PROGRESS ON CONSTRUCI’ION - STAGE I

(Up to 30th September, 1975)

 

1.    PoIgolla Complex

 

The dam across Mahaweli Ganga with 10 hook type spillway gates, a 5 mile long 19½ diameter tunnel from Polgolla to Ukuwela in the Sudu Ganga basin were included in contract A with Ingra of Yugoslavia and the work commenced in 1970. Part of the contract with the same contractor includes the construction works of Power House at Ukuwela including the surge chamber 60’ diameter and the steel penstock 13’ in diameter between the tunnel and the Power House.

 

The supply of electro-mechanical equipment for the dam, tunnel and the Power Plant was ob­tained with 7 contracts with international bidding for a value of about 35 million rupees, mainly in foreign exchange.

 

Polgolla dam is almost complete including the installation of all the 10 gates. Final painting of gates is in progressl Work on the bridge over the dam will be completed after finishing of construc­tion of pavement by the end of 1975. This was done by the State Engineering Corporation of Ceylon

as a sub-contractor to the main contractor, along with the intake structure to the tunnel and the civil works on the Power House.

 

2.    Tunnel

 

Intake structure with the gates and control mechanism has been already completed. Excava­tion of this 5-mile-long and 194’ diameter tunnel was completed by the main contractors by March 1973. Construction took place in 4 phases, by means of an Adit, namely from the Inlet side, from the outlet and from the Adit towards the inlet and outlet. A weak zone was encountered at station 234 -‘-08 from length 68’ in early 1972 during excavation which delayed tunnel excavation considerably. This was expected according to the results of geological investigations. Structural steel supports and rock support bolts were used to strengthen the rock inside the tunnel. Rock surface inside the tunnel is being protected using concrete lining in weak sections and shotcrete lining in other areas. This tunnel protection work has already been completed. Cement grouting of the work is already com­pleted. This grout mixture fills the cavities in the rock surrounding the tunnel, under pressure. Rock-trap work and the final cleaning work of the tunnel are in progress. This work will be completed by the end of the year.

 

The excavation of 60’ diameter and 110’ high vertical shaft (surge chamber) near the downstream end of this tunnel has also been completed including concrete lining.

 

3.    Power Plant & Penstock

 

Poor foundation conditions were encountered in the power house site and it necessitated shift­ing of the original location slightly. Similar bad foundation conditions prevailed along the slope where penstock pipe is to be laid. Additional foundation treatments were required in order to stabilize the foundation before installing the penstock. This work was done by State Engineering Corporation as a separate contract.

 

A 13’ diameter steel penstock joins the tunnel just downstream of the surge chamber and goes along the tunnel beyond the outlet portal, where it bifurcates and forms 2 pipes each 9’ in diameter. The twin penstock goes down the slope and joins the two hydraulic turbines inside the power house. The work on fabrication of the penstock and erection is almost completed. Construction of the power house is nearing completion. Installation of the hydro-electric machines and control equipment are in progress. Two irrigation outlets are also provided to send water down while power plant is not working. This power plant is expected to be commissioned by mid-1976.

 

 

4.    Bowatenna Complex

 

The work consists of a dam 741’ long and 100’ high with 6 spillway gates with an earth embankment. 4-mile-long tunnels from the dam and inlet and outlet canals were given on contract to the Joint Venture consisting of Ceylon Development Engineering Co., Ltd., of Sri Lanka

and Patel Engineering Co., Ltd., India

.

 

5.   Dam

 

The work on the dam is done by State Development and Construction Corporation of Sri Lanka

on a sub-contract. A quantity of 59,080 cu. yds. of total quantity of 75,160 cu. yd. (80%) of the work on concreting dam has been completed. It is expected to raise the dam to a height of 810/ m.s.l. to enable temporary water diversion and then continue to do the rest of the work (9,800 cu. yds.) for completion thereafter. About 38% of earth embankment work has been completed. This work also will be completed.

 

6.    Bowatenna Tunnel

 

The work on the intake structure is almost complete, except the wing walls and installation of gates and lifting mechanism. Excavation and concreting for the cut and cover sections of the intake channel is already completed.

 

7:          Excavation of the tunnel has been completed which took place in 4 headings as the Polgolla tunnel using an adit. A weak zone was encountered near the downstream portal. Another fault zone was encountered in the excavation from downstream which created some drainage problems and there was about 4 ft. of water inside the tunnel flowing down for sometime. These resulted in some delay in the construction programme. Concrete lining of the tunnel surface are in progress. Struc­tural concrete lining will be completed in weak areas to a total length of 2,894 L.ft. with shotcreting over the surface in other part of the section. Concrete invert will be constructed throughout the length of the tunnel. It has been programmed to complete 6,055 L.ft. of flat concreting before the temporary diversion of which 3,160 L.ft. has been already done.

 

8.    The open canal at the end of the tunnel has been already excavated up to Dambulu Oya where a drop structure will be constructed. A bifurcation upstream of the drop structure diverts a portion of the tunnel flow to Kandalarna tank along a 5-mile-long.canal. The excavation of this canal is almost completed. Work on the structures along these canals will be completed by December 1975, along. with bifurcation structure, drop. structure. A length of 850 L.ft. of the concrete lining of the first section of the outlet canal has been completed of a total of 2,200 L.ft. Work of the other bifurcation structure that will be constructed at the end of Kandalama canal for diverting a portion of this flow to Buruluwewa via a 16-mile canal has been commenced. Excavation work of this canal is almost com­pleted, except some rock excavation and structures along this canal. These work downstream of Bowatenna tunnel have been awarded to Ceylon Development Engineering CQ., Ltd., for a total amount of Rs. 14.6 millions and these will be completed by the end of 1975.

 

9.    Sudu Oanga has to be improved between Ukuwela and Bowatenna to facilitate safe discharge of the river flow augmented by Polgolla diversion. The work on Sudu Ganga improvements were given to State Development and Construction Corporation (S.D. & C.C.) This work is in progress and will be completed by end of 1975. Further one Road

Bridge

and 9 foot bridges will be constructed by the same organisation under a different contract. The work on the road bridge and 7 Nos. foot-bridges have already commenced. This work will be completed by end of 1975.

 

10.        Elahera headworks and canal will be improved to facilitate safe discharge of the increased flow along Elahera-Minneri-Kantalai-Yoda EIa. After Polgolla diversion, irrigation systems in Polonnaru­wa and Trincomalee districts will receive sufficient water for two crops of paddy under major irriga­tion schemes. Widening of the main canal and canal structures have already been awarded to Sri tanka Construction Engineers for a sum of Rupees 2,479,499. The improvements to Elahera and Kuda Ganga anicuts have been awarded to State Development & Construction Corporation, and 60% of Elahera anicut and 68% of Kudaganga anicut has already been completed. These works will also be completed before Polgolla diversion.

 

 

11.        Two Pilot Projects have been established at Maha Illuppallama and Pelwehera Agricultural Research Stations and another one at Kantalai Sugar Cane area. Agricultural research and investiga­tion are being carried out at these places by the Agricultural Department officials according to the -requirements of the Mahaweli Development Board. Field tests are carried on cropping patterns, cater management and economic use of water, optimum farm sizes, land drainage, irrigation systems and methods, soil suitability, ground water conditions, extension services, improved farm practices, etc. The results of these pilot projects were used in the proposals for new development and improve­ments to existing developments in the Mahaweli area. A detailed Feasibility Report has been

 

prepared in 8 volumes covering Engineering, Land Classification, Settlement Planning, Marketing and Credit, Agriculture and other aspects on the proposed development- in Stage II area in the Kala

Oya Basin

.

 

12.   Results of the Pilot Project at Kantalai (200 acs.) shows the possibility of increasing the present yield of sugarcane crops and the improvements required. Also the effect of the correct use of water and the adverse effects of over irrigation have been demonstrated. These results are being used at the Sugar Plantation at Kantalai in order to increase the yield. Nearly 7,000 acres of existing sugarcane plantation under Kantalai will be remodelled based on the results and findings of the 200 acre Pilot Project.

 

13.   irrigation systems under existing irrigation schemes in D, G, H, and IH areas consisting of 126,585 acres will be improved as necessary for efficient irrigation and drainage. Special Projects have been established in these areas in order to co-ordinate and improve the services available to the farmers. The work in the improvements to irrigation and drainage systems have been already started in Kanda­lama, Kaudulla, and Rajangana Schemes. Necessary improvements to other schemes also will be taken up as required. Irrigation Department has commenced the investigation and designs required for this work. Construction works in Kandalama, Kaudulla and Rajangana are being done by MDB, TCEO and Irrigation Department respectively.