TM 5-820-3/AFM 88-5, Chap. 3
e. A grating in a sloping gutter will intercept all
prevent possible clogging by debris, the safety fac-
water approaching the gross width of grate opening
tors mentioned below will be applied.
f. Discharge characteristics of gratings are pri-
if the length of grate is greater than the upper
trajectory of inflow. Grating bars will be placed
marily dependent on design and the local rainfall
parallel to the direction of gutter flow, and spacers
characteristics. A safety factor of 1.5 to 2.0 will be
between bars will be avoided or located below the
used to compensate for collection of debris on the
surface of the grate. Eighteen inches is the mini-
field gratings in turfed areas. In extensively paved
mum length of opening necessary for grates with a
areas a safety factor of 1.25 may be used in design.
g. Grates may be made of cast iron, steel, or
ratio of net to gross width of opening of 2:3. To
3-2
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