Jumat, 27 Maret 2009

DANAU TOBA (LAKE TOBA)

DANAU TOBA (LAKE TOBA)

A bird-eye view of the lake
Photo.
Photo: H. Haerumen Js

A. LOCATION

  • North Sumatra Province, Indonesia.
  • 2:21-2:56N, 98:26-99:15E; 905 m above sea level.

B. DESCRIPTION

Lake Toba lies in the northern part of Barisan Mountain Range, which is volcanic and traverses Sumatra Island from northwest to southeast as its backbone.
The laketrough is surrounded by precipitous cliffs 400-1,200 m high. Based on the topographic feature and the wide distribution of volcanic ejecta around the lake, some geologists and valcanologists have considered it to be a giant caldera or cauldron.


The water surface of L. Toba is 905 m above sea level and about 1,100 km2 wide. The total area of the lake, including the areas of Samosir and Paradapur Islands, amounts to 1,780 km2. The mountains around the lake are called Batak Highlands. The only draining river from L. Toba, the Asahan, flows southeastwards dissecting the gentle slopes of the pyroclastic plateau.

C. PHYSICAL DIMENSIONS (Q)

Surface area [km2] 1,100
Volume [km3] 1,258
Maximum depth [m] 529
Water level Unregulated
Normal range of annual water level fluctuation [m] 1.5
Catchment area [km2] 3,440

D. PHYSIOGRAPHIC FEATURES (Q)

D1 GEOGRAPHICAL

  • Sketch map: Fig. ASI-10-01.
  • Names of main islands: Samosir (640 km2) and Paradapur (7 km2).
  • Number of outflowing rivers and channels (name): 1 (Asahan R.).

D2 CLIMATIC

  • Climatic data at Parparean, 1961-1980

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
Mean temp. [deg C] 19.3 19.0 18.9 19.3 19.4 19.1 19.0 18.8 19.0 19.4 19.4 19.1 19.1
Precipitation [mm] 100 105 115 132 124 102 83 110 148 174 182 178 1,732
  • Solar radiation: 15.7 MJ m-2 day-1.
  • Water temperature [deg C]
Station Surface
Haranggaul 27
Tigaras 27
Tomok 26
Simanindo 27
Pangururan 27
Nainggolan 27
Prapat 27
Porsea 26
  • Freezing period: None.
  • Notes on water mixing and thermocline formation Mizuno observed an extremely homogeneous vertical distribution of water temperature from the surface down to 300 m depth on 23 January 1976 (13).

    Fig. ASI-10-01
    Sketch map (altitude in ft)(14).

E. LAKE WATER QUALITY (Q)

E2 pH,

1979
Station Surface
Lotung 8.4
Situmeang 7.9
Bukit 8.4
Tongging I 7.0
Tongging II 7.9
Onan Runggu 7.6
Prapat 8.2

E4 DO [mg l-1],

1979
Station Surface
Lotung 6.7
Situmeang 6.8
Bukit 9.3
Tongging I 6.3
Tongging II 7.0
Onan Runggu 7.0
Prapat 8.0

E5 COD [mg l-1],

1979
Determined by KMnO4 method.
Station Surface
Haranggaul 2.30
Prapat 2.80
Mogang 2.24
Onan Runggu 2.15
Porsea 2.06
Hashinggahan 1.30
Tomok 1.53
Sabulan 1.72
Muara 1.36
Balige 1.24

E8 PHOSPHORUS CONCENTRATION

  • Total-P [mg l-1], 1979
Station Surface
Haranggaul 0.31
Hasinggahan 0.32
Tomok 0.66

E9 CHLORIDE CONCENTRATION [mg l-1],

1979
Station Surface
Haranggaul 8.6
Prapat 8.3
Mogang 10.1
Onan Runggu 10.4
Porsea 10.3
Hasinggahan 11.8
Tomok 11.0
Sabulan 9.2
Muara 9.6
Balige 9.5

F. BIOLOGICAL FEATURES (Q)

F1 FLORA

  • Emerged macrophytes: Nelumbo nucifera, Nymphaea sp.
  • Floating macrophytes:Eichhornia crassipes, Lemna minor, Azolla pinnata, Spirodella polyrhiza.
  • Submerged macrophytes:Potamogeton malaianus, P. polygonifolius, Myriophyllum spicatum, Ceratophyllum demersum, Hydrilla verticillata, Chara sp.
  • Phytoplankton:Amphora, Cocconema, Asterionella, Synedra, Gomphonema, Orthosira, Navicula,Mastogloia, Pleurosigma, Nitzschia, Genicularia, Botryococcus, Synechococcus,Anabaena, Oscillatoria.

F2 FAUNA

  • Zooplankton: Cyclops, Cladocera.
  • Benthos: Macrobrachium sintangensis, Brotia costula, Thiara scabra, Melanoidestuberculata, Melanoides granifera, Anentome helena, Lymnaea brevispira, L.rubiginosa, Physastra sumatrana, Corbicula tobae.
  • Fish: Tilapia mossambica, Aplocheilus pachax, Lebistes reticulatus, Osphronemus goramy, Trichogaster trichopterus, Channa striata, C. gachua, Clarias batrachus, C. nieuhofi, C. sp., Nemachilus fasciatus, Cyprinus carpio, Puntius javanicus, P. binotatus, Osteochilus nasselti, Lissochilus sp., Labeobarbus sora, Rasbora sp.

F4 BIOMASS

  • Submerged macrophytes [g (wet wt.) m-2]
Station Potamogeton sp. Myriophyllum spicatum Others Total
Lotung 2,470 130 <25 2,600
Onan Runggu 2.800 150 0 2,950
Parbaloan Urat 1,833 310 520 2,663
Tongging 1,947 157 <25 2,104
Lumban Sitorus 150 1,640 0 1,750

F5 FISHERY PRODUCTS

  • Annual fish catch [metric tons] 1978: 2,820.

F6 PAST TRENDS

  • Annual fish catch [metric ton]
Year Production
Tilapia mossambica Cyprinus carpio Others Total
1967 1,039 207.8 831.2 2,078
1976 - - - 2,211
1977 - - - 2,569
1978 2,175.1 4.6 640.2 2,820

F7 NOTES ON THE REMARKABLE CHANGES OF BIOTA IN THE LAKE IN RECENT YEARS

Increasing: Tilapia mossambica. Decreasing: Cyprinus carpio.

G. SOCIO-ECONOMIC CONDITIONS (Q)

G1 LAND USE IN THE CATCHMENT AREA

1981

Area [km2] [%]
Natural landscape
Grass (alang-alang) 955 40.6
Scrub 59.24 2.5
Forest 159.66 6.8
Reforestation 388.70 16.6
Regreening 228.28 9.7
Agricultural land 512.08 21.8
Plantation 20.88 0.9
Others 23.56 1.1
Total 2,347.50 100
  • Main types of woody vegetation:Tropical high mountain forest; Pinus merkusii forest; Macadamia hildebrandii forest.
  • Main types of herbaceous vegetation:Imperata cylindrica with Rhodomyrtus tomentos, Melastoma sp. and Gleichenia linearis.
  • Main kinds of crops: Rice, sweet potato, maize, vegetables.
  • Levels of fertilizer application on crop fields: Moderate.

G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE

: No information.

G3 POPULATION IN THE CATCHMENT AREA

1980
District Area[km2] Population Family Population density [km-2]
Tapanuli Utara 2,420.5 309,111 66,744 128
Tanah Karo 63.0 3,901 731 62
Dairi 45.0 9,011 1,810 200
Total 2,528.5 322,023 69,285 127

H. LAKE UTILIZATION

H1 LAKE UTILIZATION (Q)

Source of water, navigation and transportation (amount of cargo in 1978: 1,922 metric tons), sightseeing and tourism (no. of visitors in 1978: 44,625). recreation (yachting), fisheries.

H2 THE LAKE AS WATER RESOURCE

: No information.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION

  • Extent of damage: Not serious.

I2 TOXIC CONTAMINATION

: No information.

I3 EUTROPHICATION

: No information.

I4 ACIDIFICATION

  • Extent of damage:
    None.

J. WASTEWATER TREATMENTS (Q)

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA

f) Measurable pollution without wastewater treatment.

J3 SANITARY FACILITIES AND SEWERAGES

  • Percentage of municipal population in the catchment area provided with adequate sanitary facilities (on-site treatment system) or public sewerage: None.
  • Percentage of rural population with adequate sanitary facilities (on-site treatment systems): None.
  • Municipal wastewater treatment systems: None.
  • Industrial wastewater treatment systems: None.

K. IMPROVEMENT WORKS IN THE LAKE

None.

L. DEVELOPMENT PLANS (Q)

  1. Integrated management on Toba Lake catchment area.
  2. Hydroelectric power plant under construction.

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS (Q)

M1 NATIONAL AND LOCAL LAWS CONCERNED

  • Names of the laws (the year of legislation)
    1. Act of the Republic of Indonesia No 4 concerning Basic Provisions for the Management of the Living Environment (1982)
    2. State Regulation of the Republic of Indonesia No.29 on Environmental Impact Assessment (1986)
  • Responsible authorities
    1. & (2) The State Minister for Population and Environment. Ministry of Home Affairs, Ministry of Public Works, Ministry of Forestry and Local (Provincial) Governments

M2 INSTITUTIONAL MEASURES

  1. The State Minister for Population and Environment responsible for coordinating environmental managements
  2. Ministry of Public Works responsible for lake utilization
  3. Ministry of Home affairs responsible for regional development
  4. Ministry of Forestry responsible for forest management and soil conservation

M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES

  1. Centre of Environmental Studies (University)
  2. Institute of Hydraulic Engineering Agency of Resources and Development

source www.ilec.or.jp

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