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3/30/2015
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SEDIMENTS,
GEOMORPHOLOGY,
WATER QUALITY
Presented by Lois Koehnken
BioRA Preparation Meeting PART I
Office of the Secretariat in Vientiane
18 – 19 March 2015
www.mrcmekong.org
Outline of Presentation • Sediment sources & transport
• How mountains become mud
• River geomorphology
• Channel characteristics
• Characteristics of Zones
• Water quality
• Parameters & monitoring
• Longitudinal & seasonal trends
• Catchment developments
• Changes to sediment transport
• Geomorphic changes
• DRIFT indicators
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SEDIMENT SOURCES &
TRANSPORT
www.mrcmekong.org
Rivers transport sediments & carve
landscapes
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Sediment availability in LMB
• Dependant on
• Slope
• Elevation
• Landform
• Land use
• High in northern & eastern
LMB
• Very high in UMB
From MRC Significant Tributary Report
www.mrcmekong.org
Hydrology Drives Sediment Transport
• Rainfall patterns drive river flow
• Sed transport linked to • Flow duration
• Magnitude of flow
• Frequency of flows
• Rates of river level change
• Seasonality
• Changing any 1 factor will change sediment transport
From ewater.com.au
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Hydrologic Seasons in the LMB
MRC Annual Flood Report, 2006
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Hydrology in the Mekong
• Distinct seasons
• Varies over distance
• High natural variability within well defined seasons
Runoff
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Sediment ‘Production’ in the LMB
• Combine sediment
availability and hydrology
• Northern and eastern
LMB has highest
potential for sediment
production
• Downstream Kratie is a
sediment sink
• Natural system is highly
variable
www.mrcmekong.org
Sediment Transport
• 4 dimensions
• Longitudinal
• Downstream transport
• Lateral
• Floodplain inundation
• Vertical
• Floodplain deposition
• Bed/bank deposition
• Temporal
• Seasonality
• Long-term changes FISRWG, 1998
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Downstream Transport of Sediment
• Bed load • Transported along river bed
• Rolling or ‘jumping’
• May not move under all flow conditions
• Forms bed of alluvial rivers
water surface
Wash Load Total
(Fine material Suspended
not found on Suspended Load
bed of stream) Bed Material TOTAL
Load LOAD
streamflow (Total)
Bed Material Bed
Load Load
Bed Material(after Poplawski et al. 1989)
• Wash load • Transported in suspension
• Generally <63um
• Only deposited under very low flow
• Not found on river bed
www.mrcmekong.org
Grain-size Suspended Sediment
• Composition changes over time & distance
• Fining downstream
• Silt & sand suspended during flood season at Kratie
At Kratie over 1-year Avg in mainstem
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Bedload • Coarser grained (generally silt size & larger)
• Only moved under moderate to high flow conditions
• Forms physical characteristics of river
• Bed
• Banks
• Mid-stream or point bars
• Important for ecology
• Habitat composition and quality
• Substrate for plants
• Used for construction materials
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Lateral Transport & Storage
• Sediments stored in
• Soils
• River channels
• Floodplains
• Sediment may be
transported & stored
multiple times over
long periods
• Geologic time scales
From Hoffman et al., 2011
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Lateral
Connectivity
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Seasonal changes in bed sediment
Flood season
Stung Treng
Gravel >2mm
Coarse &VC Sand0.5-2mm
Med Sand 0.25-0.5mm
Fine &VFSand 0.063-0.25mm
Silt 0.002-0.063
Luang Prabang
Gravel >2mm
Coarse &VC Sand0.5-2mm
Med Sand 0.25-0.5mm
Fine &VFSand 0.063-0.25mm
Silt 0.002-0.063
Pakse
Gravel >2mm
Coarse &VC Sand0.5-2mm
Med Sand 0.25-0.5mm
Fine &VFSand 0.063-0.25mm
Silt 0.002-0.063Dry season
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Magnitude Suspended & Bedload Sediment
• Suspended sediment transport>>Bedload
• Bedload important for riverine habitats
• Suspended important for floodplain & coastal
www.mrcmekong.org
‘Natural’ Sediment Budget
• Suspended • ~60% from UMB
• ~10% from 3S
• ~30% from remaining LMB
• Suspended Total ~160 Mt/yr
• Bedload • Difficult to estimate
• Order of magnitude ~10 Mt/yr
Sykes
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LARGE SCALE
GEOMORPHOLOGY
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Large Scale Geomorphology of LMB
• Landforms related to distribution of bedrock and sediments • Sediment transport through steeper areas (generally
bedrock)
• Sediment storage in flatter areas
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Bedrock Channel
• Concentrated in upper
LMB and between Muk
& Kratie
• Absent downstream of
Kratie
• Rocky habitat
• Rapids
• Navigation
www.mrcmekong.org
Deep Pools
• Located in bedrock
and alluvial reaches
• Hydraulics maintain
deep pools
• Evidence of a sediment
wave moving through
each season
• Provide habitat &
refuge
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Geomorphic Zones Zone Geomorphology
(UMB)
& 1
Single bedrock channel-
sediment throughput with little
storage
2 Alluvial-braided with bars;
sediment storage & reworking
with high sediment input from
tributaries;
3 Anastomosed bedrock channels,
storage & reworking
4 Meandering alluvial channels,
floodplain & Tonle Sap system
5 Deltaic alluvial channels &
distributaries
www.mrcmekong.org
WATER QUALITY
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WQ Monitoring in the LMB
• WQMN • Field based monthly
surface grab samples
• Physico chemical, Ecosystem, Human health & Agriculture indicators • pH, EC, DO, T, TSS, Ca, Mg,
Na, K, Alkalinity, Cl, SO4, TN, TP NO2+3,NH4, COD, FC
• 48 sites • 17 mainstream
• 26 tributary (incl. Tonle Sap
• 5 Tonle Sap
• 4 Bassac
• 1985 - present
www.mrcmekong.org
MRC WQMN
Aquatic Life Human Impact Agricultural
Use
Dissolved
oxygen
pH
Ammonia
Conductivity
Nitrite+Nitrate
Total
Phosphorus
Dissolved
oxygen
Chemical
Oxygen
Demand
Ammonia
Conductivity
water quality parameters used to
derive water quality indices
Indices used to produce Water
Quality Report Cards & track
changes over time
Human Impact on Water Quality
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Catchment trends - Temperature
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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Catchment trends - Temperature
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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Catchment trends - Temperature
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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Catchment trends – Total Suspended Solids
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Total Suspended Solids
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Total Suspended Solids
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Alkalinity
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Alkalinity
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Alkalinity
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Alkalinity
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Total Phosphorus
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Total Phosphorus
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Total Phosphorus
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Total Phosphorus
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Total Phosphorus
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Nitrate + Nitrite
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Nitrate + Nitrite
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Nitrate + Nitrite
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Catchment trends – Nitrate + Nitrite
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
www.mrcmekong.org
Catchment trends – Nitrate + Nitrite
• Box encompasses 25th to 75th percentile values
• ‘Whiskers’ = max & min
• Number= sample count
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www.mrcmekong.org
Water quality issues – salinity intrusion
• Related to
• Flow
• Tides
• Channel morphology
Prestin & Clayton, 2003
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Water quality issues –Acid sulfate soils
• Related to
• Water levels
• Land use
• Acidification of water
• Increase in iron, Al
• Aluminium toxicity
• Precipitation of
hydroxides
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RECENT CHANGES DUE TO
CATCHMENT DEVELOPMENT
www.mrcmekong.org
Catchment Development & Sediment
Transport • Flow Changes
• Dams have potential to alter flow regime
• Alter flow magnitude, frequency, duration, seasonality & rates of change
• Irrigation extraction
• Reduction in flows, increases in run-off
• Climate change / sea level change
• Changes in magnitude, seasonality
• Sediment availability • Land use changes
• Deforestation or land clearing increases sediment availability
• Fires
• Dams
• Sediment trapping
• Sediment extraction
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What is happening NOW in the LMB?
• Flow changes associated with Lancang HP Cascade
• Increased low flows from UMB
• Decreased wet season flows from UMB
• Delayed onset of wet season
www.mrcmekong.org
2014 Flood Season
Chiang Saen Vientiane
Kratie
• Reduced variability at CS,
VTE
• Increased dry season
flows downstream
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What is happening in the LMB?
• Decrease in sediment availability associated with dams
• Mainstream & tributary
• Decoupling of sediment transport & river flow
Sediment Loads decreasing Sediment concentrations decreasing
Chiang Saen
Suspended sediment budget now estimated at ~72 Mt/yr
www.mrcmekong.org
Sediment Extractions
• 2011-12 survey
• ~32 Mm3/yr being extracted (50 Mt/yr)
• Most from downstream of Kratie
• Sand is predominant material
• Extractions alter channel and connectivity with floodplain
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Floodplain infilling-loss of wetlands
Aug 2008
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Floodplain infilling
May 2012
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Floodplain infilling
May 2012
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Floodplain infilling
June 2012
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Floodplain infilling
Feb 13
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Floodplain infilling
Nov 13
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Depth Changes in Delta Channels
• Over 10-yr period reduction of ~200 Mm3 in Mekong & Bassac channels
www.mrcmekong.org
Council Study – DRIFT Indicators • Information provided by model for each season
• Flow parameters
• Channel shear stress
• Bed slope
• Bed elevation
• Sediment concentrations
• Sediment loads
• Sediment texture (gravel, sand, silt, clay)
• Water quality concentrations
• Geomorphic indicators • Timing of sediment delivery
• Erosion (bank / bed incision)
• Sediment fining / coarsening
• Exposure of sand bars & islands
• Exposure of rocky reefs
• Width of active back channels
• Pool depth
• Water clarity
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THANK YOU….
