Adding a Yard Drain

With spring coming and snow melting I thought I would post about the yard drain that I installed two summers ago to help with some drainage problems on my property. Following heavy rain, I had water pooling up against the back of my garage, and next to my pool shack, halfway across my back yard. The fix for the water pooling up against the back of the garage was fairly easy. Over time, the backfill around the garage foundation had obviously settled, so I had a landscaping contractor come in, lift all the interlocking brick around the back of the garage, add about 12" of compacted stone dust, and then reinstall all the interlocking brick giving me a nice slope away from the foundation.

Yard drain - installation in progress.

This however, only exacerbated the problem with the drainage in front of the pool shack. Heavy rain - three to four inch puddle of water about 150 square feet. I would also get large puddles on the other side of the pool shack, due to the landscaping at the back of the yard. Some research lead me to the concept of a yard drain - essentially a section of 4" drainage pipe coming up to a drain grate integrated with your landscaping, which allows water to run off the property. I'm fortunate that I have a fairly deep drainage ditch running across the back of my property line - so I could run a drainage line halfway back my property and have enough fall / slope in the pipe to allow for good water flow, and still be able to drain out the end of the pipe.

I was also in the process of levelling all my interlocking patio stone, so it was a good time to install the yard drain. The process started by lifting all the interlocking brick in path of the excavation. Trench digging by hand is definitely a skill - there are some good online videos on digging trenches - I made sure I had two very good shovels - one square shovel with a heavy wooden handle for cutting the sides of the trench, and one long handled spade for getting into the bottom of the trench and digging out the debris.

Start of the project - patio stone stacked on the right. Pipe and fittings in the foreground. The start of the trench.

Obviously, avoid a hot humid day or digging in the peak heat of the afternoon. One solid day of digging and we had our trench, in very hard, clay soil. I verified the slope periodically with a 4' level, to ensure I had at least a 1% slope (1/8" drop per foot of run) toward the back of the yard.

The excavation proceeds

 I wanted to install two drain points - one on each side of my pool shack, due to the way the ground sloped in my back yard. The outlet to the back of my yard had only one decent route between some mature lilac trees, and I wanted to minimize the number of roots to cross, so I had to have a cross trench in a T shape to pick up the second drain point.

T intersection in the trench.

I installed a T at each drain point, to create a shallow sump to trap sand a small rocks that may drop into the drain. Once a year, I'll remove the grating on the drain, and scoop out any debris in the bottom of the T fitting. The base of the T is plugged with a cap fitting.

The uppermost drain point. Note the duct tape closing off the drain pipe so that nothing gets into the drain while backfilling with earth. 

The long run from the uppermost drain.

Trenching across tree roots is not terribly difficult. Most roots run fairly close to the surface, and if you can avoid cutting the roots, and trenching through the roots, you give your trees the best chance of survival. It helps to have a small spade shovel (6" wide) to get inbetween the roots and faciliate cleaning out underneath the roots.

Note the T fitting and branch line to the second drain. The pipe runs underneath the lilac roots. 

Since I was going to have to reinstall my patio stone above the backfilled drain line, I took my time to ensure the drain line was very well compacted. The trick to compaction is shallow raises of your backfill - a couple of inches at a time, and compaction with a vibrating plate compactor makes it go much quicker. I rented this gas powered vibrating plate compactor for $20 for the day, including gas. Sprinkle some water on each raise to help with the compaction - just enough to make your backfilled earth moist, but not soaking wet.

Vibrating Plate Compactor, Gas Powered.

Long run partially backfilled.

Partial backfill.

With the backfill complete, it was time to reinstall the interlocking brick, and then install some grating on the drains to prevent leaves from getting into the drain pipe. 

Upper drain - completed, with grille installed. Very inconspicuous.

Lower drain on the T branch - grate installed.

These do a great job of preventing the accumulation of standing water in the back yard. The levelling and cleaning of the interlocking brick also made a big difference in how everything looks.