I've been thinking about rain gardens lately, in preparation for an upcoming workshop. In essence, they're nothing more than landscaped beds, with well-prepared soil and plants selected for sun, shade, or something in between.
Natural forested landscapes absorb almost 99% of rainfall that fall on them, releasing water slowly into nearby streams, and then into rivers. Urban and exurban landscapes shed water, because of impervious surfaces (roofs, driveways, roads, paths, and compacted soil landscapes).
Compacted landscapes? What are those, you might be thinking? They're all too familiar in the thin lawns, mowed road verges, landscape edges, and other depauperate examples of marginal vegetative cover.
Recent heavy rains had me amazed at how much water was sheeting off bermuda grass 'lawns' and adjoining paths into a prepared rain garden bed.
It's to be a demonstration site, and we were thinking about the roof runoff from the nearby building as our primary focus.
But the landscape runoff, by far, will be the biggest contributor to our newly established rain garden.
The take-home message is that creating landscapes that include trees, shrubs, and perennials with deep roots, and that are well-mulched, will pay dividends in terms of keeping water where it falls. And the result is to minimize runoff of rain water (or storm water) with any accompanying pollutants of sediments, fertilizers, pesticides, etc. (depending on your landscape practices).