner was laid in this new "stream" to direct the water away from the foundation and towards the basin, then covered with river rock. Industrious workshop participants dug a basin twelve inches deep until they hit bedrock, and used the removed dirt to create an eighteen inch berm around the lower elevation of the basin, as well as an "island" between two stream channels. The entire basin was mulched with wood chips, and native plants from SPAWN's native plant nursery (See the project: 
Native Plant Nursery) were installed.  

With the first rains that followed the rain garden filled up with water, and within twelve hours, successfully drained, the water making its way down through the soil and bedrock to feed slowly into the creek below. They have watched their rain garden grow and perform for a full year. A success story!