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Sustainability Considerations in the Design of Big Dams: Merowe, Nile Basin

Sustainability Considerations in the Design of Big Dams: Merowe, Nile Basin. Mentor: Prof. El Fatih Eltahir Group: Anthony Paris, Teresa Yamana, Suzanne Young. Outline. Introduction and motivation Nile hydrology The model Climate Sedimentation Public health

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Sustainability Considerations in the Design of Big Dams: Merowe, Nile Basin

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  1. Sustainability Considerations in the Design of Big Dams:Merowe, Nile Basin Mentor: Prof. El Fatih Eltahir Group: Anthony Paris, Teresa Yamana, Suzanne Young

  2. Outline • Introduction and motivation • Nile hydrology • The model • Climate • Sedimentation • Public health • Difficulties and lessons learned • Conclusions

  3. Goals and Motivation • Simulate the role of environmental engineers in large scale projects • Analyze the effect the Dam will have on the environment and local population, and make recommendations to mitigate effects • Assess whether long-term effects will significantly decrease Dam’s lifetime and plan accordingly

  4. Introduction • Sudan needs Energy • 19-year old Civil War • Frequent power blackouts • Merowe Dam • Utilizing Hydropower • Dam Design Details • Ten turbines – 1,250 MW Capacity • Length: 10 km • Height: 65 m • Reservoir Length: 170 km

  5. General Layout

  6. Storage to Elevation Relationship

  7. “The Model”

  8. The Effect of Climate Change on Dam PerformanceSuzanne Young

  9. Climate • How do changes in river flow caused by climate change affect the Merowe Dam’s power capacity?

  10. The Big Picture • Documented changes in chemical composition of atmosphere (e.g. CO2 is rising) • Scientists predict if this activity continues, it will impact the environment • Lots of studies on climate change and global warming done by governments in U.S., Europe • Models agree global temperatures will rise, less certain about regional impacts (precipitation) • We don’t know what is going to happen to Nile flows!

  11. Range of discharges for major points along the Nile (Summary of Yates 1998b results) Two numbers on ends of each line represent extreme discharges of six GCM scenarios, whereas boxed number is historic average; Additional tick marks on each line are remaining GCM scenarios, which indicate range of climate change induced flows of Nile Basin.

  12. TO DO • Show different results of studies, and convince audience that we don’t know what will happen = document uncertainty! • Calculate hydropower under different scenarios of climate change: • Last 100 years • Wetter climate • Drier climate • Make recommendations to dam design

  13. Potential Hydropower Power = γQh γ = ρg ρ = density of water = 1000 [kg/m3] g = gravity = 9.8 [m/s2] Q = flow at dam [m3/s] h = drop in head between intake to powerhouse and outlet to river [m]

  14. Sedimentation into the ReservoirAnthony Paris

  15. Erosion: Sources of Nile Sediments • Ethiopian Highlands (~90%) • Travels through the Blue Nile and Atbara • The sediment load is most significant during flood season (July-Oct.) • ~140 million tones per year

  16. Transportation • Suspended Load • particulates that travel while suspended in the water column • Distribution: • 30% Clay (<0.002 mm) • 40% Silt (0.002-0.02 mm) • 30% Fine Sand (0.02-0.2 mm) • High level of total suspension

  17. Reservoir Deposition I • When river flow enters a reservoir, its velocity and transport capacity is reduced and its sediment load is deposited. • The depositional pattern usually starts with coarser material depositing first followed by the fine creating a delta. • Factors • Detention Time • Shape of reservoir • Operating procedures

  18. Reservoir Deposition II

  19. Hand Calculations • Calculating QS (“Flow” of Sediments) from Q (Flow) • Find Hydrograph with corresponding Sediment Load Concentrations • Convert Load from concentration (mg/L)to volume (m3) • Do linear regression to determine correlation between QS and Q; breaking the hydrograph into two sections, monsoon, and non-monsoon. • Extrapolate over 100 year monthly data set to have QS

  20. Hand Calculations • Calculating Trapping Efficiency – 1st Round • Brune’s Curve • C = Capacity • I = Inflow

  21. The Effect of the Dam on Public HealthTeresa Yamana

  22. Dams’ Threat to Public Health • Stagnant water in reservoirs and irrigation ditches provide habitat for vectors • Constant supply of water - Dry season no longer limits vectors • Merowe Dam expected to increase incidence of Malaria, Schistosomiasis, River Blindness and Rift Valley Fever

  23. Malaria Transmission • Protozoa Plasmodium transmitted by Anopheles mosquitoes • Causes 1 million deaths per year • Fever-like symptoms • A. funestus breeds in illuminated shoreline throughout the year • A. gambiae breeds in reservoir drawdown area in dry season (November – June)

  24. DrawdownArea: 2.46 x 108 m3

  25. Drawdown Area: 2.46 x 108 m3

  26. Recommendations • Malaria – Whenever possible, relocate communities outside of mosquito flight range • River Blindness – Stop flow over spillways for two days every two weeks over wet season to inhibit blackfly breeding • More to come (hopefully)

  27. Difficulties • TOO BROAD • Model is stupid • Conflicting expectations

  28. Conclusions • ? • ? • ? • ? • ? • ? • ?

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