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 Future Work 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 Introduction Sudan needs Energy Merowe Dam 19-year old Civil War Frequent power blackouts Utilizing hydropower Creating hope Dam Design Details Ten turbines – 1,250 MW Capacity Long in relation to height Active reservoir storage 8.3 bcm General Layout Average Longterm Monthly Nile flows, 1872-1986 25 Discharge (km^3/month) 20 15 10 5 0 January February March April May June July August September October November December The New Model “The Model” Storage to Elevation Relationship Reservoir Characteristics 350 340 330 Elevation (m) 320 310 300 290 280 270 260 0 1E+09 2E+09 3E+09 4E+09 5E+09 6E+09 7E+09 Sur face Ar e a (m ^2) Reservoir Characteristics 350 340 330 Elevation (m) 320 310 300 290 280 270 260 0 2E+10 4E+10 6E+10 8E+10 Storage (m^3) 1E+11 1.2E+11 1.4E+11 Matlab Model dS/dt = inflow – evap – Q_out(turbines) – Q_out(overflow) Determines what volume to make available to turbines Pessimistic Model – use as much water as possible Gradual Release Model – ration storage in dry season Constant Head Model – Q_out=Q_in Determines the number of turbines to turn on Calculates volume, area, Power Pessimistic Gradual Release Constant Head The Effect of Climate Change on Dam Performance Suzanne Young Climate change Changes in chemical composition of atmosphere global warming Temperatures increase, precipitation? Literature review: Predictions of Nile flows confounded by different simulations giving conflicting results 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. Climate scenarios Climate scenario Years Average flow Deviation from long term [km3/yr] average 88 km3/yr No change 1943-1969 88 -- Wetter climate 1872-1898 102 +15% Drier climate 1979-1986 74 -15% Also varied maximum storage height of reservoir from 294 m to 298 m Nile discharge, 1872-1986 130 120 Longterm annual average = 88.1 km^3/year Annual discharge (km^3/year) 110 100 90 80 70 60 50 40 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 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] Results Wetter climate = highest power (~30% higher than no change in climate) Reservoir storage height increase gives linear increase in power (~10%/m) Pessimistic model > Gradual release model Drier climate power yields higher than no change in climate (!) Pessimistic model No change in climate Wetter climate Gradual release model Drier climate Pessimistic model yields higher power than Gradual Release model Pessimistic model: Comparison of climate scenarios Average annual power [Watts] 2.40E+11 2.35E+11 2.30E+11 No change 2.25E+11 Wetter climate Drier climate 2.20E+11 2.15E+11 2.10E+11 2.05E+11 294 295 296 297 Maximum storage height of reservoir [m] 298 Seasonal variations Climate scenario Wetter No change Drier January 4.95 3.82 3.30 February 3.44 2.84 2.60 March 2.79 2.21 2.17 April 2.01 1.91 3.20 May 1.71 1.95 2.81 June 2.04 2.55 2.74 July 6.02 6.92 4.87 August 20.84 18.50 14.79 September 25.05 20.77 18.24 October 17.30 14.12 9.95 November 9.53 7.62 5.36 December 6.70 4.88 3.97 Annual 102.39 88.09 73.54 Recommendations Use pessimistic model as basis for operating parameters Increase height of maximum reservoir storage pending economic analysis Sedimentation into the Reservoir Anthony Paris 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.) 50-228 million tones per year Sedimentation Analysis 1) How much sediment will settle in the reservoir? 2) Where will the sediment settle? 3) How long is the economic life of the project? 4) What things can be done to improve the situation? Hand Calculations Calculating Trapping Efficiency – 1st Round Brune’s Curve C = Capacity I = Inflow C T I Hand Calculations Calculating VS – 1st Round β = Bulk density of clay loam QC = sediment load [tons/yr] VS = Volume of sediment retained [m3/yr] VS T QC Borland & Miller Reservoir Classification H = any water lvl. HO = lowest bed lvl. VH = res. Vol. at H α = coef. M = coef. (slope) log H vs log C 10.2 10 y = 4.4794x + 2.2173 9.8 9.6 log C 9.4 9.2 9 8.8 8.6 1.45 1.5 1.55 1.6 1.65 1.7 1.75 log H-Ho Lake 65% dead storage 35% active storage V H H H O M 1.8 Economic Life of Reservoir Scenarios Flow Rate Suspended Load Estimated Bed Load Economic Life 1 44 billion m3/yr 30 million 5% 350 yrs 2 63.7 billion m3/yr 50 million 15% 205 yrs 3 44 billion m3/yr 77 million 5% 105 yrs 4 63.7 billion m3/yr 158 million 15% 65 yrs 5 44 billion m3/yr 137 million 5% 70 yrs 6 63.7 billion m3/yr 228 million 15% 45 yrs Improvements 1) Trapping 2) Sluicing Opening low level-lying sluices to flush out sediments, only effects local area 3) Dredging Creating dams upstream to catch sediment $$$ May be cost effective towards end of life 4) Flushing Allow the high sediment filled flood waters to flush through the system The Effect of the Dam on Public Health Teresa Yamana Dams’ Threat to Public Health As a development project, obligation to protect public health Merowe Dam expected to increase incidence of Malaria, Schistosomiasis, River Blindness and Rift Valley Fever Stagnant water in reservoirs and irrigation ditches provide habitat for vectors Constant supply of water - Dry season no longer limits vectors Malaria Protozoa Plasmodium transmitted by Anopheles mosquitoes A. funestus breeds in illuminated shoreline throughout the year A. gambiae breeds in reservoir drawdown area in dry season (November – June) Drawdown area: 129 km2 Illuminated shoreline: 2-48 km2 Malaria Control Strategies Reduce Mosquito habitat through operating parameters Chemical or biological control strategies Reduce bites by using window screens, bednets Provide vaccination and treatment for at risk or infected population Schistosomiasis Parasite carried by snails living in illuminated shore line Reduce human contact to water – piped water supply Provide sanitation services – break link in life cycle Control snail population River Blindness Transmitted by black fly – fast moving water Water-washed – provide piped water supply Stop flow through dam 2 days per 2 weeks July – September Annual Power Generated normal with RB control Percent reduction Var 1 2.05E+11 1.96E+11 4.39 Var 2 1.99E+11 1.89E+11 5.03 Var 3 1.87E+11 1.77E+11 5.35 River Blindness – Variation 2 Rift Valley Fever Transmitted from livestock to humans via mosquitoes Occurs when reservoirs are filled Vaccinate or remove livestock Quarantine contaminated livestock and meat Warn livestock and meat workers Control mosquito habitat Model Preferences A. gambiae – Variation 3 A. funestus and Schistosomiasis snails – Variation 1 River Blindness blackfly – add control Which is Most Important? Need more data! What diseases will cause the most problems? Formulate strategy based on regional priority GOAL – no increase in disease caused by dam Future Work Integrate 3 Climate, Sedimentology and Public Health concerns Thorough cost-benefit analysis Climate Sedimentation More experimentation with various climate scenarios 2-D and 3-D models to predict delta formations and identify problem spots Public Health Prioritize between diseases to find optimal operating parameters THANK YOU!! Prof. El Fatih Eltahir Prof. Dennis McLaughlin & Sheila Frankel Profs. Ole Madsen & Dara Entekhabi Dr. Sadeqi of the Kuwait Fund Valeri Ivanov 1E seniors!