4. Navigation in Canals
The dimensions of the canal like cross section, alignment, lining, discharges, bridges across the canals, lock dimensions, cross drainage structures, and ship dimensions are some of the important factors which determine the navigability of a canal.
The ‘design ship’ is based on accepted designs in this report for ease of analysis and standardization. The ships are therefore classified based on standards of European water ways. The four categories of ships considered are: Class I (300 T), Class II (600 T), Class III (900 T) and Class IV (1350 T). in view of narrower/shallower waterways often encountered in India, a special category of Class I* (100 Y) is also defined.
The cross section of the canal affects the traffic intensity, i.e. the ship speeds and ‘lanes’ of operation. The cross section should have adequate depth and width for steerability and safe passage for design ships at normal speeds.
The ships’ movement causes certain phenomena, resulting in forces on canal sides and bottom. These are:
- Return flow;
- Water level drop;
- Wave generation.
These result in increasing the apparent draft of the vessel, change in the trim of a vessel, and limit the speed of travel. The keel clearance (i.e. the ratio of minimum depth of the fairway to maximum draft of stationary vessel) of the vessel should be 1.3.
The ships’ movement generates two types of waves – primary waves and secondary waves. The amplitude of the waves is a function of speed, hull shape of the ship, and the ‘blockage ratio’ (the ration of wet section of the canal to submerged cross section of the vessel). Waves increase resistance of vessel’s navigation and attack canal banks.
The resistance to the ship’s movement is, within limits, proportional to the square of the ship’s speed, and the propulsive power required is proportional to the cube of the spread.
For safe navigation, the ship requires an effective path width of 1.3 times its beam, since it cannot confine itself to a perfect straight course of on account of wind, cross currents and other forces. The minimum width of a straight channel should be 2.3 times the beam of the vessel for a single lane traffic, and 4.1 times the beam for a double lane traffic respectively. Widths get modified (increase) at curves in the alignment.
The minimum bend radius is also governed by the length of the ship. At the bends, a distance of at 5 times the length of the ship should be clear to provide an unhindered view to the pilot of the ship.
Movement under a bridge needs special parameters described above, in addition to vertical clearances of at least 0.2 meters at the highest water levels. Bridge piers need be provided with protection in he form of protective dolphins and/or fenders.
The bottom and sides of navigation canals are affected by ship induced hydraulic forces. The canals need to be suitably lined to protect from washing away of the subsoil (Chapter 4).
5. Major Canals
Most of the irrigation cum navigation canals in India were constructed over 100 years back, and designed mainly for country craft movement. These are mostly located in Orissa, Andhra Pradesh, Tamilnadu and Kerala. Some of these are Taldanda Canal, Kendrapara Canal, Eluru Canal, Commamur Canal, Buckingham Canal, Kakinada Canal, West Coast Canal, Champakara Canal, etc. DVC Canal in West Bengal is of relatively recent origin, Hijli Tidal Canal (Orissa), Sone Canal (Bihar) are some other canals.
The larger potential waterways, however, exist in the form of networks of irrigation canals like Ganga Canal, Sarda Shayak Canal, Indria Gandhi Nahar (Rajasthan Canal), Narmada Canal etc. (Chapter 5). Back