Post on 24-Feb-2016
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Sediment Issues within Transboundary Basins
Presented by Paul Bireta and Fernando SalasApril 12, 2012
What is sediment? Solid particles, minerals and/or organic
material transported by water. Controlled by transport capacity of flow and
supply of sediment. Suspended sediment load, wash load, and
bed load. Channel systems, flood plains, wetlands
and estuaries. Balanced by erosion and deposition Development and extreme climate events
disturb the equilibrium
The sediment conundrum… Floods deposit
nutrients within flood plains.
Dams mitigate flood damage.
Increased sediment deposition can increase flooding.
Sediment is a complex problem… Management Issues in Large River Basins
Flooding Agriculture Erosion Reservoir sedimentation Aquatic life and biodiversity
Population growth (i.e. land use and water use) 50% of major rivers show statistically significant
upward or downward trend in sediment loads Climate Change – wetter climates leads to
increased erosion and runoff
Upstream Effects Hydropower
Adequate flows for power generation. Degradation of rotors.
Reservoir Capacity Decreasing Floods
Sedimentation in Reservoirs
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Downstream Effects Erosion
Bridges Wetlands and
estuaries Support biological
diversity – fish breeding (nutrients)
Nutrient loads on floodplains Agriculture now uses
fertilizer that can be harmful
Sediment Accumulation Flooding – backwater lakes in Mississippi have
lost 30-100% of capacity Navigation
Dredging costs are high Infrastructure
Irrigation pump intakes and canals Domestic water supplies – water treatment and
distribution Nile River – floods can generate up to 23,000 ppm
disrupting treatment; only 50% of the population has access to safe drinking water
Sediment contamination
Global Sediment Yields
Global perspective Estimated 800,000 dams in the world
today. 1/4th of sediment flux trapped.
China – 22,000 vs. United States – 6,500
HiSTORical Perspective ~ 5,000 dams built by 1950 ~ 45,000 dams built by 2000 (2 large dams
per day)
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Large dependence on hydropower
Large dependence on hydropower 70% of economically
feasible hydropower potential in developing countries 93% potential in
Africa Since 2003, the
World Bank has financed 67 large hydropower projects ~ $3.7 billion
Large dependence on hydropower
Development in Transboundary Basins Involve multiple stakeholders
Agriculture Mines and Industry Communities in flood-prone areas Reservoir managers Wetland and environmental organizations Recreational users
Focus on water quantity…not quality as much. Mekong River basin currently has 134 dams either
planned or operating (China, Myanmar, Thailand, Laos, Cambodia and Vietnam)
Regional specific solutions Climate (i.e. stationarity is dead) Tectonics and geology Topography Soils
Regional differences and within watershed differences Hydrology Vegetation and land use River control structures Soil and water conservation measures Tree cover Land use disturbances (e.g. agriculture, mining etc.)
Modeling Sediment Load and Transport Universal Soil Loss Equation Physical models Stochastic analysis of loading
Management Strategies and Approaches
Yellow River Highest sediment yield of any river in the
world 16.3 billion tonnes (1919 – 1960) 0.84 billion tonnes (1952 – 2000)
1,130.3 tonnes per km2
Average annual runoff - 47.38 billion m3
Low flow to oceans and reservoirs Loess plateau highly erodible Most the erosion comes from a relatively small
area (110,000 km2) Conservation Measures
Yellow River Highest sediment yield of any
river in the world 16.3 billion tonnes (1919 – 1960) 0.84 billion tonnes (1952 – 2000)
1,130.3 tonnes per km2
Average annual runoff - 47.38 billion m3
Dykes and Levees built to control flooding Bed of river now 5 m above
surrounding area
Yellow RiverUpstream Issues Loess plateau highly
erodible Most the erosion comes
from a relatively small area (110,000 km2)
Increased floodingDownstream issues Low flow to oceans and
reservoirs In 1997, no flow reached
ocean for 226 days
Yellow RiverMeasures Taken Sluice gates opened at dams
to release trapped sediment Decreases hydropower generation
Conversion of upstream land Cropland to Grazing Reforestation Terracing
1976 - Artificial channel constructed to discharge sediment into Bohai Sea Creates 25-50 km2 of new land
per year
Mississippi River Drains 1,245,000 sq miles River course changes every
~1000 years Results in sediment being
deposited in different areas Pre 1900, river moved an
average of 400 million tons of sediment
Last 20 years, only 145 million tons
20.5-53.3 mm/yr lost, averaged over entire watershed
Mississippi RiverCauses Levees built to protect flooding and for
navigation Plan was to control channel and reduce dredging Led to increased sedimentation, which increased
flooding and dredging Increase in agriculture
Clearing of deep-rooted vegetation Tilling of soil and planting Irrigation
Mississippi RiverEffects Mississippi delta losing
wetlands 16.57 sq miles per year Wetland loss also due to
large storm events, but significantly higher than previously measured
Increased flooding River channel now not able
to flow naturally Lakes are filling with
sediment and are not able to dampen flooding effects
Mississippi RiverPossible Solution Researchers at UT have been working to
model possible solutions Plans to cut
through two major levees downstream of New Orleans to release sediment
Release would balance out lost sediment and reestablish positive land flux
Rhine River Major pollution in the past Contaminants accumulate in
sediment Natural sedimentation
processes tend to bury these sediments
Decrease in sedimentation due to upstream development
Contaminated sediments are being exposed by both natural suspension and dredging
Rhine River is a major drinking water source
Conclusions River control devices are increasing
sedimentation in river systems Agricultural practices are increasing the
amount of erosion into these river systems Sediment dynamics need to be taken into
account for future project, both economically and environmentally
Questions Should countries be investing in dams and
reservoirs when we know of the negative environmental impacts? Who should be responsible for assisting countries with sediment modeling before projects are undertaken?
How do we balance urbanization and development with environmental sustainability? Are river control systems sustainable?
Will these systems reach a new steady-state with the river control systems or will these problems continue to compound?