PRINCIPAL CONSTRUCTIVE FEATURES.
255
5. The leveUimj culverts may with advantage be arranged so that their
inlets are behind the hollow quoin and on a level with the gate platform.
In this way they assist to
keep the platform and
wheel tracks clear of mud.
Where caissons are em-
ployed, the culverts may
have their openings into
the caisson chamber with
the same object in view.
The flow of water
through culverts is regu-
lated in several ways, one
or two of which will be
briefly described.
(a) At a certain point,
usually near the inlet, the
culvert is intersected by a
clough-paddle or penstock
(fig. 223). This consists
of a substantial frame of
wood or iron. faced with a
plane surface sliding in side
grooves, and having hori-
zontal bearings against a
head and sill in the roof
Direction
cf Pressure
Suspension.
of Slufce
Sluice
SM
And friction
Rollers
and floor of
respectively.
shaft above
the culvert
A vertical
the culvert
Vertical Section.
permits the paddle to be
entirely withdrawn from
the sectional opening of
the culvert. Raising and
lowering are performed by
manual labour or by hy-
draulic or other power.
When the culvert is not
in use the paddle is kept
down. By lifting it com-
munication between the
Plan.
Figs. 180 and 181. —Stoney Sluice
outer and inner water is
established, and if there
be any difference of level a
curient is immediately formed. Ordinary cloughs are provided with stone
(generally granite) jambs, head, and sills, the sliding surfaces being polished.