How To Build A Drainage Pit

A drainage pit, also called a dry well, is used where water drainage is poor. This pit is usually 3 feet- long, 3 feet wide and 3 to 4 feet deep — although it can be excavated deeper and wider to accommodate larger drain problems. It is then filled with gravel to within 4 inches from the top. A perforated drain pipe is installed along low lying areas of poorly drained areas, capturing water from the soil and draining it into the drain pit. You can install a drain pit in one to two days, depending on the size and scope of the project.

Step 1

Dig a square hole in the ground 3 feet wide, 3 feet long and 3 feet deep outside the perimeter of the poorly drained area of your land. For example, if you have a poorly drained, low-lying area in your backyard that is 20 feet by 20 feet, then place the drain pit just outside the perimeter of this area. Excavate the hole larger if you need to drain larger areas. Generally, for every 20-by-20 feet area that needs draining, extend your 3-by-3 feet box by 1 foot on each side, as well as to the depth.

Step 2

Excavate a trench along the center of the poorly drained area and into the drain pit that is 12 inches deep and 12 inches wide. Extend this trench from beyond the drainage area on the opposite side of the drain pit so that it will capture ample amounts of water from the soil across the entire site.

Step 3

Fill the drain pit up with gravel, stopping just beneath the excavated trench that has been extended across the drain area. Do not tamp the gravel or compact it in any way. Loose gravel drains better than compacted gravel. Add 8-inch perforated pipe into the excavated trench with the perforated holes facing up. Place a pipe cap on the pipe at the end opposite the end that extends into the drain pit. Allow 4 to 6 inches to extend into the drain pit.

Step 4

Cover the perforated pipe with landscaping fabric, tucking the fabric beneath the pipe to hold it in place. Add more gravel into the drain pit, covering the pipe that extends into the pit but stopping 4 inches below the top of the finish soil or grass. Cover the gravel in the drain pit with landscaping fabric. Cover the perforated pipe and drain pit with soil, raking the soil around to create a finished look for the landscaping. Plant grass seed over the perforated pipe and drain pipe.