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  Difficulties and lessons learned  Conclusions

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

General Layout

Storage to Elevation Relationship

“The Model”

The Effect of Climate Change on Dam Performance Suzanne Young

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

The Big Picture  Documented changes in chemical composition of atmosphere (e.g. CO 2 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!

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.

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 Last 100 years Wetter climate Wetter climate Drier climate Drier climate  Make recommendations to dam design

Potential Hydropower Power = γQh γ = ρg ρ = density of water = 1000 [kg/m 3 ] g = gravity = 9.8 [m/s 2 ] Q = flow at dam [m 3 /s] h = drop in head between intake to powerhouse and outlet to river [m]

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.)  ~140 million tones per year

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

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 Detention Time Shape of reservoir Shape of reservoir Operating procedures Operating procedures

Reservoir Deposition II

Hand Calculations  Calculating Q S (“Flow” of Sediments) from Q (Flow)  Find Hydrograph with corresponding Sediment Load Concentrations  Convert Load from concentration (mg/L)to volume (m 3 )  Do linear regression to determine correlation between Q S and Q; breaking the hydrograph into two sections, monsoon, and non-monsoon.  Extrapolate over 100 year monthly data set to have Q S

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

The Effect of the Dam on Public Health Teresa Yamana

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

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)

Drawdown Area: 2.46 x 10 8 m 3

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)

Difficulties  TOO BROAD  Model is stupid  Conflicting expectations

Conclusions ????????????????????????????