DANAU TOBA (LAKE TOBA)
A bird-eye view of the lake
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
| 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
| 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)
- Integrated management on Toba Lake catchment area.
- 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)
- Act of the Republic of Indonesia No 4 concerning Basic Provisions for the Management of the Living Environment (1982)
- State Regulation of the Republic of Indonesia No.29 on Environmental Impact Assessment (1986)
- Responsible authorities
- & (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
- The State Minister for Population and Environment responsible for coordinating environmental managements
- Ministry of Public Works responsible for lake utilization
- Ministry of Home affairs responsible for regional development
- Ministry of Forestry responsible for forest management and soil conservation
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES
- Centre of Environmental Studies (University)
- Institute of Hydraulic Engineering Agency of Resources and Development
source www.ilec.or.jp
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