Open Channels

Open channel practices treat runoff while moving it: dry swales with engineered soil beds and underdrains, wet swales that hold a shallow marsh in the channel bottom, and grass channels that provide conveyance with a treatment bonus. They replace curb and gutter along roads and residential streets, which makes them the cheapest practice group per impervious acre where the right-of-way allows — and the only group that actually reduces the pipe network instead of adding to it. Performance hinges on residence time: gentle slopes, check dams and dense vegetation. Water-quality swale medians run around 80 percent for sediment, with the dry swale the strongest variant. Limits are real: channels handle a few acres each, erode when slopes or velocities exceed their design window, and the soggy-yard complaint is the classic symptom of a swale built without its drainage layer. These sheets cover geometry, Manning checks, check dam spacing, vegetation and failure modes.