Sediment Issues within Transboundary Basins

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Sediment Issues within
Transboundary

Basins

Presented by Paul
Bireta

and Fernando Salas

April 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


A
dequate flows for power generation.


Degradation
of
rotors.


Reservoir Capacity


Decreasing


Floods

Sedimentation in Reservoirs

Meganiño

1983

Meganiño

1998

1976

Sedimentation in Reservoirs

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.


1/4
th

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)

0
200
400
600
800
1000
1200
Global

0
50
100
150
200
250
300
350
400
United States

0
50
100
150
200
250
China

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 km
2


Average annual runoff
-

47.38
billion

m
3


Low flow to oceans and reservoirs


Loess plateau highly erodible


Most the erosion comes from a relatively small area
(110,000 km
2
)


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 km
2


Average annual runoff
-

47.38
billion

m
3


Dykes and Levees built to control
flooding


Bed of river now 5 m above surrounding
area

Yellow River

Upstream Issues


Loess plateau highly erodible


Most the erosion comes from a
relatively small area (110,000
km
2
)


Increased flooding

Downstream issues


Low flow to oceans and
reservoirs


In 1997, no flow reached ocean
for 226 days


Yellow River

Measures 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 km
2
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 River

Causes


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 River

Effects


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 River

Possible 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?