Impact of past and present irrigation works on reconciliation


By Neville Ladduwahetty

Although there was a degree of awareness of the stupendous irrigation monuments built by our ancient Kings to make the "land fruitful", as stated in the Mahavamsa, it was the pioneering work of dedicated and committed British Surveyors and Governors such as Sir Henry Ward in particular, during early British colonial Ceylon who first recognized the potential of these centuries old relics that were buried in the tide of the jungle. Their records and observations became the foundation for the seminal masterpiece of R.L. Brohier’s "Ancient Irrigation Works in Ceylon", that first formally documented the awe inspiring unique engineering achievements of our creative ancestors.

The need to exploit the economic capabilities of these ancient irrigation wonders of a glorious past caused Statesmen, in particular, Hon. D.S. Senanayake, first as Minister of Agriculture and Lands and later as Prime Minister, to restore some of these ancient irrigation facilities during pre- and post- independent Sri Lanka. With time, and the conceptualization of exploiting the irrigation and power generation potential under the aegis of the Mahaweli Development Plan, a technologically ingenious past and a modern technology blended together to create a truly integrated network, the likes of which are unparalleled and therefore unquestionably unique. This fruition of the past and present took place first with the diversion of the Mahaweli waters at Polgolla in the late 1970s, and most recently with the completion of the final phase of the Accelerated Mahaweli Development Plan, which was the construction of the Moragahakanda Reservoir.

The critical feature that links the ancient past with the modern present is the major tributary of the Mahaweli – the Amban Ganga. The link with the ancient past is made possible by means of an anicut across the Amban Ganga constructed by kings as early as the first century AD at Elahera, and perhaps extended later to divert water through a major artery, the Elahera canal, to the ancient tanks at Minneriya, Kaudulla, Kantalai and Giritale, while the Parakrama Samudra receives water directly from the Amban Ganga by means of an anicut at Angamadilla and a Yoda Ela. The link with the modern present is made possible by diverting waters of the Mahaweli at Polgolla and then diverting part of the waters from Polgolla to the Kala Wewa basin, and the rest to the upper reaches of the Amban Ganga, to fill the recently completed Moragahakanda Reservoir.

One question that needs to be explored is whether there is sufficient water in the collective system to meet the desired objectives. Such an exploration would first require the determination of water availability to fill the five major ancient tanks, namely, Minneriya, Kaudulla, Kantalai, Giritalle and Parakrama Samudra from their respective catchments, with any shortfalls being augmented by discharging water stored at Moragahakanda through the Elahera canal and directly from the Amban Ganga.

Since the total storage capacity of Minneriya, Kaudulla, Kantalai, Giritale and Parakrama Saudra is 439,500 acre ft. and the storage capacity of Moragahakanda is 422,000 acre ft., the operation of the entire system would require a total of 851,000 acre ft. of water. The material presented below explores the availability of water to fulfill this collective need, bearing in mind that part of this requirement would be met from waters from the respective catchments associated with each of the tanks.

The material presented below is based on the following sources:

1. Rainfall figures over a 30 year period based on certified information provided by the Meteorological Dept.

2. Storage capacities and catchment data of ancient tanks based on data reported in "Water Resources of Ceylon" (1969) by S. Arumugam, Senior Deputy Director Irrigation Department.

3. The Runoff Coefficient is based on data from the Hydrology Division of the Irrigation Dept. This figure represents the proportion of the rainfall that runs off into rivers or collects in tanks, after evaporation and retention on the surface or underground. Furthermore, although this coefficient varies with the type of soil in the catchment area of each tank the figure of 30% assumed is very high when compared with the figure of 16% cited for Manampitiya - the area closest to the ancient tanks in the Hydrology Division report.

Total shortfall = 243000 acre ft

Despite the high figures assumed in respect of rainfall (2000mm) and runoff (30%) the shortfall of 243,000 acre ft. that represents 57.5 % of the storage capacity of Moragahakanda is needed to augment all five tanks to their full capacity. This has to be released from the Moragahakanda reservoir through the Elahera canal and directly from the Amban Ganga. This also means that since this quantity of water is available mostly during the North East Monsoon from October to March of any year, and since Moragahakanda is located above the Elahera Canal, any storage at Moragahakanda is possible ONLY AFTER the 57.5% of the storage capacity of Moragahakanda is released to the five ancient tanks.

Since storage at Moragahakanda would be at the tail end of the NorthEast Monsoon, the waters that could be stored would only be that amount of water that could be diverted from Polgolla to Amban Ganga, and from any rains from a weakened North East Monsoon plus that from the South West Monsoon. Whether such depleted quantities would be sufficient to serve the intended purpose of Moragahakanda in respect of power generation and delivery to the Upper Elahera Canal which is reported to be currently under construction should be given serious consideration.

The conclusions presented above are based on an approach that is simple and straightforward. Furthermore, it is based on assumptions in respect of intensity of rainfall of 2000mm. which is nearly 80 inches; a figure generally considered as typical for the wet zone. Such intensities of rainfall and less have occurred in 24 of the 30 year period in the Meteorological Department data. On the other hand, if the intensity of rainfall is around 1500mm and less (60 inches), the shortfall would not only be much larger but also such intensities could occur over 12years of the 30 year cycle. Combining these intensities with more realistic figures for runoff coefficients would mean requiring a considerably larger quantity of water being needed to fill the five ancient tanks. This would seriously impact on the amount of water that could be stored at Moragahakanda for generating power and for diversion to the Upper Elahera Canal. Since all these functions are intended to be fulfilled concurrently without interuption, there is serious concern whether Moragahakanda could fulfill its multiple functions for which it was built.

Prior to the construction of Moragahakanda, the North East Monsoonal rains ran freely down the Amban Ganga and augmented the shortfalls in the five ancient tanks. This enabled the vagaries of the Monsoon to be accommodated. However, with the construction of the Moragahakanda Dam, the release of water to these five ancient tanks would be limited to the discharge capacities of its sluices. Whether this would impact on the ability to fill the five ancient tanks in time for agricultural needs, would become apparent with time; a fact that would reflect on the prudence of constructing the Moragahakanda Dam in the first place.

These conclusions could be challenged by authorities who claim that sufficient water is available to fulfill the intended multiple purposes for which Moragahakanda was built based on sophisticated computer models deployed for managing water distribution efficiently. If this is in fact the case, those responsible have a bounden duty to present hard and credible facts to demonstrate and assure the public that there is no cause for concern, instead of making general statements that water could be supplied to the North.


With the diversion of water from the Mahaweli at Polgolla, and the construction of the Moragahakanda Dam across the Amban Ganga – the major tributary of the Mahaweli which had served to deliver water to five major ancient tanks, Minneriya, Kaudulla, Kantalai, Giritale and Parakrama Samudra, built by our ingenious ancestors starting from the first century AD - the final phase of the Accelerated Mahaweli Development Plan was concluded, thus blending the ancient past with the modern present. Based on the material presented above, the Moragahakanda Reservoir thus becomes the key nodal point from which it is expected to service a multiplicity of demands, such as making up the shortfalls to the five ancient tanks, the generation of power, as well as the diversion of water to the North through the Upper Elahera Canal, reported to be currently under construction.

Any inability to meet all three demands would mean having to prioritize between the competing demands. Apart from power generation which may not be such a priority, failures in balancing the other two demands mentioned above have the potential to trigger serious political and social repercussions, with implications on reconciliation. Any interruptions of deliveries or priority given to either the five ancient tanks or to the Upper Elahera Canal would impact seriously on livelihood issues of those in affected regions; issues that would be interpreted in ethnic terms giving cause for exploitation by interested parties.

People in the North have waited for decades for water from the South. The completion of Moragahakanda and the ongoing construction of the Upper Elahera Canal symbolize the fulfillment of a long awaited dream. Therefore, there is a compelling reason that absolutely no chance exists for any disappointment that could give rise to frustrations of a scale that could be the cause for ethnic based instability.

If the ongoing projects associated with Moragahakanda, such as the Upper Elahera Canal are being undertaken after a serious study, there is an obligation on the part of those who conceptualized these schemes to present the facts and justify their determinations in order to clear misgivings that are being expressed privately. On the other hand, if after review there is sufficient evidence that the decisions reached are flawed and that interruptions are a real possibility, there is a compelling need to undertake a serious study. If there is sufficient reason to acknowledge that there exists an issue of insufficient water to meet the two most critical demands, namely, water to the five ancient tanks as well as to the Upper Elahera Canal, there is an urgent need to bring such findings to the attention of the decision makers. Therefore, it is imperative that the truth in all its starkness be ascertained and made public, if serious consequences are to be prevented. Not to do so is to be socially irresponsible.

This should be followed up by investigating alternative approaches to resolve these issues, because what is at stake is that choices made in distributing water between the ancient tanks and the Upper Elahera Canal would not only affect the livelihood and wellbeing of all the people in the regions supplied by the system, but that it also has the very dangerous potential of being interpreted in terms of ethnic based human rights with deliberate intent. Therefore, while the politicians are engaged in how to stay in power or how to secure power, the technical people should act responsibly and address these issues with the seriousness they deserve as a national priority, if water is not to become the cause for the revival of future conflicts.

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