It’s been a great experience being part of the Ohlone Greenway Rain Garden from first concept to completion of construction.
Today, as the rain started, I got up from my desk and walked around the corner to see it christened by its first stormwater flow.
Plug on downstream side
To get runoff from the previously existing storm drain into the rain garden, the contractors plugged the downstream pipe with concrete. We had them put a 4-inch diameter plastic pipe inside the plug, with a cap on it. As long as the cap is on, water will back up, rise in the manhole, and discharge through a connecting pipe that comes in at a higher elevation.
Runoff collecting in the plugged manhole
The connecting pipe leads to the rain garden. When I arrived, it had been raining for a while, but there was nothing flowing into the rain garden. I went back to the house to get a tool to pop the manhole cover. When I looked down, I could see some runoff had started to collect, but was still backing up, filling up the pipe on the upstream side.
I waited a while for the manhole to fill. When runoff had backed up in the upstream pipe all the way to the pipe’s crown, the manhole began to fill quickly. I replaced the manhole cover and headed over to the rain garden.
The first runoff enters the rain garden.
I only had to wait a minute or two before the runoff exited the pipe with a gurgle and a gush and flowed across the mulch.
I went back later, at dusk, to see what the rain garden looked like after receiving runoff for much of the day.
The rain garden after a day of rain.
Here’s what it looks like when it’s not raining: a great place to play.
The rain garden on a sunny day.
