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The Waiapu River catchment (drainage area of 1734-km 2 ) is one of the most prolific conveyors of sediment in the world, annually delivering roughly 35 Mt of fine material to the ocean from eroding gullies, hillslopes, and reworked sediment on valley floors. Tectonic and geologic influences, in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes, predisposes this region to high rates of erosion. The bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse-grained, poorly sorted sediment mixture. Rapid abrasion and breakdown leads to high rates of suspended sediment yield. A wave of bedload material, manifesting as elevated bed levels and significant widening of active alluvial fills, has been triggered by large inputs of hillslope material from a few key tributary catchments following Cyclone Bola in 1988. We review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years, appraising some of the legacy effects that may endure, as associated with reworking of the considerable alluvial stores within the Waiapu system. We use Structure-from-Motion (SfM) techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades. A record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment (1958–2017) indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley-bottom deposits. The channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river, giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network. The largest impacts occur in the upper steepland rivers, closest to the landslide-derived sediment supply. Transport rates here, as inferred from cross section change, are at a maximum during an aggradational phase following Cyclone Bola then taper off, despite the large sediment accumulations remaining in the system. As of 2017, the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre-Bola conditions. The compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape, as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment. [ABSTRACT FROM AUTHOR]

Evolutionary trajectories and related control factors of the Fortore River (southern Italy) are analyzed over a 150-year period as to assess channel modifications. A multitemporal GIS analysis of topographic maps and aerial photographs together with topographic and geomorphological field surveys were performed. Attention was focused on the impact caused by human disturbance, above all the presence of the Occhito dam at only 40 km upstream of the Fortore mouth (central Adriatic coast). Results show that channel adjustments occurred in three distinct phases and were primarily driven by human disturbance that diversely affected reaches located upstream and downstream of the dam. From the last decades of the nineteenth century to the 1950s (phase 1), channel widening prevailed along upstream reaches whilst narrowing along downstream reaches. Major channel adjustments occurred from the 1950s until the end of the 1990s (phase 2), especially channel narrowing of up to 81% in upstream reaches and 98% in downstream reaches. Narrowing was accompanied by channel-bed lowering of 1 to 5 m and by pattern changes in prevalence from multithread to largely prevailing single-thread channel configurations. In-channel mining, channel works, and hydraulic interventions are considered key driving factors of observed channel adjustments. The closure of the Occhito dam in 1966 had significant and permanent effects on downstream reaches through overall discharge regulation and permanent sediment trapping as also proved by the progressive retreat of the Fortore river mouth area. From 2000 to 2015 (phase 3), a substantial trend inversion was observed with overall channel widening and partial aggradation of upstream reaches and total stabilization of downstream reaches. As highlighted by an integrated multitemporal analysis of recent channel changes and flood events, the latter have played an important role in channel recovery of upstream reaches. Comparison between the Fortore River and other rivers in southern Italy has allowed us to ascertain that the reconstructed evolutionary trajectories are quite similar and that control factors are essentially the same. In particular, it confirms the role of major hydraulic structures as to the amount of channel adjustments of downstream reaches and the ensuing scarce to nil potential to channel recovery of regulated reaches. [ABSTRACT FROM AUTHOR]

Humans have become major geomorphological agents, effecting substantial change in the characteristics of Earth's physical landscapes. The agricultural Midwest of the United States is a region marked by pronounced human influence at the landscape scale. Humans undoubtedly have strongly influenced critical zone processes, including fluvial processes, in intensively managed agricultural landscapes, yet the exact nature of human alteration of these processes is unknown. This study documents historical changes in the extent of the stream channel network and in channel planform within the upper Sangamon River basin — an intensively managed agricultural watershed in Illinois. Results indicate that the modern channel network is nearly three times more extensive than the channel network in the 1820s. Most change in drainage density has occurred in headwater portions of the basin where numerous drainage ditches have been added to the network to drain flat uplands. No detectable change in channel position is evident between 1940 and 2012 along about 60% of the total length of the Sangamon River and its major tributaries. Nearly 30% of the total length exhibits change related to meander dynamics (cutoffs and lateral migration), whereas about 8% has changed as a result of channelization. Channelized sections typically remain straight for decades following human modification, supporting the notion that humans produce long-lasting catastrophic change in channel planform in this region. The findings confirm that humans are effective agents of morphological change in fluvial systems in this intensively managed watershed. Documenting human-induced versus natural changes in fluvial systems is important for evaluating how other critical zone processes in intensively managed landscapes have been affected by these changes. Human-induced changes in channel extent and planform most likely have altered this landscape from one dominated by biogeochemical transformations and storage of water and sediment prior to agricultural development into one now characterized by enhanced fluxes of water, sediment, and nutrients. [ABSTRACT FROM AUTHOR]

Abstract: Large rivers have anabranching channels with components that may be defined as braided, meandering or straight. This paper shows that application of such holistic terminologies is complicated by recognition of within-type and transitional-type variety, a confusingly varied use of terms, and a coverage of pattern characteristics that for many large rivers is incomplete. In natural states, big rivers can be plural systems in which main, accessory, tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics. A distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems. At any one time, even at flood stage, only some channels are geomorphologically active. Six types of geomorphological connectivity are described that range from coupled, through to partially-coupled and decoupled. The interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity. For improved understanding of the dynamics as well as the forms of these large composite systems, it is helpful to: (1) adopt element-level specification, not only for sediment bodies, but also for functioning channels; (2) track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers; and (3) recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates. Such augmenting information will provide an improved platform for both river management and ecological understanding. [Copyright &y& Elsevier]

Abstract: A new index has been developed for the hydromorphological assessment of Italian rivers. The method was designed to comply with the EU Water Framework Directive requirements, but its use can be extended to other applications in river management. The evaluation of stream morphological quality is preceded by a phase of river segmentation, consisting of an initial division of the network into river reaches with homogeneous morphological characteristics. The evaluation procedure consists of a set of 28 indicators, which were defined to assess longitudinal and lateral continuity, channel pattern, cross section configuration, bed structure and substrate, and vegetation in the riparian corridor. These characteristics are analyzed in terms of geomorphological functionality, artificiality, and channel adjustments. Indicators, classes, and the scoring system were defined based on expert judgement. The scoring system leads to the definition of the Morphological Quality Index (MQI). Application of the method to 102 river reaches covering a wide range of physical conditions and human pressures of Italian streams enabled the testing of the overall methodology and the refinement of the indicators and scores. Limitations, strengths, and the applicability of the method are also discussed in the paper. [Copyright &y& Elsevier]

Abstract: The increasing extent of human activities and climate change may have notable effects on river systems; therefore, a comprehensive knowledge of these effects is essential to mitigate their unfavourable consequences. The aim of the present study is to analyse the hydromorphological changes caused by climate change and human impacts on the Hungarian section of the Hernád River and to evaluate the morphological responses of this river from a flood prevention perspective. Over the past 60years, considerable morphological changes were measured in the studied river sections, caused by the alteration of their hydrology. The main morphological change was the evolution of secondary bends on large meanders. This process was driven by extrinsic factors, as the morphometric changes were determined by an altered water regime caused by precipitation change and engineering works. Further mean discharge decreases caused the propagation of this process on smaller meanders as well. Meanwhile, the cross-sectional area of the channel also decreased, primarily as a result of narrowing. This altered morphology enhances the flood risk in the short run, as the narrow channel is not sufficient to drain the rapid flood waves. In the twenty-first century, climate change may cause decreasing mean discharge while also increasing the frequency of rapid floods, further increasing flood risk. However, the projection of the geomorphological effects of future precipitation changes is very uncertain. [Copyright &y& Elsevier]

Abstract: This study aims at estimating the rate of bed aggradation of the Jia Dhansiri River in Assam, India. It is carried out using two methods: (1) measurement of channel cross section in the field, and (2) measurement of variously dated maps for the period 1995–2006. Following these two methods, data on parameters pertaining to bed aggradation are generated and authenticated by comparison. Data on total bed aggradation during 1995–2006 are extrapolated from cross section graphs and again verified with a model proposed in this paper based on average water level of base year and current year and total bed aggradation. The rates of bed aggradations are 5.27cm/y at Dhansiri Khuti village, 5.09cm/y at Barigain village, 5.27cm/y at Bagishakash village, and 2.64cm/y at Thalthali village. No degradation zones are found in between during the study period except in minor magnitude and localized cases. If these rates of bed aggradation are continued and no significant changes in the channel morphology occur, then the river bed may merge with the low river bank after 11years at Dhansiri Khuti village, 17years at Barigaon village, 6years at Bagishakash village, and 7years at Thalthali village. The average channel aggradation during 11–years of period in the 16–km reach has estimated to be 3.65cm/y. Again, if this rate is continued then the river bed will overtop low banks of the 16–km reach after 16years. At this situation the river may attain a state of geomorphic threshold which may be channel shift following vulnerable slope(s). [Copyright &y& Elsevier]

Abstract: Built in 1930 on the Matawin River (5770km²) to supply hydroelectric plants located downstream on the Saint-Maurice River, the Taureau Reservoir caused an inversion of the natural hydrological cycle: maximum flows occur in winter and minimum flows occur in spring during snowmelt. This inversion induces a very rapid rise of the reservoir level (base level for the channel upstream from the reservoir) in April–May during the filling-up process. The goal of the study is to analyze the effect of the rapid rise of the base level on the morphological evolution of the 7-km-long sandy section of the Matawin River located immediately upstream from the reservoir and to compare it with Jiongxin''s general model. Comparison of aerial photos taken before (1928) and after (1937, 1950, 1965, 1975, 1983, and 1995) reservoir construction reveals no significant change in the bankfull mean width, sinuosity, and bankfull depth of the studied section. It follows that the morphological evolution of the Matawin River channel upstream from the dam is not consistent with the Jiongxin model. The effect of the inverted hydrological regime in fact produces high channel stability. This stability will probably contribute to a slow but progressive reduction of the channel width and an increase of the sinuosity. This morphological evolution seems typical of the semialluvial streams found upstream from the inverted-type reservoir of the Canadian Shield. [Copyright &y& Elsevier]

Abstract: This paper presents a revision of a river-flow response model by Dust and Wohl (2012). In particular, serious confusion of the relationship between sediment transport capacity and width-to-depth ratio is clarified. As a consequence, we propose a reasonable qualitative model for understanding the complexity of river responses as illustrated in an appropriately modified form of the Lane diagram, which identifies the equilibrium condition based on the balance between channel aggradation and degradation. [Copyright &y& Elsevier]