Landslides in Residential Estates in Sendai City

Abstract

Hill Surfaces around Sendai have been transformed mainly into residential area in the same way as in many other large cities. Landslide is one of serious problems occurred in these area. It is the purpose of this paper to point out that landslides in Sendai and the relations between landslide and transformation of hill land.
From 1963 to May 1970, there occurred 73 landslides on 27 days. It is well known that landslides are connected with rainfall, and in Sendai total rainfall of the two days, the one when the landslide occurred and the day just before, was found strongly influential. The number of landslides increases on days with the total rainfall exceeding 80 mm. Most landslides occurred in June, August and September in a year.
Landslides are distributed in two areas, Aobayama Hills and Hanakita Hills. The former have more number of landslides than the latter. Landslides are observed intensively around Yagiyama in Aobayama Hills, especially in Mukaiyama area. In Nanakita Hills, however, landslides are less frequent. Concerning the relations between the location of landslides and total rainfall, many landslide in Aobayama Hills occurred at the time of less total rainfall than in Nanakita Hills. The nature of surface material may be one of the factors of this distinctive difference.
Most of landslides occurred on hillslopes or slightly transformed hill area and most slid cliffs have maximum scale near them. Because there, initial slopes were steep to begin with. The number of landslides is related to the degree of transformation of initial hill surface. The typical example is Mukaiyama.