Correct slope for drainage

Old 11-10-07, 07:29 PM
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Correct slope for drainage

Is there a standard slope to run a drainage ditch away from the downspouts. There is 125 feet from the front of the yard to the exit where I want the drain to run. In this 125 feet there is 14 inches of fall. Is this enough for the drain to operate properly. Hope I didn't confuse you.

Old 11-10-07, 11:04 PM
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That's a 1% slope. Might be enough, but marginal.
Old 11-10-07, 11:24 PM
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You need an even downward slope to carry water away from the structure. Remember that water follows the path of least resistance and you want it to flow away from the structure. Place a perforated PVC pipe with holes pointing down in the bottom of the trench, line the trench with gravel, and backfill with soil. You will need the transition piece that goes on the end of the gutter and connects to the pipe. Building Codes require the exterior grade to be a minimum of 6 inches below the top of the footing and to slope away from the house at a minimum of 2% (1/4 inch per foot) to an approved drainage device. Thus, where do you plan to drain the runoff? French wells, mon ami?
Old 11-11-07, 10:41 AM
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Water seeks it's own level. The degree of pitch will determine how fast that happens. As long as the outlet is lower than the inlet and you're not trying to draijn Niagra Falls, you should be OK.

The decision to use a gravel bed with perforated pipe should depend on where you intend to terminate the drain. If you are draining into a ditch or an area where saturation isn't an issue you can just open end the drain. Don't forget a galvanized screen on the end to keep the critters out though.
Old 11-11-07, 11:34 AM
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Correct slope for drainage

If you want to carry downspout water away from the house, DO NOT use perforated pipe. Perforated pipe is to collect water or distribut it.

If you use perforated pipe, you may collect surface water during a rain storm. Even worse is by distributing the water out of the pipe along its length, you decrease the flow and the ability to carry the debris (leaves, acorns, bugs, dirt, etc.), plugging the pipe.

If you want to do both, run two pipes (one solid and one perforated) or have adequate rock around the solid pipe to collect and carry away the surface water.


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