Good Growing

Landscape drainage for homeowners

Posted: Feb. 16, 2020 12:01 am

Are you stricken with pools of water in your yard, and you don't own a pool? Instead of water moving away from your house, does it run into the basement?

If you fight these common yard maladies, then very likely there is a stormwater drainage problem in your yard. This week, we're going to cover two common drainage issues for homeowners.

Settling soil

Settling soil around a home's foundation is incredibly common but might not become an issue for years or decades after a home is built. The primary reason this occurs is improper backfill and compaction around the foundation walls during construction.

Typically, the soil around foundation structures should be added back in layers or "lifts." Each lift is compacted using lightweight compaction equipment. We can really get into the dirt here as every construction site is different, and compaction should be under the direction of a licensed soil or geotechnical engineer.

Most homeowners are not dealing with new construction, but instead older homes with settling soil around the foundation walls.

The first thing to do is rake back any wood or rock mulch and organic ground cover material. The reason we pull these items back is they don't compact well and to expose the actual soil surface. Add lifts of soil -- typically these are higher in clay content, but talk with a geotechnical engineer for recommendations based on your soil type. Compact your lifts using hand-operated equipment. Most homeowners will be using a hand tamp, which can compact 1 to 2 inches of lift at a time. For larger projects, you could rent a vibratory plate compactor or rammer that can compact lifts between 4 to 6 inches at a time. Always check the equipment manufacturer's recommendation for guidance.

Make sure the final grade of soil around the foundation walls has a minimum of 4% slope away from the house. Avoid piling soil against the siding. Leaving 18 inches of the foundation wall exposed can reduce the risk of termites using your exterior walls as an entry point.

Poorly drained yards

Water pooling in yards can develop for many reasons, but the three that I typically point to are an increase in impervious surfaces and/or a decrease in vegetation, the development grading job disrupts the natural hydrology and is not compatible with the site and landscape management practices.

For example, if you mow your lawn too low and kill the grass leaving bare soil, it can become compacted during a rain event, which can lead to settling of soil and ponding water.

To address these problems usually means going to the top of the watershed. Can downspouts be rerouted? Or is there a possibility to install a rain garden to intercept the main flow of water before it becomes a problem? Often people will ask if an area with pooling water would work well as a rain garden, and typically, these will not be good rain garden locations. Rain gardens are designed to be well-drained, and by focusing more water in a poorly drained area, it will only make the problem worse.

These situations can be further complicated by runoff occurring from adjacent properties. A landscape contractor or landscape architect should be consulted for recommendations. Often the fix will require earthwork using small equipment such as a skid steer or mini excavator. If a homeowner is fighting against a lousy grading job, retaining walls can be cleverly deployed to help create opportunities for topography and slope drainage away from structures. Other tools such as pop-up drains and French drains can be used to move excess water appropriately offsite.

If your head is spinning with grading and hydrology, this article only covers the tip of the iceberg. We dive a bit more into each drainage issue, plus hit on erosion problems in our online Good Growing blog. Read more at go.illinois.edu/GoodGrowing.

Tip of the week: Stormwater runoff can become a huge liability, sometimes pitting neighbor against neighbor in courtrooms. If you decide to adjust the drainage from your yard, make sure to consult an engineer or landscape architect to make sure you don't wind up doing more harm than good.