Debris flows have occurred annually since July 1998 at Nishinogaito River and Kotaki River, which have their headstreams in Mount Fujiwaradake (altitude: 1, 120 m) located in Fujiwara-cho, Inabe-gun, Mie Prefecture. This is considered to be ascribable to steep torrents and slopes in these areas, and friable geologic features that consist of limestone, as well as sudden, heavy rains in a short period at Mount Fujiwaradake, unlike the plain zone.
Nishinogaito River No. 2 Dam and debris flow sediments (Photo on July 18, 2002)
Falling debris flow : Kotaki River No. 1 Dam (Photo on July 17, 2002)
|Debris flow occurrence date||Torrents where debris flows occur||Discharge (m3)||Remarks|
|July 29, 1998||Nishinogaito River||-|
|August 19, 1999||Nishinogaito River||3,000||Debris flows stopped at Nishinogaito River No. 1 Sabo dam.|
|Kotaki River||10,000||Debris flows stopped downstream of Kotaki River No. 1 Sabo dam.|
|September 24, 1999||Nishinogaito River||3,700||Debris flows stopped downstream of Nishinogaito River No. 1 Sabo dam.|
|Kotaki River||5,000||Debris flows stopped downstream of Kotaki River No. 1 Sabo dam.|
|July 9-10, 2002||Nishinogaito River||-||Debris flows stopped upstream of Nishinogaito River No. 3 Dam.|
|Kotaki River||21,080||Debris flows stopped at Kotaki River No. 1 Sabo dam.|
|July 17, 2002||Nishinogaito River||39,860||Debris flows stopped at Nishinogaito River No. 1 Dam.|
|Kotaki River||20,970||Debris flows stopped at Kotaki River No. 1 Sabo dam.|
|August 8-9, 2003||Nishinogaito River||26,000||Debris flows stopped at Nishinogaito River No. 2 Dam.|
|Kotaki River||50,000||Debris flows stopped at sand pocket works.|
With Typhoon No.10 coming in 2003, it began to rain at about 21:30, August 7 around Mount Fujiwaradake and continued to rain intermittently. At about 21:30, August 8, it began to rain heavily, and suddenly precipitation of 19 mm for 10 minutes was measured at the Fujiwaradake rain gage station. This heavy rain is considered to have caused debris flows.
The total amount of rainfall caused by the typhoon reached 333 mm (22:00 on August 7 to 21:00 on August 9 ), and the maximum 24-hour rainfall, the maximum hourly rainfall, and the maximum 10-minute rainfall reached 277 mm (15:00 to 15:00, August 8 to 9 ), 43 mm (23:00, August 8 ) and 19 mm (22:30, August 8 ), respectively.