Script:2006 = second to last year for which MRC has discharge data. More recent data may be available from national government agencies or private hydropower companies (as is the case w/ Nam Theun). Other notes: The other dams with C:I > 0.01 are Nam Leuk, Nam Mang and Yali Falls. Annual inflow is based on MRC estimates, which may or may not be reliable. For instance, NN1 is 427 m3/s, way too high.
Can get rid of this slide or move it.
The new slide for Nam Ngum seasonal flow distribution effects. Can you mention that this slide shows the June-May hydrologic year with the wet season comprising the period from June to November and the dry season running from December to May? Perhaps, you could use the terms flood and low-flow season instead. It seems like the FDC model does not predict the wet season-dry season distribution at ThaNgon well.
Notes:NT2 will change flow in Mekong by 3%, map missing Nam Gnouang Res., which is critical for maintaining flows at
The top chart shows the effects of the dam on downstream flows in the Nam Kading. (The Nam Theun river becomes known as the Nam Kading d/s of the dam (?)). The inflows from August 2002 – December 2007 were deduced from water balance estimates that the Theun-Hinboun Power Company made from outflows, changes in water level and diversions. To model the period prior to August 2002, two approaches were tested. One of them utilized data from upstream gauging stations to estimate the inflow into the THPC impoundment using mean annual inflow scaling. Records from short-term stations were extended with the Ban Signo gauge upstream of the dam, which has a drainage area of 3,370 km^2 in comparison to the THPC dam DA of ~8,937 km^2. The main livelihood impact in the Nam Kading basin is for fishing. The basin is sparsely populated. The inflow with u/s station does a better job of predicting the recession. Hydropower diversions/production seems to have been lower during the first few years of operation. (CAN WE COMPARE THIS WITH TIME SERIES OF POWER PRODUCTION TO CHECK THAT IT WAS LOWER IN THE FIRST YEARS?)Still some data gap issues with outflow, 18,000 cms value in 2002 unlikely given other annual peak flows
The Influence of Dams on Downstream Flows and the Potential Effects on Livelihoods
Jory Hecht, Matthew McCartney & Guillaume Lacombe
Assessing Mekong dam impacts• Reservoir storage in Mekong basin expected to increase by an order of magnitude from 2010-2022• Significant debate about the implications of additional storage on river flows and the implications for peoples’ livelihoods and well- being
TradeoffsKey Objective Optimise Variables Overall Benefit Decisions Constraints Impacts •Livelihoods •Health •Biodiversity Irrigated Domestic Floodplain Recession Floodplain Fisheries Agriculture Water Supply Hydropower Industry products Agriculture Grazing Legislation • local/national laws Dam operation Development drive options • political imperatives • international obligations Water availability Social/economic Desired ecosystem • hydrological regime Engineering condition • reservoir storage conditions • present/future condition • outlet structures • livelihoods adaptation to dams
Nam Ngum 1 Dam, Lao PDR First large hydropower dam in Lao PDR Nam Ngum (1972), now at 155 MW Nam Song Nam Song Ban Na Largest tributary reservoir in Mekong Div. Luang Stn. (7 km3 active storage, 404 km2 area) Nam Ban Lik Increased dry season flows provide Hinheup Stn. downstream irrigation opportunities Nam Nam Leuk Ngum 1 Diversions from Nam Song and Nam Res. Leuk, two adjacent watersheds Nam Mang Tha Ngon Nam Ngum New dams upstream of NN1 reduce seasonal water level fluctuations Mekong pre-2010 schematic diagram
Nam Ngum Flow Distribution 10000 Estimated inflow ReleasesDischarge (m3/s) 1000 100 10 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 Flood frequency at NN1 (1987-2005) Flood frequency with dam 7000 3500 3000 1987-2005 6000 Discharge (m3/s) 1996-2005 Discharge (m3/s) 5000 2500 4000 2000 3000 1500 2000 1000 1000 500 0 0 1 10 100 2 5 10 20 50 Return Period (yrs) Return Interval
BELOW NN1 DAM NN1 + BAN HINHEUP THA NGON STN. 30 30 30 Dry season Wet season Dry season Wet season Dry season Wet season 25 25 25W/ 20 20 20 Flow (billion m3)O 15 15 15 10D 10 10A 5 5 5M 0 0 0 30 30 30W Dry season Wet season Dry season Wet season Dry season Wet Season 25 25 25IT 20 20 Flow (billion m3) 20H 15 15 15D 10 10 10A 5 5 5M 0 0 0
Nam Theun-Hinboun Project, Lao PDR Nam Kading• Commissioned in 1998 Nam Kading THPC Dam Outflow• Dam with live storage less than one Nam Hinboun day of the mean annual flow Headpond impounds water from Nam Theun Inflow• Water diverted to 220-MW powerhouse in Nam Hinboun basin Mekong Nam Gnouang through tunnel at up to 110 m3/s Res. during study period Nam Theun 2• Now 440 MW, 220 m3/s with Xe Bang Fai expansion of THPC project• Nam Theun 2 Reservoir filled in Nam Theun 2008
Nam Kading Flow Distribution100,000 Inflow with u/s stations Outflow to Nam Kading Minimum release requirement 10,000 1,000Discharge (m3/s) 100 10 1 0 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Average dry season flow (Dec-May) 200 Estimated inflow Discharge (m3/s) 150 Outflow to Nam Kading 100 50 0 2001 2002 2003 2004 2005 2006 2007 Hydrologic Year (Jun-May)
Effects of Diversions on Nam Hinboun basin 1000 Nam Hinboun discharge CS16 CS10 Maximum THPC discharge 800Discharge (m3/s) 600 400 200 0 2008 2009 2010 2011 120 Sample time series of dry season releases 100 Discharge (m3/s) 80 60 40 Powerhouse releases 20 0 5-Apr-09 6-Apr-09 7-Apr-09 8-Apr-09 9-Apr-09 10-Apr-09 11-Apr-09 12-Apr-09
Conclusions Dams significantly alter the downstream flow regime (and other fluxes, nutrients and sediment), which in turn has ecological impacts The response of ecosystems is varied and complex and currently difficult to predict Changes in ecosystems affect livelihoods and well-being of people living downstream Changes in flow provide both constraints and opportunities for those living downstream The environmental and social impacts the new dams in the Mekong will have consequences for many decades