The water table on our property is pretty high — it’s only about a foot below the basement floor, on average. We have French drains and sump pumps under the basement slab that keep our basement dry, but it’s still helpful to keep water away from the foundation so that it doesn’t soak through the concrete foundation wall or overwhelm the sump pumps and drainage system. I installed two drywells in the lowest parts of our back yard, as far away from the house as feasible, and plumbed our two sump pumps and the gutters that drain most of the roof into the drywells. This helps keep (literal) tons of water away from our basement, especially after heavy rain.
After marking out the trench edges, I used an iron bar to break up the compacted soil and then I shoveled out ~12″ deep trenches. Most pipe is solid, but the last 8′ section of pipe is perforated to help some of the water percolate into the ground. The drywells hold a lot of water, but they’ll fill up in a heavy rain long before the water drains away — adding perforated pipe near the end helps more water to drain away from the house, helps keep the drywell from overflowing, and minimizes puddles in the low spots in our yard.
I found this enormous concrete footing dead center in the path of the trench. This is a remnant of a concrete footing for a greenhouse that used to be on our property before the house was built in the mid-1950s. When the greenhouses were removed, the footings were left behind and covered with a shallow layer of loam.
It was easier to remove the footing than re-route the trench. I used an iron bar to lever the footing up, and shoved wood underneath the footing. I was able to gradually lift it up and out of the trench. Eventually I disposed of it along with a few other pickup truck loads of concrete debris that had been unearthed from our yard.
Several gutters and a sump pump drain through these pipes into one of the two drywells. While digging, I found that a lot of crushed gravel had been buried in this part of the yard. I screened and rinsed it so that I could use it for drainage later.
The section pictured above is the walkway area to our back yard. I wanted to add drainage underneath the walkway to help it stay dry, so I filled this section with crushed gravel. Landscape fabric stops roots and soil from clogging up the crushed gravel drainage over time. A perforated pipe was installed in this section to help water drain out of the gravel.
The drywell itself is essentially a plastic barrel that holds only about 50 gallons of water. In a heavy rain, this would fill up rapidly, so I surrounded the drywell with crushed gravel to increase the water holding capacity from about 50 gallons of water to about 150 gallons. This also dramatically increases the surface area of the drainage system so that more water can percolate into the surrounding soil.
Since this drainage system is buried underground, it’s almost completely invisible except for the plumbing at the mouth of the gutters and the pop-up emitters above the drywell at ground level. These emitters open when the drywell is completely full so that a puddle will form above the drywell instead of causing the water to back up into the plumbing. After several seasons, I’ve noticed that the only time the emitter pops up is after heavy rains in the late spring, when the soil is fully saturated and the water table is at its highest.