Man-Induced Erosion : The Rate of Erosion and an Example from Okinawa Island, Southern Japan

Erosion by Human Activities in Japan

“…Moreover, these subtropical islands are marked by a high intensity of rainfall and more frequent occurrence of heavy downpours than the higher latitude regions; erosive rains of more than 3 mm per 10 minutes in intensity occurs 50 times or more every year. Thus, as mentioned earlier, overwhelmingly high rates of erosion of the order of 10,000-50,000 m3/km 2 • yr have sometimes been measured (Kadomura and Yamamoto 1978).…”

“…In the case of land reclaimed on the former valleys (Fig 3B-III), filled-in soils are rapidly eroded away by large gullies following former stream lines, whereby the sediment yield from a single gully alone often exceed 10,000 m3/km 2 • yr. The total annual sediment yield from such areas, involving erosion by rainsplash and wash, may reach to the order of 100,000 m3/km 2 • yr (Yamamoto 1976, Kadomura andYamamoto 1978). Thus a serious silting problem due to the red-colored suspended sediment have resulted along the coral reef coast.…”