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 the North Central Province are also farmers in the Mahaweli Project areas who have been unsuccessful in their paddy cultivations due to the shortage to Mahaweli water.

The Irrigation Department commenced the collection of data about the Mahaweli water resources in the early 1950s and established 'current metering stations' at Manampitiya, Randenigala, Victoria falls, Gurudeniya, Talawakelle and Agarapatana. This was supposed to give the potential of the Mahaweli water resources. The report of the Irrigation department on the Mahaweli water resources was forwarded to the government in 1959 and it preceded the 1968/69 FAO report of the MDS. In the proposals of the MDS, 15 Mahaweli tributaries are tapped separately for the various schemes and therefore the flow of each tributary should have been studied separately for several years. The potential of the Mahaweli depends on the potential of each of 15 major tributaries and this is mainly dependent on the rainfall that each tributary catchment receives.

Based on the quantity of annual rainfall, Sri Lanka in divided in to 3 climatic zones as follows.

Climate zone	Annual Rainfall
Wet zone	more than 2500 mm
Intermediate zone	Between 1750 and 2500 mm
Dry zone	Less than 1750 mm

Apart from the quantity, there is much variation in the monthly distribution of the rainfall between these 3 zones. The water resources of the Mahaweli for the MDS are from the catchments of its 15 major tributaries in the wet and intermediate zones. The wet zone has the better distribution of rainfall with 8 continuous wet months, from April to November, in its catchments while the intermediate zone has 5 wet months (4 of October to January and 1 in April) in its catchments. Of the 15 major tributaries of the Mahaweli, 6 drain the wet zone and the balance 9 drain the intermediate zone. Although the Mahaweli catchment area in about 1/6 the of the land area of the Island, it is only the Mahaweli catchment area of the wet zone which really contributes to the MDS. If rain gauge stations were established in the catchment of these major tributaries to calculate the monthly runoff from each catchment to its tributary together with ' current metering' of each tributary, more reliable records of Mahaweli water resources could have been obtained instead of the arbitrarily located ' current metering stations' along the Mahaweli.

The details of the major tributaries and their uses are tabulated below. Each group represents its specific use and its component tributaries.

Group	Specific use	Tributary and climatic zone of its catchment.
1.	To feed Kotmale reservior	Kotmale oya - wet zone Puma oya - wet zone Pundalu Oya - wet zone.
2.	A. To feed Kalawewa + Moragahakande from the Polgolla diversion. B. To feed Victoria and Randenigala through water not diverted at Polgolla.	Hatton ganga - wet zone. Atabage - wet zone. Piga oya - wet zone.
3.	To feed the Victoria reservoir	Huluganga : 40% WZ 60% IZ Ma oya : IZ
4.	To feed the Randenigala reservoir	Belihul oya : IZ Kurundu oya : IZ
5.	To feed Rantambe reservoir	Uma oya : IZ
6.	To feed Ulhitiya, Ratkinda and Maduru oya reservoirs	Badulu oya : IZ Loggal oya : IZ
7.	To feed the Moragahakande reservoir	Suduganga (Tributary of Ambanganga) 20% WZ, 80% IZ and augmented with part of Polgolla diversion.
8.	To feed the Kaluganga reservoir	Kaluganga, (Tributary of Amban Ganga) : IZ

Comments on each group.

Group One :

Under the MDS, the Kotmale reservoir was the highest placed reservoir, with the Kotmale oya being dammed at the 2500 foot contour. If originates at about 7000 feet and flows down 48.3 inles to reach this contour. In about 2012, the Kotmale oya was dammed at Talawakelle, at about 5000 feet, to create the upper Kotmale Project (150MW). Due to this the main feeder to the Kotmale reservoir is blocked at the Upper Kotmale reservoir, although temporarily.

Group two :

At present as the waters of group one are regulated both of Kotmale and Upper Kotmale hydro power projects, group 2 forms the main Mahaweli supply to be divided at the Polgolla. One wonders whether the shortage of water at the Victoria and Randenigala reservoirs is also due to insufficient water along the Mahaweli now leaving the Polgolla barrage.

Group three :

The contribution by group 3 rivers to fill the massive Victoria reservoir for hydropower is negligible.

Group four :

The contribution by group 4 rivers to fill the massive Randenigala reservoir for hydropower is negligible.

Group five

In the future, the Uma oya water is to be divided between the Uma oya Project and the Rantambe reservoir. With the longer tributary of the Uma oya diverted to the Uma oya project, the balance to Rantambe would be far below expectations and its power supply would have to depend more on water released from Randenigala. The cost - benefits and the value of the Uma oya project, with its Uma oya supply at reduced levels for 7 months per year as well as the devastation it has caused to parts of the Badulla district due to mismanagement and inappropriate technology during its construction leaves a legacy of doubts.

The ancient irrigation schemes using Mahaweli water for dry zone agriculture commenced in 67-111AD, with King Vasabha constructing the Elahera anicut and its 20 mile transbasin canal to feed the Minneriya reservoir and continued up to the end of the reign of King Parakkrama Bahu, The Great in 1186AD, who made improvements to the Angamedilla Dam across Amban ganga and its 12 mile long canal to Parakkarama Samuddra and also made improvements to the Kalinga Nuwara Dam on the Mahaweli and its 36 mile long LB channel, the Kalinga yoda ela and its 30 mile long RB channel, the Gomati Ela. During the intervening 1119 years, 5 more Kings constructed 5 more anicuts and hundreds of miles of transbasin channels to conduct the waters of the Mahaweli which flowed, down from primeval forests, to locations now copied as the boundaries of the MDS.

The present MDS was designed between 1965 and 1968, which is only a short period of 4 years, by foreigners, who superimposed their schemes on the ancient irrigation heritage of Sri Lanka without any proper evaluation of the present day Mahaweli and in the process, irrevocably destroyed the ancient irrigation layouts and technology, resulting in the present MDS being a mirage and also spelling and the doom of the ' Ceylon Elephant'.

Mr. Henry Parker, who held the post equivalent to the present Director of Irrgation in the British Colonial government from 1873 to 1904 and recorded his observations on the Irrigation Works of Ceylon in 'Ancient Ceylon' (1909) states " If we rashly think, after a mere glance at the site (in comparison on the other hand with the actual practical experience of the Sinhalese for nearly 1000 years), that we can change all that and effect untold improvements, we may find, when too late, that they were right and we are wrong."

Yasantha De Silva.

BSc. (Agriculture)

Email: ydesilva2013@gmail.com