656 SEDIMENTARY PROCESSES/Fluvial Geomorphology be on top of coarser materials laid down in-channel by migrating streams In more detail, the set of landforms includes channel bars of various types (point bars on the inside of meander bends, together with side- and mid-channel bars exposed at low flows); eroding banks characterized by various types of failure (including particulate removal or mass failure, or beam failure where overhanging banks are undercut); levees (channel-side ridges) and crevasses (dissecting channels) at the channel margin; abandoned channel fills; and backswamp-type floodplain environments in which organic processes may dominate Each of these has been studied intensively in recent years, with documentation of the style and rate of deposition/erosion and the flow conditions responsible This has, in the case of in-channel flow and sediment monitoring and modelling, involved painstaking field measurement (sometimes under hazardous flood conditions) and theory development In other situations, historical records and maps have been used to reconstruct channel changes over a century and longer The series of case studies now available exemplifies the general point that hydraulic processes operating in contrasted energy (set by gradient and incident flows) and sedimentary (set by the type and supply volume of sediment of particular size) environments produce contrasted landform developments For example, rivers with laterally stable courses and high sand load may generate large levees and ponded backswamps behind them, whereas gravel bed streams may have a diversity of bars and bedforms but less well-developed levees and backswamps – especially where rivers are laterally mobile, such as to eliminate the incipient development of such form units Architectural Ensembles Qualitatively recognized channel-pattern types initially included braided, meandering, and straight; anabranching varieties of each (in which the river has more than one branch, with islands or swamps between) are also possible (Figure 7A) The term ‘anastomosing’ is also used for laterally rather stable anabranching styles These commonly develop in channels with levees and channel-bed aggradation, with avulsion periodically relocating the river course through a backswamp zone Braided and meandering channels have also proved to be diverse in style; some of the former have more stable islands between Figure Alluvial river channel patterns (A) Classification of types Numbers refer to the styles of anabranching channels plotted in Figure Reproduced with permission from Nanson GC and Knighton AD (1996) Anabranching rivers: their cause, character and classification Earth Surface Processes and Landforms 21: 217 239 ß John Wiley and Sons Limited Reproduced with permission (B) Forms of development in meandering patterns over time