Low impact development, or LID, is a approach to managing stormwater that works by handling rain where it falls rather than piping it away. The EPA defines it as a set of practices that reduce runoff and pollutant loadings by managing stormwater as close to its source as possible. Instead of channeling rain into storm drains and sending it downstream, LID uses natural processes like soil absorption, plant uptake, and evaporation to deal with water on site. The goal is to make a developed piece of land behave, hydrologically, more like it did before anything was built on it.
How LID Differs From Conventional Stormwater Systems
Traditional development replaces soil and vegetation with rooftops, parking lots, and roads. Rain hits these hard surfaces, picks up oil, fertilizer, and other pollutants, and rushes into storm drains that dump directly into rivers and streams. The faster water moves off a site, the more erosion it causes and the more contaminants it carries.
LID flips that model. Rather than collecting runoff at the edge of a site in a single large detention pond, LID scatters small-scale practices throughout the landscape. These features infiltrate water into the ground, filter it through soil and plant roots, store it for later use, or let it evaporate back into the atmosphere. The Ohio EPA describes the philosophy this way: the built environment should remain a functioning part of an ecosystem rather than exist apart from it.
Common LID Practices
Most LID projects combine several techniques. Which ones get used depends on the soil, climate, and type of development, but a handful appear in nearly every LID toolkit.
- Rain gardens and bioretention cells: Shallow, planted depressions filled with a porous soil mix that captures runoff and lets it soak into the ground. Bioretention cells are the more engineered version, with layers of sand, gravel, and sometimes a perforated drain pipe at the bottom. Rain gardens are simpler, relying mainly on planting media without those extra filtration layers. Both temporarily pond 6 to 12 inches of water above the soil surface during storms, then drain within a day or two.
- Permeable pavement: Parking lots, walkways, and driveways built with porous asphalt, pervious concrete, or interlocking pavers that let water pass through the surface instead of sheeting off it.
- Rainwater harvesting: Capturing roof runoff in barrels or cisterns for later use in irrigation, toilet flushing, or laundry. This directly reduces the volume of stormwater leaving a property.
- Green roofs: Vegetated layers installed on top of conventional waterproof roofing. They absorb rain, slow runoff, and provide insulation.
- Constructed wetlands: Similar to bioretention cells but designed with poorly draining soil so water pools longer, supporting wetland plants that thrive in saturated conditions. These systems are especially effective at filtering nutrients from runoff.
Site Planning as a LID Strategy
LID isn’t only about installing green infrastructure after a site is designed. It starts with how the site is laid out in the first place. Cluster development, for example, groups homes onto smaller lots while preserving 40% or more of the total land as open space. The number of homes stays the same, but the amount of pavement drops significantly, and the preserved land absorbs and filters stormwater naturally.
Other site-level strategies include aligning roads and buildings to follow existing drainage patterns, preserving mature trees and their root systems, and minimizing the total area covered by impervious surfaces. These decisions happen on the drawing board before any rain garden or permeable paver is specified.
What LID Does for Water Quality
Filtering stormwater through soil and plant roots removes a significant share of the pollutants that would otherwise reach streams and lakes. Constructed wetland systems, one of the more intensive LID practices, can remove roughly 75 to 80% of total nitrogen and 70 to 93% of total phosphorus from polluted water, depending on the filter materials used. Volcanic rock substrates tend to perform best, while gravel-based systems still remove around 65% of nitrogen and 72% of phosphorus.
Beyond nutrients, the soil layers in bioretention cells and rain gardens trap sediment, hydrocarbons from parking lots, and bacteria. Slowing water down also reduces the erosive force that carves stream banks and smothers aquatic habitats with sediment. For communities dealing with polluted waterways or aging stormwater infrastructure, LID practices offer a way to treat runoff before it ever enters a pipe.
Cooling and Urban Heat Benefits
Replacing pavement and bare rooftops with vegetation and permeable surfaces also affects temperature. Hard, dark surfaces absorb solar energy and radiate heat, which is a major driver of the urban heat island effect. LID practices that add plant cover, whether through rain gardens, green roofs, or preserved open space, introduce shade and evaporative cooling. Research modeling redesigned urban spaces in Rome found that adding vegetation and changing surface materials meaningfully reduced thermal stress indicators during summer mornings, expanding zones where outdoor temperatures felt comfortable rather than oppressive.
Maintenance Requirements
LID systems are not install-and-forget. They require ongoing care, though the work is closer to landscaping than engineering. All LID facilities should be inspected at least once a year and after any storm that exceeds the system’s design capacity.
For vegetated practices like rain gardens and bioswales, the first year involves the most effort: planting, controlling weeds, removing accumulated sediment and debris, and checking for erosion after storms. In years two through four, the routine expands to include inspecting inlets and outlets, adjusting irrigation, replacing mulch, and watching for standing water that could breed mosquitoes. By years five through ten, plants may need replacement, but the core tasks stay the same.
Permeable pavement has its own rhythm. It needs vacuum sweeping at least twice a year to keep the pores from clogging with fine sediment. If water is still ponding on the surface 48 to 72 hours after rain, that’s a sign the pavement needs cleaning or repair.
These maintenance demands are real but manageable. The tradeoff is that LID systems typically cost less to build than conventional pipe-and-pond infrastructure, and they provide benefits like habitat, cooling, and aesthetics that a concrete culvert never will.
Where LID Is Used
LID principles apply across a wide range of settings. A homeowner installing a rain barrel and a rain garden in the backyard is practicing LID. So is a city retrofitting a downtown streetscape with bioretention planter boxes, which are essentially concrete containers filled with layered soil and gravel that filter runoff from sidewalks and roads. Suburban subdivisions use cluster layouts and shared open space. Commercial developments incorporate permeable parking lots and green roofs.
The approach scales from a single residential lot to an entire watershed plan. Many municipalities now require or incentivize LID practices through stormwater ordinances, offering credits on stormwater fees for properties that manage runoff on site. This regulatory push has made LID increasingly standard in new construction and redevelopment projects across the United States.