9.2.3 Silt control at headworks
(a) Silt excluder
The silt excluder is a device constructed in the river bed just upstream of
the regulator to exclude silt from the water (source) entering the canal. It
is so designed that the top and bottom layers of flow are separated with
the least possible disturbance, the top sediment-free water being led
towards the canal while the bottom sediment-laden water is discharged
downstream of the diversion structure through undersluices. The device
basically consists of a number of tunnels (Fig. 9.21) in the floor of the
deep pocket of the river, isolated by a dividing wall. The sill level of the
regulator is kept the same as that of the top level of the roof slab of the
tunnels.
INTAKES 397
Table 9.2 Values of for parallel flow
Type of rack bar
Square nose and tail, L/s 5 2.42
Square nose and semicircular tail, L/s 5 1.83
Semicircular nose and tail, L/s 5 1.67
Round 1.79
Airfoil 0.76
Fig. 9.21 Silt excluder (undertunnel type)
Meusburger (2002) provides a comprehensive discussion of inlet rack
losses including an extensive bibliography.