Stormwater & urban surfaces

Its job in the system

Stormwater management connects land cover to downstream water quantity and quality. Roads, roofs and other hard surfaces can deliver runoff rapidly to drains. Soil, vegetation and designed storage can alter that journey. The task is to manage timing, volume and pollutants together rather than simply move every drop away as quickly as possible.

How it works

Runoff gathers material from the surfaces it crosses. A separate storm drain may carry that mixture toward a waterway without a sewage treatment plant on the route. In a combined sewer, rain joins sanitary wastewater and can increase the load on shared collection and treatment capacity. The drain’s appearance does not reveal which arrangement exists below it.

Green infrastructure can capture, filter, infiltrate, evaporate or reuse part of the runoff. A rain garden or permeable surface performs a specific function under its design conditions; it is not an unlimited sink. Storage fills, soils have finite infiltration rates and an overflow path remains important when incoming water exceeds what the feature can handle.

What it connects to

This system links the catchment, street network, sewers and receiving waters. Delaying runoff can change the peak arriving downstream even when some water eventually reaches the same outlet. Reducing pollutant sources and treating runoff address another dimension. A lower flood peak does not by itself prove that the water meets a quality objective.

Different places, different designs

Appropriate measures depend on rainfall, soil, groundwater depth, land use and existing infrastructure. Infiltration can be unsuitable where it would carry contamination toward groundwater; lined or non-infiltrating designs may serve other goals. EPA’s examples explain functions and site considerations, not a universal design recipe or a guarantee against flooding.