The human role in changing river channels

摘要: Abstract Direct consequences of the human role, where activity affects river channels through engineering works including channelization, dam construction, diversion and culverting, have been long recognised Marsh, 1864 , Thomas, 1956 . The less obvious indirect effects point reach changes occurring downstream throughout basin, however, are much more recently appreciated, dating from key contributions by Strahler [Strahler, A.N., 1956. nature induced erosion aggradation. In W. L. Thomas (Ed.), Man's Role in Changing Face Earth. University Chicago Press, Chicago, 621–638.], Wolman [Wolman, M.G., 1967. A cycle sedimentation urban channels. Geografiska Annaler 49A, 385–95.], Schumm [Schumm, S.A., 1969. River metamorphosis. Proceedings American Society Civil Engineers, Journal Hydraulics Division 95, 255–73.], Graf [Graf, W.L., 1977. rate law fluvial geomorphology. Science, 277, 178–191.]. These complemented alterations land use, such as deforestation, intensive agriculture incidence fire, with most extreme produced building urbanisation. evident channel cross-section size, shape composition now well-established, up to tenfold increases or decreases illustrated results than 200 world studies. addition overall planform, network ecology changed. Specific terms become associated changing enlargement, shrinkage Although scope adjustment has established, it not always possible predict what will happen a particular location, because complex response contingency. ways which relate clear, despite investigations showing distribution along segmented When considering role relation channels, at least five challenges persist. First, prediction amount likely change location is certain, contrasting responses humid arid systems needs be considered, modelling required reduce uncertainty, was first emphasised Burkham [Burkham, D.E., 1981. Uncertainties resulting form. Engineers Proceedings, 107, 593–610.]. Second, feedback incorporated within relationship between channel, scales can considerable implications, especially may occurred, initiated, under different environmental conditions. Third, consideration global climate imperative when sensitivity threshold Fourth, design involving geomorphology should an integral part restoration procedures. This requires, fifthly, greater awareness cultures basis for understanding constraints imposed legislative frameworks. Better perception varies culture well varying over time enhance application landscapes.