hydrology and sediment initial baseline

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Environmental study of the Lancang Mekong Development Plan (LMDP) for International Navigation Hydrology and sediment initial baseline

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

Hydrology current status

Annual flood pulse

Importance of the Upper Mekong

Dry season

Wet season

(MRC, 2005)

Sediment transport current status

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

Sediment supply – a stable river

February 2008

February 2014

Sediment supply – a stable river

April 2002

November 2015

Sediment transport capacity

(Bravard and Goichot, 2014)

Sediment supply – sandApril 2002

November 2015

Driver of change - Catchment land use

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 2000sYe

ar 1

961

Year

200

2

Year

196

1

Year

199

7(Walling, 2008)

Driver of change -Upper Mekong reservoirs

Upstream dams – hydrology

Study FindingsSimulation of effects using modellingRasanen et al, 2012

Amplitude of the annual flood pulse reducedDry season flows increased

Zhao et al, 2013

Increased flows in Jan, May and JulDecreased flows in Oct and NovMay be climate factors

Analysis of observed datasetsCampbell 2007 Decreasing August flows at Chiang SaenLu 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

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

Upstream dams – hydrology

• Lowest monthly flow has significantly decreased in many years (1993, 1995, 1997-1999, 2003-2007) at LB and CS

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)

Upstream dams - sediment

Chiang Saen Luang Prabang

(Adamson, 2009)

Driver of change - urban development

Development – embankments

2013 2016

Development – urban areas

Driver of change - Climate change

Climate change

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Nakhom Phanom CC

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Mukdahan BL Mukdahan CC

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Kratie BL Kratie CC

(ICEM, 2013)

Driver of change - Pak Beng hydropower

• 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

Pak Beng Dam – backwater extent

• 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

• 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

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.

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