1979 年 31 巻 1 号 p. 28-45
There is the historical relic of the grand canal so-called “Furuichi-ohmizo” in Minamikawachi county of Osaka prefecture, where it belongs to the region of the ancient tumuli: Furuichi-Kohun-group. “Furuichi-ohmizo” coexists with these ancient tumuli. It is considered as the big canal which was artificially cut in ancient times. However, the part which “Furuichi-ohmizo” survives is very little, the whole aspect is not yet evident.
It is the purpose of this paper to reconstruct the whole canal in detail, and to clear up its character. In this case, the author used the geomorphological and palynological research method in order to investigate the ancient geomorphological and vegetational environment.
The results are as follows:
1. Ninken-ryo, Minegatsuka-kohun and Seinei-ryo are situated in the vicinity of the mouth of the erosional valleys. (Ryo means the mausoleum of emperor. Kohun means the mausoleum of emperor or powerful family.) They were built in the place of the bad condition. It can be considered that these ancient tumuli were built to bring water of the valley to the moat.
2. The sand bed at the upper stratum of the silt bed is accumulated in the flood plain at the junction of the Yamato-gawa River and its branch: the Ishi-kawa River. Such change of sedimentary environment depends on the change of the channel of the Yamato-gawa River. This is an example that the change of the river channel greatly influences the formation of the flood plain.
3. By means of the geomorphological investigation and the examination of the placename Koaza in cadastre, the author could reconstruct the canal of the ancient “Furuichi-ohmizo” in the map. As a result, it became clear that “Furuichi-ohmizo” was a big artificial canal from the Ishi-kawa River to the Higashiyoke-gawa River. “Furuichi-ohmizo” formed the one part of the ancient network of canal which was divided into the two main canals and it had some branch canals that linked these main lines. However, it is uncertain whether these canals were built in the same times or not.
4. The artificial depression in the west of Shiroyama-kohun exists at the junction of the two main canals. This depression intersects with Ohtsu-michi. The placenames of Koaza as “Kamiohhune”, “Shimoohhune” and “Irimizu” in this place suggest this intersection. Further, it is remarked that the canal crosses the middle terrace. According to these facts, we can infer that the artificial depression is possible to be a port, and the canal was used by way of the water transportation.
5. The vegetation in this area changed in the period of early 8th century to early 12th century. The result of the pollen analysis shows it clearly. That is, the forest which was characterized by Abies, Tsuga, Cryptomeria, Sciadopitys, Cyclobalanopsis and Quercus destroyed, changed to the forest of Pinus. And Gramineae increased suddenly before such vegetational destruction. It shows that the clearance of the terrace was faster than the forest destruction of the mountain.
The pollen of the large type of Gramineae and Fagopyrum which were the cultivated plant doesn't appear on the lowest pollen zone, it seems that the terrace was not developed at the age of the lowest pollen zone. Therefore, it is assumed that “Furuichi-ohmizo” was used firstly not as the irrigation canal but as the water transportation.