Rain garden - building one in urban area

19 years ago

Well, after last night's torrential, long lasting rains, my neighbor and I decided that we need a way to promote drainage away from our homes which are about 12 ft apart. Yes, we both had water in the basements, them worse than us.

To start, we have a sidewalk running right up against our house and it runs the length of the house. Our neighbor has a small garden against part of their house, about 1/2way back from the front of their house. Both houses have downspouts and some very clever (ha!) previous owners situated the downspouts so that they point directly at each other when they turn away from the respective houses. The soil in this area is very heavy clay. The way it's graded now, it slopes a little bit downward toward our house so the extensions we added to our downspout do no good at all. Last night, we had a lake on our sidewalk, right up to the foundation.

Enter the idea of a rain garden. Here's my questions:

1. Given that this strip of land is only 12' wide and given that the earth is clay, can we fit a rain garden in this area? Will we have enough space to both garden AND stay away from both house foundations?

2. If we can, and we start digging, should we go deep enough that we can get some gravel/small rocks laid at the very bottom before adding some soil? Any other drainage considerations we should be aware of?

3. If we can, we know we'll have to have an oblong/oval shaped garden and that's good. We think it'll look ok in this area, with some other slight modifications to existing gardens. Imagine 2 city lots with the houses pretty close, would you do this?

4. I want to tear out our sidewalk but my husband says no way. For now, I'm going to back down on this. However, would you keep the sidewalk or not? Why? Our neighbor currently has stepping stones farther back in this strip which would work for access to both our backyards.

5. We're ok with plants for this area - have plenty of hostas that can be transplanted.

One very major huge consideration for this is that the cost stays pretty close to $0. Please share any thoughts you have on rain gardens in our situation.

Featured Answer

joepyeweed

19 years ago

In order to keep water out of your basement, its best to keep a rain garden (and your downspout discharge) at least 10' away from the foundation.

If there is only 12' between the two houses, you do not have enough room for a rain garden there. It would be best to route the downspouts to a point further away that is at least 10' apart from each foundation.

You don't need to add rocks and you shouldn't need to "add soil". A rain garden is a depressional area and typically involves removing soil, rather than adding it.

I recommend renting a sod cutter to remove the soil. The depression only needs to be a few inches deep and a few passes with a sod cutter is a pretty easy way to remove that much soil.

There are some great resources on the web for how to make a rain garden.

The attached link takes a while to load, but its very good and worth the wait.

Here is a link that might be useful: How To Manual for Rain gardens

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Comments (7)

vgkg Z-7 Va
19 years ago
If your main goal is to keep your basements dry - Would it be possible for both you and the neighbor to extend the down spouts parallel to the ground (on the sidewalk, up against the foundations) to discharge further down line into an open yard space? You would need to silicon caulk the joins to make them water tight.
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cwillit
19 years ago
Even if you can't build a proper rain garden, aerating the soil and mulching, anything you can do to help the soil structure, will help reduce the amount of runoff. Even if you don't have room for a proper rain garden, plantings will help!
shaxhome (Frog Rock, Australia 9b)
19 years ago
Gawd....I don't know whether to laugh or cry at this question...in scorching, arid, drought-stricken Australia, I'd be putting in a rainwater tank to catch every precious drop...and I'd take my neighbour's, too!!!!

Regards,
Shax
Linda Eastman
19 years ago
joepye, thanks for the great how-to manual for creating a rain garden. i've been interested in this and am going to keep that in my file.
another alternative for kec01 could be a french drain. this is basically a moat filled with gravel that carries large amounts of water away from the foundation area... could be towards a rain garden or not, as you wish. here is a link to a discussion of this concept.

Here is a link that might be useful: linear french drains
ziggy___
19 years ago
Is this the only area available to place it??? 10' is the rule of thumb, but clay soil may keep the water away from the foundation a bit. I would still maintain as much distance as possible. The rule of thumb here is to capture the volume of water from the 2 year storm event (the largest storm that occurs on average every two years) and infiltrate it. Your state or the National Weather Service should have this info somewhere online. Take the rainfall depth and convert it to ft. then multiply it by the square ft of the area directed to the rain garden (both roofs). This will give you the volume in cubic ft. This is the ammount of water you are trying to put in the ground. The rule of thumb for stone is that 40% of its volume is pore space (open space), so divide your volume of water by 0.4. Your volume should have gotten bigger. You have to dig a hole this big and fill it with stone to have a large enough space for the water to go. Normally we do infiltration testing and adjust the depth so that the water will infiltrate within 48 hours. We also use geotextile to line the hole to keep dirt from filling in the pore spaces over time.
Rain gardens are often used just for water quality issues, but you seem to need the water to go somewhere else and sink into the ground, which is infiltration. This is part of my career and the info is based on my experiences in PA for new construction. Your situation is a bit different, but anything you do in this direction will at least be an improvement. The link is aimed at designers, but may give you other ideas too.

Ziggy

Here is a link that might be useful: PA BMP Manual
Susan Bryan
10 years ago
Hi rain garden enthusiasts. I am going to invite my Master Rain Gardener class to post in the Great Lakes Gardening forum here. Please come and help out newbie rain gardeners! I'd love your support and help from experienced gardeners. Sometimes the questions are general gardening, like how to remove sod, or more rain-garden-specific. Your comments are welcome!