1. Still pond regulation:
- Canal draws water from still pond
- Water in excess of canal requirements is not allowed to escape under the sluice gates.
- Velocity of water in the pocket is very much reduced; silt is deposited in the pocket
- When the silt has a level about 1/2 to 1m below the crest level of Head Regulator, supply in the canal is shut off and sluice gates are opened to scour the deposited silt.
2. Open flow regulation
- Sluice gates are opened and allow excess of the canal requirement
- Top water passes into the canal
- Bottom water maintain certain velocity in the pocket to keep the silt to remain in suspension
- Canal is not closed for scouring the silt.
3. Silt control devices
- Silt control at head works:
- Entry of silt to canal can be controlled by:
- Providing a divide wall to:
- Create a trap or pocket
- Create scouring capacity of under sluices
- By concentrating the currents towards them
- Paving the bottom the approach channel to reduce disturbance because due to disturbance sediment remains in suspension
Installing silt excluders
- Making entry of clear top water by:
- Providing raised sill in the canal
- Lower sill level of scouring sluices
- Wide head regulator reduces velocity of water at intake
- Smooth entry to avoid unsteady flow
- Handling careful the regulation of weir
- Disturbance is kept at minimum in weirs
- Silt is excluded from water entering the canal, constructed in the bed infront of head regulator - excludes silt from water entering the canal
- Designed such that the top and bottom layers of flow are separated with the least possible disturbance
- Top water to canal - bottom, silt laden through under sluices
- No of tunnels resting on the floor of the pocket of different lengths
- The tunnel near th head regulator being of same length as that of the width of head regulator - tunnel of different length.
- Capacity of tunnel is about 20% of canal discharge
- Minimum velocity 2 to 3 m/s to avoid deposition in tunnel is kept the same as sill level of head regulator
- From discharge and scouring velocity the total waterway required for under water tunnels can be determined،
- Silt extractor or silt ejector:
- Device by which the silt, after it has entered the canal is extracted or thrown out.
- Constructed on the canal some distance away from head regulator
- Horizontal diaphragm above the canal bed
- Canal bed slightly depressed below the diaphragm 0.5 to 2.8m
- Under diaphragm, tunnel which extent the highly silted bottom water tunnel.
- There should be no disturbance of flow at the entry.
- Sediment - laden are diverted by curved vanes
- Forwards the escape chamber: steep slope to escape channel is provided.
- The streamlined vane passage accelerate the flow through them, thus avoiding deposition (decreasing section area increases the flow velocity)
- The tunnel discharge by gate at the outlet end (escape channel)
- If near head regulator, silt will be in suspension
- If too far away than result in silting of canal.