Advantages:

(i) Widely as spillway crest gates,

(ii) Absence of any slots or grooves thereby providing better hydraulic flow efficiency,

(iii) Trouble free operation,

(iv) Less liable to vibration and thus better suited to work at part gate openings,

(v) Absence of wheel and wheel assemblies,

(vi)Better coefficient of discharge compared to vertical lift gates,

(vii) Trunnion bearings remain above water level thereby facilitating better maintenance,

(viii) Can be operated with comparatively smaller capacity hoists,

(ix) Simple fabrication requires no precision finish except at the bearings,

(x) Easily accessible for maintenance,

(xi) Economical for large size flood gates,

(xii) Risk of jamming is very much reduced and the crack open force is not great , and

(xiii) Adapts itself easily to automatic control.

Drum Gates. Also termed as sector gates. These gates(Fig.20.33a and b) are completely enclosed on all the three faces and at ends to form a water tight vessel. It resembles the quadrant of a circle formed by skin plate on the upstream attached to internal bearings. The gate rotates about the hinge generally provided at the upper edge so that the buoyant force aids in its lifting. A recess is made in the crest of the spillway to accommodate the gate in lowered position; the skin plate surface servings as a lid over the recess conforming to the shape of the ogee crest.

The gates are usually operated by water pressure. When the water is admitted through the inlet pipe, controlled by hand operated sluice, into the recess the hollow drum gate is forced upward to the raised position. When surface regulation of reservoir is to be done by the drum gate, the gate is lifted by control equipment housed inside the piers. These controls are fairly complicated.

Drum gates are well adapted for long spans of 40 m or more and under medium heights of 10m or so for surface regulation of reservoir but are not suitable for low dams having low structures on account of the deep excavation required and the liability of the flooding of the recess in which the gate floats.

Disadvantages :

(i) Gates are very costly,

(ii) Gate in lowered position is liable to clogging, and

(iii) Controls required for operation of the gate are complex in operation and are costly.