Water runoff occurs when precipitation flows over the land surface instead of soaking into the soil. In a residential setting, this typically happens when the volume of water exceeds the ground’s ability to absorb it, or when it encounters impervious surfaces like roofs and pavement. The consequences of uncontrolled runoff include soil erosion, the transport of pollutants into local waterways, and potential damage to a home’s foundation and landscaping. Managing this water requires a layered approach, first diverting high-volume sources and then enhancing the ground’s infiltration capacity.
Managing Water from Roofs and Hard Surfaces
The most concentrated source of runoff in a yard is often the water channeled from the roof by gutters and downspouts. A single, heavy rain can quickly overwhelm the soil directly beneath a downspout, leading to pooling and erosion near the foundation. The immediate goal is to safely move this high volume of water a sufficient distance away from the home.
Downspout extensions are a straightforward and effective solution, directing water at least six feet away from the foundation. This prevents water from saturating the soil closest to the house, where it can cause structural damage. Placing a splash block—a pre-cast concrete or plastic tray—at the end of the extension helps diffuse the water’s force and spread it over a larger area of the lawn.
For a more permanent, subsurface solution, downspouts can be connected to buried pipes that lead to a dry well or a designated drainage area. A dry well is an underground chamber filled with gravel that stores water, allowing it to slowly percolate into the surrounding soil. Similarly, replacing traditional hardscaping with permeable pavers allows rainfall to filter through the gaps and into a gravel base below. Permeable materials significantly reduce the amount of water flowing across the surface, tackling runoff at the source.
Improving Soil Permeability
Even with effective diversion of roof water, the soil itself must be capable of absorbing the rain that falls directly onto the lawn and garden beds. Soil compaction, often caused by construction or heavy foot traffic, is a major contributor to runoff because it reduces the pore space needed for water infiltration. When soil is tightly packed, water cannot soak in vertically and instead flows horizontally across the surface.
To combat this, core aeration is a mechanical process that pulls small plugs of soil from the ground, creating channels that allow water and air to penetrate the dense layers. This physical loosening of the soil structure immediately improves the infiltration rate, allowing rain to be absorbed more quickly. Aeration is particularly beneficial for lawns and areas with heavy clay content.
Incorporating organic matter, such as compost or mulch, improves the soil’s spongy quality. Organic material acts like a binder, helping fine clay particles clump together into larger aggregates, which creates stable pathways for water movement. Increased soil organic matter enhances water retention and absorption, making the ground less prone to sealing over during heavy rainfall.
Ensuring the grade, or slope, of the soil immediately surrounding the home is correct prevents water from moving toward the foundation. The ground should gently slope away from the house at a rate of approximately six inches for every ten feet of distance. This adjustment, combined with a highly permeable soil structure, ensures that water near the structure is directed safely outward.
Installing Yard Drainage Features
When the volume of water exceeds the capacity of the soil, or when a property has a significant slope, structural features are required to manage the flow. These landscape solutions are designed to slow, capture, and safely redirect water that is already moving across the yard surface. The EPA encourages controlling runoff by following the mantra: “slow it down, spread it out, soak it in.”
Rain gardens are shallow, landscaped depressions planted with vegetation that tolerates both wet and dry conditions. They are designed to collect water runoff from impervious surfaces and hold it temporarily, allowing it to soak into the ground over a 24 to 48-hour period. The plants and specialized soil mix in the garden filter out pollutants while the water infiltrates, reducing the overall volume of runoff leaving the property.
Swales and berms work together as a system for controlling water flow across a slope. A swale is a wide, shallow channel designed to slow water and direct it along a controlled path, often toward a rain garden or drainage area. The soil removed to create the swale is mounded on the downhill side to form a berm, a raised barrier that helps contain and guide the water flow.
For areas with persistent subsurface water issues or where surface features are impractical, a French drain offers an underground solution. This involves a trench containing a perforated pipe surrounded by gravel and filter fabric, which collects groundwater and redirects it to a suitable discharge point. Trench drains are similarly long, grated surface drains often installed across driveways or patios to intercept sheet flow runoff before it reaches a sensitive area.
On steep terrain, terracing involves creating a series of level steps or platforms to interrupt the flow of water. Each terrace acts as a small retention area, reducing the velocity of runoff and preventing soil erosion. This method ensures water has time to be absorbed by the soil on each level rather than rushing down the entire slope.