Drainage questions

motocz · 10-23-2009, 02:09 PM

I'm installing some 12' NDS catch basins under my downspouts because I get water in the basement when it rains heavily. It just-so-happens that my city dug a storm water retention "pond" (which usually has no water in it) just adjacent to my back yard.

I'm pretty clear on most aspects of how to go about doing this, but have some questions.

1) Is there a minimum depth 4" Solid PVC pipe must be buried to? I'm in Ohio and slightly worried about freezing.

2) Is it ok to backfill with dirt or is it absolutely necessary to surround the pipe with gravel? I've looked at a lot of NDS literature/pictures and they normally don't show gravel around/under the pipe. Assuming I compact the soil well, is gravel necessary? What issues might I have with using dirt?

3) What would be the best way to prevent erosion in the retention pond? Should I just put some crushed stone under the outlet?

4) How much settling of the soil should I expect? Is it sufficient to tamp down the soil with my feet after every few inches of backfill?

5) This one is just out of curiosity. I didn't get any estimates because I have to do the work myself, but what would a normal quote be to install 5 12" catch basins and 200' of 4" solid PVC and 20' of perforated 4" pipe? I'm curious how much money I'm saving.

Some details: One basin drains to a pop-up emitter, three basins are under downspouts and all tie into the same line which drains to the pond and the last basin is at a low spot in the yard it catches water and also has 20' of perforated pipe which drain into it. This last basin also drains into the pond.

Thanks for all of your help.

Daniel Holzman · 10-23-2009, 04:17 PM

1) In Ohio you should bury them at least 3 feet to avoid freezing in the winter. If code requires deeper, go deeper.

2) As long as you do not plan to drive over the pipe, it is OK to backfill with soil, so long as the soil does not have any sharp pieces of rock in it. Use a heavy tamper on each six inch lift. You can make your own tamper by putting a 20 lb iron or steel plate on the end of a wooden dowel. If you plan to drive over the pipe, you will need to use structural fill (i.e. gravel or crushed stone) around the pipe. I recommend using Schedule 40 PVC, much tougher than Schedule 20.

3) Usually people put a plastic or better yet a concrete apron at the outlet. Check with your local code official, there is probably a standard in your town.

4) You will get only a 1/2 inch of settlement per foot of soil or so if you tamp it carefully. If you do not tamp it at all, you could get up to 25 percent settlement, depending on the type of soil you have.

5) The only way to know how much money you save is to get a couple of quotes from local contractors, then decide how much you value your time at. How were you planning to excavate the trench to the pond? If by hand, add some cost for the hospitalization charge for the bad back you will end up with (if you are over 40).

By the way, you may need a permit from the town for this work, I strongly recommend you check first. Also, be sure you call Dig Safe before you start digging, if you hit a gas line or buried electric line it could be a really bad day for you.

motocz · 10-24-2009, 09:30 PM

Thanks for the answers. I'm concerned that the pipes have to be 3 feet deep. I'm not sure I can go that deep and still have enough room to maintain the correct slope.

Daniel Holzman · 10-24-2009, 10:49 PM

You need to measure the elevation of the bottom of the pond and the elevation of your catch basins. You will need a level to do this correctly. Minimum pitch on the pipes is about 1/2 percent, usually you want at least 1 percent to keep the water moving.

However, the slope the water feels is the difference in elevation between the water in your catch basin and the water in the pond. Just because you have positive pitch on the pipe does not mean that the water will flow that way, if the water in the pond is higher than the water in your catch basin, water will flow from the pond to the catch basin. Best to measure the water elevation at the same time you measure the elevation of the bottom of the pond. Try to determine the maximum elevation the water in the pond reaches on an annual basis, you may be able to tell by water marks around the pond. Make sure you do not have the unfortunate problem where water runs from the pond to your house.

motocz · 10-26-2009, 09:40 PM

The catch basin is several feet above the top of the pond, so it's not a problem. I am concerned about someone purposely clogging up the pipe though.

Daniel Holzman · 10-26-2009, 10:50 PM

Why on earth would anyone deliberately clog up your pipe? Do you have a problem with your neighbors? Assuming you can get a permit from the town to connect to their detention pond, and assuming the bottom of your catch basin is several feet above the elevation of the water in the pond, you should be able to install the line with no trouble.

motocz · 10-28-2009, 03:15 PM

Quote:

Originally Posted by Daniel Holzman

Why on earth would anyone deliberately clog up your pipe? Do you have a problem with your neighbors?

No, but there is a lot of traffic and a lot of kids go by the pond on their way to school. It's not something I'm REALLY worried about, but you know, vandals, ex-wives, etc...