Land Grading and Drainage Solutions for New swimming Pool

by Mary
(New York)

I am planning on putting in an in ground swimming pool. I would like to solve all my drainage problems at the same time, and prevent future problems due to addition of pool. Our house is on a slope.

According to the USDA, we are on a high water table from Feb-April. The part of the yard at the back of the house where the pool will go measures 60' deep and 75' wide. (We also own the empty lot next door, which continues up the hill for another 90' I have not measured the slope on that lot, but I estimate it to be about 10' drop over the 90' length.)

The slope from the highest point - back right side of house is 8' above the lowest point - back left side of property. This drop happens over a distance of 60' back and about 65' sideways, so I figure the steepest slope is about 13%. The very bottom corner drops 2' in the last few feet, so before that point, the lowest level is 6' below the highest level. About 6'drop over 60' so the slope is really more like 10%.

We need to do the drainage work ourselves due to budget constraints, so I have been researching: Swales, channel drains, french drains, rain gardens, dry wells, etc...

I would like to create 3 levels in this space.
The highest level at the back right side of the house will be held back with a retaining wall. I would like to put drainage behind (above) the retaining wall to direct the water to the back of the property and be dispersed into the hillside above, where there is a lot of trees and ground cover.

I am not sure if I will need to install a dry well or if the land will be able to absorb the water. Since I am trying to direct the water uphill, I will have to dig very deep trenches, in order to have the water flow down, underground. Have you ever seen this done?

I would also like to connect two of the roof gutters from the right side of the house to this drainage path.

The second level would be even with the back door of the house. This would be about 1 1/2 ' below the top level. The 3rd level, where the swimming pool will go, will be about 1 1/2' - 2' below the second level. Because I need to drain water away from the house and away from the pool, I was thinking of installing channel drains between the patio on the second level and the pool on the third level.

We have a dry well at the bottom of the hill that I can connect this drain to. The roof gutters used to lead to the dry well, but the clay pipes are all broken, so we need to replace them as well. In order to put the pool at this level, we need to grade the land at the bottom of the hill to raise it up about 3'.

I was thinking we could do this with Gabion boxes. They come in 3' boxes. The new, flat land will be level/slightly higher than the top of the Gabions, so we will not see them. They will be placed about 2-3 feet from the property line at the bottom of the hill.

There is a low retaining wall at the property line with a trench that collects the water from the driveway, so I cannot interfere with that. Another thing I was thinking about doing is creating a swale on the empty lot to direct water rushing downhill towards the house towards the back of the upper lot.

I thought this might help prevent that water from rushing towards the house during a rainstorm.

The pool companies I met with are not as worried about the drainage as I am. They said we just need to put a retaining wall at the top, but at the bottom, they said we can level out the land close to the pool and then slope the land down to the property line (since there will be 25' of distance between the pool and the down hill property line.

They do not think we need a retaining wall at the bottom. I want the land to be level in that corner - that is why I want to use the Gabions (they are much cheaper/easier to build than another retaining wall.)

Please let me know what you think of this plan- could it work? Am I doing something that will make matters worse? Also, for the channel drains - I was thinking of planting some type of plant between the patio and the channel drain that would grow out over the channel drain to obscure them, but not prevent them from collecting water. Do you know of a plant/bush with this type of growth? Thank you very much!

ANSWER

Hi Mary,
You obviously have delved into this issue in great detail!

Unfortunately, although I understand most of what you explained (not all), I would have to see some photos. I would also have to plug in the elevations you provided along with wall locations to determine the proper drainage solutions. This would take a lot of time to advise you correctly as to what to do, and this is not something I can offer for free at this time.

I would not want to guess, estimate, assume etc. Water problems can be a nightmare, not to mention costly to fix so you are right to be concerned about this before hand. You really should have a grading plan. If you are investing money in the installation of a pool, and you want to work on this project yourselves, I would recommend spending the money to have it professionally designed so that no mistakes are made and also so that you have a road map to follow.

I do provide grading plans, but you also also might consider consulting with a local engineer. I strongly recommend this for the function of your project and also for your own peace of mind.