1.　OUTLINE OF THE SETO INLAND SEA

1.1 OUTLINE

　　Since the old time, many people have been enjoying the Seto Inland Sea, one of the most beautiful sea harmonized with many islands not only in Japan also in the world, which is blessed with mild climate, small precipitation and plentiful nature. The Seto Inland Sea is the largest one in Japan, which is surrounded by the three large islands, Honshu, Kyushu and Shikoku and which has more than 700 small islands. Its total shoreline is 6,868 km long. Concerning the width of the Seto Inland Sea, the east-west is about 450km and north-south is 15〜55km. The area is 23,203 km2 and average depth is 38.0m. Accordingly the volume of the Seto Inland Sea is about 881.5 km3. The Seto Inland Sea has many large straits and small ones, bays and shore reefs in the inside. There are Kii Channel(east side) and Bungo Channel(west side) between the Seto Inland Sea and there is Kanmon Strait(west side) between the Seto Inland Sea and the Sea of Japan.

　　It is said that this area was named as Seto Inland Sea since around 1882.

　　The basic dimensions of the Seto Inland Sea, Tokyo Bay and Ise Bay are shown in Table 1-1. The water body and the watershed area defined by the "Law Concerning Special Measures for Conservation of the Environment of the Seto Inland Sea" are shown in Figure 1-1. The dimensions of the open sea and the islands in each prefecture concerned to the Seto Inland Sea are summarized in Table 1-2 and Table 1-3, respectively.

Table 1-1 Basic Dimensions of the Three Largest
Enclosed seas In Japan

　

　
Seto Inland Sea
Osaka-wan
Tokyo-wan
Ise-wan
Area of Water Surface (km2)
23,203
1,447
1,380
2,130
Mean Depth (m)
38
30
45
17
Volume (100 million m3)
8,815
440
621
394
Population on Watershed (million)
30
13
25
10

Note: after the data by Environment Agency and Ministry of transport in Japan, and
　　　　 "Tokyo Bay-Transition in 100 years" edited by Norio ogura

　

Figure 1-1 Water Body and Watershed Area Defined by the "Law Concerning Special
　　　 　　　 Measures for Conservation of the Environment of the Seto Inland Sea"　　

　

Table 1-2 Dimensions of the Open Sea
　　 in the Seto Inland Sea
Name of Straits and Bays
Area (km2)
Mean Depth (m)
Volume
(100 million m3)
Kii-suido
1,938
45.8
887
Osaka-wan
1,447
30.4
440
Harima-nada
3,426
25.9
889
Bisan-seto
1,063
16.3
173
Bingo-nada
773
20.3
157
Hiuchi-nada
1,619
24.0
389
Aki-nada
744
39.9
297
Hiroshima-wan
1,043
25.8
269
Iyo-nada
4,009
55.7
2,232
Siou-nada
3,805
24.1
917
Hibiki-nada
592
32.9
195
Bungo-suido
2,744
71.8
1,970
Seto Inland Sea
23,203
38.0
8,815

Note:after the data by Environment Agency of Japan

　

Table 1-3 Number of Islands in Each Prefecture Concerned
to the Seto Inland Sea 　　　　　　　　　
　 Total Islands Main Islands Manned Island Islands in Territorial Waters Islands with more than 100m of circumfereence in Territorial Waters
Hyogo Pref.
53
6
6
53
57　 (44)
Wakayama Pref.
37
1
0
37
41　 (22)
Okayama Pref.
101
21
20
101
87 　(75)
Hiroshima　Pref.
163
36
31
163
142 (153)
Yamaguchi　Pref.
141
26
26
117
127 (105)
Tokushima　Pref.
72
3
3
72
24　 (26)
Kagawa Pref.
116
26
26
116
112 (111)
Ehime Pref.
262
39
36
160
133 (136)

Fukuoka Pref.
19
2
2
4
6 　 (7)
Oita Pref.
51
7
7
7
3 　 (2)
Total
1,015
167
160
830
727 (681)

Note:after the "Report about Envirnmental Information of the Seto Inland Sea (Fiscal Year of 1966)