TM 5820-4/AFM 885, Chap 4
conduit outlet and the barrier is placed on a slope
vert. Security regulations normally require the
to minimize deposition of sediment on the apron
guard to inspect such grills at least once every
during ordinary flow. Erosion protection, where
shift. For culverts in rough terrain, steps will be
required, is placed immediately downstream from
provided to the grill to facilitate inspection and
the barrier.
cleaning.
(2) For culverts and storm drains, barriers at
(3) If manholes must be located in the im-
mediate vicinity of a security fence their covers
the intakes would be preferable to barriers at the
must be so fastened as to prevent unauthorized
outlets because of the relative ease of debris re-
opening.
moval. However, barriers at the outfalls are usu-
ally essential; in these cases consideration should
(4) Open channels may present special prob-
lems due to the relatively large size of the water-
be given to placing debris interceptors at the in-
way and the possible requirements for passage of
lets. Bars constituting a barrier should be placed
large floating debris. For such channels a barrier
in a horizontal position, and the number of ver-
should be provided that can be unfastened and
tical members should be limited in order to min-
opened or lifted during periods of heavy runoff or
imize clogging; the total clear area should be at
when clogged. The barrier is hinged at the top and
least twice the area of the conduit or larger under
an empty tank is welded to it at the bottom to
severe debris conditions. For large conduits an
serve as a float. Open channels or swales which
elaborate cagelike structure may be required.
drain relatively small areas and whose flows carry
Provisions to facilitate cleaning during or imme-
only minor quantities of debris may be secured
diately after heavy runoff should be made. Figure
merely by extending the fence down to a concrete
44 shows a typical barrier for the outlet of a pipe
sill set into the sides and across the bottom of the
drain. It will be noted that a 6-inch underclear-
channel.
ance is provided to permit passage of normal bed-
load material, and that the apron between the
47
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