著者

林 千夏 池田 宏 HAYASHI Chinatsu IKEDA Hiroshi

出版者

筑波大学陸域環境研究センター

雑誌

筑波大学陸域環境研究センター報告 = Bulletin of the Terrestrial Environment Research Center,the University of Tsukuba (ISSN:13463381)

巻号頁・発行日

no.1, pp.43-50, 2001-02

---

The Shimanto River, in the southwest of Shikoku Island, forms incised meanders. It has been suggested that gorges are formed as meanders incise bedrock during tectonic uplift, or a lowering of the baselevel of erosion. However, it is known that the formation of incised meanders is dependent on many other factors.The Shimanto River is composed of a main stream and two major tributaries. Incised meanders occur especially in the middle section of the main stream. It is clear that scarcely any lateral erosion occurs here, as the meanders have very small terraces.The study site is located in the Shimanto Belt, which is composed of interbedded sandstone and mudstone. The sandstone is resistant to erosion, but the mudstone is easily eroded and transported by the river in suspension. There is little sediment load in the river because the area has not experienced recent uplift. Also, since the sediment load is mainly mud, there is very little bedload in the river, which results in a rough, bedrock channel floor. It is proposed that the lack of bedload supplied to the channel and the rough channel floor influence the lateral erosion of the channel and lead to the formation of incised meanders.To test this hypothesis, a flume experiment was conducted using a channel with fixed meanders and varying degrees of roughness of the channel bed. It was found that the greater the roughness of the channel bed, the weaker the concentration of streampower at meanders. It is therefore concluded that little lateral erosion is produced at channel bends over a rough bed. It seems likely that incised meanders are formed in the middle section of the Shimanto River because there is little bedload in the channel, resulting in a very rough, bedrock channel floor and a reduction in the efficient streampower for cutting banks erosion at the bends. This in turn reduces lateral erosion.

著者

関 智弥 池田 宏 SEKI Tomoya IKEDA Hiroshi

出版者

Terrestrial Environment Research Center, the University of Tsukuba

雑誌

筑波大学陸域環境研究センター報告 = Bulletin of the Terrestrial Environment Research Center,the University of Tsukuba (ISSN:13463381)

巻号頁・発行日

vol.4, pp.75-88, 2003-10

---

Lake Kasumigaura is a coastal lake, the second largest lake in Japan. There is the lacustrine lowland with a width of 0.5 - 1.0km, around Lake Kasumigaura. The lacustrine lowland consists of "Terrace I", "Terrace II" and "developing Lowland". It has been known that the lacustrine lowland formed at present, however the mechanisms and processes of formation have not been well understood. Thus, in this study, geomorphic characters and mechanism of developing lowland are revealed by distributions of reed community and grain size analysis and analysis of wave energy.Developing lowland is low and flat topography, and its relative height is 0 - 0.5m from mean water level. And its structure materials are mainly fine grains especially "very fine sand" and "silt". In addition distributions of the developing lowland and reed community have close correlation. And these distributions are determined mainly by wave energy.These results lead to the conclusion that developing lowland was formed with deposition of sands by the wave and capture of fine grains by reeds.

著者

山中 勤 田中 正 浅沼 順 濱田 洋平 YAMANAKA Tsutomu TANAKA Tadashi ASANUMA Jun HAMADA Yohei

出版者

Terrestrial Environment Research Center, the University of Tsukuba

雑誌

筑波大学陸域環境研究センター報告 = Bulletin of the Terrestrial Environment Research Center,the University of Tsukuba (ISSN:13463381)

巻号頁・発行日

vol.4, pp.51-59, 2003-10

---

Water levels were measured for 34 wells in the Nasu Fan, Tochigi prefecture, in the end of October, 2002. Water quality of groundwater (34 samples), river water (6 samples) and spring water (3 samples) were also analyzed. Local relief of groundwater table is considerably low, and the typical value of its gradient is approximately 1/100. At an elevation between 220m and 250m, groundwater table approaches to the ground surface. Revival of interrupted stream of the Sabi River and the Houki River can recharge groundwater. These facts indicate that there is active interaction between groundwater and surface streams. Groundwater level fell over most part of the fan in recent 10 years. The maximum reduction of the groundwater level exceeds 3m. Increase in electric conductivity of groundwater was detected in some areas including urban areas.

著者

小暮 哲也 青木 久 前門 晃

出版者

筑波大学陸域環境研究センター

雑誌

筑波大学陸域環境研究センター報告 (ISSN:13463381)

巻号頁・発行日

no.4, pp.97-101, 2003

被引用文献数

1