One of main research subjects in hydrology is to make clear runoff mechanism or mechanism of streamflow generation. A knowledge of this interest is significantly important for better elucidation of the mechanism of the hydrological cycle and of the material cycle in a basin. Because of complexity of basin response to rainfall events, previous studies have tended to analyze the basin response as a black box unit.
In recent years, however, there has been a burst of research activities aiming at obtaining better insight into the mechanism of streamflow generation. Three types of flow have been recognized as main sources of storm runoff, that is saturated overland flow, subsurface stormflow and groundwater flow. It is now commonly accepted that in many drainage basins in humid areas streamflow is controlled dominantly by subsurface flow. However, there remain some major questions concerning causal mechanism of feeding water into stream channels by subsurface flow.
The purpose of this study is to elucidate the main source of storm runoff during a typical storm event and to clarify the runoff mechanism of the specified main component.
The study was conducted in a small forested drainage basin with an area of approximately 2.2 ha in the headwaters of the Tama River system located in the western suburbs of Tokyo (Fig. 1). The basin is located in the Tama Hills which are underlain by the Pliocene Miura group and Pleistocene Narita group. The former is composed of sand, mud and gravel and the latter of gravel and volcanic ash soil, the so-called Kanto Loam. The topography is typical of a dissected diluvial hill having a valley floor slope of about 12% andd steep hillside slopes of about 50%. The upper 2m of the soil are broadly classified as clay loam and silty clay (Fig. 2). The vegetation consists of dense deciduous trees approximately 15 m in height and sparse bamboos 1_??_2 m high with a dense ground cover of ferns and small shrubs.
Within the drainage basin, the valley floor was instrumented for the intensive study (Fig. 3) . Precipitation was measured by a tipping bucket recording raingage located in the middle part of the valley floor. Discharge from the basin was continuously recorded at three sites as shown in Fig. 3 using a 90° V-notch weir and Parshall flumes. To analyze the dynamic response of the basin during a storm event, tensiometer and piezometer nests were utilized. Contributing areas of overland flow to the storm hydrograph were ascertained by field observations during storm events.
Intensive field observations were carried out from July to October 1981. During this period, one of the major storm events occurred on October 22, caused by the Typhoon No. 8124, which provided a total rainfall of 172.5 mm. Discharge began within a few minutes of the onset of rainfall and the peak discharge occurred within 10 minutes of the rainfall peak (Fig. 4).
In the drainage basin, overland flow occurred from restricted areas on the valley floor and no significant overland flow was produced on the steep hillside slopes during storm events. Discharge due to overland flow generating on these restricted areas was too small to account for the total discharge from the basin. This means that the saturated overland flow which has been suggested as a main source of streamflow generation in humid drainage basins on the basis of the variable source area concept does not explain the runoff mechanism of the basin.
On the basis of observations of groundwater discharge around the main weir (Fig. 7) and of the hydrograph separation using specific conductance (Fig. 9), we clarified discharge ratios and flow components between the gaging stations (Fig. 10).

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A new formula for estimating the outgoing longwave radiation at the top of the atmos-phere from surface meteorological elements has been derived theoretically, by extending Nakagawa's (1983) procedure. The derivable formula, equation (48) in the text equivalent to the summation of equations (27), (28), (32), (36) and (44), shows us that the outgoing longwave radiation at the top of the atmosphere is proportional to the black body radiation at the surface air temperature, and that its proportional coefficient is a function of water vapor pressure, carbon dioxide concentration and total ozone amount at the screen height, cloud top height and tropopause height. The meridional distribution of the outgoing longwave radiation in the northern hemisphere was predicted by the derivable formula based on climatological data. Predicted values fit those observed from meteorological satellites, except for the sub-tropical region where the predicted values are slightly smaller. By deriving this formula, the present study made it possible to discuss the changes in the outgoing longwave radiation and the climate due to the increasing carbon dioxide in the atmosphere by means of one-dimensional climate models. By applying this formula to the most sim-plified global climate model without all the feedback mechanisms based on the minimum entropy exchange theory, the meridional distribution of changes in surface air tempera-tures due to doubling the amount of carbon dioxide presently in the atmosphere has been estimated. As a result, on the global average, the increase of temperature is 0.75°C. This is comparable with Ohring and Adler's (1978) result, but remarkably smaller than Manabe and Wetherald's (1980). This is mainly because of absence of feedback mechanisms, especially ice feedback, in the present study.

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An alluvial plain develops along the head of Suruga Bay which is surrounded with Qu-aternary volcanoes such as Mts. Fuji, Ashitaka, and Hakone to the north, and volcanic groups in the Izu Peninsula to the east. This plain comprises the Tagata Plain, the Mishima Fan, the Kano River Delta, the Ukishimagahara and the Fuji River Fan. These areas have distinct nature in landforms owing to variety of the geologic and geomorphic conditions of respective drainage area (Fig. 1).
The aim of this paper is to clarify the stratigraphy and the ;distribution of the recent for-mations in each area, and to reconstruct their palaeo-sedimentary environments. This study is based on the geological discriptions of borehole logs, the observations of core samples, foraminiferal analysis of core samples and the results of radio carbon dates. Then the geo-morphic development of the region was considered on the basis of correlation of the recent formations among these sub-regions.
The Tagata Plain is a valley plain situated in the middle to lower reach of the Kano River. The recent formations in the Tagata Plain are composed of basal sand and gravel (B), lower fluvial deposits (L), middle clay (M), upper pumiceous sand and gravel (U) and top alluvial deposits (T). The basal sand and gravel is considered to represent the former river bed gravel. The middle clay deposited under the low salinity environment, and it is divided into two parts of marine clay (MC) in the lower and brackish clay (BC) in the upper. The pumice contained in the pumiceous sand and gravel (PG) was derived from the pumice fall and flow deposits ejected at about 3, 000 years ago from Kawagodaira volcano located in the upper reach of the Kano River. The Mishima Fan is situated in the lower reach of the Kise River which flows from the east foot of Mt. Fuji. The fan is consisted of the Mishima lava flowed from Fuji volcano at about 10, 000 years ago and fan gravel (FG) covering the Mishima lava. Marine sand (MS) is distributed in the south end of the fan area. The Mishima lava abuts on the foot of the Shizuura Mountains to the south, and a narrow pass was formed between the Mishima lava and the Tertiary rocks of the Shizuura Mountains (Fig, 7).
The Kano River Delta develops in the mouth of the Kano River flowing into Suruga Bay. The delta is composed of marine gravel (MG), humic clay (HC) and deltaic sand (DS) from the bottom to the top.
The Ukishimagahara is a swamp distributed along the southern foot of Fuji and Ashitaka volcanoes, and the southern side is bounded by a coastal barrier formed of sand and gravel which were mainly derived from the Fuji River. In this area, peaty clay (PC) forming the swamp was underlain by marine gravel (MG). The height of a subsurface of MG becomes deeper towards the flanks of Mt. Ashitaka.
The Fuji River Fan is distributed from the Tagonoura area to the mouth of the Fuji River.
The bases of the correlation among the sub-regions are as follows.
1. In the N-S section of the Mishima Fan (Fig, 7), marine sediments were restricted in the narrow pass between the Mishima lava and the Shizuura Mountains. This reveals that the sea water invaded into the Tagata Plain area through the narrow pass after the Mishima lava had flowed out.
2. Brackish clay (BC) in the Tagata Plain, humic clay (HC) in the Kano River Delta and peaty clay (PC) in the Ukishimagahara are inferred to be the sediments 'under the common low salinity environment during the same period (ca. 4, 500-3, 500 yr B. P.).
The coastal barrier consisted of marine sand and gravel (MG) blocked up the landward area at about 4, 500 yr B. P.
3. The supply of coarse materials had increased since 3, 000 years ago in both the Tagata Plain and the Mishima Fan regions. Pumiceous gravel (PG) was accumulated in the Tagata Plain in association with the eruption of the pumiceous fall and flow from Kawa godaira volcano at about 3, 000 yr B. P..

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