Past project: Yard drainage and roof runoff

Home office; cloudy, fog/drizzle, 48F 0643

Any area where water does not readily seep into the ground will have to deal with runoff. In urban areas, roads, parking lots, roof tops, generate a lot of run off that needs to be routed to a dispersal system. Otherwise large unsafe unsanitary ponds will develop.

Our soil is mostly clay. When it is dry, it will absorb a certain amount of water until it is wet. After that, everything just stays on the surface. As the house is built into the side of a slight slope, water running across the back yard tends to run into the foundation. Water from the roof on the back of the house also contributed to the foundation water. All of this contributed to the repeated basement flooding encountered the first few years we lived here.

The equivalent flat area of the roof on the house is 2,052 square feet. I like data, so to quantify the problem, I made the following chart to show how many gallons of water comes off of the roof for every 1/10 inch of rainfall:

Rainfall amount (inches)Cubic inchesGallonsLiters
0.129,548128485
0.259,096256969
0.388,6443841,454
0.4118,1925121,938
0.5 – 1/2147,7406402,423
0.6177,2887672,903
0.7206,8368953,388
0.8236,3841,0233,872
0.9265,9321,1514,357
1295,4881,2794,842
Gallons per 1/10 inch of rainfall

Some of the water in the first 1/10 inch of rain goes towards wetting a dry roof down. I estimate that to be 1/2 of the first 1/10 inch stays on the roof and eventually evaporates. Everything else runs into the gutters.

As you can see, an average storm of 1 inch of rain produces 1,219 gallons of runoff from the roof alone. When larger storms arrive and the ground becomes saturated, then real problems can happen. During Hurricane Irene in late August of 2011, we received approximately 10 inches of rain in 12 hours. The basement sump pumps could not keep up with the incoming water and at one point the basement was flooded with 18 inches of water. Fortunately, the power stayed on and eventually it stopped raining and the pumps did their work.

The first thing I did was install drain pipes to take the water gutter down spouts and conduct it away from the foundation to the downhill side of the yard. To do this, required a small excavator.

Digging trenches for drainage pipes, Cat 303 Excavator

From each corner of the house, I installed 3 inch DW PVC pipe, 18 inches in the ground. The pipe on the north side of the house also connects to the sump pumps, thus that drains into a small dry well in the front yard. Unfortunately, I cannot find any pictures of laying the pipe.

Dry well with water cleaning plants

When we bought the house, only the back had gutters. It seems the previous owner had made some attempts at routing the water away from the basement. I hired a company who came and installed Seamless Gutters on the entire house, which was well worth it.

I also dug up a good bit of asphalt around the back of the house which was a patio of sorts. That was hauled off to the recyclers.

Retaining wall and drainage swale to east of house

The run off from around the yard was directed away from the house by use of two swales; one to the south and another going from east to north. The east to north swale was completed as part of building the patio and retaining wall.

This made a difference in the amount of water getting in the basement, however, there was still water getting into the basement…

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