Dealing with Off-site Runoff

I remember the first big storm that occurred after we moved into our current home: a river carved its way under the fence and through the newly sodded backyard. Where did it come from? A peek over the fence showed me something I hadn't noticed before. The adjacent backyard was a concrete slab, funnelling runoff from the house, outbuildings, and pavement through our yard. Granted, it wasn't my neighbor's fault. The problem had been there for decades and they inherited it just like us.

A number of people have similar experiences, though, when neighbors add on or developers substitute McMansions for bungalows. New guidance being developed by the City should address some of those infill issues, but what can you do about "run-on" short of legal action? In this case we looked at redirecting the river and decreasing its energy. And the application may give you ideas about how to handle your own off-site problem.

First, we talked with our neighbors about what we were observing. They made some changes to their yard, including switching two parking spaces to loose gravel. Tremendous! And it looks great too.

On our side of the fence, we used recycled concrete, which came from tearing out our own paved yard, to provide energy dissipation for the flow entering from the fenceline. Basically, that means putting something in the way of the stream to smack it around and is provided by the larger stone in the middle of the garden to the left. We then used the same materials to edge a planting bed along the fence and provided spaces between the concrete to allow water flow. The water then enters a horizontal gravel filter, made up of river rock, which dissipates the flow further and allows it to pass through the yard without being seen. The filter also acts as a walkway from the house to the play yard. On the downstream side of the walkway, I added a raingarden that is a few inches lower than the gravel bed.

Overall, the system dissipates the energy of the water entering the yard, filters the water, conveys it, and provides some infiltration. Afterwards, water exits into the alley. During high rainfall events, water flows through this system as well as overflows to the yard and a shallow lined channel directly to the alley.

I mentioned the design to someone recently and they asked "Isn't that just a walkway?" And I thought, "Yes, and No." I'll highlight again that stormwater controls don't have to look different, they just have to work different. And if it is mistaken for a walkway, great. That tells me its a job well done.