The purpose of this paper is to describe the grain size distribution of littoral suspended sand. The samples were collected at the offshore area of the Tatado Coast near Shimoda, Izu Peninsula, Central Japan, where bottom material is stirred up to some extent by wave action. The collection work was conducted by using a vacuum system fixed to the sea bottom for drawing up the sea water from the nozzles arranged at various heights (Table 1). The results of the grain size analyses of the samples are plotted on Fig. 1, in which the ordinate represents the probability density function. Each sample consists of two populations, i.e. sand particle population (coarser than about 3.5_??_) and finer particle population (finer than about 3.5_??_); this is similar to those of wind blown sand and river suspended sand which have been described in the previous paper (Inokuchi, 1980). In Fig. 1, it seems that the points of the sand particle population for each sample deviate systematically from the broken line which represents theoretical log-normal curve for that population. This tendency of deviation corresponds to that indicated by Bagnold and Barndorff-Nielsen (1980) and suggests that the distribution pattern of the points conforms to the hyperbolic distribution. A pair of solid straight lines is the hyperbolic asymptotes for each sample. Table 2 shows the values of the slopes of the asymptotes, in which S means value of the finer wing slope and C the coaser wing slope. It is found that for all samples the values of the slopes are confined into a limited range and that for each sample S and C are approximately equivalent. This fact may imply a regularity in suspension of sand particles affected by fluid actions. Grain size distribution of the four samples from beach sand was also examined. As shown in Fig. 2, each of them consists of sand particle population and their grain size distributions show hyperbolic type. However, the pattern of the size distribution is different from that of suspended sediments as shown in Fig. 1.
This symposium was the first attempt in the Association of Japanese Geographers to discuss the problems on large-scale land transformation and related environmental changes, which became not to be disregarded even in geomorphology. In 1980, the Working Group on the Man-Made Landforms and Land Transformation was organized in the Association for the promotion of systematic and comprehensive studies on such problems, which led us to organize this symposium. The following 10 papers were presented under 6 topics. T. TAMURA, H. YAMAMOTO and S. YOSHIOKA: National summary of recent studies on large-scale land transformation. A. MORIYAMA: Genetic approach to man-made landforms resulting from porcelain clay mining in the Seto Area. S. TANAKA and T. OKIMURA: Land transformation due to urbanization in the Rokko Mountains, Kobe, Kinki Metropolitan Area. T. YAMAKAWA: Land transformation attendant on urbanization in Western Kanagawa Prefecture. S. HIGASHI: Role of forest management in the exploitation of mountainous environment. T. TATEISHI: Coastal sand dunes historically inherited from planting for erosion control, a case of Shonai Sand Dunes. M. KUSAKA: Implications of ancient land transformation in the olden provinces of Settsu, Kawachi and Izumi. Y. AKAGI: Landforms resulting from iron sand mining in the Chugoku Mountains. K. KATSURAGI: Changes of social environment affected by dehydration of paddy fields and construction of a new port in the Imizu Plain, Toyama Prefecture. S. MEZAKI and K. KANEMURA: Land transformation and effects on sedimentation and coastal environment on Okinawa Island. The discussions by commentators and audience were focused on the following subjects. 1. Accumulation and management of quantitative data. 2. Role of geographical approach to land transformation. 3. Classification and evaluation of man-made landforms. 4. Measures against accelerated or catastrophic phenomena.