近年，河道内の樹木が定着範囲を拡大させる「樹林化」が日本全国で生じている．治水対策として，樹木の伐採に加え高水敷を掘削する対策が実施されているが，掘削後にヤナギ類等の樹木が再び繁茂する事例が報告されている．効率的な樹木管理を実施する上で，掘削後に再び樹林化することを考慮した管理計画が求められる．しかし，どの程度の速さで再び樹林が拡がるかについての知見は乏しい．本研究では，26 箇所の掘削地を対象として，掘削後に撮影された衛星写真と空中写真から河道内における樹木の繁茂状況を判読した．そして得られた繁茂状況の年変化から，ヤナギ類を中心とした樹林の拡大速度と，河床勾配による違いについて検証した．その結果，樹林は掘削から約 5 年が経過すると拡大速度を増し，掘削から約 10 年が経過した頃には掘削した範囲の約 50 ％を覆うことが明らかとなった．掘削地には，ヤナギ類の種子が多量に運ばれ，約 ...

This paper investigates the determination of flow resistance caused by stiff and flexible woody vegetation. A new procedure has been developed which allows the determination of friction factor f or Manning’s n using measurable characteristics of vegetation and flow. The procedure is capable of predicting flow resistance due to: (1) leafless bushes or trees and (2) leafy bushes or trees. The app...

The functioning of large river systems with adjacent floodplains is strongly influenced by the flood pulse. This phenomenon is the main structuring force for the biota, including fish communities that use floodplain environments for spawning, feeding, nursery and refuge. In floodplains and in the entire basin, the volume of water controls internal flows. During rising water, the high discharge ...

We use the stratigraphy of floodplains on Alaska’s North Slope to describe how tundra watersheds responded to climate changes over the last 15,000 calibrated years BP (15 cal ka BP). Two episodes of extremely rapid floodplain alluviation occurred during the PleistoceneeHolocene transition, one between 14 and 12.8 cal ka BP and the other between 11.5 and 9.5 cal ka BP. These aggradation episodes...

The paper examines the impacts of climate change, agroecology and socio-economic factors on agricultural land use diversity (ALUD) using a panel data of 17 regions of Bangladesh covering a 61 year period (1948–2008) by applying a dynamic panel GMM estimator. Results revealed that ALUD and total rainfall have actually increased @ 0.19% and 0.02% per year whereas variability in temperature has de...

Coastal flood assessments often require the analysis of a complex system of flood sources, pathways and receptors. This can be challenging for traditional numerical modelling approaches. In this paper we use a Bayesian networks approach to assess coastal floodplains as networks of inter-linked elements. A Bayesian network (Bn) model is built to describe flood pathways and estimate flood extents...

The majority of the world's floodplains are dammed. Although some implications of dams for riverine ecology and for river channel morphology are well understood, there is less research on the impacts of dams on floodplain geomorphology. We review studies from dammed and undammed rivers and include influences on vertical and lateral accretion, meander migration and cutoff formation, avulsion, an...