Water flowing quickly over land surfaces can cause significant problems for homeowners and the environment. This rapid movement prevents water from soaking into the ground, which leads to soil erosion, the loss of valuable topsoil and nutrients, and localized flooding as drainage systems become overwhelmed. By implementing strategies to reduce the speed of this flow and increase the land’s ability to absorb water, you can protect your property.
Modifying Soil Health and Ground Cover
The most fundamental way to slow runoff is by transforming the soil beneath your yard into a highly absorbent material. Healthy soil acts like a sponge, a capacity largely determined by the amount of organic matter it contains and its physical structure. For instance, a 1% increase in soil organic matter can enable an acre of soil to hold approximately 16,500 gallons of plant-available water.
Incorporating organic matter, such as compost or aged manure, helps soil particles clump together into aggregates, creating pore spaces that allow water to infiltrate quickly instead of running off. This process also reduces the effects of compaction, where soil particles are pressed together, causing the ground to behave more like a concrete slab. Aerating heavily trafficked areas helps break up this compaction, immediately improving the rate at which water can enter the soil profile.
Selecting the right vegetation also plays a significant role in runoff control and soil health. Dense groundcovers and native grasses are highly effective because they stabilize the soil and intercept rainfall before it hits the ground. Many native species develop deep, fibrous root systems that can extend up to 15 feet or more, creating continuous channels for water to follow deep into the soil. Applying a thick layer of organic mulch, like wood chips or shredded leaves, acts as a protective layer that absorbs the impact of rain and keeps the soil surface loose for maximum infiltration.
Directing Water Flow with Landscape Grading
Physically altering the landscape’s shape is an effective way to decrease the velocity of concentrated water flow. These structural methods redirect runoff across a longer path, giving it more time to soak into the soil. One common technique is the use of swales, which are shallow, broad, and vegetated channels designed to convey water at a non-erosive pace.
Swales are constructed to run perpendicular to the slope’s direction, forcing water to spread out and move horizontally across the contour of the land rather than rushing straight down. The vegetation within the swale further slows the flow, promoting sedimentation and infiltration into the underlying soil. For slopes with a grade of less than 4.0%, a gentle swale can significantly reduce the speed of runoff and allow for considerable absorption.
For steeper or longer slopes, constructing berms and terracing is necessary to interrupt the flow path. A berm is a low earthen mound built on the contour and perpendicular to the water’s sheet flow, designed to contain the water and prevent bypass. Terracing breaks a long, continuous slope into a series of shorter, level steps, which drastically cuts erosion rates by intercepting runoff at each level and allowing it to settle and soak in. Check dams, which are small barriers made of rocks or logs, can also be installed within swales or gullies to create small pooling areas that further slow the water’s momentum and increase the infiltration time.
Installing Permeable Systems and Storage
Engineered solutions and collection systems are useful for managing concentrated flow from impervious surfaces like rooftops, driveways, and patios. Rain barrels and cisterns directly intercept water before it becomes surface runoff by connecting to a downspout and storing the water for later use. Rain barrels typically store 50 to 200 gallons, while cisterns are much larger, often holding 1,000 to 5,000 gallons.
The stored rainwater, which is naturally soft and free of chlorine, can be used for watering landscapes, washing cars, or other non-potable uses. The systems can be connected with an overflow pipe that directs any excess to a safe location.
Another effective method is the creation of rain gardens, which are shallow, landscaped depressions built to temporarily hold and soak in runoff from nearby hardscapes. These systems use specialized soil and deep-rooted native plants to filter pollutants, removing up to 90% of chemicals and 80% of sediments from the captured water.
Replacing traditional hardscapes with permeable paving systems allows water to filter through the surface layer rather than creating sheet flow. These systems can be made of specialized pavers, porous asphalt, or pervious concrete, all designed to allow water to pass through joints or pores into a gravel sub-base below. While a newly installed permeable surface can have an extremely high infiltration rate, maintaining this capacity requires periodic cleaning to remove accumulated fine sediments that can cause clogging over time.