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AN ANALYSIS OF THE FACTORS CONTROLLING FLOODING IN GUYANA IN 2005, 2006 & 2008. Presenter: Garvin Cummings Research Supervisor : Dr. David Farrell, CIMH. PRESENTATION OUTLINE. AIM AND OBJECTIVES OF THE RESEARCH INTRODUCTION FLOODING IN GUYANA - PowerPoint PPT Presentation
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AN ANALYSIS OF THE FACTORS CONTROLLING FLOODING IN GUYANA IN
2005, 2006 & 2008
Presenter:Presenter:Garvin CummingsGarvin Cummings
Research SupervisorResearch Supervisor: : Dr. David Farrell, CIMHDr. David Farrell, CIMH
Presenter:Presenter:Garvin CummingsGarvin Cummings
Research SupervisorResearch Supervisor: : Dr. David Farrell, CIMHDr. David Farrell, CIMH
PRESENTATION OUTLINE
• AIM AND OBJECTIVES OF THE RESEARCH
• INTRODUCTION
FLOODING IN GUYANA
• IMPACTS OF THE 2005, 2006 & 2008 FLOODS
• RESEARCH METHODOLOGY
• ANALYSIS OF RAINFALL DATA
• RESULTS – RAINFALL DATA ANALYSIS
• RESULTS – GOVERNMENT INVESTMENTS
• CONCLUSION
AIM OF THE RESEARCH
The aim of the research was to analyze the rainfall patterns associated with three flood events in 2005, 2006 and 2008 in Guyana and evaluate whether structural and non-structural investments made by the Government of Guyana after the 2005 flood mitigated the impact of the 2006 and 2008 floods.
OBJECTIVES OF THE RESEARCH
The research sought to achieve the following objectives:
1. Analyze the rainfall patterns that influenced the 2005, 2006 and 2008 flood events; this included a comparison of the spatial and temporal rainfall variability that gave rise to the three flood events. In addition, this objective also included a
characterisation of the antecedent moisture conditions before each of the flood events
OBJECTIVES OF THE RESEARCH
2. Assess the structural and non-structural investments made by the Government of Guyana (GOG) and Non Governmental Organisations (NGOs) toward flood mitigation subsequent to the 2005 flood and evaluate how these investments influenced the impact of the 2006 and 2008 floods.
3. Investigate how land-use practices may have changed before and after the 2005 flood and how these may have influenced the impacts of
subsequent floods.
INTRODUCTION
In January, 2005; February 2006 and December 2008 Guyana suffered three (3) of its most catastrophic flood events.
These three events were particularly noticeable because they all caused significant damages and occurred in Guyana’s secondary rainfall season (mid-Nov to mid-Feb); rainfall amounts and intensities are generally expected to be less than the primary rainfall season (mid-Apr to mid-Jul).
INTRODUCTION
All three (3) flood events impacted primarily Guyana’s Coastal Plain:
10% of land space 90% of total population below mean sea level most fertile lands centre for agriculture (35% GDP), commerce, culture, education and communication prone to (fluvial, pluvial and coastal) flooding
Atlantic Ocean
Brazil
Venezuela
Surinam
INTRODUCTION
Flooding on the Coastal Plain is driven by:
Extreme rainfallProximity to the Atlantic Ocean and the EDWCIt’s below mean sea level and is subject to storm surges
All three of these factors contributed to the three flood events in some way
East Demerara Water Conservancy (EDWC)
RAINFALL EVENTS
2005 Months prior to January, 2005 were dry 87% of December, 2004 rain fell in the last 9 days In January:- the 2, 3, 4 & 5-day rainfall records were exceeded- 30 year avg. of 185.2 mm was exceeded with 1108.2 mm surpassing the Dec.,1942 record of 1022 mm There was a period of high tides during this time of heavy rainsEDWC overflowed its banks
RAINFALL EVENTS
2006 Rainfall began on November 30, 2005 The highest 1-day rainfall in Georgetown (147.6 mm) on Nov 30 All stations along the coast exceeded their 30-year average in Dec 22 consecutive rain-days in Dec New 5-day maxima rainfall of 300.5 mm – surpassed 1942 record of 299.9 mm In January, 2006 stations exceeded their 30-year average by 2 to 5 times
RAINFALL EVENTS
2008 Rain began in early December, 2008 On December 10 several stations recorded in excess of 50 mm with as much as 236.5 mm in one location. Georgetown recorded 89.9 mm in 2.5 hrs and 115.5 mm in 24 hrs – the 9th Most locations surpassed their 30-year average
Rainfall and Normals for Selected Stations December 2008
0
200
400
600
800
1000
1200
1400
Anna
Reg
ina
Char
ity
McN
aab
Back
Ond
erne
emin
g
Wak
apoa
Wal
es F
ront
Boer
asiri
e
Uitv
lugt
Fro
nt
Diam
ond
Geor
geto
wn
LBI f
ront
Enm
ore
Fron
t
Cane
Gro
ve F
ront
Cane
Gro
ve B
ack
MAR
DS
New
Am
ster
dam
No.7
3 Vi
llage
Whi
m
Skel
don
Rose
Hal
l
Albi
on
Stations
Rain
fall
(mm
)
Monthly total
30-year average
SUMMARY OF FLOOD IMPACTS
2005 2006 2008Approx. 278,000 persons (37 % of country’s population )affected
Over 35,000 persons affected 2,000 to 3,0000 persons affected
34 deaths and water borne diseases
No deaths, but waterborne diseases
No deaths, but waterborne diseases
Losses of approx. US D 465.1 million /65% of GDP
Total losses estimated at USD 30.1 million /4.8% of GDP
Losses in excess of USD 5 million
In excess of USD 275 in losses suffered in the housing sector
Agriculture sector bore 74% of the losses
Approximately 190 sq. Km of rice affected and 32.5 sq. Km affected
Region 4 suffered 55% of the total losses
Region 5 suffered 79.2% of the total losses
Region 2 suffered the greatest losses
4 to 5ft of flood water on the ground for 4 to 5 weeks in some locations
1 to 3ft of flood water on the ground for 1 to 2 weeks in some locations
1to 2ft of flood water on the ground for 1 to 2 weeks in some locations
Source: ECLAC/Min of Agri
METHODOLOGY: Study Area
Source: ECLAC Source: Bureau of Statsistics
METHODOLOGY: Data Collection
1. Desk Study: Collection of reports and literature from which
secondary data on the 2005, 2006 & 2008 were retrieved
This included environmental background data, rainfall distribution, weather reports, social and economic impact assessments of the floods, previous work, newspaper articles
Sources included: the Ministries of Agriculture, Education, Health; Guyana Red Cross; Parliament Library, etc.
METHODOLOGY: Data Collection
Data collected included: Daily rainfall data for thirty-eight (38) locations in
the study area for the flood periods Historical data for the 38 locations were collected for
the computation of return periods Interview of senior government officials to ascertain: -
- the state of the drainage infrastructure prior to 2005 -- what investments were made after 2005 to reduce the impacts of future floods
- investments made into infrastructural development
METHODOLOGY: Data Analysis
Antecedent Moisture Condition: An analysis of the rainfall data for two (2) months prior
to the three flood events was done . The analysis included:
- comparison of rainfall amounts with the 30-year average- the number of rain days (greater than 1 mm in 24 hrs)- the number of wet days (greater than 5 mm in 24 hrs)
This analysis allowed for inferences on soil saturation levels and infiltration capacities immediately before the onset of the rainfall events that triggered the flooding.
METHODOLOGY: Data Analysis
Rainfall data analysis: Rainfall data for the three flood events for 38 stations
within the study area were analyzed to determine the return period of the rainfall event at each location. The analysis included:
- Simple Arithmetic Averaging to estimate missing data
- Statistical tests to remove outliers (Grubbs-Beck Test)
- Frequency Analysis/Gumbel plots to determine return periods for each flood event for the 38 locations
METHODOLOGY: Data Analysis
Rainfall duration: CIMH conducted a study in 2008 which showed that
floods in Guyana are not always intensity-driven, but are more volumetrically-driven.
The study showed that even though the 2005 flood was the most catastrophic for Guyana the 24 hour rainfall was rarely in excess of 25 years for any location
This research used 7-day maxima rainfall with a 4-day overlapping window for each location to ascertain the return period
RESULTS: Antecedent Moisture
Rainfall and Normals for Selected Coastal StationsNovember 2004
0
50
100
150
200
250
300
350
Anna
Reg
ina
Char
ity
McN
aab
Back
Ond
erne
emin
g
Wak
apoa
Wal
es F
ront
Boer
asiri
e
Uitv
lugt
Fro
nt
Diam
ond
Geor
geto
wn
LBI f
ront
Enm
ore
Fron
t
Cane
Gro
ve F
ront
Cane
Gro
ve B
ack
MAR
DS
New
Am
ster
dam
No.7
3 Vi
llage
Whi
m
Skel
don
Rose
Hal
l
Albi
on
Stations
Rain
fall
(mm
)
Monthly total
30-year average
Rainfall and Normals for Selected StationsDecember 2004
0
50
100
150
200
250
300
350
400
450
Anna
Reg
ina
Char
ity
McN
aab
Back
Onde
rnee
min
g
Wak
apoa
Wale
s Fro
nt
Boer
asiri
e
Uitv
lugt
Fron
t
Diam
ond
Geor
geto
wn
LBI f
ront
Enm
ore F
ront
Cane
Gro
ve Fr
ont
Cane
Gro
ve B
ack
MAR
DS
New
Amste
rdam
No.7
3 Vi
llage
Whi
m
Skeld
on
Rose
Hall
Albi
on
Stations
Rain
fall (
mm
)
Monthly total
30-year average
BEFORE THE JANUARY 2005 FLOOD
RESULTS: Antecedent Moisture
BEFORE THE JANUARY 2006 FLOOD
Rainfall and Normals for Selected Coastal Stations November 2005
0
50
100
150
200
250
300
350
Anna
Reg
ina
Char
ity
McN
aab
Back
Onde
rnee
min
g
Wak
apoa
Wale
s Fro
nt
Boer
asiri
e
Uitv
lugt
Fron
t
Diam
ond
Geor
geto
wn
Enm
ore F
ront
Cane
Gro
ve Fr
ont
Cane
Gro
ve B
ack
MAR
DS
New
Amste
rdam
No.7
3 Vi
llage
Whi
m
Skeld
on
Rose
Hall
Albi
on
Stations
Rain
fall (
mm
)
Monthly total
30-year average
Rainfall and Normals for Selected Coastal Stations December 2005
0
100
200
300
400
500
600
700
800
Anna
Reg
ina
Char
ity
McN
aab
Back
Ond
erne
emin
g
Wak
apoa
Wal
es F
ront
Boer
asiri
e
Uitv
lugt
Fro
nt
Diam
ond
Geor
geto
wn
Enm
ore
Fron
t
Cane
Gro
ve F
ront
Cane
Gro
ve B
ack
MAR
DS
New
Am
ster
dam
No.7
3 Vi
llage
Whi
m
Skel
don
Rose
Hal
l
Albi
on
Stations
Rain
fall
(mm
)
Monthly rainfall
30-year average
RESULTS: Antecedent Moisture
BEFORE THE JANUARY 2008 FLOOD
Rainfall and Normals for Selected Coastal Stations November 2008
0
50
100
150
200
250
300
350
Anna
Reg
ina
Char
ity
McN
aab
Back
Onde
rnee
min
g
Wak
apoa
Wale
s Fro
nt
Boer
asiri
e
Uitv
lugt
Fron
t
Diam
ond
Geor
geto
wn
LBI f
ront
Enm
ore F
ront
Cane
Gro
ve Fr
ont
Cane
Gro
ve B
ack
MAR
DS
New
Amste
rdam
No.7
3 Vi
llage
Whi
m
Skeld
on
Rose
Hall
Albi
on
Stations
Rain
fall (
mm
)
Monthly total
30-year average
Rainfall and Normals for Selected Stations December 2008
0
200
400
600
800
1000
1200
1400
Anna
Reg
ina
Char
ity
McN
aab
Back
Ond
erne
emin
g
Wak
apoa
Wal
es F
ront
Boer
asiri
e
Uitv
lugt
Fro
nt
Diam
ond
Geor
geto
wn
LBI f
ront
Enm
ore
Fron
t
Cane
Gro
ve F
ront
Cane
Gro
ve B
ack
MAR
DS
New
Am
ster
dam
No.7
3 Vi
llage
Whi
m
Skel
don
Rose
Hal
l
Albi
on
Stations
Rain
fall
(mm
)
Monthly total
30-year average
RESULTS: Rain days
BEFORE THE FLOODS
RESULTS: Wet days
BEFORE THE FLOODS
RESULTS: Return Periods
In general, Return Periods for 7-day maxima rainfall across the Study Area in 2005 was in the extreme range with the greatest return periods being 2500 years in Leonora Back, Region 3 and 1097 years in Georgetown.
The Return Periods for 2006 and 2008 were noticeably less than 2005 for most locations.
RESULTS: Return Periods
REGION 4
Yr George-town
Tr (yrs) Ogle Front
Tr
(yrs)Ogle Back
Tr
(yrs)LBI
FrontTr
(yrs)Mon Repos Agri Stn
Tr
(yrs)
`05 658.1 1097† 595.4 344† 426.1 37 700.1 147† -
`06 301.1 8 254.6 5 345.6 12 517.7 64† 229.4 8
`08 287.4 7 197.3 2 257 3 263.5 8 - Yr Enmore
FrontTr (yrs) Cane
Grove Back
Tr
(yrs)Cane Grove Front
Tr
(yrs)Timehri Tr
(yrs)
`05 392 182† 412 25 387.3 24 326.8 47.5
`06 257 5 264.2 4 288.2 7 231.1 8
`08 407.5 306† 303 7 131 1 216.5 6
WATER LEVELS IN THE EDWC, 2005
WATER LEVELS IN THE EDWC, 2006
Average Water-level in the EDWC, 2005/2006
50
51
52
53
54
55
56
57
58
59
60
Date
Wate
r-l
evel
(ft-
GD
)
Average Water-level in the EDWC, 2008/2009
54.00
55.00
56.00
57.00
58.00
59.00
60.00
Date
Wate
r-le
vel
(ft-
GD
)WATER LEVELS IN THE EDWC, 2008
EMPTYING THE EDWC IN 2006 & 2008
POST 2005 INVESTMENTS
Annual Drainage & Irrigation Allocations
6168.5 6159.5
17033.5
13254
20447
14414
4000
7000
10000
13000
16000
19000
22000
2003 2004 2005 2006 2007 2008 2009
Years
US
D (
x1
00
0)
POST 2005 INVESTMENTSBE
FOR
E 2
005
AFT
ER 2
005
POST 2005 INVESTMENTS
BEFORE 2005
AFTER 2005
CONCLUSION
1. There were considerable spatial and temporal variation in the rainfall influencing the three flood events – the same general locations were not impacted by all three events
2. In 2005, the flood was triggered by a 7-8 day period of extreme rainfall
3. While the rainfall was extreme, it was also clear that the drainage infrastructure (including pumps and sluices) did not follow a strict maintenance schedule prior to 2005
4. In 2006 and 2008 there were instances of extreme rainfall, but it was distributed over a of 2-3 week period prior to the flood events
CONCLUSION
5. There were considerable investments directed toward improving the drainage system after the 2005 flood – approx. 100 million US dollars from 2005 to 2009
6. There was uncertainty in the effectiveness of the investments in mitigating the impacts of the 2006 and 2008 for the following reasons:
the extensive variability of rainfall over the three flood events made comparison difficult
the areas where significant investments were made after the 2005 flood did not receive rainfall of a similar magnitude in 2006 and 2008
CONCLUSION
the floods of 2006 and 2008 were caused primarily by the release of water from the EDWC and therefore it was difficult to ascertain the contribution of direct rainfall
7. Flood insurance was proposed as a further safeguard for the physical infrastructure and livelihoods in light of the projected impacts of climate change.
THANK YOU!