Abstract
1) PREFACE This paper is concerned with research into the changes in the watercourses network in the metropolitan area of Tokyo. In paticular, the investigation is concerned with industrialization, modernization, and the development of the motor car-oriented society and its influence in reducing the amount of watercourses. The scope of the investigation is as follows : (1) Within a radius of 50 km of the Tokyo Station. (2) 23-ku in Yokyo. Period of the investigation is 68 years. In the metropolitan area, the city has changed its function and form over the past 68 years. As a result, rivers and canals have largely been influenced by that change. The subject of this paper is the investigation and research into the degree of reduction of rivers, canals and ponds as caused by the modernization of the city. The scope of the water environment we have chosen to investigate is very broad from small blocks to large rivers and the sea. Here, we used a "Space modular coordination chart" presented by Dr. Ojima in 1982. The Topographical Survey Institute of Japan. Other references used are : to pographicals maps from the past years, documents related to geography, statistical data, townplans, etc. A blank map was prepared as the base map on which the watercourses network was drawn. Measuring method of the total length of water-front : the digitizer (measurement precision : 1/10 mm) set into a microcomputer measured each water-front length five times, and the average value was used. This paper uses the concept of water-front density. The water-front density is given as the following formula. W_d= W_l/S, where W_d : water front density (km/km^2), W_l : total length of water-front (km), S : area of a certain region (km^2). 2) THE CHANGE IN THE WATER-FRONT LENGTH IN THE REGION WITHIN A RADIUS OF 50 KM OF THE METROPOLITAN AREA Table 2, 3 and Fig. 2, 3 shows the transition in watercourse, the number of which has been reduced in the past 68 years. In the whole region within a radius of 50 km of the metropolitan area, 624.3 km of water-front length has been lost. This is equal to 32.4 % of the total water-front length in 1914. The nearer to the center of the metropolitan area, the more marked is the tendency to reduction of the watercourse. Concentration of industrial base areas has proceeded around the bay of Tokyo for these 68 years. Concentration of population the center of the metropolitan area and rapid progress of commercial activity has been a primary cause of the reduction of watercourse length. 3) INVESTGATION OF ACTUAL CONDITION IN TOKYO 23-KU Fig. 5 shows transition in the waterfront length in Tokyo 23-ku the past 68-years. Waterfront length was 2 107.5km in 1909, but decreased to 904.6km in 1980, This indicates the average decrease of 17km every year. Waterfront length in 1980 corresponds to 57 % of the 1909 figure. Fig. 6〜10 shows changes in the watercourses network from 1909 to 1980. Changes in conditions of waterfront length have been processed by mesh data processing and shown in Fig. 11〜16. Waterfront length of 100m per mesh was constructed with the radius of 2 mm in the original drawing. Fig. 16 shows the complete changes from 1909 to 1980. The areas with dark shading in Fig. 5〜9 indicate the partially Tokyo Bay. This area of the Tokyo Bay was decreased by 75.14 km during 71 years. Its area in 1980 corresponds to 68.4 % of the 1909 figure. 4) RESULTS There are various problems concerning the rivers in the city. The problem can reclamation of those, permament reclamation has been studied. Since 1914, 32.4 % of watercourses in the metropolitan area within a radius of 50-km, and 4.9 % of that in the metropolitan area within a radius of 10km has been lost. Fifty-seven percent of watercourse in the Tokyo 23-ku has been lost since 1909.
