A puddle
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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?  Are you constantly battling eroded hillsides? If you fight these common water maladies, then very likely there is a stormwater drainage problem in your yard. In this post, we’re going to cover the three most common drainage issues for homeowners.

Settling Soil Around Foundation Walls

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 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. So many things affect how well a soil can be compacted. The soil type (sand/silt/clay) is a major influence, plus how much moisture is in the soil will determine how well it compacts.

I recall while installing a new landscape, watching a backhoe replace several feet of fill around a newly built home next to our job site. The only compaction that took place was when the backhoe operator used the bucket to tap down on the finished fill. And then landscapers like me come along and install shrubs and mulch as foundation plantings. It looks good, but the potential for settling can turn into a water-stricken nightmare.

However, 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 groundcover 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 heavier in clay content, but talk with a geotechnical engineer for their 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. A big incentive to avoid piling soil against your home is by leaving eighteen inches of the concrete foundation wall exposed it 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 1) an increase in impervious surfaces and/or a decrease in vegetation, 2) the development’s grading disrupts the natural hydrology and is not compatible with the site, and 3) 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 their 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.

Erosion

To get those walkout basements, create magnificent views from home, and to quickly drain water away, developers often build up the soil to raise the house up. This can in many situations create hillsides that frequently erode. Erosion is when natural forces, such as precipitation, dislodge soil particles which then travel with the movement of the stormwater runoff. These soil particles must go somewhere and often will settle in low spots in the yard, patios, or driveways. Stormwater sewers can become clogged with eroded sediment which can affect entire communities. Even worse, eroded sediment can choke out streams, lakes, and rivers, killing aquatic life and destroying ecosystems.

Water, the very life-giving liquid is also incredibly destructive. The faster water flows the more damage it can do and the more sediment it can carry. By slowing down the flow of water, it cannot carry as much eroded soil. Therefore, one of the primary solutions to slowing water is to make hills less steep by installing retaining walls. Most retaining walls under four feet in height can be built by a landscape contractor, but when we get walls higher than four feet, we often need to bring in an engineer to assess the situation so the wall can resist failure.

While engineers and retaining walls are great solutions, the best tool to control erosion is plants. Plants evolved to be the natural protectors of soil. If soils were unstable, plants would not be able to survive. By protecting and building up the soil, plants can reproduce filling an area with roots, vegetation, and detritus that completely covers and holds the soil.

Lawns are a fantastic groundcover in terms of economy, and they can help protect, even build up soils. However, nature has created an effective system of protecting the soil by having plant communities co-exist in layers. From the debris on the soil to groundcovers, herbaceous annuals and perennials, shrubs, small trees, and massive overstory trees, this creates a multitude of canopies to slow rainfall, allowing it to be absorbed slowly by the soil below. So, if you have a lawn, but still encounter erosion issues, consider planting in layers.

There are prescribed slopes to move water appropriately without encouraging excessive erosion. Those slopes are provided in the table below.

Landcover Type

Min %

Desirable %

Max %

Streets & Driveways

½

1-10

20

Sidewalks

½

1-5

8.33 (for ADA)

Patios

½

1

2

Lawns

1

1.5-10

25

Mowed Slopes

1

<20

25

Unmowed Slopes

-

<25

-

Bioswale/Ditch

1

1.5-4

8

The slopes provided are represented as a percentage from dividing the rise (height of the slope) by the run (length of the slope). Most designers will start with their target slope percentages in mind and work backward to determine the rise and run of a proposed landscape. It is how we make grading plans! I wish I could tell my high school self that I actually use this algebra stuff.

When talking about slopes as a percentage, some people have learned these as ratios. As an example, a 2:1 slope drops one foot of height for every two feet of horizontal run. This is incredibly steep. This slope cannot support most plants. Many building codes specify a 3:1 slope as the steepest you can go. Ideally, you want an even more gentle slope than 3:1, especially if you plan to run a riding mower over that hillside.

If you are installing a new lawn or landscape on a hillside you will need to perform some type of soil protection while the plants become established. Biodegradable erosion control materials such as mats of burlap, jute, or coir can be installed over top a seeded lawn to protect the soil. A 2 to 4-inch layer of coarse woodchips is another great tool to use as a mulch when landscape plants are becoming established. Avoid using the plastic netting, as this will not decompose, and I have seen these get caught up in mower blades destroying large patches of lawn. The corners of these plastic nets can also work their way up to the surface and pose a tripping hazard.

If your head is spinning with grading and hydrology, this article only covers the tip of the iceberg. I could go on and on. Perhaps this will be a springboard into future blog posts, but for now, it is time to hang up the keyboard.

 

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.