SAGAMI-KO (SAGAMI RESERVOIR)

A lake view from the eastern shore


Photo: A. Kurata

A. LOCATION

• Kanagawa Prefecture, Japan.
• 35:36N, 139:11E; 167 m above sea level.

B. DESCRIPTION

This is a man-made lake, completed in 1947 by damming up the Sagami River in its middle course. The river comes from Yamanaka-ko, one of the Five Lakes of Fuji, and flows into Sagami Bay on the Pacific side of the island of Honshu. The drainage basin of the lake is therefore large for its size, having more than 300 times the surface area of the lake itself. With an effective storage of some 48 million tons, water for city and industrial use in such big cities of Kanagawa Prefecture as Yokohama and Kawasaki, for irrigating upland fields on the Sagamihara Plateau, and for hydroelectric power generation can all be provided by the lake.
Excess water is discharged through the dam gate in time of flood, but otherwise it passes through a duet 24 m under the water surface, mainly to a hydroelectric power station. During the warm season from late spring to early fall, as is often the case with many other reservoirs used for hydroelectricity, two thermoclines are observed at depths corresponding, respectively, to the bottom of normal metalimnion and the level of subsurface outlet. The inflowing river water forms a continuous density current leading to the subsurface discharge between these two thermoclines. Most of the inflowing nutrients may therefore not be available for biological production during this period.
In spite of such hydrographical constraints, the large amount of nutrient loading from the wide drainage basin has furthered the progress of eutrophication in Sagami-ko since its construction. Spring blooms of diatoms lead to clogging trouble in the filtration bed, while the growth of certain blue-green algae often gives an unpleasant smell to tap water. To suppress the bloom of Microcystis, which has appeared every summer since 1967, a device for vertical water mixing and aeration is being tested, together with other measures (1).

C. PHYSICAL DIMENSIONS

Surface area [km2]	3
Volume [km3]	0.0632
Maximum depth [m]	32
Mean depth [m]	19
Water level	Regulated
Normal range of annual water
- level fluctuation [m]	5-10*
Length of shoreline [km]	34.4
Residence time [yr]	0.1
Catchment area [km2]	1,064

* 1981-1985.

D. PHYSIOGRAPHIC FEATURES

D1 GEOGRAPHICAL

• Bathymetric map: Fig. ASI-18-01.
• Number of outflowing rivers and channels (name): 1 (Sagami R.).

D2 CLIMATIC

• Climatic data, 1983-1985 (Qk, 3)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Ann.
Mean temp. [deg C]*1	0.6	0.9	5.1	12.6	19.9	19.6	24.0	26.5	22.0	15.4	8.9	1.8	12.9
Precipitation [mm]*2	32	116	104	144	87	274	138	228	132	100	63	23	1,441

*1 Tsukui. *2 Sagami-ko.

• Number of hours of bright sunshine (Ebina): 2,236 hr yr-1 (Qk, 3).

Fig. ASI-18-01
Bathymetric map (2).

• Water temperature [deg C]

Station 1, April 1983-March 1986 (Qk)
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	6.1	6.6	8.7	12.8	18.1	19.8	24.1	25.1	20.7	16.7	12.0	8.7
B*	5.9	6.2	7.0	9.2	11.1	12.8	14.4	14.7	15.6	15.1	11.3	8.5

*1 Surface. *2 Bottom.

• Freezing period: None.
• Mixing type: Monomictic.
• Notes on water mixing and thermocline formation
  The thermocline is formed from June to October.

E. LAKE WATER QUALITY

E1 TRANSPARENCY [m](Qk)

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
	3.1	1.7	1.6	1.8	1.2	1.8	1.6	1.5	1.3	1.9	2.6	2.7

E2 pH (Qk)

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	7.6	7.3	7.5	8.0	9.0	8.4	9.7	8.7	8.9	8.1	7.6	7.6

* Surfce.

E3 SS [mg l-1](Qk)

Station 1, April 1983-March 1986
Depth	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	2	2	4	4	7	8	3	5	6	3	3	2
B*2	3	3	5	7	8	6	4	15	11	10	4	3

*1 Surface. *2 Bottom.

E4 DO [mg l-1](Qk)

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	9.7	9.8	9.6	10.8	12.9	12.1	13.7	11.1	13.3	9.9	9.7	9.5
B*2	9.6	9.4	7.7	9.4	3.2	2.8	4.0	3.1	2.2	7.1	9.3	9.5

*1 Surface. *2 Bottom.

E5 COD [mg l-1](Qk)

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	2.1	1.9	2.4	2.7	3.6	4.2	4.4	3.2	5.4	2.4	1.9	1.6
B*2	2.1	1.8	2.2	2.0	1.9	2.3	1.6	2.2	2.4	2.1	1.7	1.4

*1 Surface. *2 Bottom.

E6 CHLOROPHYLL CONCENTRATION [micro l-1](Qk)

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*	2.2	1.8	3.0	10	33	37	29	15	58	9.7	9.9	1.3

* Surface.

E7 NITROGEN CONCENTRATION (Qk)

• Total-N [mg l-1]

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	1.5	1.4	1.5	1.3	1.3	1.3	1.1	1.3	1.4	1.2	1.4	1.4
B*2	1.5	1.6	1.5	1.3	1.4	1.4	1.3	1.3	1.4	1.5	1.3	1.4

*1 Surface. *2 Bottom.

E8 PHOSPHORUS CONCENTRATION (Qk)

• Total-P [mg l-1]

Station 1, April 1983-March 1986
Depth [m]	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
S*1	.110	.120	.110	.085	.076	.081	.067	.056	.077	.065	.096	.100
B*2	.110	.120	.097	.071	.065	.068	.078	.072	.078	.078	.093	.110

*1 Surface. *2 Bottom.

E10 PAST TRENDS: Fig. ASI-18-02, 03 and 04.

Fig. ASI-18-02
Trend of transparency and pH (annual mean, Station 2)(Qk).

Fig. ASI-18-03
Trend of COD and BOD (annual mean, Station 2)(Qk).

Fig. ASI-18-04
Trend of chlorophyll a, Total-P and Total-N (annual mean, Station 2)(Qk).

F. BIOLOGICAL FEATURES (Qk)

F1 FLORA

• Emerged macrophytes: None.
• Floating macrophytes: None.
• Submerged macrophytes: None.
• Phytoplankton
  Microcystis aeruginosa, Stephanodiscus hantzschii, Fragilaria crotonensis, Synedra acus, Cyclotella spp.

F2 FAUNA

• Zooplankton
  Kellicotia longispina, Daphnia longispina, Synchaeta spp., Ploesoma sp.
• Benthos: Tubificids, Chironomids (Tanypus sp., Chironomus, Sergentia).
• Fish
  Hypomesus Iidus, Carassius cuvieri, Zacco platypus, Leuciscus hakonensis.

F3 PRIMARY PRODUCTION RATE: Fig. ASI-18-05.

Fig. ASI-18-05
Primary production rate, May 1978-March 1979 (6).

F5 FISHERY PRODUCTS

• Annual fish catch: None.

F7 NOTES ON THE REMARKABLE CHANGES OF BIOTA IN THE LAKE IN RECENT YEARS

No remarkable change.

G. SOCIO-ECONOMIC CONDITIONS

G1 LAND USE IN THE CATCHMENT AREA (Qk, Qy)

1983
	Area [km2]	[%]
Natural landscape	931	87.5
Agricultural land	49	4.6
Residential area	84	7.9
& Others
Total	1,064	100.0

• Main types of woody vegetation (7, 8)
  Deciduous broadleaf forest (Quercus serrata, Q. acutissima, Q. mongolica var. grosseserrata, Castanea crenata); pine forest (Pinus densiflora); conifer plantation (Pinus densiflora, Cryptomeria japonica, Chamaecyparis obtusa, Larix kaempferi).
• Main types of herbaceous vegetation: Grasslands and weeds (7, 8).
• Main kinds of crops: Rice and vegetables (7, 8).
• Levels of fertilizer application on crop fields: Moderate.

G2 INDUSTRIES IN THE CATCHMENT AREA AND THE LAKE (9-11)

1980
	Gross product per year [yen]*	No.of persons engaged	No.of establishments
Primary industry
- Crop production	N.A.	5,039	N.A.
- Animal husbandry	N.A.	N.A.	N.A.
- Fisheries	N.A.	N.A.	N.A.
- Others	N.A.	449	N.A.
Secondary industry	1,558,000,000	30,547	6,590
Tertiary industry	N.A.	46,602	9,303

* l60 yen = US$1.00.

• Numbers of domestic animals in the catchment area (Qk, Qy)
  1983: Cattle 1,600, swine 4,300, poultry 276,000.

G3 POPULATION IN THE CATCHMENT AREA (Qk, 12, 13)

1985
	Population	Population density [km-2]	Major cities (population)
Urban	122,900	-	Fujiyoshida (54,800)
Rural	77.400	-	Ohtsuri (34,900)
Total	200,300	188.3	Tsuru (33,200)

H. LAKE UTILIZATION

H1 LAKE UTILIZATION

Source of water, sightseeing and tourism (no. of visitors in 1985: 1,880,000), recreation (sport-fishing, boating), and others (canoe race).

H2 THE LAKE AS WATER RESOURCE (Qk)

1985
	Use rate [m3 sec-1]
Domestic	10.34
Irrigation	4.16
Industrial	2.15
Power plant	85 (31,000 kW hr-1)

I. DETERIORATION OF LAKE ENVIRONMENTS AND HAZARDS

I1 ENHANCED SILTATION

• Extent of damage: None.
• Supplementary note
  Up to December 1985, the total amount of sediments was about 13,400,000 m3 (21% of total pondage). The sedimentation rate is estimated to be about 350 [m3 km-2 yr-1].

I2 TOXIC CONTAMINATION

• Present status: None.
• Main contaminants, their concentrations and sources (Qk)

Station 1, 1985
Name of contaminant	Range of concentration [ppm] Water
Cd	<0.002
CN, Organic P,	N.D.
PCB, Alkyl-Hg
Pb	<0.02
Cr(III)	<0.05
As	<0.02
Total Hg	<0.005
CNP	<0.00001

• Environmental quality standards for contaminations in the lake
  Cd: <0.01 mg l-1, CN: N.D. (<0.1 mg l-1), Organic P: N.D. (<0.1 mg l-1), Pb:. <0.1 mg l-1, Cr (IV): <0.05 mg l-1, As: <0.05 mg l-1, Total Hg: <0.005 mg l-1, Alkyl Hg: N.D. (<0.0005 mg l-1), PCB: N.D. (<0.0005 mg l-1).

I3 EUTROPHICATION

• Nuisance caused by eutrophication
  Unusual algal bloom (Microcystis aeruginosa), disturbed filtration in cleaning beds, foul smell of tap water.
• Supplementary notes
  To suppress the bloom of Microcystis, a device for intermittent aeration and vertical water mixing is being tested. Records of Microcystis bloom in Lake Sagami.

Year	Blooming period	Max. cell no. [ml-1]*	Note
1967	Aug-Sep	2,200	First observation
1968	Aug	380,000
1969	Aug-Sep	1,500
1970	Aug	380
1971	May-Aug	13,000
1972	Jun-Aug	3,100
1973	Jul-Oct	590,000	Water supply rate was reduced due to clogging of sand filters.
1974	Jul-Oct	1,000,000
1975	Jun-Oct	180,000	A floating fence was built to prevent algal dispersion
1976	Jun-Jul	1,200,000
1977	Jul-Aug	2,000,000
1978	Jul-Sep	130,000
1979	Jul-Oct	2,500,000

* Surface water.(Compiled from the data of Kawasaki Municipal Waterworks Bureau)

I4 ACIDIFICATION

• Extent of damage: None.

J. WASTEWATER TREATMENTS

J1 GENERATION OF POLLUTANTS IN THE CATCHMENT AREA

c) Limited pollution with wastewater treatment.

J3 SANITARY FACILITIES AND SEWERAGE (Qk, Qy)

• Percentage of municipal population in the catchment area provided with
  adequate sanitary facilities (on-site treatment systems) or public sewerage : 19% (1985).
• Percentage of rural population with adequate sanitary facilities (on-site
  treatment systems): 13% (1985).
• Municipal wastewater treatment systems
  No. of secondary treatment systems: 1 (activated sludge). No. of other types: 3 (anaerobic treatment).
• Industrial wastewater treatment systems
  No. of industrial wastewater treatment systems: 170 (1984)(activated sludge).

K. IMPROVEMENT WORKS IN THE LAKE

K2 AERATION

Intermittent aeration system.

K3 OTHERS

Dredging at the upper stream of the reservoir.

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. Kanagawa Prefectural Pollution Control Ordinance (1978)
3. Yamanashi Prefectural Pollution Control Ordinance (1975)
• Responsible authorities
1. Kanagawa Prefectural Government
2. Yamanashi Prefectural Government
• Main items of control
1. Permit system for construction of industrial premises, control of fuelgas and wastewater.
2. Permit system for construction of industrial premises, control of smoke and soot, and wastewater.

M2 INSTITUTIONAL MEASURES

1. Water Quality Preservation Section, Department of Environment, Kanagawa Prefectural Government, Yokohama
2. Public Nuisances Control Centre of Kanagawa Prefecture, Yokohama
3. Preservation of Environment Section, Department of Livelihood, Yamanashi Prefectural Government, Kofu

N. SOURCES OF DATA

17. Questionnaire filled by Kanagawa Prefectural Government.
17. Questionnaire filled by Yamanashi Prefectural Government.
1. Mori, K. (1970) On the depth of inflowing layer of river water in the Sagami Reservoir. Jap. J. Limnol., 31: 111-128.
2. Ishibashi, T. (1978) A research on sediment and its contents in Lake Sagami. J. Waterworks, 3.
3. Yokohama Local Meteorological Observatory (1986) Monthly Report of Meteorology in Kanagawa Prefecture (1983-1985).
4. Shiraishi, H. & Fukushima, S. (1949) Report of the Studies on Sagami-ko (a Man-made Lake), I. Freshwater Fisheries Research Laboratory, Fisheries Agency.
5. Shiraishi, H., Tokunaga, H., Furuta, Y. & Kitamori, R. (1953) Limnological Studies on Sagami-ko, a Man-made Lake (1949-1950). Freshwater Fisheries Research Laboratory, Fisheries Agency.
6. Maeda, S. (1982) The bacterial mineralization of organic matter in Lake Sagami. Jap. J. Limnol., 43: 88-95.
7. Miyawaki, A., Suzuki, K., Okuda, S., Fujiwara, K., Minowa, R., Harada, H., Sasaki, Y., Nakamura, Y., Ohyama, H., Hotta, K., Kimura, M., Ogawa, Y. & Yamada, M. (1977) Vegetationskarte der Prafektur Yamanashi. Yamanashi Prefectural Government, Kofu.
8. Environment Agency (1982) The 2nd National Survey on the Natural Environment (Vegetation), Actual Vegetation Map, Kanagawa Prefecture. Japan Wildlife Research Centre, Tokyo.
9. Research and Statistics Department, Minister's Secretariat, Ministry of International Trade and Industry (1985) Census of Manufactures for 1983, Report by Cities, Towns and Villages.
10. Statistics Bureau, Prime Minister's Office (1982) Population Census of Japan for 1980, Vol.3, Part 2; 14, Kanagawa Prefecture; 19,Yamanashi Prefecture.
11. Statistics Bureau, Prime Minister's Office (1982) Establishment Census of Japan for 1981, Vol. 2, Results for Prefectures (Cities, Wards, Towns, Villages).
12. Statistics Bureau, Prime Minister's Office (1986) Population Census of Japan for 1985, Vol.2, Part 2; 19, Yamanashi Prefecture.
13. Statistics Bureau, Prime Minister's Office (1986) Population Census of Japan for 1985, Vol.2, Part 2; 14, Kanagawa Prefecture.

* All printed in Japanese.