Water runoff - drybed/drywell (sort of)

[celticsoc]

There is a corner of my house where water tended to collect, to the point that the window well filled up. There is a downspoutthere, as well as a low area. I corrected the problem by trenching away from the house, and I am building up the dirt a little there. I put extensions on the downspout to feed into the top of the trench, which is shallow and gradually sloped.

The problem of the water collecting there seems to have been solved, but now it is diverted toward the sidewalk, maybe 50 feet away. This is not a problem with normal rain, but when we get a torrential downpour, dirt tends to get on the sidewalk. In the Srping, with snowmelts, I think it may be the same. To alleviate this, we are planning to put in a drybed with river rock over landscape fabric. On either side, we have put in a garden with mulch. I think the appearance will be great, and more important, my wife thinks so.

On to my question. My intention right now is to put the drybed in with the hope that the rocks and landscape fabric will contain most of the dirt runoff. In order to minimize the runoff of water onto the sidewalk, I was considering digging postholes 4 feet down, every 10 feet or so and putting in 4" PVC to carry water down, sort of like a drywell. To keep the rocks from falling into the PVC pipes, I thought I would put hardware cloth over them.

So, the plan is this: Along the approximately 50' swale, sink 5 or 6 PVC mini-drywells with hardware cloth to keep them open, laying landscape fabric over the entire thing, and putting in about 2" of river rock.

Any comments, suggestions, "you're crazy, that won't work" comments?

[Sonny]

Digging 4" post holes, 4' down, every 10' is a waste of time and energy. Those holes aren't big enough to handle any significant volume of runoff.

Along your sidewalk, where your drybed will be, dig the center a bit deeper, enough to lay a 4" PVC sewer field line (the one with holes in it), to be covered (hidden) with your river rocks. Essentially, you'll be making an enhanced French drain along the sidewalk. At the house end of the PVC line, you might want to install an elbow, pointing upward, with a grill cover (clean-out access).

Sonny

[DanG]

If you are trying to get water to flow to a lower strata, you would be better off digging your "post holes" and filling with gravel - no pipe. Let the water join the subsoil wherever nature will take it. The deeper the holes, the better, especially if you get to a change of soil consistency like a shift from clay to shale or loam to sand or similar.

[celticsoc]

The drybed will not run along the sidewalk, but to it (perpendicular, not parallel). There is a significant buildup of soil on either side of the trench, so laying something parallel would entail significant digging. I am not averse to digging there, but would prefer to avoid it because there are some plants and bushes I have already been told are off limits for removal.

I was originally considering running a 4" PVC line from an elbow at the point of water entry (near the house) with a grill, but as a drain at ground level. My intention there was to run the water through this as a drain line, but I still have the same problem of water letting out at the sidewalk. The surface runoff would still put sediment on the walk.

My alternate consideration was to run the same line, with perforated and sleeved drain pipe rather than solid. Although there might be a little less sediment, none of this alleviates the problem of runoff. I am trying to find a way to deal with the water before it gets to the sidewalk.

From what I have read, small drywells can be constructed much as I was planning in the original post, but with fabric sleeve filled with pea gravel (similar to DanG's suggestion), and perhaps twice as many as I was originally planning (every 4-5 feet). This relies on the soil below having good drainage, which I think it may, since the rest of the yard is dry and all the digging and tilling I'v done in the are so far has netted virtually no clay. Plus, it is only in this particular area, when the rainfall is excessive, that there is a real problem.

I will probably go with this method for now, unless someone comes up with a compelling reason not to, since I can always dig a deeper trench later if it doesn't work. It looks like I will need to dig

10-12 postholes.

Comments?

[hrhofmann]

What is wrong with water crossing over the sidewalk and then into the street or wherever it goes??? Sidewalks are concrete or asphalt, just like streets and where I live, Chicago suburbs, no one worries if water crosses the sidewalks on the way to the streets. Almost every driveway channels water down the driveway, crossing the sidewalk, and then into the streets and non one gives it a second thought.

[celticsoc]

No major problem if it is just water, but after a major storm, quite a bit of sediment gets carried with it, and it can be a littlemessy. I imagine that after a period of time the amount of sediment will decrease substantially. Also, in the case of a driveway, the water flow is not restricted by the parkway on the other side of the sidewalk. In that case, it runs into the street. In this case, it runs onto the sidewalk, flow is slowed by the grass on the other side of the sidewalk, and dirt settles there.

[Sonny]

Sounds like the slope toward the sidewalk is pretty steep, compared to lawn levels here in Louisiana (flat). I'm not so knowledgeable with runoff/erosion of those conditions, but....

Is this sidewalk next to the street or is it across your lawn, leading to another area?

If it's not along the street, is there a way to tunnel under the sidewalk and have a/some drain (piping) bypass the sidewalk?

If the sidewalk is next to the street, about the only thing, I can think of, is incorporating some type of grill edging, on the lawn side of some plants that line the sidewalk. I would suppose a landscape service can advise what type of grill edging would be use for such runoff/erosion problems. ....Some type of edging that isn't unsightly and coordinates with a variety of lawn decor styles, maybe.

I still don't think 4" holes, with gravel, can handle any significant volume of runoff.

A more expensive approach than what you're presently prepared to do: In conjunction with your present plans, build a small rock wall along the sidewalk (cordinated with your landscaping scheme), with grilled drains, every so often, along the wall, allowing drainage onto the sidewalk.

Sonny

[celticsoc]

My front lawn has a slightly higher elevation than many, ut it is just one area where the water ran to the walk. It was a combination of my undamming an area near the house when I saw the window well fill with water, the fact that this area was under a lot of trees and so had no grass, and the city cutting down a huge tree right next to the walk in fornt of the mud-prone area.

What I ended up doing was similar to what I had planned originally, but following the suggestion of DanG and some further research I did not usePVC to direct the water downward. I dug the postholes, 7 or 8, to varying depths from 2 to 4 feet, widening some a bit if I didn't get the depth I wanted due to tree roots. The deeper ones were dug to the point where it was apparent that I was going to be removing clay beyond my tool's depth. I filled these holes with stone from another project on anothe part of the lot. At the end, I used a shovel to dig down about a foot deep and a couple feet square. I then went down another foot or two, kind of stepping it down into an area about 2 feet by 3 feet. In this area I put more of the stone removed from the other project. This worked perfectly that very night when we got another storm. In fact, it worked well during a couple downpours.

Then I laid down landscape fabric and ordered a couple tons of decorative stone in order to make this look better. After laying down the stone, it was again tested with a storm. This resulted in my going out during the storm to A) unclog the damn gutters and B) furiously hurl decorative stone out of the way, as it was damming up the area near the window well again and C) swear.

I have since added a section of downspout to carry the roof runoff past the point where it was dammed, and I will regrade above that area with some added dirt, since it is still a little lower by the window well. I am going to cover the downspout as best I can with the decorative river rock. It is larger rock (2"-3"+), so burying it may be difficult. I will re-grade the top of the trench as well.

So, there is the project. Thoughts?

[trader4]

If you post some pics on the web that we can see, you'd get much better suggestions.

I'd agree with the posters that have suggested having 6 four inch "drywells" along a 50 ft run isn't going to have any significant effect.