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  Adequate flows for power generation.  Degradation of rotors.  Reservoir Capacity  Decreasing  Floods

Sedimentation in Reservoirs 1976 Meganiño 1983 Meganiño

Sedimentation in Reservoirs 1976

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 % 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)

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 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 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  Artificial channel constructed to discharge sediment into Bohai Sea  Creates 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  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  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?