Mahaweli Project – North Central Province canal: A tunnel in the wilderness?
by Eng. L.V. Talagala
C Eng., B Sc. Eng (Cey), M Sc (Southampton), MIE. MASCE
former Director (System B&C), Mahaweli Engineering and Construction Agency of Mahaweli Authority of Sri Lanka.
The Mahaweli Multi-Purpose Development Project is based on the Master Plan for maximum utilisation of water resources of the Mahaweli Ganga, prepared in 1965/68. The plan envisages development of 360,000 ha of irrigable land, mainly in the dry Zone in Mahaweli and adjoining river basins designated as Systems A to M, as well as 900 MW of Hydropower. The works involve the construction of several Dams and river diversion structures, together with a network of tunnels and canals.
During the 1970-77 period the Polgolla and Bowatenna river diversion works with power stations, improvements to Kalawewa, together with some land development works in the Kala Oya basin, feeder canal to Huruluwewa, and widening of Elahera Minneriya Yoda Ela were completed. Since 1977, under the Accelerated Mahaweli Development Programme, five major projects Viz, Kotmale, Victoria, Randenigala, Rantembe and Maduru Oya Dams and Hydropower plants with the total potential of around 600 MW , downstream development of about 112,000 ha in Systems B, C, H and G, and settlement of around 100,000 farmer families were carried out. A total of around Rs,1000 m (approx. 900 m US$) has been invested and direct benefits were accrued through hydropower and agricultural production. The completed projects continue to make a significant contribution to the national economy.
The current development works commenced in 2007, after Feasibility and Environmental studies, with the construction of the Moragahakanda and Kaluganga reservoirs in the Ambanganga basin. These were completed in 2018 and 2022 respectively, at a cost of over 400 m US$, and are linked together by short canals and tunnels. The combined storage capacity is around 700 million cubic meters(mcm), which is more than the capacity of Minneriya, Parakrama Samudra, Kaudulla and Kantalai tanks together.
The water stored in these reservoirs have to be conveyed to the designated areas in the North Central and Northern Provinces for agriculture. The conveyance waterway, from Moragahakanda, is called the North Central Province Canal (Ref. Fig 1). The first 20 km of the waterway runs parallel to the existing Elahera Minneriya Yoda Ela (EMYE) on a higher elevation contour and gradually turns in a Northerly direction along the centre spinal ridge that divides the river basins flowing to the west and eastern coasts of the island to end at Chennadikulam tank. This would be the most expensive and the longest (155 km approx.) waterway in Sri Lanka.
The construction work is undertaken under the North Central Province Canal Project (NCPCP) in two stages and implemented by the Mahaweli Water Security Investment Project (MWSIP) under the Ministry of Irrigation with ADB funding. A sum of around 600 m US$ is committed for the next few years for the construction of NCPCP Stage 1 works and is expected to be completed in 2026. The work involved for Stage 2 is yet to be finalized and would cost over 500 m US$. Additional costs will be incurred for Downstream Development works including the provision of irrigation facilities for the agricultural lands. (See Fig 1 and Fig 2)
North Central Province Canal Project (NCPCP) – Stage 1
(also referred to as Upper Elahera Canal (UEC) (Ref. Fig 2)
The NCPCP Stage 1 works involve
the construction of the first 65 km, of the conveyance waterway of capacity 40 m3/s, with 27 km long Tunnel and the upstream and downstream canal sections, for conveyance of water from Moragahakanda reservoir to a Trifurcation structure at Yakalla close to Huruluwewa. From this Trifurcation structure three branch canals will take off. One feeding Manankattiya, Eruwewa and Mahakanadarawa tanks in the Anuradhapura district. The second to Huruluwewa tank and the third branch will be an extension of UEC (NCPCP Stage 2), a further around 90 km up to Chennadikulam around Vavuniya, to feed new and existing tanks for development of mainly new lands. It is expected to convey around 500 mcm of water after Stage 1 and a further 500 mcm after Stage 2, a total of around 1000 mcm at final completion. Accordingly, only around 50 %of the tunnel capacity will be utilized on completion of Stage 1.
The canal sections should be completed at the time when the Tunnel, which is progressing satisfactorily with 2 Tunnel Boring Machines (TBM), is completed in 2026 to convey water to the expected destinations. The water conveyed at such high cost, is so precious, like gold, at this point and each cubic metre should be used wisely to obtain the best economic returns as soon as it is available.
Water Availability – Stage 1
Moragahakanda Reservoir of storage capacity of around 550 mcm is the focal point for water distribution of the system. It receives water from its own catchment through Ambanganga, Mahaweli water from Polgolla through Bowatenna and from the Kaluganga reservoir through the Link canal. After meeting the present commitments to the Elahera Anicut and additional requirements to meet. deficits in the tanks fed by the Elahera Anicut, the water availability for diversion through Stage 1 works at the Trifurcation structure at Yakalla is estimated at around 450 mcm. This is a very large quantity equivalent to about the combined storage capacity of four major irrigation tanks, viz Minneriya, Kaudulla, Parakrama Samudraya and Kantale.
From the Trifurcation at Yakalla, around 110 mcm will be diverted through branch canals, to the designated existing tanks in the Anuradhapura district to meet the irrigation deficits and water supply requirements. Accordingly, around 450-110 = 340 mcm of water is available for development of new lands for irrigated agriculture through the extension of the UEC.
Downstream Development
Downstream Development is the term used for the land development and provision of irrigation facilities for agriculture together with the social and other facilities for maximum production. Getting carried away with large dams, vast expanses of water, long tunnels, with sophisticated tunnelling equipment, and other heavy engineering works and to forget the downstream development activities has to be resisted.
With possible savings in water use, there would be at least around 350 mcm, equivalent to about the combined capacity of Minneriya, Kaudulla and Kantale tanks, for the development of at least 15,000 ha (40,000 ac) at a water usage duty of 2m. The area can be increased with time with efficient water management practices.
Sri Lanka is now nearly self-sufficient in rice and further investment to increase extent under Paddy cultivation is not needed. What is necessary is to enhance paddy yields to feed the increasing population. It is now essential to cultivate other crops for import substitution, for exports and to create allied economic activities in the newly developed lands. Hence all efforts need to be directed for modernized intensive irrigated agriculture as the President emphasizes in most of his speeches and discussions with relevant officials. Engagement of the Private Sector in this effort may be useful with suitable government administrative mechanisms to realize the desired objective.
A complex set of activities will be involved in the Planning and Construction of downstream development works with relevant items for consideration are identified below.
* Identification of probable land considering proximity to conveyance system, ownership, resettlement issues, etc.
* Suitability for agriculture, soil types etc.
* Selection of crops (cash crops, sugar cane, fruit, vegetables, horticulture, and other high value crops), Cropping Calendar, etc. Paddy under flood irrigation should not be encouraged except in existing small tank cascades.
* Settlement planning activities, selection of suitable farmers etc.
* The present system of allocation of 1 ha to each farmer has led to subsistence farming, with many continuing to be below the poverty line, and sustainable intensive irrigated agriculture envisaged would not materialize. New workable model to be worked out (E.g. Cooperative societies made up of individual farmers to run a large extent, Management by private companies with emphasis on the commercial aspect, Mechanization, etc.). Private investment in on-farm development including modern irrigation methods (furrow, sprinkler, drip irrigation, harnessing groundwater, etc.) to be encouraged.
* Farmer organizations should be more involved in equitable water distribution, facilitate agricultural services to farmers, marketing aspects, etc., and less on political activities.
* Design and Construction of irrigation facilities to suit cropping systems and farming models. Designs to incorporate measures for reduction of seepage losses, canal controls, night storage, reuse systems, demand water issues, conjunctive water use and other state of the art systems. Extension of UEC may be needed, if so design to required capacity with provision for future expansion
* Environmental, Wildlife and forest conservation.
* Provision of social infrastructure facilities.
* Marketing and Storage facilities. This aspect is very important as previous attempts for crop diversification failed manly due to lack of proper storage and marketing facilities
* Packaging, Processing and Agroindustry.
* On-farm Water Management and O&M
* Other related activities
All these activities should be in place with related infrastructure to utilize this golden resource, probably by the end of 2026. Completion of all Stage 1 construction works; downstream infrastructure works and development activities should be taken up immediately as a priority. If all activities are not properly planned and implemented the huge investment made would lie idle without yielding any return and only add to the debt burden.
North Central Province Canal Project (NCPCP) – Stage 2
The Stage 1 conveyance system (UEC) has been designed for 40 m3/s discharge capacity and expected to convey around 1000 mcm annually, on the basis that an additional 500 mcm is diverted from Randenigala and tapping water resources in Hasalaka and Heenganga tributaries on the eastern slope of the Knuckles range on-route to Kalu ganga during Stage 2 works.
Water Availability
At planning stage, it is intended to transfer around 500 mcm of water from Randenigala reservoir to Kaluganga and then to Moragahakanda reservoir through a system of Canals, Tunnels and Dams (Total length of around 40 km) This configuration would cause a huge loss (almost 25%) of peak power at existing power stations of Randenigala and Rantembe, which is not acceptable. In addition, there will be a reduction of water issues for irrigation from Minipe Anicut into systems B, C and E. Therefore, alternative conveyance routes and water sources have to be identified for conveyance of more water, around 500 mcm, through NCPCP Stage 2 works into Moragahakanda Reservoir.
An alternative conveyance route (Ref. Fig 3) is to let all water pass through power stations at Randenigala and Rantembe up to the Minipe Anicut, as at present, and then to divert the excess, through LB canal up to Existing Hasalaka reservoir. From here water to be pumped, may be in 2 Stages as a high lift will be involved, to the new upper Hasalaka Reservoir on the planned Randenigala Kaluganga route and then to follow the planned route through Heenganga into the Kaluganga reservoir.
The advantages of this alternative are that,
(i) there will be no reduction in power at existing Power stations at Randenigala and Rantembe,
(ii) not necessary to hold Randenigala (FSL 232) at high water level to allow gravity flow into Kaluganga (FSL 210). avoid expensive Tunnel (20 km) and inlet, outlet structures from Randenigala to Upper Hasalaka Oya lying through environmentally sensitive forest land in the Knuckles range and also avoid difficult operational conditions.
(iii) the possibility of incorporating Pump storage systems to generate Hydropower with the Pumping stations on the Reservoir cascade, of Upper, Intermediate and existing, dams on Hasalaka Oya.
(iv) no reduction of irrigation issues and curtailment of future developments in System B.
(v) less expensive than the proposed configuration.
The disadvantages are that
(i) power requirement for Pump stations at Hasalaka Reservoirs and associated operating costs. This can be overcome as Pump stations can operate at non peak hours with pump storage systems, and solar power can also be used for pumping.
(ii) the existing Minipe canal would have to carry the increased discharge. Whether the present canal can carry the additional discharge needs to be studied. If not, widening may be necessary mainly in the cut sections and probably modification of some structures. All depends on the water availability and at what time.
Another option, as suggested in previous studies, is to pump the drainage water in Mahaweli at Kalinga Nuwara to a new reservoir at Angamedilla and then to pump into Minneriya. This amount of water can be reduced from Moragahakanda issues to Elahera and transferred through the NCPCP.
A combination of both options may be necessary to meet the full requirement of the NCPCP, and need to be decided after further studies
Downstream Development
Together with the works of the extension of the NCPCP from Yakalla Trifurcation Northwards to the Chennadikulam a distance of around 90 km and the associated downstream development of the new lands needs to be undertaken. A large extent of new lands in systems J, K, L and M are available for development. It will be necessary to improve the existing tanks and construct new reservoirs to utilize the runoff in the basins during the rainy season and use the water from NCPCP to supplement the available water resources. (See Fig. 3)
4. Conclusions
While retaining the present emphasis on completing the infrastructure of NCPCP Stage 1 by 2026, with ADB funding it is necessary to focus on the downstream development works and activities to realize benefits as early as possible.
The water balance studies need to be updated with operational data from the new reservoirs and with pragmatic assumptions before commencement of NCPCP Stage 2 works to ensure that the new infrastructure built is not over designed.
The investment is too large for decision making on water resources allocations, when and where to invest to be left to an implementation agency, funding agency and consultancy firms. Establishment of a high-level steering committee with advice from multidisciplinary technical experts for directing and monitoring all activities is suggested.
Note
All analyses are based on the experience and studies made by the author with data and information from EIA report (MCB, Jun 2014, Updated Master Plan Study (SMEC 2016), MASL and ID websites and other sources.
