A summary of field studies since 1959 on how and to what extent the rivers around TokyR in the KantR District were contaminated by the urbanization of the district is given.
1. The neutralization project of the Agazuma River by using calcium, which was made possible both economically and technically, has changed inorganic acid water of the Agazuma River, a branch of the Tone, the quality of which was a matter of concern for many years, to neutral or alkali. As a result of the project, the water quality system of the lower stream of the Tone, from the junction with the Agazuma River, has been changing since 1964 from what it used to be.
2. A method of classification of pollution degree is established by using a combination of COD, BOD₅ and ABS contents so as to indicate the water quality influenced by urban waste water. According to the pollution distribution map for tested stations of the Tone and Arakawa water systems constructed by using the above classification, three groups are distinguished such as (a) water is polluted due to the enlargement of built-up areas, (b) water is influenced by middle class cities and (c) there is no pollution by human activities.
3. The quality of river water influenced by human activities changes greatly, particularly, by season (due to seasonal changes in the flow volume and, generally speaking, winter is the most polluted season) and by hour (influenced by the discharged amount of waste water). As to the Nakagawa of which water is used for irrigation to a great extent, some of its water systems are found more polluted during the non-irrigation period because less water flows into them during that period while in other water systems pollution is relatively reduced during that period because the water is not used for irrigation. In the future study, it is necessary to obtain accumulated value of flow volume by pollution degree.
4. The result of observations heretofore conducted tells us that the most polluted water system among the four systems of the Nakagawa is the Moto-Arakawa. Though its pollution degree was No. 3 in 1962, it became No. 1 in 1967 as shown in Fig. 2. due to the increase in organic contents and salts in the water on account of the development of the area Even with the least polluted Edogawa River, the water is getting more and more polluted as it flows down stream because of the in-flow of contaminated water from tributaries joining it from the left bank. The pollution of the stream lower than Matsudo City is worth to be mentioned. Since 1960 there has been a close relationship between the annual change in the water quality and the increase in population, particularly in Matsudo City. The relationship is shown by an exponential curve.
5. The author tried a regional classification on the basis of relationship of water qualities. The area can be divided into: (a) where agriculture is still maintained, (b) where agricultural areas are kept in the suburbs but changeable to the non-agricultural regions, and (c) where it is little worth while to keep it as an agricultural region. (See Fig. 8)

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The effects of water pollution on the rate of evaporation from the surface of water were examined. The evaporation from the surface of several kinds of polluted water, such as polluted river water, sea water, pulp-mill waste water and diesel oil-polluted water, from vessels were compared with the evaporation from distilled water.
Reduction of evaporaton following to the decrease of vapor pressure with increased solutes in the water was rather small. The colored water and suspended matters increased the absorption of the solar radiation which raised the temperature of the surface of water leading to the increase of evaporation.
Evaporation from the surface was disturbed significantly by the coverage with oil film. The stability of the oil film depended on the wind speed over the surface.
Though the direct measurement of the amount of evaporation from the natural water bodies is difficult, some possibilities of the change of the rate of evaporation by water pollution is estimated from these experiments. Further, it is expected that the future expansion of oil pollution on the surface of the ocean may cause some climatic changes on the earth.

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The movement of lake waters has been considered as one of the basic field of limnology. However an accurate and satisfactory observation of the movements could not be easily taken due to the non-steadiness of lake currents as well as indistinctness of the movements.
The movements can be classified as waves and lake currents and the latter is the main concern of this paper. The research was carried out by the following methods:
1. Measurements of lake currents by special floats.
2. Measurements of lake currents by lake sediments.
What should be noted here is the type float that the author used for the measurement. It could be used at the any depth of the lake unlike ordinary ones. The following points have been concluded:
1. A certain amount of water movements can be seen around the lower part of thermo cline where no current was ordinarily thought to exist so far.
2. During the stagnation period of thermal stratification in summer, turbulent flow exsists down to the depth of 2 meters from the surface and beyond that depth laminar flow can be seen. These results led to the conclusion that diffusion phenomena of substance should not be thought to be active except near the surface layer.
3. In autumn, the depth of the layer of turbulent flow becomes around 10 meters. This shows that substance diffusion by turbulence plays an important role during the cooling stage from summer to autumn. Eddy diff usivity calculated from temperature changes was obtained to be several decuple as large compared with molecular diffusivity.
4. In the summer stagnation period water circulation as well as substance diffusion are horizontal while they are vertical in the autumn partial circulation period.

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In Japan, shortage of water is a very grave problem. It is very important to develop water resources and to use water more effectively. A field investigation on the usage of water from reservoirs for the irrigation of paddy fields has been made since April 1960. As the study reservoir, the MannR Reservoir (located in Kagawa Prefecture in southwestern Japan) having a water area of 1.385km², 1540×10⁴m³ of water planned pondage, and 19.7km in circumference was selected.
From the reservoir, 45.37 km2 of paddy fields is irrigated throughout 12 main irrigation channels, 54.2k in total length, during the entire irrigation period (from June to September). The drainage basin (96.02km²) into the Mannô Reservoir consists of two kind of basins: an indirect basin containing 85.71% of the total area, and a direct basin containing 14.29% of the area.
The following has been observed and calculated every day: 1) the water level of the reservoir, 2) the water pondage of the reservoir, 3) the water volume used for the irrigation from the reservoir, 4) the water volume of inflow into the reservoir from the indirect basin, and 5) the precipitation on the basin and the irrigation area. The following are some major results obtained:
1) During the nine years from 1960 to 1968, the water efficiency ratio of the reservoir, m, changed from 0.39 to 1.15. In the formula m=Q_T/Q_E, QT is the irrigation water used during an irrigation period and Q_E is the planned effective water pondage of the MannR Reservoir (=1540×10⁴m³). The value of _??_ (average of m from 1960 to 1963) was 0.77. During the nine years, only one year was with m_??_1.
2) The water distribution system of the MannR Reservoir has about 50 small sub-reservoirs connected by the 12 main channels. Water conveyed from the Mannô Reservoir by these main channels flows into these sub-reservoirs, and then it is distributed into every paddy field.
These sub-reservoirs are used several times in a year, because they are easily filled with rain and are easily emptied when water is used.
Therefore, water is poured into these sub-reservoirs from the MannR Reservoir only one or two times in a year. The water in the reservoir is reserved for usage during shortages of water. This is one of the reasons why the mean value of m of the Mann J Reservoir is as small as 0.77 for the nine years.
3) The relationship between m and P_yK (yearly precipitation at Kanakuragawa in the irrigation area, in mm) was expressed in the following equation, where r is the coefficient of correlation:
m=1.947-0.0009P_yK, r=-0.942
4) The relationship between the volume of irrigation water used during an irrigation period, Q_T (10⁷m³) and P_yK (10³mm) is shown by the following equation:
Q_T=3.123-1.432P_yK, r=-0.922
5) The value of Q_O/Q_E (Q_O is the water volume of the reservoir at the beginning of an irrigation period) varies from 0.99 to 1.01. Therefore, the reservoir is full of water at the beginning of every irrigation period.
The value of q_i/Q_E (q_i is the water volume flowed into the reservoir from the drainage basin during an irrigation period) varies from 0.25 to 0.49 and the average was 0.36.

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It can readily be imagined that the result of morphometry of a given region will be different according to the scale of topographical map used in morphometry. Stream order analysis is attempted on the drainage basin of the Ôguri River, a tributary of the Tama River. Four kinds of topographical maps of different scale (1:3, 000, 1:10, 000, 1:25, 000, 1:50, 000) are used. Drainage system maps are drawn from these maps respectively. The Strahler system of stream ordering is adopted and the whole basin is subdivided into 26 subbasins. The drainage networks of these subbasins are shown in Figures 1, 2, 3 and 4. The result of the stream order analysis obtained from each map system is tabulated on Table 1.
Comparison of these figures enables us to recognize the effect of map scale especially at the head of stream network where the number of first order streams decreases with the de crease in map scale. As can be seen from Fig. 7, plots of the logarithms of the number of first order streams against denominator of map scale show a linear relationship between them. The regression equation for this line is expressed approximately in the form of
LogN=LogK-LogS
where K denotes the vertical intercept of the line.
Although the Strahler's stream number assigned to a particular stream segment depend on the scale of topographical map used in ordering the stream network, the Horton-Strahler straight line for the stream number is found to be independent of map scale as shown in Fig. 8. The result obtained supports the Yangs' conclusion that the Horton-Strahler relationship obtained from topographical maps of different scales for the same stream system have the same bifurcation ratio of stream number. Concerning stream length, most of the stream net works of subbasins do not conform to the law of stream length. Sometimes in some basins, the higher order stream segments are shorter than they should be. It may be that, in this case, lack of agreement with the Horton's law is a result of the Strahler method of ordering. Comparison of actual stream system and that of the largest scale map suggest that stream system obtained from larger scale maps includes intermittent streams, which is considered to be less effective as an erosive agents. Therefore, maps of larger scales are not necessarily indispensable for stream order analysis.

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The Atsumi Peninsula is located 60 km southeast of Nagoya City, and extends in the direction of ENE-WSW. Its maximum length is 35km and the maximum width is 7km.
Bed rock of this peninsula consists of Palaeozoic chert and covered with unconsolidated sand, gravel, silt and mud. The total thickness of unconsolidated rocks is 100m or more and sand and gravel layers contain groundwater, which was originally confined but has changed to unconfined groundwater due to the increased pumping in recent years.
The aquifer slopes toward the center of the Atsumi Bay. Its average specific yield is 324m³/d/m, for wells of 0.15-0.38m in diameter. The relation between T and Q/S is T=1. 15 Q/S in which T: transmissivility in m³/d/m, S: drawdown, in meter, Q a discharge of pumped well, in m3/d. The unit storage of groundwater in this area is estimated as 10.3×10⁶m³/km².

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It is true that the rainfall causes to rise the level of ground water, but the rate of rising is dependent on the characteristics of rainfall, antecedent rain and evapotranspiration etc. The author carried out an investigation on the rainfall effects which influenced the change in the ground water level on the basis of rainfall characteristics and the nature of soil layer of the sand dune in natural condition.
In selecting an observation well, the author examined several conditions such as the depth to ground water table, the effect of lateral ground water flow and the effect of tide. The southern part of Kashima (Fig. 1) was selected as the study field where no appreciable influences mentioned above were found.
To obtain basic data, precipitation was measured by a self-recording gauge, water table level by a self-recording water level gauge, infiltration by an infiltration gauge (made by myself) and soil moisture by the oven-dry method (Fig. 3). The investigation was made during three months from June 27 th to November 25th in 1967 (Fig. 4).
The results obtained were summarized as follow:
(1) Soil moisture increase caused by a single rain amounting to 155.0mm depth was calculated to be 132.7mm, while 22.3mm was lost by evapotranspiration.
(2) Deficit of soil moisture before rainfall is an important factor influencing the rate of rising of ground water level.
(3) The following point was made clear by measuring the effective porosity of the shallower (sand) and the deeper part (clayey sand under 80cm from the surface) of the soil column at the observation site that the smaller effective porosity in the deeper part was caused by capillary rise of ground water.

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A severe storm as shown in Figure 3 attacked Japan from January 31 to Feburary 1 in 1970 and caused one of the highest storm surge along the Japan Sea coast. At this time a great amount of sea water invaded a small fishing village named Ashizaki located on a sand dune at the periphery of the Kurobe Alluvial Fan. The topography and geology of the sand dune are shown in Figures 1 and 2. The invaded sea water infiltrated into the sand dune and about three-hundred wells which have been used for drinking were polluted by salt water. The decrease in Cl^- concentration had been investigated from April to November at the interval of one or two-month in order to estimate the residence time of groundwater in the sand dune. The residence time defined here refers to the mean residence time spent by individual water molecules in a reservoir, i. e. a sand dune aquifer in this case. An exponential decay of Cl^- concentration as can be read from Figures 5 and 7 is found by observation and the decay constant is calculated to be about 0.02 day^-1 by the method of least squares. Theoretical solution of Cl^- concentration in the sand dune may be expressed by the following equation provided the circulation is in steady state and the reservoir is well mixed;
S=S₀e^-αt
where S denotes the Cl^- concentration of groundwater, So refers to the initial value of S at the time of sea water invasion, t is the time, and 1/α means the residence time of groundwater. From the theory and observations it is concluded that the residence time of groundwater in this sand dune is about 50 days. The value is very short compared with the residence time of other groundwaters. This may be caused by the ample groundwater supply from the upstream side of the alluvial fan which have a relatively steep surface slope.

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[in Japanese]

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This is a brief review of the geographers' contributions to hydrology in Japan made after 1969. The author had already published reviews in 1966¹⁾ and 1968²⁾ on the same topic.
A commission on hydrology was established in 1967 in the Association of Japanese Geographers (Nippon-Chiri-Gakkai). This commission (Chairman: Yokichi Mino-Ishikawa), corresponding to the Commission on IHD in IGU, stimulated many hydrologic and hydrographic studies in Japan. Taking this opportunity of issuing a special volume for hydrology in the Geographical Review of Japan (Chirigaku Hyoron), the author compiled a summary of the original articles on hydrology by geographers. The purposes of this paper is restricted only to show the current trend of hydrologic researches through published works without making any comments on item.
Titles of all full papers published since 1968 to 1971, as well as short summaries and abstracts during this period are listed on the last pages of this volume.
He expresses his sincere thanks for their kind collaboration to Messrs. Isamu Kayane, Shigemi Takayama, Tadashi Arai, Makoto Aramaki, Kazuki Mori, Noboru Hida and Masahiro Shôda.
During this period, two attractive international conferences were organized and worked out by geographers. The first one was the International Conference on Land Subsidence³⁾⁴⁾ in Tôkyô in 1969 (President: Kiyoo Wadati, General Secretary: Sôki Yamamoto) and the second was the Asian Regional Conference of the International Association of Hydrogeologists in Tôkyô in 1971 (President: Sôki Yamamoto).
One book entitled “Water Circulation on Alluvial Fan”⁵⁾ was published in 1971. This book shows a top stage of progress in the systems approach to hydrology and geography with various new technics, including tritium analysis and electric analog models. They discussed ground water balances in connection to surface water on the Kurobe Fan, Toyama Prefecture.

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