中心機能従業者の規模と通勤圏の分析の結果得られた356の中心都市とその周辺市町村とを対象として,人口,従業者数および主要3機能の1980～1985年の変化について考察した.その結果, (1) わが国では大都市圏の発展が著しいが,地方の中小都市には衰退するものが多く,わが国の都市化の現状はアメリカ合衆国などでみられた反都市化現象とは異なること, (2) 周辺市町村が中心都市に対して求めるほど,中心都市の成長にとって周辺市町村との関係は重要でないこと, (3) 中小都市では製造業従業者比率や増加率はたしかに高いが,製造業従業者増加率は中小都市の人口増加率とは相関が低く,中小都市の成長を支えているとはいい切れないこと, (4) 中枢管理機能従業者や製造業従業者は周辺市町村に向かってそれぞれ特色ある分散をなすのに対して,中心機能従業者は大都市に集積し,中心機能従業者が大都市の成長の基盤をなすようにみえること, (5) 全国的変化との対比によると,主要3機能はいずれも東京大都市圏周辺部に集積すること,が判明した.

抄録全体を表示

本稿では,多層構造を有する丘陵地斜面において地中水の挙動を観測し,その結果以下のことが明らかになった. (1) 降雨浸透プロセスについては,降雨開始後速やかに,難透水層上で飽和域が形成され,そこから下方の透水層に地中水が供給された.その後山体内部まで浸透すると,山体内部で地中水の圧力水頭の増加が生じた. (2) 山体内部での圧力水頭は,多摩ローム層中に飽和域が存在する場合, 50～60 mmの積算降雨で増加した。しかし,飽和域が存在しない場合は, 90 mmの降雨を要した. (3) 山体内部の圧力水頭の急増は,御殿峠礫層内の飽和域が多摩ローム層中の飽和域と連続したときに生じた.そして,飽和域からの圧力と礫層上部に封入された空気を通して多摩ローム層から伝達された圧力とにより,山体内部での圧力水頭の上昇は15 m H₂O以上にも達した. (4) 山体内部で圧力水頭が増加することに伴い,透水層において山体内部から地表へ向かう横方向の地中水の流れが生じ,斜面末端部でも山体内部からの流出成分が増加した.

抄録全体を表示

Japanese mountain rivers are supplied with large quantities of gravel from their tributaries. This paper discusses the relationship between downstream change in gravel size and bed form and the types of gravel transport process along a river's tributaries with steep slope, in order to clarify the influences on gravel supply for main streams from tributaries.
Along seven steep slope rivers which are tributaries of the Asahi River in the Asahi Mts. and the Tama River in the Kanto Mts., eastern Japan (Fig. 1 and Table 1), the following features are investigated along each stream (Fig. 3): 1) maximum diameter of river bed gravels, 2) the char-acteristics of bed form, such as the lobate forms on the river bed and falls, and 3) the distribution of the points where gravels are supplied from landslides or small streams. The lobate form is char-acterized by huge gravel, as large as 1 m in diameter, gathered at the front of it and recognized in the convex cross section. Its deposits consist of imbedded and nonsorted material.
The rivers are divided into three types of section, named (in order from the upper reaches) the A, B, and C sections, on the basis of maximum diameter and bed form. Each type of section is located in a different range of the channel slope (Table 2). The A section, where the channel slope is steeper than about 200 is characterized by small maximum diameter, many falls, and a few lobate forms. The B section, where the range of the channel slope is generally between 80 and 200‰, is characterized by large maximum diameter and many lobate forms. The C section, where the channel slope is gentler than 80‰ is characterized by small maximum diameter, no falls, and few lobate forms.
The A and B sections are found in all of the rivers. In the rivers whose minimum channel slope is steeper than 200‰ the B section is located on a steeper part than the B sections of the other rivers, and the A section extends near the junction with the main stream. The C section is found only in three rivers whose minimum channel slope is gentler than 80‰.
Each type of section is formed by a different type of gravel transport process depending on the value of the channel slope, and the influence on gravel supply for the main stream from the tributaries differs according to the type of section located near the junction with the main stream (Fig. 4).
The A section is characterized by occurrence and runout of debris flows. The fronts of debris flows, including huge gravels, are swept down this section and only finer particles remain. Many debris flows, which occur in the tributaries where the A section extends near the junction, flow into the main stream.
The B section is characterized by deposition of debris flows, and is formed by deposition of de-bris on a long-term basis. Although many of the occured debris flows in the tributaries that have a B section at the junction are deposited in the B section, some of them runout into the main stream. The above-mentioned type of tributaries supply huge gravels to the main stream.
Because almost all debris flows are deposited in the B section, in the C section gravels are trans-ported by traction. Therefore none of the huge gravels found in the B section can be transported into the C section. The channel slope at the junction is steeper, so the coarser gravels flow into the main stream from the tributaries that have a C section. This type of tributary supplies no huge gravels for the main stream.

抄録全体を表示