Question
Hi, I'm in the pacific northwest.  I have a back yard (about 1.5-2 acres of grass# that is relatively flat.  However, there are 5-6 low spots that collect water when it #rarely :-)) rains.  I was thinking about creating drainage ditches for each low spot and have them meet at a large hole at the back of my yard, which I would dig with a kabota.
One question is, would using a ditch-witch, which would create a 4in wide trench, be sufficient or should I make the ditch wider?  I guess my concern is, a 4in wide ditch would leave little to no room/space for drainage rock on either side of the drainage pipe.  Should there be a good amount of drainage rock all around the drainage pipe?
My second question is, the low spots in my yard are spaced such that I can have them flow into a main trench which would lead to the collecting 'pond'.  However, this main trench would be approximately 110 feet.  Given the necessary pitch, is this length to long?

Thank you,
Kyle

Answer
Hello:

You dont need drainage gravel in the trenches. The water will simply flow into the pipe from the soil. The rock or gravel would be used in place of pipe,not with pipe.

If your pipe is up to 3-1/2 inch in diameter,then a 4 inch trench should be sufficient.  If the main collector pipe is 8 inch diameter or larger,pitch it at a minimum of 1/16 inch per foot.  A 3 to 6 inch pipe would require a minimum pitch of 1/8 inch per foot.

Mark Harshman


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