Drainage/Holding Basin Questions

peachymomo(Ca 8)April 25, 2011

I have a property has some drainage problems in heavy rains, large ponds tend to form during the wettest weather but most of the time it is just muddy. I love the look of dry creeks, but since the property is flat I don't think that will work for us.

The plot is 110 ft x 205 ft, there is a storm drain near the south-eastern corner and the largest pond forms in the back of the backyard on the western end of the property. There is a septic tank and a grey water disposal system, so there are a lot of leech lines running the length of the back yard. I learned this winter that ours is the only property in the neighborhood that that doesn't drain any water to the street side where the storm drains are, all of ours goes into the back where the septic/grey water systems are. On top of that the neighbors on the south side raised their places so that the water drains off onto our property, as a result we get some pretty big ponds in the winter.

There are a few factors that make the drainage problems in our backyard difficult to solve. Our property is flat - there are some higher spots and lower spots but there is no grade to speak of, we have leech lines that we can't dig trenches through, and we have oak trees whose roots I don't want to disturb.

I would like to install one or more 'holding basin' water gardens to deal with the rain water and to be a landscape feature in the relatively featureless backyard. I was thinking it might be best to have a smaller holding basin closer to the house where there is a smaller pond, and a larger detention pool with a spillway into a dry well that has a pump to move water to the front yard farther back where the largest pond forms. There is a small slope towards the storm drain in the south-eastern corner, would it be possible pump the water to a little dry creek that runs to the storm drain? Can the holding basins sit above the leech lines or should they be kept away, if so how far away?

I have the plans for the septic and grey water systems, but the sketches are a little sketchy so I'm not sure as to the exact location of the leech lines, so in my plans I just drew them larger than I think they actually are. I will consult with a professional before doing anything back there, but I wanted to get a better idea of my options and plans first.

I want the backyard design theme to be 'Woodland Meadow' and I think a couple of water gardens with a lot of stone will go with that.

Here are some plans I drew as well as a pic of the backyard taken from outside the back door.

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You said:
On top of that the neighbors on the south side raised their places so that the water drains off onto our property, as a result we get some pretty big ponds in the winter.

I've read on here before that it's illegal most places for someone to change their drainage in a way that the water ends up on someone else's property for them to deal with, so perhaps that's an issue that needs to be considered before you go to the expense and a considerable amount of work to solve the problem in a way that might or might not work with the rest of your plan. (Though I could understand if you didn't want to get into a dispute with your neighbor.) When you speak with the professional, be sure to mention that the neighbor changed their drainage.

Sorry, I don't know much about drainage, other than "water runs downhill." :)

    Bookmark   April 30, 2011 at 11:14AM
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peachymomo(Ca 8)

No problem, I will have to consult a pro but I don't have the money for it now and I can't hire someone if I can't pay them. I'm just frustrated trying to do my own design and was hoping for a couple of pointers. So far the only feedback I've gotten from friends and family is: 'nice yard, great trees.' And that doesn't help me much.

I'd be delighted if my post got hijacked, I'm starved for input... Or you can just ignore it and it will go away, and so will I. ; )

    Bookmark   May 1, 2011 at 9:51AM
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You may want to also consult with your city. They may have some kind of stormwater help. Also, they may have some kind of answers about the neighbor causing additional drainage to your site. I would make some phone calls. City government folk are usually pretty helpful. I would avoid calling on a Monday or Friday though as those are the days they tend to be busiest and may not be able to help.

I don't know your city but mine has all kinds of help for people wanting to deal with rain.

Here is a link that might be useful: Rain garden information

    Bookmark   May 1, 2011 at 2:50PM
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Flat lots often present major problems in the disposal of excess water. Lack of slope leaves little resources with which to work. On these lots, precision of grade elevation is necessary to understand what solutions are available.

You are off to a good start with the scaled plan of the property, but now you need to add the vertical data to it. I have to say that I am a little confused as to where the photo was taken relative to the plan drawing. More photos would help me to guide you through making the vertical measurements needed. That is, if you want to go through all the work to develop a plan that can be predicted to solve your problems.

    Bookmark   May 2, 2011 at 11:06AM
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Apparently the photo is looking north toward the two oak trees,with either the storage shed or the neighbors house in the foreground. On the drawing the trees appear to be much further from what appears to be the main house. Perhaps their location was not measured but just estimated.

The septic field should not be flooded and so a holding basin should not be placed over them. The size of the field is determined by the permeability of the soil and the average gallons per day placed into the field. You should keep the pond outside the leech zone. The location and dimensions of the leech zone may be indicated on the plans you mentioned. Your municipality may have certain field sizes set by code. If your septic lines are being flooded as indicated on your map then your system has already been compromised and can pose a health hazard. The effluent from the septic tank must have an unimpeded flow and flooding of any kind will compromise that.

Basically,if the drainage onto your property caused by the neighbor is something that he could have been remedied,then you have a civil case against him. Harmful drainage onto another property is generally illegal.

You cannot make a direct connection to a storm sewer without a permit and then in most cases a licensed plumber must make the connection. I dont know in regard to the storm sewer if you are talking about a manhole or a curb inlet but you cannot dump a large quantity of water into the street.

Your plan to detain the water and allow some of it to infiltrate into the soil and then take the rest to a disposal point is sound but how well will it work. Is the soil permeable enough to allow enough water to be infiltrated into it to solve your drainage problem. If not,then perhaps most of the water will have to be taken to a disposal point,such as the storm drain. Perhaps catch basins could be used or an under drain installed under the detention pond.

The problem with pumps is that they will fail during power outage and so I would try to design the system to work by gravity.

I would be glad to talk to you more about this. Good luck.

    Bookmark   May 18, 2011 at 10:31PM
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