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Old 11-13-2015, 08:45 AM   #1
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French Drain or Drywell or ?


Hi all,

I just purchased my first home a couple months ago, and now im focusing on what my best options would be for solving my wet yard. Im unsure of what my best solution would be? There is no standing water and my yard is pretty flat, just about half of my back yard stays soaking wet for 5-6 days after a decent rain. Im new to the area but supposedly my water table is very high, I was told if I dig down 4-7 ft id be in water.

I was originally thinking of just doing a French drain around the perimeter and tie all my down spouts into it and run out to a ditch that runs adjacent to my property. That would focus on most of the water coming from the roof and then if necessary I could branch off that line and run it out to other point in the yard.

Would adding a couple of drywells instead be out of the question with how high my water table is? Im just imagining it would be a lot easier/cheaper than to dig a trench around the house.

Thanks for any advice
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Old 11-13-2015, 08:58 AM   #2
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Giving advise with a written description or even with photos is poor at best in these situations so your best option would be to hire a soils engineer to come to the site.
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Old 11-13-2015, 09:27 AM   #3
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All drainage projects need to start with you preparing an accurate topographic map of the area around your house. Generally you want to be accurate to within a few inches, which is easily accomplished using a builder's level or a laser level, which can be rented if you don't care to purchase one. Typically you grid the area around the house, and take shots every 10 feet or so.

The idea is to understand which way the water flows, and in particular can you drain to the ditches. For effective surface drainage, you need a slope of at least 1%, preferably 2% or more. It is simply impossible to eyeball this, you have to make the topographic plan.

As to the water table, there is no need to guess at the depth of the water, you can dig a small hole, or pound in a piezometer to measure the water table. A piezometer is simply an open tube driven down below water table, you measure the water level in the tube, and that is the water table. If the water table is really 4 to 7 feet down, you may be able to install a drywell, or you may be able to use perforated pipe drains to the ditch to handle the groundwater.
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Old 11-15-2015, 10:13 AM   #4
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Can you achieve downslope from all around the house to the existing ditch with just a very gentle and wide new ditch or trench (called a swale) with no gravel and no buried perforated pipe?

Better would be a downslope away starting immediately at the foundation so the swale is not right at the foundation.

There should not be a layer of gravel or mulch or other soil below grade at the foundation more porous than the dirt or soil or earth farther away.

One possible reason the yard stays squishy for long periods of time is a layer of less porous soil just a few inches below the surface. This can produce a secondary water table just a few inches below grade if the real water table was not already that close to the surface.

A perimeter French drain is usually not effective at draining water from a large tract of land exposed to the rain. The French drain desaturates the surrounding soil only for a few feet to each side which would mean you would need several French drains, running parallel say 5 feet apart, through your back yard.
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Stick to your lawn watering schedule until it really starts to pour. After the storm you have only the same number of rest days you always had and then you need to start watering again.

Last edited by AllanJ; 11-15-2015 at 10:40 AM.
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