6. Design of Irrigation cum Navigation Canals
An irrigation cum navigation canal would have to satisfy basic requirements of both irrigation and navigation uses of the waterway 0 giving priority to irrigation as per the Water Resources Policy of the Government of India.
- The navigability criteria are based on
- The transport capacity
- The length of the transport linkage
- The transport demand.
The first two are functions of physical characteristics and dimensions of the canal. The third is determined by the traffic potential of the hinterland.
The transport capacity of a canal is defined as the number of ships that can be passed in each direction in a unit time multiplied by the carrying capacity.
The ‘canal lane’ is defined as “the rectangular cross sectional area formed by the lane width and the minimum water depth which would permit safe movement of a vessel of particular class.”
A simulation exercise on ships’ operational parameters has been carried out for the design vessels discussed earlier.
On the basis of this, two Navigability Criteria are recommended:
Navigability Criteria I- An existing irrigation canal, its cross-sectional parameters should be at least equal to that required for the Narrow Section for the Class I vessels i.e. the channel bottom width of 17.5 m and top-width of 22.5 m with water depth of 3.12 m. In case the requisite minimum canal width is available but the canal water depth is less than 3.12 m, it could still be considered for navigation of the Class I vessel with loading restrictions. At the minimum loaded draught of 1.2 m (requiring a minimum water depth of 1.6 m), it would have a carrying capacity of 150 T.
Even if canal cross section is very wide and deep, it still does not provide for a viable transport link unless is also has a reasonable navigable length. For this, a break-even distance based on representative cost of competing modes is looked at.
Navigability Criteria II – The canal should also have a navigable length of at least 60 km.
Based on these criteria, 18 canal stretched from those listed in Chapter 5 (vide table 5.4, last row) are found to be candidates for possible adaptation for navigation, and three others with reservations.
7. Indira Gandhi Nehar Project & Narmada Canal System
- Indira Gandhi Nehar Project
- The construction of Indira Gandhi Nehar Project is taken up in two stages:
- Stage I - 204 km feeder from Harike Barrage and 189 km long main canal.
- Stage II - Further 256 km of main canal and 5112 km long distribution system.
It is found based on the navigability criteria developed earlier, that the main canal including the feeder canal could provide navigation with Class II vessels (600 T). in the tail-end section of last 152 km, due to blockage ratio constraints, the navigation restriction would have to be imposed by way of allowing only unladen vessel to overtake a laden vessel with caution. The upper 497 km would have unrestricted navigation, with laden vessel overtaking another laden vessel with caution. Though the upper 393 km reach can support navigation of 1350 T vessels, these are not recommended on the bass of standardization and overall economics.
The Class II vessels would therefore be the design vessels for sizing up various facilities along the canal like the Locks, bridge clearances, bend radii, minimum water depth etc. it would have a turnaround time of 280 hrs (operational time), make 20 round-trips in a year, and have a throughput potential of 15.24 Million T-Km per year, or equivalently an annual transport capacity of 11740 T each way.
Hydraulic structures across the main canal do not have provision for navigation. In order to pride navigation even during periods of no discharge, 22 locks would be required with a water level drop of 3 m for 649 km long main canal, to provide a minimum navigable depth of 3.25 m.
The transport potential of this corridor is estimated to be of the order of 6000 T/Hr. the corresponding annual transport potential in each direction works out to about 21.8 billion Tkm., or annual transport capacity of 22.7 million tonnes each way over the entire stretch. Speed restrictions are estimated to reduce the transport capacity by about 15-20%.
Modifications in structures can be effected in three phases. Phases I should coincide with the completion of the Command Area Works while the Phase II & III would be dependent on the utilization of the transport capacity created and the performance of the existing canal lining.
The total modification costs for phase I, II and III are estimated to be of the order of Rs. 226 million, Rs. 620 million and Rs. 2087 million respectively.
Traffic level to break-even with annual costs is estimate at about Rs. 84.37 Million T-Km., or equivalent to 130000 T of originating traffic on the waterway or 65000 T of traffic in both upstream and downstream direction annually, or equivalent to transport of 186 T of cargo in both directions everyday for 350 days operations in a year. Back