Stormwater inlets collect runoff from streets, typically along curbsides, and direct water to underground pipes for discharge to a river or stream. Cities are retrofilling inlets with filtering design & devices to treat runoff before it enters waterways.

Benefits & Problems Addressed

Cleaner waterways: Inlet retrofits clean otherwise-untreated runoff before discharge into waterways of pollutants, oil, garbage and/or heat. 

Less system maintenance: Treating water at the source lessens maintenance for clogged and backed-up pipes. Some inlets feed first into accessible, underground catch basins that catch trash and hold excess water.

Add landscaping & green: Landscaped treatment beds built around inlet areas treat runoff and add asthetics.

Tips & Techniques

Where to start: Cities with populations over 50,000 typically have formal regulated programs in Stormwater management, pollution prevention plans & watershed.

Temporary filters: Use mainly during periods of construction or spills, temporary filtering booms, cloth & sandbags trap mud and pollutants at inlets.

Simple filters & inserts: Enhanced grates can trap larger garbage. Companies sell inserts that fit into inlets.

Curbside & inlet retrofits: On a larger scale, the entire inlet area is reconfigured. Improvements include larger "gray" approaches like prefabricated vaults as well as green (bioswales) to handle larger drainage areas and storm events.

Stormwater pollution hotspots: When water monitoring shows elevated pollutant levels, engineers examine possible sources (for example oil from parking lots). Where a single source is not apparant, cities can test inlet filters to catch pollutants from diffuse sources.

Maintenance : Filters get clogged so inspection and replacement are key.  Bioswales (plants & soil) also need periodic cleaning and maintenance.  

Hot Buttons: Cost & maintenance responsibility. 

Resources

Image: Flickr/NYCWater