HAMANA-KO (LAKE HAMANA)

Eastern part of the lake from the top of Mt.Okusa

Photo.
Photo: A.Kurata


A. LOCATION

  • Shizuoka Prefecture, Japan.

  • 34:45N, 137:35E; 0 m above sea level.


B. DESCRIPTION

    Lake Hamana is one of the largest brackish lakes in Japan and is located at the western end of Shizuoka Prefecture. It is connected to the Sea of Enshu- nada, a local name for the Pacific Ocean, through a 200 m wide channel named Imagiriguchi. The lake has a surface area of 69 km2 and its coast stretches over a distance of 103 km. It has a water volume of 330,000,000 m3.
    There are 3 cities, 6 towns and 1 village located within the Lake Hamana catchment basin which has a total area of 630 km2. The lake is heavily subjected to tidal flows and, together with substantial freshwater inflow through numerous rivers and streams flowing into the upper part of the lake and a geographical formation of the lake consisting of numerous inlets, provides ideal habitats for aquatic flora and fauna. It has therefore been famous in fishery throughout history. There has been organized efforts made to transform the fishery industry to aquaculture industry. Much greater emphasis has been placed in recent years on culturing of sea weed Undaria pinnatifida, oyster, as well as on growing fingerling of Acanthopagrus schlegeli, Lateolabrax japonicus, Portunus (Portunus) trituberculatus, Penaeus (Melicertus) japonicus for local culturing and for marketing elsewhere.
    Lake Hamana is also blessed with scenic spots and has been designated as a Prefectural Park. Its clean water, greeneries along the coastline, and rolling hills in the catchment area, are great assets for tourist industry. Geographically, it is located just about equidistant from eastern and western economic zones in Japan. Tomei National Highway system and Hamana-ko Lakesideway highway system, among other transportation systems, provide convenient access to the lake, making Lake Hamana even more attractive for promotion of tourism.

C. PHYSICAL DIMENSIONS

    Surface area [km2] 69
    Volume [km3] 0.33
    Maximum depth [m] 15.8
    Mean depth [m] 5
    Water level Unregulated
    Normal range of annual water level fluctuation [m] 0
    Length of shoreline [km] 92
    Residence time [yr] 7.8
    Catchment area [km2] 630

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
  • Bathymetric map: Fig. ASI-44-01.

  • Names of main islands: Benten-jima (64.9 km2).

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

D2 CLIMATIC
  • Climatic data at Hamamatsu, 1984-1986

    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann.
    Mean temp. [deg C] 3.8 4.7 8.3 14.0 18.2 21.5 27.0 27.0 23.8 17.8 12.9 8.0 14.8
    Precipitation [mm] 26 57 136 165 215 325 114 152 149 29 71 95 1,533
  • Number of hours of bright sunshine: 2,347 hr yr-1.

    Fig. ASI-44-01
    Bathymetric map (Q).

  • Water temperature [deg C]

    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 4.8 6.5 10.2 18.6 22.2 21.4 30.8 30.2 24.6 19.9 11.9 7.6
    2.0 4.6 6.4 9.8 17.9 21.8 21.6 29.5 29.8 24.6 19.2 12.6 6.7
    4.0 4.6 6.2 9.4 17.0 20.8 21.4 25.6 28.9 24.5 19.8 12.6 7.6
    6.0 4.5 6.2 9.1 16.1 19.2 20.4 24.8 28.0 23.9 20.5 12.6 7.6
    8.0 4.9 6.2 9.1 16.0 17.8 17.2 21.7 22.2 23.2 20.2 12.7 7.8
    10.0 4.9 6.2 9.1 13.6 16.8 16.8 19.9 21.4 23.0 20.4 12.6 8.4
  • Freezing period: None.

  • Mixing type: Monomictic.

  • Notes on water mixing and thermocline formation
    In the northern basin, thermocline is formed during summer season. There are warmer low salinity layer at a depth over 4-6 m, and cooler anoxic water mass beneath it. In the southern part there is no thermocline but the tidal front appears between lake water and sea water during summer.

E. LAKE WATER QUALITY

E1 TRANSPARENCY [m]
    Station 1, 1984
    Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    5.8 2.9 5.8 4.3 2.5 3.1 1.1 2.0 1.5 2.5 2.3 3.5
E2 pH
    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 8.3 8.3 8.2 8.3 8.7 8.7 8.8 8.8 8.4 8.3 8.4 8.1
    2.0 8.3 8.3 8.3 8.3 8.7 8.8 8.7 8.8 8.4 8.3 8.4 8.2
    4.0 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.3 8.2 8.4 8.3
    6.0 8.3 8.3 8.3 8.2 8.0 8.3 8.3 8.3 8.3 8.1 8.4 8.3
    8.0 8.3 8.3 8.3 8.2 8.0 8.1 8.2 8.1 8.3 8.1 8.4 8.3
    10.0 8.3 8.3 8.3 8.0 8.0 8.0 8.1 8.0 8.3 8.1 8.3 8.3
E6 CHLOROPHYLL CONCENTRATION: Fig. ASI-44-02.

    Fig. ASI-44-02
    Chlorophyll a at Station 1, 1979 [micro l-1].

E4 DO [mg l-1]
    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 10 10 9.8 9.0 9.4 8.3 8.3 7.9 6.9 8.5 9.1 9.3
    2.0 11 10 10 8.9 9.5 8.1 7.5 6.7 6.1 7.9 9.8 9.4
    4.0 10 10 9.9 7.8 6.6 5.3 4.0 3.9 1.0 6.3 9.2 9.0
    6.0 10 10 10 6.0 3.2 4.8 3.0 3.0 0.9 5.0 8.6 9.1
    8.0 11 9.9 9.1 4.8 0.9 <0.5 1.0 <0.5 1.4 7.2 8.2 9.3
    10.0 11 9.8 8.8 1.6 <0.5 <0.5 <0.5 <0.5 1.5 4.1 6.8 8.2
E5 COD [mg l-1]
    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 1.1 1.4 1.4 <0.5 2.9 2.1 1.5 2.1 2.9 2.7 1.6 1.9
    2.0 1.2 0.8 1.1 <0.5 1.5 2.3 1.2 2.3 2.3 3.9 1.1 1.8
    4.0 1.3 0.8 1.1 0.9 2.0 1.8 1.0 2.0 2.2 2.0 1.2 1.9
    6.0 1.2 0.9 1.4 <0.5 1.8 1.3 0.9 2.0 1.9 1.6 1.6 2.1
    8.0 1.0 0.6 0.9 <0.5 2.2 2.1 0.9 4.1 2.2 1.6 0.8 1.9
    10.0 1.3 0.7 1.3 <0.5 2.0 3.2 2.3 6.3 2.1 1.6 1.7 1.8
E7 NITROGEN CONCENTRATION
  • Total-N [mg l-1]

    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 0.20 0.30 0.28 0.63 0.52 0.41 0.77 0.51 0.64 0.48 0.24 0.21
    2.0 0.27 0.27 0.33 0.67 0.53 0.47 0.52 0.51 0.60 0.48 0.22 0.21
E8 PHOSPHORUS CONCENTRATION
  • Total-P [mg l-1]

    Station 1, 1984
    Depth [m] Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    0.5 0.020 0.031 0.019 0.016 0.033 0.031 0.049 0.043 0.070 0.051 0.022 0.022
    2.0 0.018 0.022 0.020 0.023 0.032 0.040 0.047 0.042 0.069 0.058 0.021 0.020

F. BIOLOGICAL FEATURES

F1 FLORA
  • Emerged macrophytes
    Phragmites communis, Zizania latifolia, Typha angustifolia, Carex scabrifolia.
  • Submerged macrophytes: Zostera marina.

  • Phytoplankton
    Bacteriastrum, Chaetoceros, Thalassiosira, Rhizosolenia, Guinardia.
F2 FAUNA
  • Zooplankton: Copepoda, Noctiluca, Rotifera, Gastropoda.

  • Benthos
    Tapes japonica, Thais clavigera, Littorina brevicula, Batillaria multiformis, Musculus senhousia, Mytilus coruscus, Monodonta labio, Mya arenaria, Solen strictus, Scylla serrata.
  • Fish
    Acanthogobius flavimanus*, Mugil cephalus*, Lateolabrax japonicus*, Clupanodon punctatus*, Anguilla japonica. * Economically important.
  • Supplementary notes on the biota
    Summer stratification causes serious damage to benthic animals very often in the innermost part.
F5 FISHERY PRODUCTS
  • Annual fish catch [metric tons]
    1986: 3,758.
  • Fishery products other than fish [metric tons] (1986)
    Tapes japonica: 2,976.
    Shrimps and crabs: 130.
    Squid and octopus: 9.
F6 PAST TRENDS
  • Annual fish catch [metric tons]

    Year Fishes Shrimps and crabs Tapes japonica
    1982 584 180 7,832
    1983 681 196 6,361
    1984 525 106 6,234
    1985 635 143 3,577
    1986 643 130 2,976

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (1972)
    Area [km2] [%]
    Natural landscape
    - Woody vegetation 199.66 32.0
    - Herbaceous vegetation 4.58 0.7
    - Others 24.14 3.9
    Agricultural land
    - Crop field 204.61 32.7
    - Pasture land 0.93 0.2
    Residential area 120.74 19.3
    Others 70.13 11.2
    Total 624.79 100.0
  • Main types of woody vegetation
    Conifer plantation (Cryptomeria japonica, Chamaecyparis obtusa, Pinus densiflora, P. thunbergii).
  • Main kinds of crops
    Tea, orange, pear, kaki (persimmon), radish, potato, etc.
  • Levels of fertilizer application on crop fields: Heavy.

G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (1985)
    Gross product during the year [mill. yen] No.of persons engaged No. of establishments Main products or major industries
    Primary industry 30,969
    - Agriculture 4,734,100 22,472 Orange
    - Stock raising 2,213,400
    - Others 54,500 Eel, Tapes japonica
    Secondaryindustry 274,580,763*1 174,163 12,580 Motorcycle, musical instrument
    Tertiary industry 267,175,719*2 177,441 28,207 Wholesale trade
    *1 Manufacturing only; establishments with more than four employees.
    *2 Value of commodity sale.
  • Numbers of domestic animals in the catchment area
    Cattle 17,995, swine 79,875, poultry 1,218,833.
G3 POPULATION IN THE CATCHMENT AREA (1985)
    Population Population density [km-2] Major cities (population)
    Urban 632,717 1,701 Hamamatsu (491,000)
    Rural 105,451 416
    Total 738,168 1,180

H. LAKE UTILIZATION

H1 LAKE UTILIZATION
    Tourism and sightseeing (no. of visitors in 1985: 1,440,000), recreation (swimming, sport-fishing) and fisheries.

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS

I1 ENHANCED SILTATION
  • Extent of damage: Not serious.

  • Supplementary notes: Obstruction for sailing.

I2 TOXIC CONTAMINATION
  • Present status: Not detected.

  • Standards of contaminants for human health

    Maximum permissible
    Substance limit [ppm]
    Cd 0.01
    Cyanides N.D.
    Organic P N.D.
    Pb 0.1
    Cr6+ 0.05
    As 0.05
    Total Hg 0.0005
    Alkyl Hg N.D.
    PCB N.D.
I3 EUTROPHICATION
  • Nuisance caused by eutrophication
    Unusual algal bloom Prorocentrum micans, P. minimum (1982), Olithodiscus luteus (1981).
  • Nitrogen and phosphorus loadings to the lake [t yr-1]

    Sources Industrial Domestic Agricultural Total
    Domestic animal Field
    T-N 292 620.5 255.5 766.5 1,934.5
    T-P 32.9 142.4 76.7 7.3 259.2
I4 ACIDIFICATION
  • Extent of damage: None.


J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    (c) Limited pollution with wastewater treatment.
J2 APPROXIMATE PERCENTAGE DISTRIBUTION OF POLLUTANT LOADS
    COD [%] [t day-1]
    Natural fall 1 0.10
    Domestic wastewater 61.4 6.38
    Industrial wastewater 19 1.98
    Agricultural runoff 2 0.21
    Stock-raising wastewater 14 1.46
    Municipal wastewater 2.6 0.27
    Total 100 10.40
J3 SANITARY FACILITIES AND SEWERAGE
  • Percentage of municipal population in the catchment area provided with
    adequate sanitary facilities (on-site treatment systems) and public sewerage: 46.5%.
  • Percentage of rural population with adequate sanitary facilities (on-site
    treatment systems): 43.7%.
  • Municipal wastewater treatment systems
    No. of secondary treatment systems: 6 (activated sludge with long-term aeration).
  • Industrial wastewater treatment systems
    No. of industrial wastewater treatment system: 160 (activated sludge with coagulation processes).

K. IMPROVEMENT WORKS IN THE LAKE

K1 RESTORATION
    Dredging in Washitsu Bay area.

L. DEVELOPMENT PLANS

    A harmonized cultural and frontier science industrial city plan, so-called "technopolis plan", is going on the eastern shore of the lake including three cities and two towns (65.3 km2).

M. LEGISLATIVE AND INSTITUTIONAL MEASURES FOR UPGRADING LAKE ENVIRONMENTS

M1 NATIONAL AND LOCAL LAWS CONCERNED
  • Names of the laws (the year of legislation)

    1. For national laws see "Biwa-ko".
    2. Shizuoka Prefectural Environmental Pollution Control Ordinance
  • Responsible authority

    1. Shizuoka Prefectural Government
  • Main items of control

    1. BOD, COD, SS, pH
    2. BOD, COD, SS, pH, standards for human health, Cu, Zn, Cr
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES
  1. School of Marine Science and Technology, Tokai University
  2. Faculty of Domestic Science, Shizuoka Women's University

N. SOURCE OF DATA

  1. Questionnaire filled by Shizuoka Prefectural Government.