- An important principle for any lot development is positive drainage; water should flow away from structures. Moisture around foundations is one of the most serious problems in house construction; it can result in wet basements and weakened foundations. Building codes specify measures for waterproofing and dampproofing foundations. Downspouts should be placed a minimum of 5 feet from the property's foundation and the adjacent property and discharged to a safe location where structures won't be harmed.
- Grading establishes the drainage patterns for the site and prepares it for the finish paving and planting. The grade should establish a minimum of 2 percent, or 2 feet drop for every 100 feet length for landscaped areas; 2 percent slope looks flat to the eye. Building codes in some regions may specify a minimum 5 percent slope from the foundation over several feet. Exterior paving can be sloped at minimum 1 percent but 2 percent is preferred.
- Surface drainage is channeled with swales and berms. Swales are shallow depressions and berms are mounds. Swales carry water to an approved outlet, such as a municipal drain, or to an open area where the water can disperse. Grassed swales slow the water flow and allow it to infiltrate into the soil. Berms block runoff, channeling it to swales; they can be planted with shrubs and trees or grass.
- For certain areas subsurface pipes are needed to convey runoff. Downspouts are especially critical, where stormwater discharge can cause erosion and water collection. Perforated pipes may be buried in a shallow trench and covered with gravel, sloped to carry water to a discharge area. The trench can be an open channel or covered with turf. Another technique is a dry well, a small underground pit lined with gravel. Subsurface drainage should be installed by a professional contractor and may be regulated by the local authority.
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