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 million ha %Unclassified State Forests 0.73 5.08Hill Forests 0.67 4.65Mangrove Forests 0.60 4.09Village Forests 0.27 1.83Coastal Afforestation 0.18 1.24Inland Sal Forests 0.12 0.83TOTAL 2.57 17.72

Hill Forests 4.65%

Unclassified State Forests 5.08%

Forest Types of Bangladesh

Mangrove Forests 4.09%

Forest Types of Bangladesh

Coastal afforestation 1.24% (Mangrove)

Sal Forests 0.83%(Shorea robusta)

Forest Types of Bangladesh

Village Forests 1.83% ?

Forest Types of BangladeshSOCIAL FORESTRY (IN MARGINAL LANDS)

Block PlantationAgroforestry

Roadside PlantationRailway Plantation Embankment 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 57With India 54With 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 Karnaphuliis 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 Kaptai LakeThe 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 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 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 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 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 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 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 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 LakeThe 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 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 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 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 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 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 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 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 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 Kaptai LakeThe 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 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 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 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 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 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 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 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.

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

Watershed

 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.

Topography, Soil & Climate

Climate

Source:

Months Average rainfall

No. of

rainy days

Max. air temperature

(°C)

Min. air temperature

(°C)

Relative humidity

(%)

Evaporation (mm)

Wind velocity (km/hr)

Seasons considered

for this study

Jan 7.2 2 26.4 15.7 70 104 3.2Dry season

Feb 19.4 2 29.1 18.5 66 76 3.5Mar 29.8 3 31.5 22.4 63 83 5.8Apr 33.4 4 32.7 25.2 61 79 9.1

Wet season

May 238.6 10 32.9 26.1 69 76 9.3

Jun 165 13 32.1 26.3 83 85 8.2

Jul 295.5 15 32.4 26.4 85 82 7.9Aug 275.3 15 32.6 26.3 82 130 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 1.9Dry season

Dec 1 1 27.4 17.1 73 106 1.8

Multipurpose Kaptai LakeRequirement 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.

Multipurpose Kaptai LakeIt also plays a vital role for -

Sports

Navigation

Fishery

Recreation

Agriculture

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 :

Stations 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

SamplingWater samples were collected from 0.2D and 0.8D of the cross-section 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

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)

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

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)

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)

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

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).

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).

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.

CONCLUSIONSMassive 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