By now we know the value of rain gardens. They keep water that runs off driveways and rooftops on the property allowing it to percolate into the soil instead of racing down the storm drain into the Puget Sound. You may be reminded that this is good for groundwater recharge (i.e. drinking water) and for protecting the Sound from the gunk that flows with that rain water from driveways and rooftops.
Thanks to the press that Ballard’s rain gardens received, we also know the pit falls of rain gardens. http://kplu.org/post/seattle-removes-rain-gardens-ballard The principle of a rain garden is to capture water and have it quickly soak into the ground. Rain gardens may have standing water during a big storm, but a healthy rain garden, the water disappears into the prepared soils into the ground. Ballard’s rain gardens turned into a standing pond. It failed to deal with the torrents of rain that we received in early 2011. Lessons learned: a) Don’t rush the process. b) Do a thorough perk test!
Why do I think KPUD needs a rain garden? Watching the sheeting of water down our sloping driveway gave me a clue. This water was washing into the storm drains and straight out to the sound. Plus, KPUD is naturally, a proponent for aquifer recharge. I would like to walk the talk and provide a model rain garden for the community.
Messing around with the storm water coming off of a commercial site is nothing to jump into. That’s why I asked Kitsap Rain Garden Mentors to lend me a hand. The mentors are carefully assessing the possibility for a rain garden here. They mentioned that they reject more projects that they accept. Will KPUD’s sit pass the tests? Here are the preliminary steps they took:
Locate a space
Our rain garden needs to be 50 feet away from drain fields and reserve drain fields which narrowed the location down a bit. We chose an area which was visible from the road and where water from the driveway could be diverted. We had a utility locate done so we would not interfere with water lines, power lines or buried storm drains.
Our rain garden needs to be 50 feet away from drain fields and reserve drain fields which narrowed the location down a bit. We chose an area which was visible from the road and where water from the driveway could be diverted. We had a utility locate done so we would not interfere with water lines, power lines or buried storm drains.
Measure twice – dig once
We got out the measuring tape. We identified the parking lot that would drain into our proposed rain garden and measured the area. We determined that rain water hitting 3,000 feet of impervious surface would find its way to the rain garden. Are we going to have enough space for that much water? Doing the math, it is going to be tight.
We got out the measuring tape. We identified the parking lot that would drain into our proposed rain garden and measured the area. We determined that rain water hitting 3,000 feet of impervious surface would find its way to the rain garden. Are we going to have enough space for that much water? Doing the math, it is going to be tight.
Do the soil squeeze
Knowing what kind of soil is on-site is important to think about infiltration during the winter rains. My mentor got a handful of soil and added a small amount of water. She squeezed the soil and worked it with her thumb and forefinger. Soil is great, gritty and crumbly which means drainage is good!
Knowing what kind of soil is on-site is important to think about infiltration during the winter rains. My mentor got a handful of soil and added a small amount of water. She squeezed the soil and worked it with her thumb and forefinger. Soil is great, gritty and crumbly which means drainage is good!
Test for “perk”
The mentors brought their shovels, buckets and measuring devices. A two foot hole was dug. A measuring stick inserted. The hole was filled with eight inches of water. The water disappeared quickly. Since it is summer the test was repeated three times. It was determined that the soil perks well!
The mentors brought their shovels, buckets and measuring devices. A two foot hole was dug. A measuring stick inserted. The hole was filled with eight inches of water. The water disappeared quickly. Since it is summer the test was repeated three times. It was determined that the soil perks well!
Calculate the slope
The selected rain garden location is on a slight slope. We measured the rise, divided it by the length of the slope and multiplied by 100 to determine the percent slope. This factors into the design of the depth of the garden.
The selected rain garden location is on a slight slope. We measured the rise, divided it by the length of the slope and multiplied by 100 to determine the percent slope. This factors into the design of the depth of the garden.
After a morning of measuring and testing, the mentors took back the information to their designer. I’m still waiting to hear the verdict. The soils are good, perk is good, the drawback is the large area that will drain into the garden. Is there enough room to accommodate the runoff. A rain garden that is twenty percent of the impervious surface is needed for 100% filtration. Hopefully, the designer will come up with a solution and we will have a showcase rain garden in the near future.
To find out more about those busy, dedicated rain garden mentors visit: http://raingarden.wsu.edu/HomeownerResources.html .
