If your home suffers from wet soil conditions or frequent flooding or standing water from even the smallest amount of rainfall, maybe you should consider installing some underground drainage piping or catch basins. There are several options for a homeowner to choose from and we will cover some them in this article.
You must first determine if the water condition is due to a heavy clay soil that will not allow water to penetrate and seep into the ground below perhaps or is the water coming from an overflowing nearby brook or stream. Does the water stay a few days and then disappear or does it take weeks to evaporate? These are two entirely different situations. Standing water that steadily drains by itself may indicate poor soil conditions that simply does not absorb water quickly. Re-grading this area may shed the water away from your home further protecting your foundation and basement. The use of longer downspout piping to move water away from the house will also aid in this effort.
If the water simply sits in a puddle for days and days, you may be a candidate for some yard drainage piping. A long trench filled with a perforated pipe and stone and ending at daylight is called a French Drain. Usually the trench is about one foot wide and the stone stays exposed at ground or lawn level. This allows not only the standing water on the grounds surface to drain down through the stone and into the perforated piping but any water in the soil will also migrate to the stone filled trench and drain the area as well. Removing the top water and the underground migrating water will result in a much drier yard area.
There are available today several types of plastic/poly catch basins intended for use in residential lawn areas. They will support a lawn tractors weight but not a car. If you have a low area that ponds water you may start your drainage the piping with a catch basin set slightly below the elevation of the surrounding lawns. Basins range in diameters but an 18 inch or 24 inch basin is fairly common.. These will rapidly take on water much quicker than waiting for the water to seep down through the stone and into the perforated piping. By connecting the perforated pipe to the basin you are taking away water through the French drain trench and the catch basin all at the same time. Make sure the pipe you select is capable of carrying the amount of water you are getting in an average rainfall. Four and six inch perforated pipe comes in large rolls which is easy to roll out and back fill. Eight inch and larger diameter piping comes in ten and twenty foot lengths These need couplings to assemble together and are nowhere near as flexible as the smaller sizes. Curving trenches is a snap using the roll piping.
Filter fabric is required in all French drain installations. Both four and six inch sizes are available with a fabric sock thereby saving the labor to wrap or cover the pipe. If you are using the wrapped pipe, a small amount of stone is placed along the trench bottom, graded on a slope to the low end of the trench and the pipe then rolled out in the trench. Trying to keep the pipe centered in the trench as much as possible, carefully add stone to cover the pipe and anchor it in place. Once the pipe is covered, back fill the trench to grade level.
The easiest way to determine the slope of your trench and piping is to use a simple level and rod available for rent at all rental stores. After mounting the level on the proper tripod and making sure the level itself is level using the three screws on the bottom of the level and the bubble level on the base of the level, place the rod on the top of the catch basin and read the numbers in the cross hairs of the level. Most rods used today are metric measurement and are very easy to use. Notice the rods between the feet marks are only from one to 10. There is no 12 on the stick. The one foot distance is broken up into 10 tenths and 100 hundreths. If the horizontal cross hair is on the 3 foot plus a large 2 plus 4 of the little black hash marks. You are reading 3.24 feet. Each side or edge of a hash mark is one, so 3 full marks is 6 and so on. Now take a measurement at the end where the pipe is going to come out to daylight. Perhaps fifty feet away or so. Now be careful here. This measurement is going to be higher or longer than your last one as it is lower in elevation. You read 7.46 feet on the stick. Now deduct the 3.24 from the 7.46 and you see you will lose 4.22 feet in elevation over the fifty foot distance. Doing rough math for every twelve and 1/2 feet of trench you will drop your pipe approximately one foot. Over the entire length the pipe will drop 4.22 feet. The.22 feet (3 inches) being made up in the last length of pipe at the end. Soooo if we started with a measurement of 3.24 on top of the basin and the basin is 12"deep we should read 4.24 at the bottom of the pipe at the basin itself no matter what size pipe you are using. It is the bottom that matters not the top. Now every 12 1/2 feet add one foot to the measurement to determine the pipe bottom elevation at that point. 5.24, 6.24, 7.24 and so on. Once you get used to doing this work, it is easier to do your math adding the stone thickness you are using under the pipe (say 4") and just measure to the earth while the machine is digging the trench. Then by placing the 4" of stone the pipe will always be on proper elevation grade. Just check every once in awhile to assure everything is correct.
If you are using a catch basin in your drainage system, that should be installed first. Excavate the hole to the required depth so the top of the catch basin is slightly below the surrounding area. Over excavate a few inches and place some stone below the basin. This will provide both a solid base for the basin and some additional sump area for water to gather underground. Placing some base stone in your trench, attach the pipe to the basin and roll the pipe out 20 feet or so. Now back fill the basin and pipe making sure there are no humps in the piping as you go. If the pipe is allowed to go up and down, it will trap water. Some slight left and right alignment is fine but keep it as straight as possible. Now proceed with the rest of your trenching and piping work. A word of caution here. If your trench at any time exceeds four feet deep, you must install shoring to hold back the banks of the trench. If you were kneeling down to join two lengths of piping or to remove a large stone and the bank caved in on your back, you will quickly suffocate and die. Don t take chances! If you are filling your trenches with pure stone, it is a good idea to use a plate compactor every foot or so to push the stone into place leaving no voids. Trenches are seldom perfectly straight sided and any voids left behind will cave in and make your trenches sink later on. If done correctly, the trenches should be as stable as the original ground only much drier.
Lastly, if water is being retained on top of the ground due to subsurface rock that will not allow the water to drain, heavier equipment is going to be required to excavate the drainage trenches. Piping laid flat will still conduct water as long as the end of the pipe comes to daylight. Water will seek it's own level and the pipe will provide a sluice or passageway that is much easier for the water to escape than seeping through cracks in the rock. If an area simply wont allow a flat or downward condition for the pipe, a machine mounted hammer may be required. Generally you would excavate the entire trench if possible, rent the hammer for a day and do all the rock removals at once. Make sure you protect your open trenches from pedestrians, animals or children from falling in a ditch. It is your responsibility.
Pete
Your Friendly Building Inspector
http://www.Wagsys.com
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