Abstract
It has been well known that the flood-type varies greatly accordiag to the topographical elements the moutains, the basin and so forth. Accordingly, if we subclassify the topography of those flood visited areas, we can tell their flood-types. For example, in the case of the plain, the greater part of the plains in Japan is alluvial and they are formed by sand and gravels transported by the frequent flood-waters. So the microrelief of the plain and the state of the accumulated sand and gravels show the history of flood. If we have floods in future, it is possible for us to foretell the flood-type by the studying the micro-topography of the plain.
From this point of view, the writer surveyed the topography of the middle and lower courses of the Kanogawa river basin, Izu peninsula in the central part of Japan, by means of aerial photograph and by field survey. And he has drawn up the “topographical survey map of the middle and lower courses of the Kanogawa river basin showing classification of flood stricken areas.” Furthermore, he surveyed the great flood which visited the Kanogawa river basin on Septermber 26th, 1958 and has drawn up the “Map of the Kanogawa river basin showing the state of flood which visited the place on September 26th, 1958.” And he found the depth of the stagnant water, its period of the stagnation, the direction of the current, the velocity of the current, the erosion and deposit vary remarkably according to its area. In such a case, the following factors, for example the valley plain, the fan and the the delta, have a decisive influence upon deciding the types of flood. And then, he divided the flood-type in this district into the following five types.
(1) The flood-type seen in the valley plain. (2) The flood-type seen in the natural levee and back-marsh. (3) The flood-type seen in the dum up basin. (4) The flood-type seen in the narrow (canyon). (5) The flood-type seen in the delta.
