AFTERTHOUGHTS ON THE MORAGAHAKANDA RESERVOIR.

            The Mahaweli Project Reports (MPR) were submitted to the government of Sri Lanka (then ' Ceylon') in 1968/69 by the FAO.
            The geological site investigations of the Moragahakanda Multipurpose unit, as stated in the MPR, reports that the results of 'exploratory drilling' to a depth of 100 feet had indicated that two fault zones, highly weathered and highly fractured gneiss, altogether to a depth of hundred feet, sediments to depths so much as thirty four feet, notable for their high water permeability and also possessing a high water absorption capacity of fifty gallons per minute. The recommendations of the geologists were that these fractures required careful washing and grouting.
            It therefore appears that the prevailing geological conditions at Moragahakanda were not the best for the construction of a dam and reservoir and  meant that a tremendous amount of preliminary preparatory work mentioned as ' careful washing and grouting' had to precede the actual construction of the dam proper, Unfortunately, though the investigation report mentions of the fractures and the depths of the fragmented sediments, the exact  area of the spread of the fractures is not defined. Generally, the loss of water by absorption (seepage) would be directly proportional to the area of spread at the fractures and fragmented sediments and if any of such areas escape grouting, these areas would cause seepage and lead to the loss of water in the reservoir. Actually, the construction of the reservoir cannot be contemplated as the geological investigation in incomplete because the surface area denoting the spread of the fractures, fragmented gniess in  not defined. The given geological report for Moaragahakanda could also be interpreted as an indirect message by the geologists that Moaragahakanda in not a suitable site for a reservoir and if a researcher is constructed it would only be a bucket with a gaping hole.
            The construction work at Moaragahakanda commenced after the termination of the civil war by a Chinese Construction Company, but the work proceeded only in fits and starts. The filling up of the Moaragahakanade a reservoir commenced on 11th January, 2017. One month later, on about the 10th February  2017, a news item of a state media telecast mentioned that  a tract of paddy fields of about 100 acres extent in the Hasalaka area subsided, in some places to a depth of about 10 feet. Hasalaka in about 28 kms from the central area of the Moragahakanda reservoir. One cannot stop wondering whether the water accumulating in the reservoir was seeping into the depths of bedrock through fractures of the underlying rock strata and had found a convenient subterranean path to flow beneath the Hasalaka area, causing some subsidence of cultivation land.
Yasanthe De Silva
B.Sc. (Agriculture)
           


Comments

Post a Comment

Popular posts from this blog

ANCIENT IRRIGATION SCHEMES BASED ON THE MAHAWELI GANGA.

ANCIENT IRRIGATION SCHEMES BASED ON THE MAHAWELI GANGA.             The 'Mahaweli" Development Scheme (MDS) to provide water for dry zone, Agriculture, which commenced in 1969, is preceded by an Ancient Irrigation   scheme, which utilized the Mahaweli Ganga. The ancient chronicles, the Mahavansa, Culavansa, Pujawaliya etc, the notes by Sir Emerson Tennent and Mr. C.U.Nicholas and Survey work by Mr. Henry Parker and Dr.R.L. Brohier indicate that the Mahaweli Ganga and its tributary the Amban Ganga were the perennial sources of water for the intricate   irrigation network.             4 anicuts across the Amban Ganga and 2 across the Mahaweli Ganga fed seven channels while provided water and augmented a large number of major tanks and thousands of small tanks spread in the basins of the Kalaoya, Moderagam Aru, Malvatu Oya, Yan Oya, Kantale Oya, Amban Ganga and th...
Read more

Failure of the Mahaweli Development Scheme (MDS) on Hydro power in Sri Lanka.

            By 1968, Sri Lankan hydro power engineers had established the tradition of hydro power development, through the projects at Laksapahana (50MW), Nawalakasapahana (100MW), Wimalasurendra (50MW) , samanala (75MW), Canyon I (30MW) and Canyon II (30MW) , which gave a total of 335MW, from the upper attachment area of the Kelani Ganga, Situated in wet zone up country. The catchment of the Mahaweli Ganga in the up country wet zone is several times larger than the Kelani catchment on which the above hydro projects are based.             In the early 1950s , the Irrigation department started the collection of data for the use of the Mahaweli Ganga water resources by doing the preliminary surveys and the essential investigations. Of the six water flow (current) metering stations on the Mahweli Ganga set up by the irrigation department,   two were located at Agarap...
Read more

CAN THE MAHAWELI GANGA SATISFY THE NEEDS OF THE MAHAWELI DEVELOPMENT SCHEME (MDS) ?

The Mahaweli Ganga was to supply the water requirements for irrigarion of the lowland paddy areas to be developed in the Project area of the MDS as well as for the 7 hydro power projects of Ukuwela (30MW), Bowatenne (40MW), Kotmale (201MW), Victoria (210MW), Randenigala (126mW, Rantambe (50MW) and Moragahakande (75MW) The ability of the Mahaweli ganga to supply all this water seems to have been based on the assumpion that it is a perennial water source of infinite capacity! After 49 years since the inception of the MDS in 1968/69, the belief that the Mahaweli would be able to supply this water is now suspect. Due to the shortage of Mahaweli water for both irrigation and power production, in 2016, the paddy production in the Mahaweli systems were for below the projected which entailed urgent imports of rice while the production of electricity at Victoria and Randenigala were also curtailed. At present, a substantial proportion of farmers being provided with monthly drought relief in th...
Read more