Storm drain inlet protection measures prevent soil and debris from entering storm drain drop inlets. These measures are usually temporary and are implemented before a site is disturbed.
There are several types of inlet protection:
- Excavation around the perimeter of the drop inlet: Excavating a small area around an inlet creates a settling pool that removes sediments as water is released slowly into the inlet through small holes protected by gravel and filter fabric.
- Fabric barriers around inlet entrances: Erecting a barrier made of porous fabric around an inlet creates a shield against sediment while allowing water to flow into the drain. This barrier slows runoff while catching soil and other debris at the drain inlet.
- Block and gravel protection: Standard concrete blocks and gravel can be used to form a barrier to sediments that permits water runoff to flow through select blocks laid sideways.
- Sandbags also can be used to create temporary sediment barriers at inlets. For permanent inlet protection after the surrounding area has been stabilized, sod can be installed. This permanent measure is an aesthetically pleasing way to slow stormwater near drop inlet entrances and to remove sediments and other pollutants from runoff.
To increase the effectiveness of these inlet protection types, use them with other measures, such as small impoundments or sediment traps (USEPA, 1992). In general, stormwater inlet protection solutions and measures are practical for areas receiving relatively clean runoff that is not heavily laden with sediment.
Another method is to use a filtration system like a catch basin insert or curb inlet filter. Filtration is used to capture particular industrial or commercial pollutants such as hydrocarbons or metals, where other BMPs might be cost-prohibitive or ineffective. Filtration devices also can work well as pretreatment systems for other types of BMPs, such as pretreatment for certain contaminants before moving water directly to ground aquifers. These can be useful and cost effective devices for urban hot-spot applications where a particular pollutant is being targeted.