Whenever anyone builds a house or garden structure on a piece of ground, the ability of that piece of ground to absorb and gently drain away a downpour of rain is greatly reduced. Roofs and patios do not retain water; they run it off somewhere immediately. And the excavations, fills, and leveling made during any construction change the ground’s contours, with the result that puddles and washouts may occur even in a gentle rain.
Most of these drainage problems are usually solved during the actual construction process by some of the means described below, but during the first year that the structure is new, you should keep a close watch on how and where rainwater collects and drains away.
If your house is several years old and your garden is fairly well established, the drainage has probably been well taken care of. It is further helped by landscaping. Established plants and lawns hold soil and water in place, and they transpire a sizable amount of excess rainwater into the atmosphere. But even a fully landscaped home can have some drainage problems that will never go away with the usual procedures. The examples below show you ways in which you can solve them.
Ground water (rain water which seeps down through the ground). Level is usually deeper below surface on high ground; closer in the valleys. Its nature determines the proper solution.
Foundation drainage. Use non-perforated 3 or 4-inch drain pipe to carry the downspout water toward a storm sewer, drainage ditch, or any area that has soft and permeable soil.
Ground water under slab. Place one or more lines of drain piping underneath the slab before it is laid; completely around perimeter of slab and about a foot below it if already In place.
Intercepting ditches. On a sloping lot, use a line of perforated pipe or drainage tile in a foot-wide ditch filled with gravel to carry the water away. Place one ditch under roof line of house.
Retaining wall. On hillside lots, use a line of drain pipe or tile laid in a gravel-filled ditch behind the wall to prevent excessive water pressure from building up behind the wall.
Dry wells. For lowland drainage, dig holes to sandy or gravelly subsoil. (For holes over six feet deep, use a power auger.) Fill holes with coarse gravel, run drain pipe to them, cap with wood.
If you must grade around a big tree
Big trees on your property must have protection when you change the soil level around them. Grading for landscaping or building can cause serious trouble whether you have to remove soil from a tree’s root area, or add soil to it. The photographs below show five ways to minimize problems that may occur when either approach is used.
If grading removes only a few inches of soil, you can offset this by applying a thick mulch of peat moss, ground bark, or other organic matter. After a more drastic lowering of grades, it’s best to leave the ground close to the tree undisturbed and build a retaining wall, preferably at the drip line under the outer-most branches .
Raising the grade almost always causes problems. Old trees have lived for years with a certain balance of air, water, and nutrients, and it’s hard for them to adjust to sudden changes. Even a few inches of soil piled on top of the root zone seals off enough oxygen to harm roots of trees. Tree walls can reduce the disturbance to the tree’s environment. The tree grows in soil at the original level, while farther out the grade is raised.
Cedar wall retains soil at original level around base of tree next to lowered drive.
Edging and deck surround the tree base; area beyond was lowered considerably.
Stones fill the well left open in a raised terrace, which lets in air and moisture.
Bench masks the open trench around the root crown of this large tree. Galvanized Redwood edging, raised platform lets air nails join the 2 by 4’s for the bench top. The spokes are supported on 4 by 4 posts. Circulate below in a well 3Vi feet deep.