“President Mahinda Rajapksa and Iranian President Mahmoud Ahmadinejad will lay the foundation to divert Uma Oya for the nenefit of Hambantota and Monaragala districts on April 29. It is understood that this will be followed soon by an another ceremony where the President of Iran, Mahmoud Ahmadinejad and President Mahinda Rajapaksha will grace the occasion.”____________________________
by G.T.Dharmasena
(April 25, Colombo, Sri Lanka Guardian) It has to be noted that it is not logical to assume that all available water at the dam sites can be diverted due to the downstream water requirements and also due to the rapid fluctuations of water levels in the river caused by flash floods. From detailed studies it was found that from the annual total of 211 MCM of water volume only 130 MCM can be diverted to Kirindi Oya based on the most recent estimate of 211MCM of total water. Based on this, the annual generation of power was estimated as 175 Gwh. This is a reduction of 56 % in comparison to the estimate of 312 Gwh made by the consultant SNC-LAVLIN.
Former Director General of Irrigation and presently the Consultant to the United Nation’s Office for Project Services in Sri Lanka (UNOPS)
President Mahinda Rajapksa and Iranian President Mahmoud Ahmadinejad will lay the foundation to divert Uma Oya for the nenefit of Hambantota and Monaragala districts on April 29. It is understood that this will be followed soon by an another ceremony where the President of Iran, Mahmoud Ahmadinejad and President Mahinda Rajapaksha will grace the occasion.
This planned reservoir by the Department of Irrigation brings benefit to both districts by providing much needed water for the development of 2000 ha of arid lands in Monaragala and industrial and drinking water needed for the development of mega city at Hambantota including the Hambantota harbour and Weerawila international air port in addition to 312 Gwh of annual electrical energy needed to the industrial sector.
According to the proposal, Uma Oya water will be diverted to Kirindi Oya at Welimada via a 24 km long tunnel. The 90 MW power house will be located at Wellawaya. The cost of the project was Rs.16,000 million in the year 2000 and funds for the project were assured by the government of Iran as a gesture after the recent visit to Iran by the President.
This decision to lay the foundation stone to divert Uma Oya water to down south, prompted me to unearth some background information of this major multi-purpose scheme.
It has to be noted that soon after the laying of the foundation for the gigantic Moragahakanda reservoir in the Mahaweli basin in January 2007 by the President, laying of the foundation for the construction of the Rambukkan Oya reservoir in Ampara District took place, a month later. Minister for Irrigation, Chamal Rajapaksha laid the foundation for this project. These three projects can be viewed as significant and historic events in water resources development during the recent past.
Previous studies carried out on Uma Oya
Uma Oya is a major tributary of Mahaweli Ganga originating from Nuwara Eliya. The Oya traverses Welimada and Kandaketiya in Badulla district. Its confluence with Mahaweli Ganga is just above the Rantabe reservoir. The drainage area of Uma Oya is about 700 sq.kms. Studies for the development of water resources of Uma Oya have been made from time to time mainly for the purpose of hydro power development in the Mahaweli basin. From the early planning stage of the Mahaweli Development Programme, several proposals for the development and utilisation of water resources of the Uma Oya basin have been made by United States Operations Mission (USOM) and the Canadian Hunting Survey Corporation (CHSC) as early as 1959. Later UNDP/FAO Master Plan studies (1968/1969) for accelerated Mahaweli programme proposed the construction of the Upper and Lower Uma Oya reservoirs.
Later the "Master Plan for the Electricity Supply in Sri Lanka" carried out by the Lahmeyer International Company in Germany during 1988-1989 identified three-stage development in Uma Oya to generate hydro power. Subsequently the concept of three stage development of the Master Plan Study was reviewed in 1989 by a panel of experts from Germany and recommended a two-stage plan.
The Government of Sri Lanka launched the accelerated water resources programme of Mahaweli Ganga in 1978 with a view to increase the production of food and power and to alleviate unemployment. However no attention was paid to the development of Hambantota, Monaragala and Ampara districts. While large extents of suitable land are available in these districts, the lack of adequate water resources acted as a major constraint for development. The need to augment water resources of the area became a vita when pursuing a development policy based on irrigated agriculture as the fundamental economic activity. Among identified possibilities, the trans basin diversion of water from the upper catchment of the Uma Oya into the Kirindi Oya basin appeared to be one such option.
In view of that, a pre-feasibility study of the Uma Oya Multi-purpose Project (Trans basin option) was carried out by the Central Engineering Consultancy Bureau (CECB) in 1991. While looking for various possibilities for augmenting irrigation water supplies to this dry zone region, the CECB conceived a multi-purpose scheme for the development of the Uma Oya water resources as an alternative to the in-basin hydro power development. According to this concept, water from the Uma Oya would be diverted through a 24 km tunnel to the upper Kirindi Oya basin to augment the Kirindi Oya flow and in the process generate a large quantity of electrical energy per annum, utilizing the drop of about 550 mg in a single-stage power development.
The latest study of the Uma Oya basin is the trans-basin scheme prepared by SNC Lavalin Inc.(Canada) in 2000. This study was aimed at a comprehensive evaluation and assessment of the best scheme, from in-basin and trans-basin alternatives which have previously been studied. The consultant, SNC-LAVALIN, recommended the trans basin diversion option based on the conditions prevailing at that time.
The proposal in a nutshell is to construct a medium high dam across Uma Oya and a small dam across Mahatotila Oya, which is a tributary of Uma Oya with its confluence at Etampitiya. It is proposed to divert 192 mcm of water annually through a 23.2 km long tunnel to a underground power house at Randeniya on the right bank of Kirindi Oya, The installed capacity of the power house is 90 MW to produce 312 GWh of electrical energy. The water released from the power house will be used to supplement Handapanagala and Lunugamvehera Reservoirs in addition to 5000 ha of new land cultivated in Wellawaya, Buttala areas in Monaragala district. The total cost of the project in year 2000 was Rs.16,000 million.
Water availability
The key issue regarding the development scenarios discussed for the development of water resources of Uma Oya is the assessment of water availability of Uma Oya by different consultants at different times. According to Lahmeyer International the flow at the Welimada stream gauging site which is slightly upstream of the diversion site was estimated as 258 MCM. The NEDECO Hydrological Crash Program(HCP) in 1980-1984 ,had the principal objective to review the status. According to NEDECO study the annual average flow at the dam sites,which intercepts 254 sq.kms of Uma Oya catchment can be interpreted as 188 MCM and the NEDECO also had expressed their concerns over the poor quality of historical data at the river gauging site in the Uma Oya. The pre feasibility study carried out by the CECB in 1991 reported 277 MCM of annual flow. According to the more recent study by SNC-LAVALIN Inc the water availability at the proposed site was estimated as 228 MCM of annual flow. The most recent review of the water availability by the Ministry of Irrigation was 211 MCM.
Development...
In view of the above, the reason for this drastic difference in the estimates was a matter of concern. All previous reports on Uma Oya reported unreliable and poor quality of available hydrological data.
Diversion of water
It has to be noted that it is not logical to assume that all available water at the dam sites can be diverted due to the downstream water requirements and also due to the rapid fluctuations of water levels in the river caused by flash floods. From detailed studies it was found that from the annual total of 211 MCM of water volume only 130 MCM can be diverted to Kirindi Oya based on the most recent estimate of 211MCM of total water. Based on this, the annual generation of power was estimated as 175 Gwh. This is a reduction of 56 % in comparison to the estimate of 312 Gwh made by the consultant SNC-LAVLIN.
Recent developments in the region
a. For the development of international airport at Weerawila about 1500 ha of irrigable lands under Lunugamvehera reservoir is to be taken over for infrastructure development. Therefore present demand for irrigation water under Lunugamvehera will be reduced by 25%.
b. The Menik Ganga reservoir nearly completed will bring 60 MCM of water to Lunugamvehera from Menik Ganga basin to meet the previous shortage which existed at Lunugamvehera when the total irrigable new lands under the reservoir was 6000 ha.
c. The Kumbukkan Oya is a major river in the Monaragala district discharging about 470 MCM of water annually to the sea. There is no possibility of utilizing this water within Kubukkan Oya basin due to the geographical location of the Yala National Park. Most of the irrigable lands lie within the sanctuary and therefore this water has to be diverted to an another basin for development. One of the most attractive diversion proposal is to divert this water by damming Kubukkan Oya at a suitable location to Veheragala reservoir in Menik Ganga basin via a trans basin canal. Then this water can be diverted from Veheragala reservoir to Lunugamvehera via the existing system.
d. At present Uma Oya water goes through Rantabe reservoir by developing certain amount of hydro power. It also supplements the irrigation water supply to System B(Maduru Oya) and System C of Mahaweli basin. Hydro power development capacity is higher in the in-basin proposal in comparison to the trans basin diversion proposal.
In view of the above it is expected from the officials engaged in the planning of the final lay out of the project to take following matters into consideration during the initial stage of the implementation of this project:
I. The water availability in Uma Oya has to be refined by an intensive hydrological study using the current techniques and most recent hydrological and land use data.
ii. Down stream Irrigation and water supply requirements within Uma Oya below the dam sites should be thoroughly assessed.
iii. Environmental and social implications due to the diminished flow in Uma Oya and acceptable minimum flow have to be established.
iv. The impact on Mahaweli system C (Aranaganwila) and B (Maduru Oya) as a result of the diversion has to be considered.
v. Based on a critical review of water availability in Uma Oya for trans basin diversion, it is appropriate to review the economic viability of the project once again.
- Sri Lanka Guardian
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