NAGASE-DAMU-KO (NAGASE RESERVOIR)

A view of the dam site

Photo. Photo: T. Nishijima  

A. LOCATION

  • Kochi Prefecture, Japan.
  • 33 2 N, 133 2 E; 196 m above sea level.
 

B. DESCRIPTION

    Nagase-damu-ko is a multiple-purpose reservoir located in the upper reaches of Monobe River, which is 71 km long and flows through the granary area of Kochi Prefecture on Shikoku Island. The river's watershed,508 km2 wide, is one of the areas in Japan where frequent visits of typhoon bring the heaviest rainfall. However, the rainfall is so variable that paddy fields in the watershed often suffered from severe drought, while flood disasters were also frequent.
    The Japanese Ministry of Construction initiated in 1949 a comprehensive development project for the river system including the construction of this reservoir. The Nagase Dam was completed in 1957 with the total cost of 3,939 billion yen, and now supplies irrigation water at an average rate of 30 m3 sec-1 together with the hydroelectric power of about 111x1.0E+8 kWh. The Prefectural Government of Kochi is now responsible for the management of this reservoir.
    TThe catchment area of the reservoir (295 km2) is largely covered by dense forest, containing only a small village situated near the dam site. The water has remained oligotrophic, the annual mean of total phosphorus concentration being 0.006-0.008 mg l-1, though the bloom of flagellate algae, Peridinium spp., has occurred in May-September annually in recent years. The density of algal population usually ranges from 1,000 to 10,000 cells per litre. Otherwise the lake water quality has been free from the effects of siltation, acid rain and chemical pollution and suitable for drinking (Q).
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C. PHYSICAL DIMENSIONS

     
    Surface area [km2]2
    Volume [km3]0.0588
    Maximum depth [m]67.0
    Mean depth [m]28.2
    Water levelRegulated
    Normal range of annual water 
    level fluctuation [m]    		26
    Residence time [yr]0.1
    Catchment area [km2]295
     
 

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL
  • Sketch map: Fig. ASI-06-01 and 02.
  • Number of outflowing rivers and channels (name): 1 (Monobe R.).
D2 CLIMATIC (Q)
  • Climatic data at Station A, 1983-1985
     
    JanFebMarAprMayJun JulAugSepOctNovDecAnn.
    Mean temp. [deg C]2.53.5 7.614.919.6 22.527.727.7 24.217.411.0 5.315.3
    Precipitation [mm]5489 211276259 413249208 29015046 552,300
     
 
  • Number of hours of bright sunshine (Chugushi, Nikko, 1983-1985): 140 hr month-1 (Summer).
 

    Fig. ASI-06-01
    Sketch map of the reservoir (1).
 
 

    Fig. ASI-06-02
    Sketch map of the catchment area (1).
 
  • Water temperature [deg C](Q)
     
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    06.47.410.4 14.918.819.6 23.125.525.0 18.513.89.0
    106.37.08.7 11.614.814.2 16.218.919.5 16.113.59.0
    206.26.37.0 9.67.56.4 13.415.07.9 15.58.97.5
    305.85.86.1 6.75.55.4 6.36.76.5 9.16.87.0
    40--6.0 6.05.55.3 6.16.36.5 6.76.87.0
     
 
  • Freezing period: None.
  • Notes on water mixing and thermocline formation
    Usually the thermocline is formed from May to November, but not in 1982 owing to heavy floods.
 

E. LAKE WATER QUALITY

E1 TRANSPARENCY [m](Q)
     
    Station A, 1985
    JanFebMarAprMayJun JulAugSepOctNovDec
    1.00.43.02.0 2.01.72.8 1.84.51.8 3.84.0 
     
E2 pH (Q)
     
    Station B, 1982-1983
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    07.68.17.9 8.58.99.2 8.09.39.3 8.58.08.2
    107.08.07.8 7.77.88.1 8.08.98.4 7.98.08.0
    206.98.17.8 7.28.28.0 7.88.28.2 7.98.08.2
    306.98.07.7 --8.0 7.78.17.9 8.18.08.1
    40--7.6 --8.2 7.9-7.3 ---
     
E3 SS [mg l-1](Q)
     
    Station B, 1985-1986
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    0-2- -3 -4- 3-2
    10--- <1-2 -5- 5--
    20--- <1-3 -5- 6--
    30--- --2 -3- 3--
    40--- --- --- 7--
    45--- <1-- --- ---
     
E4 DO [mg l-1](Q)
     
    Station B, 1982-1983
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    0--12.2 11.79.8- -9.811.6 10.28.010.1
    10--11.7 10.99.6- -8.39.0 9.28.0-
    20--11.2 11.16.6- -7.09.7 9.18.3-
    30--10.0 --- -5.08.1 8.88.610.3
    40--10.2 --- --8.2 ---
     
E5 COD [mg l-1](Q)
    Determined by KMnO4 method.
     
    Station B, 1985-1986
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    0-1.0- 1.4-1.3 -3.4- 1.5-0.6
    10--- 0.8-1.1 -1.5- 1.1--
    20--- 0.8-0.5 -0.8- 0.7--
    30--- --0.6 -1.1- 0.7--
    40--- --- --- 0.7--
    45--- 0.6-- --- ---
     
E6 CHLOROPHYLL CONCENTRATION [micro g l-1](Q)
     
    Station B, 1982-1983
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    02.43.06.1 7.76.54.1 37.64.39.3 5.94.22.2
    101.41.70.6 2.36.52.1 0.91.63.6 6.31.41.8
    201.51.50.8 2.10.41.0 0.31.22.3 1.61.80.2
    301.81.60.7 --0.2 0.21.73.2 2.22.30.4
    40--0.9 --0.5 0.1-0.4 ---
     
E7 NITROGEN CONCENTRATION(Q)
  • Total-N [mg l-1]
     
    Station B, 1982-1983
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    00.200.180.52 0.341.410.45 1.150.160.18 0.330.230.28
    100.320.160.29 0.230.400.29 0.390.220.20 0.260.240.30
    200.220.150.35 0.360.720.31 0.380.290.31 0.300.210.35
    300.230.250.23 --0.51 0.370.290.36 0.260.210.29
    40--0.29 --0.34 0.35-0.96 ---
     
E8 PHOSPHORUS CONCENTRATION (Q)
  • Total-P [mg l-1]
     
    Station B, 1982-1983
    Depth [m]JanFebMarAprMayJun JulAugSepOctNovDec
    00.0060.0120.027 0.0200.0110.023 0.1830.0100.011 0.0110.0080.014
    100.0210.0110.015 0.0140.0100.006 0.0180.0150.006 0.0090.0110.019
    200.0070.0740.028 0.0260.0060.010 0.0160.0150.031 0.0100.0190.019
    300.0070.1060.018 --0.011 0.007-0.028 0.0130.0200.019
    40--0.038 --0.008 0.007-0.325 ---
     
 

F. BIOLOGICAL FEATURES (Q)

F1 FLORA
    Station A
  • Emerged macrophytes: None.
  • Floating macrophytes: None.
  • Submerged macrophytes: None.
  • Phytoplankton
    • Spring (March-May): Peridinium penardii, Synedra sp.
    • Summer (June-August): P. cunnigtonii, P. africanum, Pandrina monum.
    • Autumn (September-November: Cyclotella sp., P. africanum.
    • Winter (December-February): P. penardii.
F2 FAUNA
  • Fish: Cyprinus carpio, Carassius spp., Zacco termincki.
F7 NOTES ON THE REMARKABLE CHANGES OF BIOTA IN THE LAKE IN RECENT YEARS
    Since 1962, the red tide of Peridinium spp. has occurred annually from May to September.
 

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (1)
     
    1979
    Area [km2][%]
    Natural landscape
    - Woody vegetation29198.6
    Agricultural land41.4
    Total295100.0
     
 
  • Levels of fertilizer application on crop fields: Light.
G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (Q) 1981
  • Number of domestic animals in the catchment area: Cattle 60.
G3 POPULATION IN THE CATCHMENT AREA (Q)
     
    1981
    PopulationPopulation density [km-2]Major cities (population)
    Rural5,00016.9None
    Total5,000
     
 

H. LAKE UTILIZATION

H1 LAKE UTILIZATION (Q)
    Generation of electricity and source of irrigation water.
H2 THE LAKE AS WATER RESOURCE
     
    Use rate
    IrrigationN.A.
    Power plant30 [m3 sec-1] (106,400,000 kWh)
     
 

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS (Q)

I1 ENHANCED SILTATION
  • Extent of damage: None.
I2 TOXIC CONTAMINATION (Q)
  • Present status: None.
I3 EUTROPHICATION (Q)
  • Nuisance caused by eutrophication: Unusual algal bloom (Peridinium).
  • Nitrogen and phosphorus loadings to the lake [t yr-1]
     
    1981
    SourcesIndustrialDomesticAgriculturalNaturalTotal
    T-N -6.629.368.9102.3
    T-P -2.20.35.27.7
     
I4 ACIDIFICATION
  • Extent of damage: None.
 

J. WASTEWATER TREATMENTS (Q)

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA
    (b) No sources of significant pollution.
 

L. DEVELOPMENT PLANS (Q)

    None.
 

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. See "Biwa-ko" concerning national laws
  • Responsible authorities
  1. National Government and Kochi Prefectural Government
M3 RESEARCH INSTITUTES ENGAGED IN THE LAKE ENVIRONMENT STUDIES
  1. Department of Agriculture, Kochi University, Nangoku-shi
  2. Kochi Prefectural Environmental Pollution Prevention Centre, Kochi
 

N. SOURCES OF DATA

  1. Questionnaire filled by the Kochi Prefectural Government.
  2. Hata, S. (ed.)(1984) Report on the mechanism of occurrence of algal bloom by Peridinium spp. in Nagase-damu-ko (in Japanese).