A rainfall infiltration analysis was performed for one year using daily weather data to clarify the formation and the mechanism of maintenance of a spring- water marsh located on a gravel formation. The ground was divided into the soil layer and gravel layer, with these both composed of a vertical percolation layer，lateral drainage layer，and barrier soil layer. The analysis showed that the largest water discharge from the ground was that from the soil layer, by evapotranspiration. Water storage in the gravel layer was about 20 times that in the soil layer. Water was stored in the gravel layer during the wet season and discharged slowly in other seasons. The existence of a thick gravel layer was the cause for continuous drainage throughout the year.

This paper discussed the characteristics of delta front deposits, especially lower part of them, based on the analysis of three borehole core sediments (NB, SW, and AP1 cores) obtained from the Nobi Plain, central Japan. Lower delta front deposits have the following features: (1) upward-coarsening succession and upward-decreasing mud content showing convex-upward trend, (2) small luminosity compared with the underlying prodelta deposits under the wet condition, and (3) increase in accumulation rates from the prodelta deposits with concave-upward trend, and large accumulation rates (more than 10 mm/yr). When we determine the timing of passage of delta front through a site with sufficient accuracy, it is possibly effective using the horizon with mud content of fifty percent (almost equivalent to the boundary of sand and mud) because the horizon is identified easily, found commonly in the almost same depth among borehole sites, and can be formed near the river mouth with a relatively short period. It is expected that research on Holocene coastal and fluvial depositional systems will further progress by applying the detailed analysis result of borehole core sediments to reexamination of a huge number of existing boring logs.

Typhoon 23 induced many soil slips and debris flows on the granite-porphyry mountains in Nachikatsuura Town, Wakayama Prefecture, in September 2011. We investigated rainfall characteristics, slope forms, soil-layer structure, and soil properties of soil-slip scars to elucidate slope process on the granite-porphyry mountains. Many soil slips occurred on slopes steeper than 40°and with soil thickness thinner than 2 m. Simplified dynamic cone penetrometer testing and infiltration tests showed that the soil thicknesses in and around the soil-slip scar and the soil permeabilities at the soil-slip plane varied greatly within a narrow range of several meters. This indicates that the rainfall easily infiltrates the deeper part below the slip plane. This infiltration characteristics were a cause of larger critical rainfall amounts for triggering the severe sediment disaster that were slightly less than or equal to (1) about 100 mm of hourly rainfall, (2) about 350 mm of 6-h rainfall, and (3) about 650 mm of 24-h rainfall. Field observation showed that the soil layer was fully saturated at the time of the soil slip, indicating that soil formation rate strongly controlled the erosion rate due to soil slips on the granite-porphyry slopes. The results of a shear vane test and slope stability analysis showed that the average saturated c and φ-values at the slip plane were estimated to be 78 gf/cm² and 40°, respectively. From XRD and XRF analyses, plagioclase and biotite decomposed into kaolin minerals, smectite and gibbsite in the soil layer.

Block streams are distributed on the low-relief slopes near Lake Ota-ike, Mineyama highland (750 ～ 950m amsl), in the central part of Hyogo Prefecture, western Japan. Based on the aerial photo interpretation, the block streams were classified into the upper stream (Block stream I) and the lower stream (Block stream II). A 100 m long section of the block stream was observed by their morphological and sedimentological features. At the bottom of the geologic section, an older fan deposits composed of well-sorted and weathered sands and gravels were found. Deposits of block stream II about 2m thick covers the older fan deposits. This deposit is composed of non-sorted boulders (size: 60 ～ 80 cm in average, 160cm in maximum) with fine matrix and of patches of embedded AT tephra (26000 ～ 29000 y.B.P.). The surface of the block stream II is covered with Kuroboku soil whose origin is Ah tephra (6,300 y.B.P.) mainly. Clearly, as the tephra show, block stream II formed during the later substage of the Last Glacial Period. The formation of recent fans followed the dissection of the block stream II by channels. This landform development is suggests that predominant geomorphological processes change from periglacial to the fluvial ones in the area. The block stream I and older fans are considered to have been formed during or before the early part of the Last Glacial Period.

In hardly accessible areas, aerial photogrammetry and laser scanning with manned flight are normally used for topographic measurement. However, those methods are expensive and therefore frequent measurement is practically difficult. To solve such problem, the authors have experimented an aerial photography based SfM (Structure from Motion) technique on a ‘peninsular-rock’ surrounded on three sides by the sea at a Pacific coast in Chiba Prefecture. The research was carried out using UAS (Unmanned Aerial System) combined with a commercial small UAV (Unmanned Aerial Vehicle) carrying a compact camera. The 3D model has been constructed by digital photogrammetry using a commercial SfM software which can generate sparse and dense point-clouds, from which polygonal models and orthophotographs can be calculated. Using the ‘flight-log’ and/or GCPs (Ground Control Points), the software can generate digital surface model. As a result, high-resolution aerial orthophotographs and a 3D model were obtained. The results have shown that it was possible to survey the sea cliff and the wave cut-bench, which are unobservable from land side. This system has several merits: firstly lower cost than the existing measuring methods such as manned-flight survey and aerial laser scanning. Secondly, compared to these other methods, the one the authors have presented also enables frequent measurements. Thirdly lightweight and compact system realizes higher applicability to various fields.