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

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

N. SOURCES OF DATA

17. Questionnaire filled by Dr. Herman Haerumen is, Ministry of State for Popula tion and Environment, Indonesia, based on the following literature (1)-(12).
1. Abdullah Angaedi (1980) Studi Perencanaan Perbaikan Keadaan Danau Toba,Suma tra Utara, PT. Indah Karya & Ministry of Public Works.
2. Asahan Development Authority (1984) Laporan Penyelesaian Pelaksanaan Pemban gunan Proyek Asahan.
3. Directorate of Forest Planning & Programme (1981) Pola Pengelolaan Catchmen t Area Danau Toba, Sumatra Utara. Ministry of Agriculture.
4. Hehanussa P. E. (1982) Tefra Toba. National Geology & Mining Institute. Na tional Institute of Sciences.
5. --- (1982) Penanggalan Radiometri Formasi Samosir Tefra Toba.National Geology & Mining Institute, National Institute of Sciences.
6. --- (1983) Tefra Toba disekitar Danau Toba, Sumatra Utara.National Geology & Mining Institute, National Institute of Sciences.
7. ---, Fujii, S. & Yokoyama, T. (1983) New dates of fluvio-iacustrine deposits from Lake Toba, Indonesia.
8. Ibnu Fajar (1983) Laporan Penyelidikan Geologi Lingkungan Daerah Tadah Danau Toba, Sumatra Utara. Directorate of Environmental Planning of Geology.
9. --- (1984) Laporan Penyelidikan Geologi Tata Lingkungan Daerah Aliran Sungai Asahan, Sumatra Utara. Directorate of Environmental Planning of Geology.
10. University of Indonesia & Ministry of Public Works (1979) Survai Ekologi Danau Toba.
11. University of Sumatra Utara & The Office of State Minister for Development Supervision & Environment (1979) Komunitas, Lingkungan Perairan & Kehidupan Biologis Danau Toba, Sumatra Utara.
12. Yusron Loebis (1982) Penelitian Keseimbangan Tata Air Danau Toba.Institute of Hydraulic Engineering, Ministry of Public Works.
13. Mizuno, T. (1977) Water temperature and some other environmental factors in inland waters of tropical Asia. Suion no Kenkyu, 21 (1): 12-19 (in Japanese).
14. --- (1980) Lakes and Forests of Tropical Asia. 232 pp. Tokai Univ. Press, Tokyo (in Japanese).