Table of Contents
SCOURING OR UNDER SLUICES
- These are the openings in the weir.
- They are forme by depressing the weir.
- They have gates fitt in them.
- The scouring sluices are locat on the side of the weir on which head regulation of the canal, taking off from here, is locat.
- If two canals are taking off on either side of the river two sets of under sluices should be locat on either side of the weir.
Undersluices perform the following functions.
- A clear well-defined approach channel is preserve in the river just U/S of the canal head regulator.
- Silt entry into the off taking canals is controlled.
- When sluices remain close for a few days, silt gets accumulat in the get just U/S of the sluices.
- This can be easily scour to the D/S side by opening the under sluices from time to time.
- Low floods can be passed through them without weir shutters being dropped.
- During high floods, they provide greater waterway, and thus rise in the reservoir level can be restricted.
- They help store a fair amount of receding floodwater.
- The capacity of under sluices depends upon many factors.
However, it should be fixed base upon the following considerations.
- Twice the rated discharge of the taking off canal.
- 10 to 20% of the high flood discharge.
- Winter floods should pass through them without the weir crest shutters being dropp.
Design of undersluices.
- In this case, the intensity of discharge per meter length, and crest level of the under sluices are different from the weir proper.
- Hence it is necessary to design them separately.
- The design of under sluices is done based on the principles of weir design.
Following considerations, however, should be made in the design.
- The thickness and length of the impervious floor should be design in the same way as explained for weirs.
- The crest level of under sluices should be about 1 m below the crest level of the head regulator of the canal, if no silt excluding device is provid in the river.
- If silt excluding device, in form of silt excluder, has been provid in the river, the crest of head regulator should be about 2 m above the crest level of the under-sluices.
- In the case of under sluices, the discharge is the more intensive, and hence more protective length on the D/S side is require.
- The total length of the apron and Talus on the D/S side (l 3) should be as follows:
\[l_{3}= 27C\sqrt{\frac{H_{s}}{13}\times \frac{q}{75}} metres\]
where q is the intensity of discharge in cumecs/metre.
4. Length of impervious apron on U/S side of the sluice gate, should be as follows
\[l_{2}= 3.9C\sqrt{\frac{H_{s}}{13}}metres\]