Rain Gardens vs. Swales

I am researching rain gardens for a new garden design.  The clients live in Richmond, and have a high water table--inches below the surface of their lawn.  They have asked me to design a garden with a rain garden feature, that would tie into a drain.

I have been pondering how to design a rain garden when water frequently sits close to the surface.  If there is no drain, the rain garden will be a pond for most of the winter months.  If there is a drain, where should it be located to be effective?

Rain Garden

Part of my research has been to define the term rain garden.  In fact, a rain garden is a planted garden that holds water for, ideally, no more than 48 hours.  A rain garden may look no different than the rest of the garden, but the soil could be boggy at rainy times of the year.

Dry River Bed

Construction of bioswales on
Blenheim Street, Vancouver

The photographs my clients sent me of their favourite gardens are in fact dry river beds. Dry river beds are not planted, and they may or may not have a lining.  If a dry river bed has a lining, it is designed to move water.  If a dry river bed does not have a lining, it is designed to absorb water, and may have a French drain beneath, which moves water.  A dry river bed should be located at a lower grade than the rest of the garden.






A swale slows the pace of water down a slope. In Vancouver, there are a series of swales on Blenheim street.  Before these were installed, rainfall was channeled down the hill and into drains strategically placed by the road side. Now, the water is channeled into curb breaks, and collects in the swale with much of the water absorbing into the ground.  If too much water is channeled through the curb break at one time, a catch basin at the end of the swale stops the water from flowing over the sidewalk and back onto the street.  The catch basin is higher than the bottom of the swale.  If the catch basin was placed at the bottom of the swale, water would simply collect in that and be swept into the ocean.  The bottom of the swale should be designed with pervious soils to allow water to be absorbed into the ground.