Implications of Changes to the Mekong River on Fish and Fishers Livelihoods from Hydropower: A Case in the Tonle Sap Cambodia

written by Mak Sithirith Fisheries Action Coalition Team (FACT) Paper prepared for the workshop on Mekong Environment and Livelihood: The Changing situation and Trans-boundary Implications Cantho City, Vietnam 3-4 February 2010
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   1 Implications of Changes to the Mekong River on Fish and FishersLivelihoods from Hydropower: A Case in the Tonle Sap Cambodia Mak SithirithFisheries Action Coalition Team (FACT) Paper prepared for the workshop on Mekong Environment and Livelihood:The Changing situation and Trans-boundary ImplicationsCantho City, Vietnam3-4 February 2010 CAMBODIA covers an area of 181,035 km 2 . It borders Vietnam in the east, Laos inthe northeast, and Thailand in the north and west. The Gulf of Thailand bordersCambodia to the south. The estimated 2008 population of Cambodia was 13.4 millionin 24 provinces, consisting of 185 districts, 1,621 communes and more than 14,073villages 1 (MoP, 2004 & 2006; RGC, 2006; NIS, 2008). Approximately four-fifths of the Cambodian population is rural (World Bank 2004). This population is centredprimarily around the Mekong River and the Tonle Sap Lake (Lamberts, 2001). Of thetotal number of villages in Cambodia, about 1158 villages are located in the TonleSap floodplain and of these villages; about 170 are floating villages (Keskinen, 2003;MoP, 1999). The Tonle Sap Lake plays a vital role in Cambodian economy andlivelihoods for millions of Cambodians. Many people are directly dependent onresources from the Lake. The Tonle Sap and the Mekong River The Tonle Sap was formed about 5500-6,000 years ago (Penny, 2002; Penny et al., 2005; Tsukawaki, 1997). The Tonle Sap Basin is located in the northwest partof Cambodia between approximately latitudes 102° 15'to 105° 50' Eand longitudes 11° 40'to 14° 28' Nthat covers an area of about 80,000 km²,including the Tonle Sap Lake,which constitutes about 44% of the total land area of the country (Wright et al., 2004 ). About 95% of the Tonle Sap Basin lies within Cambodia while about 5 percent(about 5,000 km²) lies in Thailand (CNMC &NEDECO, 1998; ADB, 2004).The Tonle Sap Basin extends over 44% of Cambodia’s total land area, and ishome to 32% of Cambodia’s population, or about 3.6 million people, covering 8 1 www.nis.gov.kh/index.php/statistics/surveys/census2008/provincial-population-totals.   2provinces in Cambodia 2 . It constitutes a critical part of the lower Mekong basin: itsupplies 6% of the average annual flow of the Mekong but, more significantly, makesup 16% of its dry season flow (thereby helping to control salinity intrusion andconserve mangrove in the Mekong delta) (ADB, 2004) 3 .The average annual inflow into the Tonle Sap lake is estimated at about 79km³(Kummu et al., 2008); about 30% of the flow srcinates from 13 tributaries located inthe lakes's watershed (Kummu et al., 2008; Sithirith, 2007) 4 . Due to its distincthydrology,from the Mekong mainstream, any long term decrease in mainstreamMekong discharge due to upstream Chinese hydro development will result in a 40-50% increase in the contribution of local catchment runoff as a percentage of the totalwater supply to Tonle Sap Lake (ADB, FAO, DoF, 2003). 5  The Tonle Sap River connects the Tonle Sap Lake with the Mekong River. Itflows from the Southeastern end of the Tonle Sap Lake and meets the Mekong Riverat Chatomouk confluence, north of Phnom Penh, after which the river immediatelysplits into the smaller Bassac River and the larger Mekong River (Kummu et al., 2008). The Tonle Sap River has total length of 120 km extending from Phnom Penhto Kampong Chhnang province (CNMC, 2004; Keskinen, 2003).In the wet season (May to December), flooding in the Mekong River causesthe Tonle Sap River to change its direction of flow northwestward into the Tonle SapLake causing a dramatic rise in water level. About 52% of inflow into the lake is fromthe Tonle Sap River (Kummu et al., 2008). In the dry season, the water reverses itsflow to the Mekong River. Thus, the Tonle Sap River plays a vital role in sustainingthe Tonle Sap Lake. The inflow and outflow moves fish, nutrients and aquaticproductivity to and from the lake, making it unique in the world (Van Zalinge et al., 2000; Degen and Thouk, 2000).The Tonle Sap Lake is an integral part of the Mekong River and it is thelargest freshwater body in Southeast Asia. The seasonal variations in the lake's area 2 The Tonle Sap Basin covers 8 provinces in Cambodia: Battambang, Siem Reap, Pursat, KampongThom, Kampong Chhang, Banteay Meanchey, Preah Vihar and Oddar Meanchey (ADB, 2004). 3 ADB (2005a). Tonle Sap and its fisheries: Future solutions now. The Tonle Sap Initiative; AsianDevelopment Bank, Manila, Philippines. 4 Some 13 major tributaries contribute a high volume of water to the Lake including the Stung Sen,Stung Sangke, Stung Chinit, Stung Chikreng, Stung Stung, Stung Monkul  Bor  ei Rivers, all of themlocated in the watershed areas of the Tonle Sap Basin (Sithirith, 2007). 5 (REF?) suggests that the resident dry season stocks of some species in the Great Lake may representseparate stocks from those which are carried into the Lake by the annual back-flooding of the MekongRiver.   3and depth are remarkable. The lake is usually illustrated in the maps in its smallest,dry season form. The length of the lake varies from approximately 160km long 6 and35km wide during the dry season 7 , to 250km long and almost 100km wide during thepeak of the flooded seasons (Matsui et al, 2005; Kummu and Sarkkula, 2008) 8 .The Tonle Sap Lake has an exceptional water regime. The lake covers an areavarying between 250,000 -300,000 ha in the dry season with an average depth of lessthan two meters 9 , and it increases to 1.0-1.3 million ha 10 in the rainy season with amaximum depth of often more than 10 m (CNMC and NEDECO, 1998; ADB, FAOand DoF, 2003; MRC, 2003 11 ). The water level in the Tonle Sap Lake varies from1.00-1.44 m in the dry season to 8.00-9.5m in the wet season, but some yearsincreases to 11m (Kummu et al., 2008; Nikula, 2004; ADB, 2005a). During the wet season, the volume of the lake increases from about 1.3 km 3  during the dry season up to 79-83 km 3 , depending on the flood intensity. The bottomof the lake lies approximately 0.5–0.7 m above the mean sea level in Hatien datum(Kummu et al., 2008). Table 1. The size of the Tonle Sap Lake by the dry and wet season Season Lake area(Km 2 )Water level(m)Lake area(Km 2 )Waterlevel(m)Lake area(Km 2 )Waterlevel (m) Dry seasonlake area2,300 1.44 2,500 1.2 2,500–3,0001-2Wet seasonlake area13,260 9.17 15,000 9 10,000-16,0008–11Source Kummu et al., 2008 Nikula, 2004 ADB, 2005 Tuk tonle (river water) is active in the wet season from May to October.During May and June, Tuk tonle increases only gradually. In July and August itincreases noticeably when the Mekong River rises and flows into the Tonle Sap Lakedue to the water level rise in the Mekong resulting from heavy rains and snow melt on 6 Heinonen U. unpublished thesis(ref? not clear) (2004) estimates that the length of the lake is 140 km.The dry season covers an area of 2,590 km 2 and in rainy season 10,400 km 2 . Heinonen, U. (2004)Integrated and socially just water resource management in the Lower Mekong River Region andCambodia: How to control water related rural push. Helsinki University of Technology. Department of Civil and Environmental Engineering, La bor  atory of Water Resources, Finland. 7 Somony, T. and Schmidt, U. 2004. Aquatic Resource Management: Tonle Sap Great Lake,Cambodia. Somony and Schmidt, 2004 estimates that length of the Lake is about 100 km long and 35wide 8 (Matsui, S. et al., 2005. Tonle Sap: Experience and Lessons Learned Brief. 9 Somony, T. and Schmidt, U. 2004. Aquatic Resource Management: Tonle Sap Great Lake,Cambodia. Department of Fisheries. In this paper, it is estimated that the water level in the dry seasonis estimated at 0.8-1m and in rainy season 10-12m. 10 Nikula (2004) states that the size of the lake increases from 2,700 km 2 to 9,000 - 16,000 km 2  (MRCS/MRC/WUP-FIN, 2003). 11 MRC, 2003. State of the Basin Report. Mekong River Commission.   4the Tibetan Plateau (Lambert, 2001). The flow of water from the Mekong to the TonleSap results in ‘rising water’. The average annual inflow varies, but it is estimated atabout 79-83 km³ (See Table 2). It comes from four sources; the reverse flow fromMekong River via the Tonle Sap River; the tributaries around the Lake; the rainfall;and the overland flow from the Mekong. It is estimated that about 40-45 km 3 of watercomes from the Mekong River and 4 km³ from the overland flow. These two sourcesaccount for 57 percent of the water volume in the Tonle Sap Lake. Approximately 24-25 km 3 or 30 percent of water comes from the Tonle Sap tributaries, and rainfallprovides 10-14 km 3 or the remaining 13 percent (Kummu et al., 2008; Matsui et al., 2005; CNMC, 2004). The annual average outflow of the outflow the Tonle Sap Lakeis estimated at about 78.6 km³. About 69 km³ (88% of outflow) from the Tonle SapLake returns to the Mekong River via the Tonle Sap River (Kummu et al., 2008;Matsui et al , 2005; CNMC, 2004). Table 2. The Water Volume of the Tonle Sap Water SourceStoring capacity of TSL estimatedby Kumu et al., 2008(km 3 )Storing capacity of TSL estimatedBy Matsui et al (km 3 )Storing capacity of TSL estimatedby CNMC (km 3 )Estimate(km 3 )Mekong 40.64 45 45 40-45Tributary 24.7 24 24.3 24-25Overland flow 3.98 n/a n/a 4Precipitation 10.36 14 13.9 10-14Total 79.68 83 83.2 79-83Source: Kumu et al., 2008; Matsui et al , 2005; CNMC, 2004. The Tonle Sap as a Heart of the Mekong Region The lake is unique due to the natural phenomenon of reverse water flow. Onehalf of the annual pulse in which the lake fills from the Mekong River during the wetseason (May to October) and empties back during the dry season. 12 This is the floodpulse of the Tonle Sap. Anders Poulsen calls the Tonle Sap Lake the pulsating heartof the Mekong, and goes on to say “the flood pulse is what keeps the heart beating. If the heart stops, the system dies” (Poulsen in Nikkula, 2005) 13 .The entire ecosystemwould be adversely transformed, In theis case, fisheries would collapse, indigenousknowledge would be subverted, the poor would go hungry, livelihoods would be 12 In the wet season, the surface area of the Lake increases from 250,000-300,000 ha to approximately1.0-1.6 million ha, with depth increasing correspondingly from 1–2 m amsl to 9–11 m amsl (CNMCand Nedeco, 1998), and storage capacity reaching a maximum of 80 million cubic meters (Sopharith,1998). It absorbs 20 per cent of the Mekong River's floodwaters and serves as a flood regulator (MRC,2004; ADB, 2002). The drop of the water level in the Mekong in the dry season creates the “reverseflow” from the Lake into the Mekong. 13 Jussi Nikkula, The Lake and its People . MSc Thesis, Helsinki University of Technology, 2005.
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