Flow line The flow line is the lowest point along a gutter or roadway where stormwater naturally travels toward a catch basin or drain. It is a key reference point for street grading.
Proper flow line elevation helps prevent standing water and directs runoff away from sidewalks and roadways. During curb, gutter, or driveway construction, contractors establish grades so water continues flowing efficiently along the intended path. Maintaining the correct flow line is an important part of durable street and drainage design in NYC.
Frequently Asked Questions About Flow line
What is a flow line?
The lowest point along a gutter or roadway where stormwater naturally travels toward a catch basin or drain. It is a key reference for street grading.
Why does the flow line matter in sidewalk work?
Curb, gutter and apron construction must preserve it, or water ponds instead of draining to the catch basin.
What happens when the flow line is disrupted?
Standing water forms along the curb, which accelerates pavement damage, creates ice in winter, and can be cited as a drainage defect.