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Solutions to landscape drainage problems
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February 19, 2003
Puddles of water that never seem to drain away can leave western Oregon home landscapes in extremely soggy condition during the rainy season.
Drainage problems around the home are usually caused by seasonal high water tables, ponding of surface water or poor soil permeability, said Jan McNeilan, Oregon State University Extension Service consumer horticulture agent. She offers the following drainage solutions:
Seasonal High Water Table The term water table refers to the level below which the soil is saturated with water. The water table usually fluctuates by several feet throughout the year. On some homesites, the seasonal high water table may be at or near the ground surface for long periods. Subsurface drains around the outside foundation walls may lower the water table. Subsurface drains should be at least four inches in diameter and surrounded with six to 12 inches of gravel.
Subsurface drains are made from various materials. McNeilan suggests checking local building codes for approved materials and other drainage regulations.
On lawns where only a small area is affected by a high water table, a small excavated pond may be the answer. However, before building a pond, be sure to check state and local safety regulations about pond construction.
Ponding Surface Water Small diversion ditches will channel surface water off the lawn or driveway. In developed residential areas, these structures usually are installed near property lines, or in back of or alongside houses. Generally, yards should be graded so the surface water drains away from the house. A minimum grade of one foot in 100 feet is sufficient, said McNeilan.
Installing downspouts to control roof water may prevent ponding in low areas of the yard. Downspouts can empty into a subsurface drain or into dry wells that carry the water away from the house.
Poor Soil Permeability Some homesites have a dense layer of clay soil that restricts the flow of water and creates puddles or ponds. If the dense layer is near the surface, a small trench can be dug through the layer and filled with sand, gravel or other coarse material to improve the drainage in a low-lying wet spot.
For large areas, subsurface drains four to six inches in diameter at a depth of two to five feet may be necessary. Pack the drain with six to 12 inches of gravel. If possible, use sand and gravel to backfill the drain trench to within a foot of the ground surface.
Even on well-drained soil, heavy foot traffic during rainy periods will compact the soil and reduce its permeability. Restricting foot traffic in the wet yard helps prevent soil compaction. Before installing any drain lines to drain water off their property, homeowners are advised to consult local county and city regulations, McNeilan noted.
Source: Jan McNeilan