Stormwater Management
Controlling rain runoff so developed sites don't cause flooding or pollution.
Quick Answer
Stormwater management is the design and operation of systems that collect, slow, treat, and release rainwater runoff from developed land. Detention and retention basins, drainage pipes, and green infrastructure keep runoff from flooding downstream properties or carrying pollutants into waterways, and projects are typically regulated by local and state rules.
The Full Picture
Buildings, parking lots, and roads replace absorbent ground with impervious surfaces, so rainfall runs off faster and in greater volume. Stormwater management aims to limit those effects, usually by requiring that post-development peak runoff does not exceed pre-development rates and that water quality is protected.
Common tools include storm sewer pipes and inlets, detention basins that hold water temporarily and release it slowly, and retention basins that hold water longer. Green infrastructure, such as bioswales, permeable pavement, rain gardens, and green roofs, helps water soak in or be filtered close to where it falls. These practices are often grouped as best management practices, or BMPs, and as low impact development.
Two phases are regulated. During construction, the US EPA's National Pollutant Discharge Elimination System (NPDES) program generally requires permit coverage for sites disturbing one acre or more, which in turn calls for a stormwater pollution prevention plan, or SWPPP, with erosion and sediment controls such as silt fence, inlet protection, and stabilized entrances. After construction, permanent controls must be maintained according to local requirements.
For contractors, stormwater is both a scope and a compliance item. Underground pipes, structures, basins, and BMPs carry cost, and SWPPP inspections, maintenance, and corrective actions continue through the job. Precon teams review civil drawings and permit conditions to price stormwater scope, plan sequencing around erosion controls, and coordinate with site grading and utilities.
Real Examples
Common Misconceptions
People assume: Detention and retention are the same.
Actually: Detention basins hold runoff temporarily and release it. Retention basins hold water for longer, often by infiltration or evaporation, and are designed differently.
People assume: Stormwater rules only apply after the building is finished.
Actually: Construction-phase controls and permits apply while the site is disturbed, and permanent systems are required afterward.
Frequently Asked Questions
What is a SWPPP?
A stormwater pollution prevention plan describes the erosion, sediment, and pollution controls a construction site will use and how they will be inspected and maintained.
What is the NPDES program?
It is the federal permitting program under the Clean Water Act that regulates discharges to waters of the United States, including stormwater from construction sites, usually administered by states.
What are BMPs?
Best management practices are structural or procedural measures that reduce runoff volume or pollutants, such as basins, swales, and silt fence.
Who designs stormwater systems?
A licensed civil engineer, following local and state drainage and water quality requirements.