ON EFFECTS OF MAP SCALE ON CHARACTERISTICS OF CHANNEL NETWORK

Abstract

In this paper, the authors propose a method of standardizing a number of first-order streams and a drainage density for different map scales. Measurements of channel network are done at 8 drainage basins in the Kanto District, using topographic maps with the scales of 1:25, 000 and 1:50, 000 in order to analyze effects of map scale on characteristics of channel network. There are some differences between channel network drawn from 1:25, 000 and 1:50, 000 as shown in Figs. 1 and 2. Results of measurement at 8 drainage basins are shown in Table 1. The ratio of the number of first-order streams between 1:25, 000 and 1:50, 000 maps is about 2.0, and the ratio of the drainage density is about 1.4. The number of the first-order streams and the drainage density are smaller in the smaller scale map. On the contrary, the ratio of the average length of the first-order streams is about 0.7 and the ratio of the average drainage area of the first-order streams is about 0.5. The average length and the average drainage area of the first-order streams are larger in the smaller scale map. In general, however, the parameters of Horton's law are not affected by map scale (Fig. 3). The ratios of the average length of the first-order streams, the average drainage area of the first-order streams and the drainage density between different map scales are derived as a function of the ratio of the number of the first-order streams (Eqs. (9), (10) and (12)). The calculated ratios and the measured ones are summarized in Table 3. For analyzing the channel networks, it is important to indicate the map scale used in the analysis, and if one needs the comparisons between the values from the different map scales, the conversion by Eq. (14) could be possible.