Although alluvial-fan development reflects the fluctuation in the amount of sediments supplied from its source basin, previous alluvial-fan studies tended to pay insufficient attention to the erosional history of the hillslopes in the source basin. This paper discusses the Late Quaternary geomorphic development of three alluvial fan/source basin systems in the Yamagata region of northeastern Japan, with special reference to changes in hillslope processes and their influence on the sediment supply and fan development. All fluvial surfaces and hillslopes in the fan/basin systems were classified based on chronological and morphological criteria. Around the Last Glacial Maximum, periglacial processes prevailed on mountain slopes to form smooth and rounded slopes. After the onset of a warm and humid climate during the Pleni Glacial-Late Glacial transition, the magnitude of periglacial processes declined and the smooth slopes were incised by shallow slope failure and gullying. Although this change in slope processes was common to all the three basins, fan aggradation occurred in two basins but degradation in one basin. Such different responses of the river basins to the Late Quaternary climatic change are concordant with those reported from other two regions in Japan. Morphometric measurements performed on the slope classification maps have revealed that the areal ratio of the incised parts to all mountain slopes corresponds to the mode of fan development since the Late Glacial. This finding provides a three-stage model of the development of the fan/basin systems, showing that the progress of the slope incision led to changes in the amounts of the sediment supply and the size of the active aggradational fan.
Using experimental results on berms created in a small-scale wave flume, the position and height of berms in an equilibrium state were examined. The berm position, X, which is defined as the horizontal length from the shoreline to the berm crest, was found to be expressed by: X/(gT2)3/8Hb5/8φ=0.605 and 0.305 for collapsing related berets and for surging related berms, respectively, where Hb is the breaker height, T is the wave period, g is the gravitational acceleration, and φ is the reduction factor due to the roughness and permeability of the beach. The reduction factor was given by φ=exp(-0.04D*0.55), where D* is the dimensionless grain diameter of sediment, D*=[g(ps/p-1)/v2]1/3D, D is the sediment diameter, Ps is the sediment density, p is the fluid density, and v is the kinematic viscosity of fluid. The beret height, Bh, was given by: Bh/(gT2)5/8Hb1/8D1/4φ=0.117and 0.067 for the collapsing related berms and for surging related beans, respectively. Analyses of the existing prototype-scale experiment data indicated that no scale effect is involved in these laboratory relations as far as collapsing related beans are concerned. Time-series data of the beach profile obtained at Ajiga-ura Beach, Ibaraki, Japan, were used for the examination of applicability of these relations to the field situation, where collapsing related berms developed. The height of the mean high waters was used as a reference level in measuring the bean position and height. The breaker height, Hb, and wave period, T, of mean waves averaged over the period of beret development were substituted respectively for the wave characteristics in the laboratory-based equations. The bean position, X', was described by X'/(gT2)3/8Hb5/8φ=1.14 and the berm height, B'h, was expressed by B'h/(gT2)5/8Hb1/8D1/4φ=0.134.
This paper aims to review and present a framework for geographical research on modern fisheries through the examination of previous studies and the author's survey on Choshi. Geographical studies firstly must explain the development of modern fisheries centered on large fishing ports, since this is the way modern fisheries in Japan have developed. Large ports are cores of the fishing industries because of large quantity of fish, and they are the most important nodal points of fish distribution in production areas. The framework of “modern fisheries' space”, integrating large fishing ports and their related space, is sufficient to explain the spatial structure of modern fisheries. The modern fisheries' space consists of fishing space, fish landing and processing space, and fish distribution (consumers) space. These sub-spaces have been formed around the distribution routes of fish. The characteristics of such spaces are derived from the seasonality and periodicity of fishing. The basic structure of modern fisheries' space is similar to the distribution space of commodity goods in com-mercial society, which consists of areas of production, nodal points of distribution and areas of consumption. It is a structural characteristic of modern fisheries' space that resources in the production areas are aquatic organisms moving seasonally and periodically, and that limits of production have been conquered by accumulation and development of technology and facilities in the space.