tied to an open trench or underground piping net-
changes in slope, and at no greater than 400-foot
work, or combination thereof, and conveyed by
(121.9-meter) intervals on straight runs. Gravity
gravity to the sediment basin for primary treatment.
collection systems without flushers that empty into
If site conditions and grades permit, the collection
the sediment basin are designed to maintain a
system for stormwater to the sediment basin should
minimum velocity of 5 fps (1.5 meters per second).
be an open channel for easy cleaning of the open
A minimum of 2 percent slope shall be required on
trench. Lines and channels should be as straight as
all gravity wastewater lines.
possible. Minimizing the number of changes in
Materials. Open channels are cast concrete rectan-
direction will avoid mud and debris accumulation.
Manholes should be provided for pipe systems at
gular, trapezoidal, or semicircular cross sections.
pipe intersections, changes in direction, and
Semicircular channels limit areas where dirt and