Pretreatment - Screening and straining devices, including forebays
Pretreatment - Screening and straining devices, including forebays

Information: Reference to any specific commercial product, process, or service by trade name, trademark, service mark, manufacturer, or otherwise does not constitute or imply endorsement, recommendation, or favoring by the Minnesota Pollution Control Agency.

Photograph of an example of check dams, which are designed to reduce velocity and thus enhance settling of sediment behind the dams (image courtesy: Massachusetts Clean Water Toolkit, Massachusetts DEP).

Screening and straining devices trap trash and coarse debris using smaller apertures such as grates or screens. While many pretreatment devices utilize screening and straining in tandem with their main treatment process, the examples in this category are constrained to those that primarily remove larger particles and sediment by screening or straining. These devices are often visible from ground level as they generally sit above grade or slightly below grade before or just following inlets in order to protect the downstream drainage system/BMP from clogging. This table contains both proprietary and nonproprietary devices, with the proprietary systems often applying the same or similar mechanisms to the nonproprietary systems but with convenient and sometimes easier construction or ease of maintenance.

System design

Screening and straining devices can often be installed in parallel to accommodate larger drainage areas, but in general, each unit is intended for a small drainage area (< 1acre).

System and component sizing

Most important for the sizing is the anticipated frequency of operation and maintenance as well as the considerations of how well the device provides protection of downstream BMPs and receiving waters.