LID City: Low Impact Urban Development


  • Sandeep Mehrotra, P.E.

Porous pavement captures stormwater and allows it to percolate into the ground or a catch basin.

Vegetation conservation helps reserve the natural ecological processes and water balance of the area, reducing runoff and maintaining the natural flow paths.

Green roofs are capable of absorbing and retaining large amounts of stormwater; they also absorb air and noise pollution and provide rooftop cooling.

Blue roofs are non-vegetated source controls that detain stormwater and provide sustainability benefits such as rooftop cooling.

Enhanced tree pits and infiltration swales absorb and often detain stormwater for an extended period of time, creating a self-sustaining ecology.

Rain barrels connect directly to a gutter downspout and detain stormwater that can then be used for irrigation or other purposes.

Bioswales/Rain Gardens add to the aesthetics of the property as well as provide for a hydrologically rough landscape that lengthens flow paths, increases time of concentration, and promotes infiltration.

In a natural area left undisturbed, fallen rain filters gradually through the soil, recharging the groundwater supply and providing for the health of surrounding flora and fauna. When development disturbs this cycle, the burden of channeling stormwater where it needs to go, and providing the necessary water management and treatment, falls to us.

Fortunately, nature provides a guidebook for us in how to most efficiently and effectively mimic the water cycle. The current industry term for relying on natural processes to channel and treat water is Low Impact Development or LID. LID seeks to maintain the functional ecosystem relationships between the atmosphere, land, and water by retaining and reusing stormwater where it falls. Controlling stormwater at its source is typically the most cost-effective management solution, as it reduces overall dependence on the sewers and increased wet weather capacity at wastewater treatment plants – each of which are costly to build, expand, and maintain.

LID also typically improves the aesthetics and ecology of a developed area, adding trees, shrubs, and flowers to swales and enhanced tree pits – areas that might otherwise just be gray. By putting nature to work, LID also represents the most sustainable stormwater solution, as the maintenance investment is minimal once the system is established. LID allows natural processes such as infiltration, soil storage, filtration, evaporation, and vegetative uptake to provide the necessary quantity and quality control of stormwater runoff, restoring the natural flow regimes that channel stormwater gradually back into our natural water bodies, streams, and river systems.

In our developed, sparsely-permeable environment, LID stands as the most attractive solution for the cost-effective management of stormwater. A well-designed LID integrated stormwater management system will minimize runoff volume, maximize the treatment capabilities of the landscape, be easy to maintain, and create a more appealing environment for everyone.

This article is reprinted from the Winter 2010 Horizons.

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Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

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