OGOCHI-DAMU-KO (OKUTAMA RESERVOIR)

A bird-eye view of the reservoir

Photo.
Photo: Tokyo Metropolitan Government


A. LOCATION

  • Tokyo, Japan.

  • 35:46N, 139:03E; 550 m above sea level.


B. DESCRIPTION

    Ogochi-damu-ko, or Okutama-ko, was formed by the construction of Ogochi Dam in the upstream of Tama River to serve as a reservoir of drinking water for Tokyo metropolitan area. It extends for 4 km in east-west direction, is 1.5 km wide (north-south), and has a water surface of 4.25 km2. The lake is said to be the world's largest among the reservoirs used solely for city water supply. The construction work needed 19 years from November 1938 to November 1957.
    Twenty percent of the lake's catchment area belongs to Tokyo Metropolis and the rest to Yamanashi Prefecture. The catchment is mostly mountainous, ranging in altitude from 2,018 m on the top of Mt. Kumotori to about 550 m at the lake surface. Flat lands are limited only to the immediate vicinity of the lake. Mountain slopes are mostly covered by mixed beech-fir forests and evergreen conifer (Cryptomeria) plantations (Q).


C. PHYSICAL DIMENSIONS (Q)

    Surface area [km2] 4
    Volume [km3] 0.1891
    Maximum depth [m] 142.5
    Mean depth [m] 44.4
    Water level Regulated
    Normal range of annual water
    - level fluctuation [m] 4
    Length of shoreline [km] 45.4
    Residence time [yr] 0.7
    Catchment area [km2] 259

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL (Q)
  • Bathymetric map: Fig. ASI-24-01.

  • Number of outflowing rivers and channels (name): 1 (Tama R).

D2 CLIMATIC (Q)
  • Climatic data at the control office site

    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C]*1 1.4 1.5 5.1 13.1 18.5 19.9 22.8 25.7 21.2 14.8 10.8 5.4 13.4
    Precipitation [mm]*2 39 53 71 104 122 181 222 281 225 185 76 39 1,597
    *1 1982-1984. *2 1941-1984.
  • Solar radiation (1974-1980): 11.4 MJ m-2 day-1.

    Fig. ASI-24-01
    Bathymetric map [m](Q).

  • Water temperature [deg C]

    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 8.8 7.2 7.0 10.2 16.9 20.4 22.6 24.9 22.2 17.8 14.7 12.0
    M*1 8.5 6.9 6.2 6.2 6.4 6.5 6.6 8.2 11.0 12.1 12.2 11.4
    B*2 7.9 6.8 6.2 6.1 6.3 6.5 6.5 7.7 7.6 7.6 7.7 7.8
    *1 Middle. *2 Bottom.
  • Freezing period: None.

  • Mixing type: Monomictic.

  • Notes on water mixing and thermocline formation
    Thermocline is formed at about 73 m depth.

E. LAKE WATER QUALITY (Q)

E1 TRANSPARENCY [m]
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    1.4 2.7 3.6 3.9 5.1 6.7 8.0 3.7 4.5 3.2 1.7 1.5
E2 pH
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 7.1 7.1 7.2 7.7 8.2 8.2 8.2 8.2 8.3 7.3 7.1 7.1
    M*1 7.0 7.1 7.1 7.1 7.0 7.1 7.0 6.9 6.9 7.0 7.0 7.0
    B*2 6.8 7.0 7.0 6.9 6.8 6.7 6.6 6.6 6.6 6.6 6.6 6.6
    *1 Middle. *2 Bottom.
E3 TURBIDITY [mg l-1]
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 7.2 4.3 2.8 2.1 1.3 0.8 0.7 7.4 2.2 10.3 25.6 9.7
    M*1 9.9 5.8 3.9 2.7 2.0 1.7 1.2 65 97 76 15 13
    B*2 25 12 7.8 21 11 9.8 9.3 144 109 61 36 35
    *1 Middle. *2 Bottom.
E4 DO [mg l-1]
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 9.3 10.1 10.8 11.3 9.9 9.1 8.7 8.5 8.8 8.2 8.1 8.7
    M*1 9.2 9.9 10.3 10.2 10.0 9.7 9.2 8.1 7.9 8.2 8.1 8.3
    B*2 6.1 8.5 10.1 8.8 6.9 3.2 1.5 3.0 4.3 3.2 2.1 2.2
    *1 Middle. *2 Bottom.
E5 COD [mg l-1]
    Determined by KMnO4 method.
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 1.4 1.2 1.2 1.4 1.6 1.5 1.5 2.1 2.2 1.9 1.9 1.5
    M*1 1.4 1.2 1.2 1.1 1.1 1.1 1.2 4.0 4.0 3.3 1.6 1.6
    B*2 1.9 1.4 1.3 1.8 1.7 1.9 2.2 6.6 4.7 3.4 2.7 2.8
    *1 Middle. *2 Bottom.
E6 CHLOROPHYLL CONCENTRATION [micro l-1]
    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 2.8 9.2 23.6 55.8 68.9 87.7 77.2 57.2 74.5 31.1 13.8 8.0
E7 NITROGEN CONCENTRATION
  • NO3-N [mg l-1]

    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 0.68 0.37 0.47 0.53 0.35 0.38 0.38 0.42 0.50 0.45 0.43 0.38
    M*1 0.47 0.42 0.47 0.55 0.37 0.38 0.45 0.68 0.33 0.47 0.53 0.28
    B*2 0.95 0.45 0.45 0.57 0.38 0.48 0.58 0.70 0.32 0.47 0.63 0.72
    *1 Middle. *2 Bottom.
E8 PHOSPHORUS CONCENTRATION
  • Total-P [mg l-1]

    Near the dam, 1982-1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0 .008 .007 .005 .005 .003 .000 .002 .006 .028 .020 .018 .011
    M*1 .009 .006 .005 .004 .003 .001 .001 .020 .055 .038 .012 .013
    B*2 .008 .012 .006 .020 .011 .018 .014 .049 .055 .050 .030 .031
    *1 Middle. *2 Bottom.

F. BIOLOGICAL FEATURES (Q)

F1 FLORA
  • Emerged macrophytes: None.

  • Floating macrophytes: None.

  • Submerged macrophytes: None.

  • Phytoplankton
    Cyclotella, Kirchneriella, Cryptomonas, Rhizosolenia, Synedra, Asterionella.
F2 FAUNA
  • Zooplankton: Daphnia, Bosmina.

  • Fish
    Oncorhynchus masou masou*, Salmo gairdneri*, Cyprinus carpio*, Hypomesus nipponensis*, Carassius, Zacco Platypus, Tribolodon hakonensis, Micropterus salmonides. * Economically important.
F3 PRIMARY PRODUCTION RATE [g O2 m-2 day-1]
    Near the dam, April 1984-March 1985
    Net production
    Jan Feb Mar Apr May Jun Jul*1 Aug Sep Oct Nov Dec
    .41 .54 3.22 53.2*2 1.37*2 2.47*2 .67*2 1.85 1.66 1.32 .50 .64
    *1 Unusual value. *2 Estimated from chlorophyll concentration.
    Dark respiration
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    .22 .24 2.00 - - - 1.66 .59 .67 .97 .35 .38
    Gross production
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    .63 .78 5.21 - - - 2.33 2.44 2.34 2.29 .85 1.02
F7 NOTES ON THE REMARKABLE CHANGES OF BIOTA IN THE LAKE IN RECENT YEARS
    Bloom of Microcystis was first observed in 1984. Micropterus salmonides has newly appeared in the lake.

G. SOCIO-ECONOMIC CONDITIONS (Q)

G1 LAND USE IN THE CATCHMENT AREA
    1989
    Area [km2] [%]
    Natural landscape
    - Woody vegetation 245 94.6
    - Others 0.08 0.03
    Agricultural land
    - Crop field 4.5 1.7
    Residential area 0.41 0.0
    Others 8.9 3.5
    Total 259 100.0
  • Main types of woody vegetation
    Evergreen conifer plantation (Cryptomeria japonica); mixed forest (Fagus crenata, Abies homolepis).
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE
    1984
    No.of establishments Main products or major industries
    Secondary industry 5 Concrete mixing
    Tertiary industry 85 Hotel services
  • Numbers of domestic animals in the catchment area
    Small numbers of sheep, goat, rabbit, poultry, etc.
G3 POPULATION IN THE CATCHMENT AREA
    Population Population density [km-2] Major cities (population)
    Rural 3,258 -
    Total 3,258 12.4

H. LAKE UTILIZATION (Q)

H1 LAKE UTILIZATION
    Source of water, sightseeing and tourism (no. of visitors in 1983: ca. 770,000) and recreation (sport-fishing).

H2 THE LAKE AS WATER RESOURCE
    1986
    Use rate [m3 sec-1]
    Domestic 7.8
    Irrigation -
    Industrial -
    Power plant 7.7

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION
  • Extent of damage: None.

I2 TOXIC CONTAMINATION
  • Present status: None.

I3 EUTROPHICATION
  • Nuisance caused by eutrophication
    Unusual algal bloom: Peridinium, Microcystis and Uroglena.
  • Nitrogen and phosphorus loadings to the lake [t yr-1]

    1984
    Sources Industrial Domestic Agricultural and fish culture Natural Total
    T-N 0 6.42 3.43 68.88 78.73
    T-P 0 0.70 1.31 2.64 4.65
  • Supplementary notes
    Bloom of Microcystis first appeared in 1984. Sewage treatment plants for two villages in Yamanashi Prefecture are now under construction.
I4 ACIDIFICATION
  • Extent of damage: None.


J. WASTEWATER TREATMENTS (Q)

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    c) Limited pollution with wastewater treatment.
J2 APPROXIMATE PERCENTAGE DISTRIBUTION OF POLLUTANT LOADS
    Non-point sources 100%.
J3 SANITARY FACILITIES AND SEWERAGE
  • Percentage of rural population with adequate sanitary facilities (on-site
    treatment systems): 8.9%.
  • Industrial wastewater treatment systems
    No. of industrial wastewater treatment systems: 5 (primary treatment: precipitation).

L. DEVELOPMENT PLANS (Q)

    Facilities for camping and sport-fishing and a barbecue restaurant are offered. Further plans for utilizing the lake area for recreation and nature observation are being developed by Tokyo Metropolitan Government.

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. For national laws see "Biwa-ko"
    2. Pollution Control Ordinance, Tokyo Metropolis
    3. Pollution Control Ordinance, Yamanashi Prefecture
  • Responsible authorities

    1. Tokyo Metropolitan Government
    2. Yamanashi Prefectural Government
M2 INSTITUTIONAL MEASURES
  1. Bureau of Environmental Protection, Tokyo Metropolitan Government Bureau of Water Works, Tokyo Metropolitan Government
  2. Yamanashi Prefectural Government

N. SOURCES OF DATA

  1. Questionnaire filled by Tokyo Metropolitan Government, based on the following data sources. Annual Report on the Management of Ogochi Reservoir for 1982, 1983 and 1984 (in Japanese). Report of survey for Determining Environmental Standards for Okutama-ko (1985) Bureau of Environmental Protection, Tokyo Metropolitan Government, Tokyo (in Japanese). Report of Survey for Reducing Pollution Loads to Okutama-ko (1986) Bureau of Environmental Protection, Tokyo Metropolitan Government, Tokyo (in Japanese).