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

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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?