With an average of 40 inches of rainfall per year coupled with our notoriously heavy clay soil, drainage issues are a common occurrence in the Portland area. The accumulation of rain can lead to expensive problems: leaky basements, wet crawl spaces, soggy lawns, erosion, and flooding to name a few. Consistently wet crawl spaces and basements can encourage mold growth, which can cause health issues with many people and cause property damage. There are several approaches to help mitigate these issues:
1. Positive slope
Many drainage issues on a property stem from runoff not being directed away from the house properly. The soil around the foundation needs to have a positive slope, otherwise water will have a chance to seep into basements and crawl spaces. Build up the soil around the house, keeping it 6″ below the siding. Slopes of patios and other impervious surfaces should be directed away from the house to safe locations like lawns or planting beds.
2. French Drains
French drains are often the best way to keep water out of crawl spaces and basements as well as dry out a soggy lawn. Perforated pipe is laid in a trench and surrounded with gravel. The runoff is directed away from the problem area to a safer location.
3. Dry Wells
A dry well is another good solution for draining a soggy lawn or dealing with large volumes of water. It consists of a hole in the ground filled with a perforated tank surrounded with gravel. Runoff enters the tank and is slowly dispersed into the surrounding soil.
If excess runoff is coming from an uphill direction, a swale may be an inexpensive method to solve the problem. A swale is a shallow ditch, dug on contour. It intercepts the runoff, allowing it to slow down and seep into the ground. Additional swales may be used downhill from each other to handle more runoff volume.
5. Rain Gardens
Rain gardens have become a popular and attractive way to handle excess runoff. Rain gardens help keep runoff onsite, so it doesn’t enter the stormwater system and benefits the soil. Runoff overflow from downspouts, french drains, and swales can be directed into the rain garden. Specific plants can be used to create a functional, attractive landscape element.
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