A train of roller is generally placed in between gate and d/s guide. These rollers may be placed independent of gate and guide thus eliminating axle friction but rolls vertically between two when gate is moved.

The vertical distance from crown of siphon down to discharging point or HGL should not exceed a value of 7.5 m under average conditions. This is necessary to avoid cavitation.
Limiting vaccum pressure = Atmospheric pressure ? Vapour pressure = 10 ? 2.5 = 7.5 m.

A convex vertical curve shall have to be provided when slope of chute changes from milder to steeper. The curvature should approximate to a parabolic shape. A concave vertical curve is provided whenever slope changes from steeper to milder.

When TWC is lying above JHC at all discharges, problem can be solved by-
1) By constructing a sloping apron above river bed
2) By providing a roller bucket type of energy dissipator.
In this case, jump is formed at toe will be drowned by tail-water and little energy will be dissipated.

A concave vertical curve is provided whenever slope changes from steeper to milder. The radius of this curve should be less than 10 times depth of water (in meters).

In case of dams and spillways, jump is steady and length of jump is almost constant and is equal to 6 y₂ where y₂ is post jump depth. The length of basin is related to Froude number as economy in length of basin up to about 35% i.e. 4.3 y₂ is thus obtained for auxiliary devices.

For square abutment with headwall at 90° to direction of flow, abutment contraction coefficient is 0.2. For rounded abutment with headwall at 90° to direction of flow, value is taken as 0.1.

Rollers are generally attached to gate and ride in tracks on downstream side of groove guide. The openings between upstream leaf plate and sides of pier grooves are sealed using rubber seals.

The side channel spillway is suitable when valley is too narrow. When re is no room for provision of chute spillway (as side flanks of sufficient width are required), this type is adopted as it requires limited space. The situation required for chute spillway and side-channel spillway is mostly same.

If upstream face of spillway is kept vertical, crest shape confirms to lower nappe of a vertical sharp-crested weir under maximum head. But if u/s face is kept sloping crest shape should also confirm to lower nappe obtained for an inclined sharp-crested weir.