Transcript Sustainability Considerations in the Design of Big Dams

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
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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
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Sudan needs Energy
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Merowe Dam
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19-year old Civil War
Frequent power blackouts
Utilizing Hydropower
Dam Design Details
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Ten turbines – 1,250 MW Capacity
Length: 10 km
Height: 65 m
Reservoir Length: 170 km
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
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
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
“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
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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!
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:
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Last 100 years
Wetter climate
Drier climate
 Make
recommendations to dam design
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]
Sedimentation into the Reservoir
Anthony Paris
Erosion: Sources of Nile
Sediments
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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
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Suspended Load
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Distribution:
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particulates that travel
while suspended in the
water column
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
Reservoir Deposition I
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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
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Detention Time
Shape of reservoir
Operating procedures
Reservoir Deposition II
Hand Calculations
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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
Hand Calculations
Calculating Trapping Efficiency – 1st Round
 Brune’s Curve
 C = Capacity
 I = Inflow
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C
 T
I
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
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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 108 m3
Drawdown Area: 2.46 x 108 m3
Recommendations
– 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)
 Malaria
Difficulties
 TOO
BROAD
 Model is stupid
 Conflicting expectations
Conclusions
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