Hydrology and sediment initial baseline
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This presentation was delivered by Simon Tilleard at the Lancang – Mekong Environmental Study Workshop that took place at the 2016 Greater Mekong Forum on Water, Food and Energy. The presentation documents the current condition and drivers of change for hydrology and sediment transport in the study section. It also provides information for biodiversity teams so that they can understand habitat availability.
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Hydrology and sediment initial baseline
- 1. Environmental study of the Lancang Mekong Development Plan (LMDP) for International Navigation Hydrology and sediment initial baseline
- 2. Purpose • Document the current condition and drivers of change for hydrology and sediment transport in the study section • Provide information for biodiversity teams so they can understand habitat availability Caveats • Desktop study based on literature review and data analysis • Findings needs to be expanded and confirmed through field visit/s Purpose of the study
- 6. Importance of the Upper Mekong Dry season Wet season (MRC, 2005)
- 8. Sediment supply • UPSTREAM CATCHMENTS – Main source of sediment supply (estimated as producing Suspended Sediment Yield of 700 t/km2/year (Walling, 2009) • TRIBUTARY CONFLUENCES – Could not be quantified – Qualitative assessment using satellite imagery shows seven tributaries likely to be supplying large amounts of sediment to the mainstream • BANK AND CHANNEL EROSION – Temporal-spatial analysis of satellite imagery shows that the river is not highly active therefore unlikely to be supply large sediment loads
- 9. Sediment supply – a stable river February 2008 February 2014
- 10. Sediment supply – a stable river April 2002 November 2015
- 11. Sediment transport capacity (Bravard and Goichot, 2014)
- 12. Sediment supply – sand April 2002 November 2015
- 13. Driver of change - Catchment land use
- 14. Change in catchment land use • 22% decrease in forest cover between 1960 to 2000 in Upper catchments, and similar decrease in catchments of tributaries entering study reach • No increase in flow over this period • Increasing sediment loads between the 1960s and early 2000sYear1961 Year2002 Year1961 Year1997 (Walling, 2008)
- 15. Driver of change - Upper Mekong reservoirs
- 16. Upstream dams – hydrology Study Findings Simulation of effects using modelling Rasanen et al, 2012 Amplitude of the annual flood pulse reduced Dry season flows increased Zhao et al, 2013 Increased flows in Jan, May and Jul Decreased flows in Oct and Nov May be climate factors Analysis of observed datasets Campbell 2007 Decreasing August flows at Chiang Saen Lu et al, 2014 Decreasing August flows at Chiang Saen More variable flows in the dry season Li and He, 2008 Decrease in dry season flows
- 17. Upstream dams – hydrology • Volume of flow during the dry season has significantly decreased in many years (1993, 1997-1999, 2004) at both Luang Prabang and Chiang Saen
- 18. Upstream dams – hydrology • Lowest monthly flow has significantly decreased in many years (1993, 1995, 1997- 1999, 2003-2007) at LB and CS
- 19. Upstream dams – hydrology • Our analysis based on 1950/60 to 2006/07 and observed change • New analysis using data up to 2014/15 shows that the later larger dams are having a more significant impact (baseline is changing further)
- 20. Upstream dams - sediment Chiang Saen Luang Prabang (Adamson, 2009)
- 21. Driver of change - urban development
- 22. Development – embankments 2013 2016
- 23. Development – urban areas
- 24. Driver of change - Climate change
- 25. Climate change 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Averagedailydischarge(m3/s) ChiangSen BL Chiangsen CC 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Averagedailydischarge(m3/s) Luang Prabang BL Luang Prabang C homPhanom BL homPhanom CC 25,000 30,000 35,000 40,000 45,000 50,000 lydischarge(m3/s) MukdahanBL MukdahanCC 25,000 30,000 35,000 40,000 45,000 50,000 lydischarge(m3/s) 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Averagedailydischarge(m3/s) ChiangSen BL Chiangsen CC 0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000 18,000 20,000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Averagedailydischarge(m3/s) Luang Prabang BL Luang Prabang CC (ICEM, 2013)
- 26. Driver of change - Pak Beng hydropower
- 27. • Located on Mekong River 14km upstream of Pak Beng town • Concrete run-of-river gate dam • Installed capacity of 815 MW • Navigation lock for 500t capacity boats Pak Beng – project details
- 28. Pak Beng Dam – backwater extent
- 29. • Run-of-river so, once filled, should be negligible effect on downstream hydrology • Blocking of sediment behind dam wall leading to downstream sedimentation starvation • Changes in flow within the backwater extent Pak Beng – possible impacts
- 30. • Hydrology – Annual flood pulse – Importance of Upper Mekong catchment • Sediment transport – Importance of Upper Mekong catchments – Zone of deposition • A changing situation – Land use change – increasing sediment loads – Upper Mekong reservoirs – altering hydrology and sediment – Climate change – will alter hydrology – Lower Mekong reservoirs (Pak Beng) - TBC In conclusion
- 31. We are passionate about the protection and restoration of waterways, catchments and water resources. We strive to make a positive difference to the world we live in.
Hinweis der Redaktion
- Image: Delta region, Netherlands. Along the southern coast of the Netherlands , sediment laden rivers have created a massive delta of islands and waterways in the gaps between coastal dunes. After unusually severe spring tides devastated this region in 1953, the Dutch built an elaborate system of dikes, canals, dams and locks to hold back the North Sea. SOURCE: US Geological Survey.
- Fundamentally altered baseline If we went back to pre-1992 then the baseline would be different and if we look over the last five years the it has shifted again as larger dams are constructed upstream, Naturally a annual flood pulse and high sediment loads, but these have been shifting
- Image: The Niger River. Coursing through parches, landlocked Mali in Western Africa, the Niger River flows north through an ancient sand sea before turning sharply east to skirt the edge of the dune-striped Sahara. At the confluence of the Bani and Niger Rivers is an inland delta complete with narrows, twisting waterways, lagoons and tiny islands. SOURCE: US Geological Survey.
- Clear flood pulse in the study reach - Water levels recorded at Chiang Saen fluctuate by up to 10 m between mid-April and mid-August, and at Luang Prabang, the seasonal changes in water levels can exceed 15 m Not as significant as further downstream Large amount of flow enters within the study reach (Annual flow volumes at Luang Prabang average around 40,000 Mm3 higher than that at Chiang Saen)
- Importance of the upper catchment for the hydrology of the study reach At Chiang Saen the Upper Mekong catchments contribute 70% of wet season and almost all the dry season flow At Luang Prabang, the Chinese catchments contribute 55% of wet season flow and 80% of dry season flow – still a significant amount
- Image: The Niger River. Coursing through parches, landlocked Mali in Western Africa, the Niger River flows north through an ancient sand sea before turning sharply east to skirt the edge of the dune-striped Sahara. At the confluence of the Bani and Niger Rivers is an inland delta complete with narrows, twisting waterways, lagoons and tiny islands. SOURCE: US Geological Survey.
- Some disagreement on the reliability but average suspended sediment load at Chiang Saen is around 81.7 million tonnes/year, compared to 76.8 million tonnes a year at Luang Prabang The study section is therefore an area of net deposition
- Image: The Niger River. Coursing through parches, landlocked Mali in Western Africa, the Niger River flows north through an ancient sand sea before turning sharply east to skirt the edge of the dune-striped Sahara. At the confluence of the Bani and Niger Rivers is an inland delta complete with narrows, twisting waterways, lagoons and tiny islands. SOURCE: US Geological Survey.
- the land use changes have not been significant enough to affect the hydrological regime of the study reach Suspended sediment load of the Mekong River at Chiang Saen, and Luang Prabang for 1961 with the load for a recent year and similar water discharge
- point is that there is some contention on what the impacts So we did our own analysis for stations in the study reach
- Used Flow Health software developed in Australia. Compares baseline against test period for nine hydrological indicators
- Climate change is projected to increase rainfall across the Mekong Basin, leading to increased annual flows in the Mekong mainstream At Chiang Saen and Luang Prabang the flow is projected to increase throughout the year, with the greatest increases occurring during the wet season The timing of the flood peak is also expected to change, with a delay of a few days at Luang Prabang and a delay of up to 14 days at Chiang Saen
- Fundamentally altered baseline If we went back to pre-1992 then the baseline would be different and if we look over the last five years the it has shifted again as larger dams are constructed upstream, Naturally a annual flood pulse and high sediment loads, but these have been shifting
- Image: Mississippi River Delta. Turbid waters spill out into the Gulf of Mexico where their suspended sediment is deposited to form the Mississippi River Delta. Like the webbing on a ducks foot, the marshes and mudflats prevail between the shipping channels that have been cut into the delta. SOURCE: US Geological Survey.