Backyard design help

6 years ago

last modified: 6 years ago

Hello, we recently had a swale dug to channel our rain run off as well as our neighbor's back yard run off. However, the swale is too low as now the seasonal creek that the swale was supposed to drain to, now fills the swale in measurable rainfall. We received 2 inches over 48 hours and the swale over flowed.Step 1: we built a temporary dam to keep the creek water out of the swale to pump the swale dry. We also dug a temporary, small dry well.Step 2: the obvious action is to get the swale filled in so run off still drains to it and back to the creek, yet high enough so the creek doesn't drain into the swale. There is a small difference between the deepest portion of the swale and the most shallow spot, so, we will have keep the slope minimal.My idea is to do a pseudo french drain by digging a 6" wide, 4" deep trench at the base of the swale. Then, fill said trench with 1" to 2" rock. Then fill the rest of the swale with sand. The idea being that the storm water can penetrate sand easier that topsoil, then it is allowed to collect in the subsurface and perculate easier.I'm trying to calculate for the worst case scenario, we instantly have 2.inches of rain:Vitals:.Size drainage area: Approximately .35 acres drain to the swale.Volume of 2 inch rainfall: 18,700 galSwale: 60 ft long, ranging from .5 to 4 ft wideSoil type: sandy loamShade: PartialGround cover: established turf grass, growing)immature grass, and open dirt (grass growing soon)Climate: Twin Cities Minnesota, wettest month is June (average 4.25")Theoretical stats:Total volumn of run off (2" rain fall) = 2,000 cu ft or 14,961 galReady Capacity:Ps French Drain: 897 galCurrent swale: 1,514.81 galI am open to other ideas on how to tackle this. Our city government, who suggested the original design, won't respond to any communications and attempts to see them in person.The swale on the right if the one giving us trouble.

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Comments (5)

PRO
Yardvaark
6 years ago
By remote, on a forum, it's about impossible to help with drainage by using a lot of numbers and words. And the more of them there are, seemingly, the worse it gets. Instead, show the problem in pictures. Start with a zoomed out picture that shows the overall area and lay of land, then show slightly zoomed in pics that further explain the problem. The pictures must explain what you are talking about.

That said, I suspect you're on the wrong track with your french drain idea. You should be able to entirely solve the problem with grading.
Mo thanked Yardvaark
Mo
Original Author
6 years ago
Oh no! My visuals didn't post
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Mo
Original Author
6 years ago
nicholsworth Z6 Indianapolis
6 years ago
I feel your pain..I have issues too..a pic from today taken from my dining room window after a rain last night..see the water?..and a pic from late winter/early spring at it's worst..took 5 days to disappear..years ago Yardvaark commented on my post..I printed it to give to a potential buyer someday Lol..my water is trapped..the entire end of my yard is essentially a swale..if I sit in the low point on a garden seat I'm in a bowl..after several contractor and city visits..many conversations with knowledgeable people (one a soil scientist from Purdue) I still have no solution..I'm just happy that I don't have a basement or that my house floods..have you considered rain gardens, dry creek beds etc?..if you find a solution I'll steal your idea Lol..good luck..
Mo thanked nicholsworth Z6 Indianapolis
PRO
Yardvaark
6 years ago
It looks like the swale was extended a bit too far into the yard area. You can add a little topsoil to feather it a little farther back, such as where standing water would be just the other side of the next farther back pair of trees.

I can't see how any dam, temporary or not, at the end of the swale can help you. It would only be in the way of the swale draining and isn't going to help anything if it is breached by rising water. The only practical way you can can eliminate the swale is to pitch the entire back yard at a greater slope toward the drainage creek. But we can't see what possibilities you have for doing that. We can see that there are a lot of existing trees and none of those like to have their soil level changed, and some would probably not tolerate it. It's probably best to accept the swale solution in order to avoid a major full, start-over regrade (where the trees are removed.)