The above picture taken earlier this week shows the progress so far in constructing our rain garden. By means of background, the north side of our home is perpetually wet with four down-spouts that drain a flat slanted roof of about 1,500 square feet. Do the numbers and that's lots of rainwater. We started by installing two cisterns to collect some of this water for use in irrigating our garden areas. But then what do we do when the cisterns get full - they are not that big and will regularly overflow unless alternative drainage is provided. So what about a rain garden for the overflow? Sounded like a great idea.
Initially, my goals were pretty modest. The roof built in the late 1950's as part of a cabin expansion at the time isn't what you would call perfectly "plumb". Drainage to the northwest end far exceeds flow volumes collected by the two downspouts nearer the chimney. We even had to add a fourth downspout several years ago as we repaired the dry rot that had developed in the eaves due to the inadequate drain capacity. If there is a "moss heaven", you'll find it on our walkway. So, away we go.
My first decision was to do all the digging myself. Afterall, two downspouts couldn't possibly require too much area particularly given the virtual "gravel pit" we have in our yard. When I started digging, reality finally struck. This is tough work. Rocks were everywhere and trying to salvage any soil would require screening what was dug. Ok, let's screen it.
Any idea how many rocks there are in this "soil" (what soil)? No problem - personal determination always overcomes physical challenges.
I used a pick-axe to loosen the ground. Then, right where the downspout with the biggest flow volumes dump into the cisterns and presumably our raingarden, my pick hits a big thud right into concrete. One thing that you learn living in an old cabin dating back to the early 50's, there are always surprises. In this case an old heating oil tank, since abandoned and filled in with concrete, happened to be located in the critical area. They must have had excess concrete when decomissioning the oil tank and chose to dump this excess into our yard, just below the surface. Oh well, minor problem - we can overcome this by giving our rain garden an interesting shape.
Next, I am out there digging and screening away while Judy is up on the roof of the original cabin clearing away debris - a flat roof of about 1,000 square feet and totally disconnected from the 1956 expansion roof. Earlier, I had dug down and found a 6" black pipe that had been cut through by another contractor installing our yard irrigation system. I cleaned out the pipe but thought nothing more of it. A small lake had formed on top of the old roof as the drainspouts up top had clogged and as Judy cleared it ankle deep in water, guess who got wet? All of a sudden, water was just gushing out of this old clogged pipe even though the roof drain was located on a completely different roof on the other side of our home. Hmmm? We might want to make this rain garden a bit bigger.
After digging deeper for a while and lengthening the "rain garden", we got hit with a cloudburst and I get wet again. This time we learn that not only is there now a total of 2,500 square feet of roof area draining through into our rain garden, but the entire 200 feet of our paved driveway is also draining here too. In the middle of this deluge, I start digging more drainage area further east. If only the ground were flat. As it turns out it's not and water as we know is kind of like being a lawyer - it's lazy and will flow in the easiest direction which is down hill (sorry about the lawyer analogy, I do understand that lawyers are real people too - well almost). There is quite a slope downhill from our first downspout utlimately into the lake. What happens if you dig more drainage downhill? Duh - it drains downstream and in this case flooded my recently planted shade tolerant plants, draining the storage area upstream that I had dug earlier. Now you understand why I am not an engineer! But adapt I did and "damned" the river with rocks and a few expletives so that upstream surge storage could be utilized. I did have to dig this area deeper and better account for surges, but as of now it's working just fine. And we are getting the filtering of stormwater we want through the soil and eventually into groundwater. Within 2 hours, our rain garden was nearly dry.
For one downspout we ended up using just a french drain - maybe we should call this all a "French Rain Garden"?
Seth Boetcher, City Public Works Director, has reported that the City's rain garden installed earlier this year has become a bit less permeable as fines accumulate on top of the rain garden's soil. Maintenance, however, is pretty simple, so we can expect excellent long term performance.
In the end, I anticipate that Judy and I will end up, in large part due to the highly permeable soils we have here around the lake, with a much more effective rain garden than we orignially intended. To have so much stormwater from our roof areas and driveway drain through a rain garden can do nothing but help our environment. As our cisterns overflow, they now drain into the raingarden and we still have access to the water that they can store for irrigation of our gardens. Looks to me like a winner.