flow regulating functions of natural ecosystems for dam synchronization in the zambezi river basin
DESCRIPTION
Transboundary Water Management Workshop held in Johannesburg, South Africa from April 29-30, 2014.TRANSCRIPT
Ph
oto
: D
avid
Bra
zie
r/IW
MI
Ph
oto
:T
om
va
n C
ake
nb
erg
he
/IW
MI
Ph
oto
: T
om
va
n C
ake
nb
erg
he
/IW
MI
www.iwmi.org
Water for a food-secure world
Xueliang Cai
29/04/2014, Johannesburg, South Africa
Flow Regulating Functions
of Natural Ecosystems for
Dam synchronization in the
Zambezi River Basin
www.iwmi.org
Water for a food-secure world
Outline
• Introduction
• The Zambezi river basin
• Flow duration curves for analysing
hydrological functions
• Results
• Conclusions
www.iwmi.org
Water for a food-secure world
Introduction – why does it matter
• Africa, and to less extent Asia, landscape largely
characterized with natural vegetation and untamed areas;
• Forests, wetlands and floodplains big influence on
hydrological processes;
• Natural ecosystems into
water resources planning
and management (e.g.
dam operations) for green
economy;
• Lack of understanding on
hydrological functions of
ecosystems.
www.iwmi.org
Water for a food-secure world
Mixed findings of wetland hydrological functions
• 30/66: headwater wetlands reduce flood peaks, but 27 concluded the other way around.
• 11/20: headwater wetlands increased flood event volumes.
• 48/77: wetlands increase evaporation or reduce river flow.
• 47/71: wetlands reduce downstream flows during dry periods but in 20% of cases verse visa.
• 23/28: floodplains reduce or delay downstream floods
Bullock and Acreman, 2003, based on review of 169 studies
www.iwmi.org
Water for a food-secure world
ESA GlobCover
GLWDThe Zambezi
River Basin
www.iwmi.org
Water for a food-secure world
The Zambezi
River Basin
102 stations with 25 years
or more data
18 sites identified
www.iwmi.org
Water for a food-secure world
The method
Downstream
gauge
Upstream
gauge
Reference
gauges
www.iwmi.org
Water for a food-secure world
Establishing reference (no ecosystem) flow duration curve
Standardized FDCs derived from mean daily flow measured at gauges located in the
vicinity of the Luswishi floodplain
0.01
0.1
1
10
0.1 2 12 22 32 42 52 62 72 82 92 99.3
Q/Q
me
an
% time flow exceeded
Normalised reference FDC
Regional FDC (avg) GRDC 1591500 (Reference) FRIEND 60334250 (Reference)
www.iwmi.org
Water for a food-secure world
Transferring the reference flow duration curve to the
site of interest
0.1
1
10
100
1000
0.1
0.5
0.9 4 8
12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96
99.1
99.5
99.9
Flo
w (m
3 s-1 )
% time flow exceeded
Reference FDC GRDC 1591440 (Downstream)
Comparison of the “reference” FDC and the observed FDC at the gauge
downstream of the Luwishi floodplain
FDCdestination = FDCreference * Qdes. mean
www.iwmi.org
Water for a food-secure world
Generating the reference flow time series
Pdes = (Pupstream + Pdownstream)/2
0.1
1
10
100
1000
0.1 2 12 22 32 42 52 62 72 82 92 99.3
Q/Q
me
an
% time flow exceeded
Reference FDC downstream of floodplain
Regional FDC (avg)
www.iwmi.org
Water for a food-secure world
Results
0
20
40
60
80
100
120
1-O
ct-8
4
1-N
ov-
84
1-D
ec-
84
1-J
an
-85
1-F
eb
-85
1-M
ar-
85
1-A
pr-
85
1-M
ay-
85
1-J
un
-85
1-J
ul-
85
1-A
ug
-85
1-S
ep
-85
1-O
ct-8
5
1-N
ov-
85
1-D
ec-
85
1-J
an
-86
1-F
eb
-86
1-M
ar-
86
1-A
pr-
86
1-M
ay-
86
1-J
un
-86
1-J
ul-
86
1-A
ug
-86
1-S
ep
-86
Flo
w (
m3s-1
)
Daily flow with and without floodplain: HY1984 and HY1985
Without floodplain (simulated) With floodplain (observed) Upstream floodplain (observed)
Flood plains
www.iwmi.org
Water for a food-secure world
ResultsBase flow index Mean annual minimum (m3s-1)
1-day 10-day
With floodplain 0.994 2.96 3.04
Without floodplain 0.886 2.02 2.13
Return
period
(yrs)
Flood Magnitude (m3s-1) %
reduction
With
floodplain
Without
floodplain
1.1 27.3 37.0 26.3
1.5 41.0 62.0 33.9
2 47.3 73.3 35.5
5 56.2 94.3 37.2
10 65.2 104.6 37.7
25 71.4 115.3 38.0
50 75.4 121.9 38.2
100 78.9 127.8 38.3
200 82.0 133.0 38.3
0
20
40
60
80
100
120
140
1 10 100
Pe
ak
flo
od
flo
w (
m3s-1
)
Return period (yrs)
Flood Frequency
With floodplain Without floodplain (simulated)
Extrapolated
0
20
40
60
80
100
120
140
1 10 100
Pe
ak
flo
od
flo
w (
m3s-1
)
Return period (yrs)
Flood Frequency
With floodplain Without floodplain (simulated)
Extrapolated
Flood plains
www.iwmi.org
Water for a food-secure world
ResultsHeadwater wetlands
0.00001
0.0001
0.001
0.01
0.1
1
10
100
0.1
0.5
0.9 4 8
12
16
20
24
28
32
36
40
44
48
52
56
60
64
68
72
76
80
84
88
92
96
99
.1
99
.5
99
.9
Q/Q
me
an
% time flow exceeded
Regional FDC (avg) - inc 65312102 FRIEND 65312602 (downstream)
0
50
100
150
200
250
300
350
400
450
5001
-Oct
-85
1-N
ov
-85
1-D
ec-
85
1-J
an
-86
1-F
eb
-86
1-M
ar-
86
1-A
pr-
86
1-M
ay
-86
1-J
un
-86
1-J
ul-
86
1-A
ug
-86
1-S
ep
-86
1-O
ct-8
6
1-N
ov
-86
1-D
ec-
86
1-J
an
-87
1-F
eb
-87
1-M
ar-
87
1-A
pr-
87
1-M
ay
-87
1-J
un
-87
1-J
ul-
87
1-A
ug
-87
1-S
ep
-87
Flo
w (
m3s-
1)
Daily flow with and without headwater wetlands: HY1984 and HY1985
Without headwater wetlands (simulated) With headwater wetlands (observed)
Percentile Flow (m3s-1) % difference
With
wetlands
Without
wetlands
99 0.0 0.1 -
95 0.0 0.5 -
90 0.0 0.8 -
75 0.2 2.1 980.4
50 2.2 5.3 142.1
25 20.1 17.1 -15.3
10 70.3 46.2 -34.3
5 107.0 73.5 -31.4
1 152.9 208.2 36.2
Bua River in Malawi
Total catchment area: 4,777 km2
Area of wetlands: 823 km2 (17.2% of
total catchment)
www.iwmi.org
Water for a food-secure world
ResultsHeadwater wetlands
BFI Mean annual minimum (m3s-1)
1-day 10-day
With wetlands 0.96 0.028 0.032
Without wetlands 0.74 0.389 0.443
Return
period
(yrs)
Flood Magnitude
(m3s-1)
%
reductio
nWith
wetlands
Without
wetlands
1.1 31.9 15.0 -112.7
1.5 75.0 24.8 -202.4
2 96.5 47.8 -101.9
5 140.5 161.8 13.2
10 164.4 272.2 39.6
25 190.8 439.6 56.6
50 208.3 579.2 64.0
100 224.3 728.3 69.2
200 239.2 885.9 73.0
0
100
200
300
400
500
600
700
800
900
1000
1 10 100
Pe
ak
flo
od
flo
w (
m3s-1
)
Return period (yrs)
With headwater wetlands (observed) Without headwater wetlands (simulated)
Extrapolated
www.iwmi.org
Water for a food-secure world
ResultsMiombo forest
Luchelemu River in Malawi
Total catchment area: 261 km2
Area of wetlands: 244 km2 (93.5% of
total catchment)
0.01
0.1
1
10
100
0.1 2 12 22 32 42 52 62 72 82 92 99.3
Flow
(m3 s-1
)
% time flow exceeded
Regional FDC (avg) Downstream (65312505)
0
5
10
15
20
25
1-O
ct-7
2
1-N
ov
-72
1-D
ec-
72
1-J
an
-73
1-F
eb
-73
1-M
ar-
73
1-A
pr-
73
1-M
ay
-73
1-J
un
-73
1-J
ul-
73
1-A
ug
-73
1-S
ep
-73
1-O
ct-7
3
1-N
ov
-73
1-D
ec-
73
1-J
an
-74
1-F
eb
-74
1-M
ar-
74
1-A
pr-
74
1-M
ay
-74
1-J
un
-74
1-J
ul-
74
1-A
ug
-74
1-S
ep
-74
Flo
w (
m3s-1
)Daily flow with and without forest: HY1972 and HY1973
Without forest (simulated) With forest (observed)
www.iwmi.org
Water for a food-secure world
ResultsMiombo forest
BFI Mean annual minimum (m3s-1)
1-day 10-day
With forest 0.79 0.552 0.628
Without forest 0.67 0.465 0.508
Return
period
(yrs)
Flood Magnitude
(m3s-1)
%
reductio
nWith
forest
Without
forest
1.1 6.5 7.9 17.7
1.5 9.6 17.0 43.3
2 11.7 19.7 40.6
5 16.8 30.6 45.1
10 20.4 38.3 46.7
25 25.3 48.5 47.8
50 29.1 56.2 48.2
100 33.1 64.2 48.4
200 37.3 72.4 48.5
0
10
20
30
40
50
60
70
80
1 10 100
Pe
ak
flo
od
flo
w (
m3s-1
)
Return period (yrs)
With forest (observed) Without forest (simulated)
Extrapolated
www.iwmi.org
Water for a food-secure world
Conclusions• A simple yet effective approach proposed and
tested capable of application in the Zambezi with
limitations;
• In the Zambezi:
• floodplains decrease the magnitude of flood
flows and increase low flows;
• headwater wetlands increase the magnitude of
flood flows and decrease low flows;
• miombo forest, when covering more than 70%
of the catchment, decrease the magnitude of
flood flows and also decrease low flows.
www.iwmi.org
Water for a food-secure world
Conclusions
Some further potential developments to separate
other factors:
• Land use, topography, climate soil, geology;
• Society development (Population, infrastructure,
farming, deforestation);
• Groundwater contribution.
• And feed into synchronized
operations.
www.iwmi.org
Water for a food-secure world
Thank you!