EFFECTS OF WATERSHED RESTORATION ON
WATER QUALITY AND QUANTITY OF KAPTAI
LAKE IN BANGLADESH
Laskar Muqsudur Rahman, PhD
Conservator of Forests
FOREST DEPARTMENT , BANGLADESH
Forest types of Bangladesh
Forest Types
Unclassified State Forests
Hill Forests
Mangrove Forests
Village Forests
Coastal Afforestation
Inland Sal Forests
TOTAL
million ha
%
0.73 5.08
0.67 4.65
0.60 4.09
0.27 1.83
0.18 1.24
0.12 0.83
2.57 17.72
Forest Types of Bangladesh
Unclassified State Forests 5.08%
Hill Forests 4.65%
Forest Types of Bangladesh
Mangrove Forests 4.09%
Coastal afforestation 1.24%
(Mangrove)
Forest Types of Bangladesh
Sal Forests 0.83%
(Shorea robusta)
Village Forests 1.83% ?
Forest Types of Bangladesh
SOCIAL FORESTRY (IN MARGINAL LANDS)
Block Plantation
Railway Plantation
Agroforestry
Embankment Plantation
Roadside Plantation
Forest Types of Bangladesh
Rubber plantation
Bamboo groves
Tea garden
River Network of Bangladesh
River Network of Bangladesh
Bangladesh is a riverine country .
About 800 rivers
including tributaries flow through
the country constituting a
waterway of total length
around 24,140 km
Transboundary Rivers
Total Rivers 57
With India 54
With Myanmar 3
Wetlands of Bangladesh
Total area of wetlands throughout
Bangladesh exceeds 8 million ha.
i.e., about 50% of the total national land.
Less than 10% of the total water flow originates
from country’s own catchments and rest comes
from India, Nepal and Bhutan.
River Karnaphuli
is the principal river
of CHT &
Chittagong
oiginating from the
Lushai hills in
Mizoram State of
India,
flows 270 km
southwest through
Rangamati to empty
into the Bay of
Bengal, through
Port City Chittagong.
The dam has a 745 feet (227 m) long spillway containing 16 gates. Through the spillway 5,250,000 cu ft/s (149,000 m3/s) of water can pass.
The Kaptai Lake
The Karnaphuli River, was dammed in 1962
primarily for development of hydroelectric
power, flooding an area of about 68,000
ha, to become the Kaptai Lake.
It is the largest man-made
freshwater lake in Bangladesh.
The dam has a 745 feet (227 m) long spillway containing 16 gates. Through the spillway 5,250,000 cu ft/s (149,000 m3/s) of water can pass.
The Kaptai Lake
 The lower part of the Kassalong River,
major tributary of the river Karnaphuli,
has formed the lake.
 The lake is “H” shaped, bearing two
arms, joined by a narrow gorge.
 The Karnaphuli, Kassalong & Myani Rivers
feed the right arm and
 The Chengri and the Rainkhiong Rivers
feed the left arm.
The dam has a 745 feet (227 m) long spillway containing 16 gates. Through the spillway 5,250,000 cu ft/s (149,000 m3/s) of water can pass.
The Kaptai Lake
Watershed
Kassalong RF
137863 ha
Maini Headwater RF
21586 ha
Rainkhiong RF
76330 ha
Sitapahar-Rampahar RF
5876 ha
Borkol RF
203 ha
TOTAL FOREST WATERSHED
2,71,658 ha
Unclassified State Forests (USF)
&
Other land use is roughly double
of the Forested Watershed area
Topography, Soil & Climate
 Most parts of this watershed are
mountainous with some up to 2438 m MSL.
 The beautiful landscape
is comprised of semi-consolidated and
consolidated rocks, possessing steep slope
of elevation ranging from 350 to 1 000 m
above MSL.
 The soils are mainly acrisols in the hills and
lixisols in the valleys.
Climate
No.
Months Average of
rainfall rainy
days
Min. air
Relative
Max. air
temperature temperature humidity
(%)
(°C)
(°C)
Evaporation
(mm)
Wind
velocity
(km/hr)
Seasons
considered
for this
study
Jan
7.2
2
26.4
15.7
70
104
3.2
Feb
Mar
Apr
19.4
29.8
33.4
2
3
4
29.1
31.5
32.7
18.5
22.4
25.2
66
63
61
76
83
79
3.5
5.8
9.1
May
238.6
10
32.9
26.1
69
76
9.3
Jun
165
13
32.1
26.3
83
85
8.2
Jul
Aug
295.5
275.3
15
15
32.4
32.6
26.4
26.3
85
82
82
130
7.9 Wet season
7.3
Sep
143
13
31.6
25.9
88
119
5.7
Oct
87.6
8
32.6
22.8
86
107
3.7
Nov
27.3
3
30.6
25.2
72
78
1.9
Dec
1
1
27.4
17.1
73
106
1.8
Source:
Dry season
Dry season
Multipurpose Kaptai Lake
Requirement of water level:
 27.07 m MSL is required
for safe operation of the power plant .
 below 24.38 m MSL the generation of hydro
electricity power disrupted.
 When the water level falls below 22.25 m MSL
the generation of hydro-electricity is ceased at
all five units of the 230-MW plant.
Water level status & requirement
35
33.22
m MSL
30
27.07
24.38
25
20.11
22.25
20
15
10
5
0
Max.
Min.
Safe
Disrrupt Cease
Water level
Multipurpose Kaptai Lake
It also plays a vital role for Navigation
Agriculture
Sports
Fishery
Recreation
Control deadly floods due to
torrential monsoon rain
Shifting cultivation: Threats to Kaptai Lake
Shifting cultivation reduced the natural system of
soil conservation.
• 60,000 families use 85,000 ha of the hill forests
• Soil loss 26–68 t ha-1 yr-1
Deforestation: Threats to Kaptai Lake
Except the Kassalong RF and
Rankhiang RF, the almost entire
watershed area of the lake has
been deforested.
As a result, the hill lands are
mostly covered with scrubs
which include scattered trees of
different species, bamboos,
grasses and shrubs.
For this reason, soil cover has
been exposed and rainwater
easily causes soil erosion, severe
run-off and landslides during
monsoon.
Human settlement: Threats to Kaptai Lake
Growing agriculture: Threats to Kaptai Lake
Population pressure
increased in the vicinity of
the Kaptai Lake for
swallowing most of the best
valley-bottom land for
cultivation.
Unscientific cultivation
causes soil erosion.
Massive teak plantation: Threats to Kaptai Lake
Besides, there are concerns that
teak plantations cause excessive
erosion and soil depletion.
RESTORATION & REHIBILITATION
FD initiated in 1980s a rehabilitation programme for Jhumias
RESTORATION & REHIBILITATION
Between 1990 and 2010 about 33000 ha of forest plantations were raised.
RESTORATION & REHIBILITATION
 2300 shifting cultivator families have been settled.
 Another 6,500 households were rehabilitated by the Chittagong Hill
Tracts Development Board.
 Each family allotted 2 ha land for housing & horticulture, also cash
capital for Alternate Income Generation.
RESTORATION & REHIBILITATION
The projects have provided alternatives to jhum cultivation,
particularly home gardening since the 1980s.
MATERIAL AND METHODS
Sampling sites
FOUR sampling stations were selected :
Station
s
Description
A
A point of the lake beyond main stream,
surrounded by forested areas (Barkal)
B
A point of the lake beyond main stream,
surrounded by degraded areas (Barkal)
C
A point of the main channel passing
through forested areas (Nannerchar)
D
A point of the main stream passing
through degraded areas (Nannerchar)
MATERIAL AND METHODS
Sampling
Water samples were collected from 0.2D and 0.8D of the crosssection at three equal distance points using water samplers
(DoF, Bangladesh).
MATERIAL AND METHODS
Physicochemical analysis of water samples
Water samples were analyzed to obtain readings on following
physicochemical properties of lake water :
1. pH (TOA pH Meter)
2. TSS (filtering, drying & weighing method)
3. Turbidity (Geopack Digital Turbidity Meter)
4. DO (measured by Jenway 970 DO2 Meter)
5. BOD5 (difference between initial DO and 5 day DO measured
by DO2 Meter), and
6. Velocity (was measured by Geopack Digital Velocity Meter)
Results
pH
7
6
pH Value
5
4
A
3
2
1
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sampling stations
pH ranged from 5.3-6.2 and 5.1-6.1 in station A and station B, respectively with
low pH value in station B during wet season.
Although these small changes in pH are not likely to have any direct impact on
aquatic life, they greatly influence the availability and solubility of all chemical
forms in the lake and may aggravate nutrient problems.
Total Suspended Solids (TSS)
2000
1800
1600
TSS (mg/L)
1400
1200
1000
A
800
B
600
400
200
0
Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct Nov Dec
Sampling stations
TSS ranged from 121.1 to 1358.4 mg/L and 126.3 to
1793.2 mg/L in station A and station B, respectively with
higher quantity of TSS in station B during wet season.
Turbidity
900
800
700
NTU
600
500
400
A
300
B
200
100
0
Jan Feb Mar Apr May Jun
Jul
Aug Sep Oct Nov Dec
Sampling stations
Turbidity ranged from 123.1 to 745.3 NTU and 145.5 to
825.8 NTU in station A and station B, respectively with
higher turbidity in station B during wet season.
Dissolved oxygen (DO)
8
7
DO (mg/L)
6
5
4
A
3
B
2
1
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sampling stations
DO varied between 6.0 mg/L to 7.3 mg/L and 5.1
mg/L to 6.9 mg/L in station A and station B,
respectively with lower DO in station B throughout
the year except during rainy period.
Biological Oxygen Demand (BOD5)
12
A
B
BOD5 (mg/L)
10
8
6
4
2
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Sampling stations
 It varied between 5.1 mg/L to 8.3 mg/L and 5.7 mg/L to 10.2 mg/L in
station A and station B, respectively with higher BOD in station B
throughout the year.
 During wet season BOD was comparatively higher in both the
stations.
Velocity of stream flow
3.5
3
Similar variation in velocity was
observed in the cross-section of
main channel C (1.16 to 2.89 m/s)
and D (1.08 to 3.32 m/s).
2.5
Velocity (m/s)
Velocity of stream flow is slightly
low (0.04 m/s) at B cross-section
during dry season as compared to
that from A cross-section. (0.05
m/s) Conversely, it is high during
wet season at B cross-section
(0.63 m/s).
2
A
B
1.5
C
D
1
0.5
0
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Sampling stations
DISCUSSIONS
Excessive TSS and higher turbidity where the lake-bank was devoid
of vegetation and under shifting cultivation indicates high rate of
siltation to shorten the life-time of the lake. The situation is further
aggravated during the monsoon.
On the other hand the lake passing through its watershed with forest
plantations and controlled shifting cultivation exhibited
comparatively better physicochemical properties
The results indicates that tree cover retards run-off and soil erosion
and help maintain water quality and influence stream flow.
Further in-depth study will generate data to help impress policymaker
to bring the watersheds of Kaptai Lake under forest plantation
programmes, control of shifting cultivation and adoption of policy for
environmentally sustainabale agriculture.
CONCLUSIONS
Massive tree restoration programmes in the vital watersheds, and
forestry practices should be planned in such a way that the forest
production, and water yield and quality are in complete harmony.
ACKNOWLEDGEMENTS
Forestry Development & Training Centre, Kaptai
Pulpwood Forest Division, Kaptai
Karnaphuli Hydro Power Station Authority, Kaptai
Bangladesh Water Development Board
Bangladesh Department of Fishery
THANK YOU