Effects of Construction and Operation of Mini Hydropower Plants on Fish Fauna Endemic to Sri Lanka – A Case Study on Kelani River Basin

Conference Paper · October 2015
Prof. E. I. L. Silva
Water Resources Science and Technology
R.A.S.N. Jayawardhana, N.P.P. Liyanage and E.N.S. Silva
Uva Wellassa University
Published by Rainforest Protectors of Sri Lanka with Permission from the Author Prof. E.I.L. Silva


The establishment of small hydropower schemes has become a lucrative business today considering streams and rivers as hydraulic systems rather than living ecosystems. It is assumed that the negative effects of construction and operation of small hydropower are small because of relatively small generation capacities in comparison to large hydropower projects. The operation of small hydropower plants in Kelani River basin was investigated with special emphasis on power generation capacities and affected stream stretches between the intake weir and the powerhouse. Detailed studies were conducted at Wee
Oya, a major tributary of the Kelani on habitat alteration and fish fauna endemic to Sri Lanka in relation to small hydropower operation. The Kelani River has 31 mini hydropower plants with total generation capacity of 56 MW ranging from 0.060 MW to 9.928 MW per power plant. The results show that the length of the affected stream stretch is a function of the generation capacity of the power plant. The percentage of natural stream loss is high in Kehelgamu Oya (60.3 %) and Maskeliya Oya (62.9%) due to previously established major hydropower schemes whereas the high percentage of natural stream loss computed for Seethawaka Ganga (43.8 %) can be attributed to the large number of mini hydropower plants. A marked decline in fish population and a number of endemic fish species were found in the Wee Oya, which has four operational mini hydropower plants within 24 km stream length with 32.5% loss of natural stream. Although, 18 endemic fish species have been recorded from the Kelani River basin, only three species were reported from the Wee Oya during the present study.



Small hydropower (SHP) generation by arresting mountain streams is being viewed as environmentally benign energy source compared with large dams and fuel fossil combustion as it has no effects on global climate change (Egrea and Milewski 2002). They can, however, exert multiple negative effects locally, especially on riverine and riparian ecosystems and eventually on aquatic biodiversity and human health of riparian communities, but reported studies on these aspects are hardly any (Bhushan et al. 2013). Ecological risk of cascade operation of SHP established on the trunk stream poses adverse effects, as it leads to almost drying up of the natural river channels during dry season (Bhushan et al. 2013, Silva et al.2013) whereas small hydropower plants affect not only fish but also ecological integrity of lotic ecosystems. Apparently, the present knowledge and findings have fueled that principles of ecosystem science need to be fully integrated into water resources planning and management (Poff 2009). Unfortunately, these aspects have been ignored to a greater extent by project approving agencies in developing countries when permissions are granted to establish and operate SHPPs on hill streams that are rich in endemism. Nevertheless, developed countries pose direct or indirect taboos or rigid environmental legislation discouraging entrepreneurs with respect to small hydropower development. If SHPPs are designed, constructed, monitored and managed stipulating correct norms, can minimize the effects on the ecosystems and some eco-friendly examples are there in the western world as well as shown for ancient irrigation in Sri Lanka by Silva et al. (2014).

Sri Lanka has the SHP potential of about 400 MW according to Ceylon Electricity Board and the government has encouraged and facilitated private sector to undertake the development of SHP ventures with flexible power purchasing agreements as the country has already tapped almost every potential sites for large hydropower developments. A preliminary study conducted on Mahaweli Areas by Water Resources Science and Technology (WRST) revealed that the construction and operation of seven SHPPs within 23 km stretch on Sudu Ganga (= River) in the Mahaweli River basin has significant negative effects on fish fauna (Silva et al., 2013). As Sri Lanka is identified as a biodiversity hotspot with rich endemic ichthyofauna confined to hill streams, the present study extended to the headwater streams of the Kelani River with special emphasis on Wee Oya, flowing from See Forth to Yatiyantota. The focus of the extended study was to collate necessary information to determine the gravity of poorly designed and scientifically unsound construction and operation of small hydropower plants on ichthyofauna endemic to Sri Lanka with a view to transferring knowledge on the importance of maintaining ecological flow in streams and rivers to sustain aquatic biodiversity evolved for millions of years.


Materials and methods

Study site

Kelani River, the 4th longest river in the country (145 km) with the 2nd largest watershed (2292 sq km) drains exclusively the wet zone including the central mountain massif and discharges 5389 MCM annually into the Indian Ocean. The watershed of the Kelani River receiving maximum rainfall of 5500 mm/yr is located in densely populated and most fertilized wet zone of the island with elevation ranging from mean sea level to above 2000 m AMSL. The river basin is boarded by Kalu Ganga in the highland and Bolgoda Lake in the lowland from South and the Hatton Plateau and Dolosbage Hills from east and northeast respectively. The northeast and northwest boundaries of the watershed are marked by the divide between the westward flowing rivers, the Maha Oya and Attanagalu Oya respectively. The headwaters of the Kelani River rise on the western flanks of the central mountain massif (Peak Wilderness) as Hambantota Oya and Maskeliya Oya. Both tributaries have been arrested creating two hydropower reservoirs namely Castlereagh and Maussakelle respectively. The Kehelgamu Oya, rises as the Hambantota Oya has been dammed again at Norton Bridge for generation of hydropower and then flows parallel to Maskeliya Oya until they merge together at Broadlands Estate forming the Kelani River
proper. The Kelani River turns almost westward and flows up to the Pallegama Estate where it turns northwards twice (with a westward bend) before it intercepts Yatiyantota town and merges with Wee Oya (Figure 1). The river turns south-westward at Yatiyantota town and flows 4.8 km downstream up to Karawanella town where it shows a sharp northward turn and flows further 3.2 km downstream up to Ruwanwella town where it bends southwestward and merges with Gurugoda Oya, which receives water from Ritigaha Oya on its left bank. Seethawaka Ganga, the largest left bank tributary of the Kelani River
merges with the mainstream 10 km downstream of Ruwanwella township (Figure 1).

The Seethawaka Ganga, whose headwater tributaries are rising from Kitulgala-Maliboda range drains the area by five main tributaries called Kadiran Oya, Mandagal Oya, Halthura Oya, Naye Ganga, and Magal Ganga. The confluence of these tributaries gives rise to the Magala Ganga, which is also fed by three other tributaries on its right bank (Panamura Oya) and left bank (Miyanavita Oya and Kumburugama Oya) forming Seethawaka Gganga. After the confluence with Seethawaka Ganga, the Kelani River flows westward up to Crow Island while receiving several minor left and right bank tributaries and empties into
the Indian ocean (Figure 1).

Wee Oya: Wee Oya (= stream), a left bank tributary, which merges with the mainstream of the Kelani River at Yatiyantota rises from Dolosbage hills and Ampana forest. The stream draining the Dolosbage hills merges with Monera Ela whose headwaters are confined to Ampana forest forming Wee Oya, which is also fed by Kandal Oya and Andhadola on its left bank and several other minor tributaries on its way to Yatiyantota. Between See Forth and Yatiyantota, the Wee Oya flows parallel to the Yatiyantota-Ginigathhena road (B482) for 25 kilometers with a steep gradient performing a diverse flowing pattern including waterfalls, riffles, pools, and cascades. Some lateral tributaries and the mainstream of Wee Oya contribute to form several waterfalls including Olu Ella, the fifth highest waterfall (200 m) of the country, which merges into the Wee Oya at Punugala on its left bank.

Preliminary data on mini hydropower development in the Kelani River basin were collected from relevant government institutes (viz., Sustainable Energy Authority, Central Environmental Authority, Ceylon Electricity Board, and Public Utility Commission of Sri Lanka). With reference to available geographical coordinates, Google Earth Pro images were used to locate the mini-hydropower schemes that are in operation or under construction in the Kelani River basin. Following the validation of geographic positions of mini hydropower plants, the stream lengths between the weir and the powerhouse designated as Affected Stream Stretch (ASS) were estimated for each mini-hydropower project. Field visits were also made to over 20 SHPPs or MHPPs (mini hydropower plants) in the Kelani River basin and an extensive study was conducted on four MHPPs (physical structures and operations) established on the Wee Oya (viz., Wee Oya, Punugala, Amanawela and Monara Ela) and the proposed weir site of the Berannawa MHPP was also visited. In addition, observations were made on riparian vegetation and water distribution between the intake weir and powerhouse of the four mini hydropower projects.

Fish samples were collected using cast nets and hand traps and species were identified with the help of field guides. Further information were collected from riparian community on the local names of fish found in the Wee Oya before the construction and operation of mini hydropower plants, In addition, endemic fishes restricted to hill streams in Sri Lanka and reported from the Kelani River basin were collected from literature (Deraniyagala 1952, Pethiyagoda 1991, Shirantha 2004, De Silva et al. 2015). EIA/IEE reports, the basis for granting permission to establish mini hydropower plants on the Wee Oya examined carefully with especial emphasis on fish fauna, project design plans, mitigation measures and environmental flow. Data analysis was comparative in nature and attempts were made to exhibit the results in graphical forms and correlation analysis.


Results and Discussion

Since the inception of the construction and operation of SHPPs in Sri Lanka in the 1990s, 31 SHPPs constructed in the Kelani River basin have been connected to the national grid by the end of 2014. These power plants generate 56 MW and another five are under construction (Table 1). Although plant designs indicate projects as run-of-river systems, none of the visited projects in the Kelani River basin did not maintain required flow between the weir and powerhouse creating dead stream stretches unless lateral tributary inputs were available. Table 1 also shows the total lengths of affected stream stretches (ASS) in major tributaries of the Kelani River. In the case for Kekelagamu Oya and Maskeliya Oya, downstream dead stream lengths of Castlereagh and Maussakelle reservoirs and Norton and Canion ponds were also added to the ASS. A significant linear relationship was found between the generation capacity and the ASS (Pearson Correlation = 0.817; p = 0.000 ). The Kehelguamu Oya and Maskeliya Oya had the longest affected stream stretches amounting 27.3 km and 25.5 km respectively resulting in 60.3 % stream loss in Kehelgomu Oya and it was 62.9% for Maskeliya Oya. Extremely high stream losses in two major tributaries were primarily due to the construction of major hydropower reservoirs (Castlereagh and Maussakelle) and storage ponds (Norton and Canion) without facilitating downstream environmental flows. The highest number of mini hydropower plants has been established in the Seethawaka Ganga sub-watershed compared to the other watersheds (Table 1). In Seethawaka Ganga watershed except Magal Oya SHPP (9.90 MW) the majority of the other SHPPs has the generation capacity of less than 1.00 MW (Table 1).

In addition, the Seethawaka Ganga had the longest cumulative stream stretch affected by the construction of mini hydropower plants (43.8 %). The values of percentage stream loss for the Guguguda Oya and Ritigaha Oya sub-watersheds were 11.7% and 10.8% respectively whereas it was 32.5% for the Wee Oya. Low hydropower generation and subsequent low affected stream stretch in Gurugoda Oya and Ritigaha Oya may be attributed to the relief of the terrain and the water resource potential of the sub-watersheds. In the case of Wee Oya, four hydropower plants have the generation capacity of 11.8 MW (Figure 2). Nevertheless, instead of natural stream stretches, there were isolated stagnant pools, exposed bedrocks and dried up ripple areas between the weir and the powerhouse in all four cases in the Wee Oya, or in other words a dramatic alteration of natural habitats. The same situation may occur in other sub-watersheds of the Kelani River headwaters, which has 103.9 km of affected stream stretches due to the establishment of 31 small hydropower operations.

The number of hill stream fishes in Sri Lanka is 57 belonging to 12 families of which 44 are endemic (De Silva et al. 2015). Of the endemic fishes, 34 are found only in hill streams between 100 -1000 m AMSL where their type habitats are located. Eighteen endemic fishes restricted to hill streams have been reported from the Kelani River by various authors (Deraniyagala 1952, Pethiyagoda 1991 Shirantha 2004, De Silva et al. 2015) of which five species were found in Wee Oya in 2005 before the construction of the first MHPP, Wee Oya mini hydropower plant. The present study found only four endemic fishes restricted to
hill streams where water is brought to the mainstream from lateral tributaries (Table 2). The number of fish species reported in other EIA/IEE reports is also given Table 2. It is a common practice to indicate a least number of fish species in EIA/IEE reports. Although these reports are in public domain there are difficulties to access them in certain cases. The results of this study demonstrate devastating effects of inappropriate construction and incorrect operation of hydropower on running water ecosystems and ichthyofauna endemic respective area as reported at several occasions (Silva and Davies 1986, Silva 1993, Arthington et al. 2006, Poff 2009, Bhushan et al. 2013, Silva et al. 2013). The situation is worse in the case of small hydropower operation than that of large hydropower with respect to the extent of affected stream stetches. The effects of exposed stream beds on ecological integrity and human health of riparian communities are to be investigated.

According to Dudgeon (2000) freshwater fishes in Asian rivers and associated wetlands are susceptible for the anthropogenic threats resulting from deforestation, infrastructure development, stream-flow regulation, diffused and point-source pollution and over-exploitation. The situation in Sri Lanka is also similar with several exceptions (e.g., urbanization, gem-mining, over-use of pesticides, ornamental fish trade, use of destructive fishing methods and introduction exotic fish) as reported by several authors (Senanayake and Moyle 1982, Wijeyaratne 1993, Pethiyagoda 1994, 2006, Gunasekara 1996, Bambaradeniya 2002 ). Most of these factors are interrelated with each other, but habitat degradation and impairment of water quality are among the main decisive factors attributable to population decline and gradual extinction. Fish species inhabiting agricultural watersheds are eco-physiologically substandard compared with their counterparts found in forested watersheds (Jayakody et al. 2011). Further, the negative effects of large dams on riverine fish fauna have been discussed in detailed in many instances (Silva 1993, Arthington et al. 2006, Poff 2009, Bhushan et al. 2013). The effects of a cascade of small hydro dams on Sudu Ganga (a major tributary of Amban Ganga) in Matale District were highlighted by Silva et al. ( 2013). The results of this study further highlight the devastating negative effects of inappropriate and incorrect construction and operation of mini hydropower plants on fish fauna endemic to Sri Lanka.


The negative effects of incorrect and unacceptable operations of mini hydropower plants in Sri Lanka on endemic fish fauna as a result of alteration and elimination of type habitats are obvious. Evidence are there for declining and vanishing of endemic fishes from hill streams over the last two decades with escalating small hydropower development. Many stakeholders including so-called ecologists are responsible for this pathetic ecological crime.




The authors are pleased to thank Asia Pacific Network for Climate Change Research (APN) for the grant awarded (CBA 2015-06NSY-Silva) to Water Resources Science and Technology (WRST) to implement certain components of the ongoing research project on Environmental Effects of Small Hydropower Development. We also thank Mr. Gamini Kulasuriya and Mr. Ananda Ramanayake, of Hill Rose Estate, See Forth, Yatiyantota for the facilities provided during the field activities and for their hospitality.
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