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With the increased recent attention on understanding the complex pathways and fluxes of material, energy, and organisms and the multidimensional coupling between various geomorphic process domains, the 47th Binghamton Geomorphology Symposium was organized around the theme of Connectivity in Geomorphology . Six key subthemes emerged: sediment connectivity, hydrologic connectivity, geochemical connectivity, riverine connectivity, landscape connectivity, and modeling of connectivity. Papers presented at the symposium and collected in this special issue elucidate the theoretical and conceptual underpinnings of connectivity but also provide field-based and analytical approaches to document the fundamental role of connectivity in geomorphic and ecological functioning. Among the consistent themes that emerged from the papers and from discussion during the symposium were (1) the interconnectedness of diverse forms of connectivity, (2) the appropriateness (or not) of conceptualizing connectivity as a gradient or continuum, and (3) the importance of an explicit recognition of disconnectivity as a mechanism to retain ecologically important materials and organisms within landscapes. Knowledge gaps identified in discussions during the symposium include: identifying questions that can be usefully addressed within a framework emphasizing connectivity; identifying feedbacks that enhance and limit connectivity; and quantification – of diverse aspects of connectivity, of thresholds of connectivity, and of interactions among different types of connectivity. [ABSTRACT FROM AUTHOR]

Human-induced landscape change is difficult to predict due to the complexity inherent in both geomorphic and social systems as well as due to the coupling relationships between them. To better understand system complexity and system response to changing inputs, “connectivity thinking” has become an important recent paradigm within various disciplines including ecology, hydrology and geomorphology. With the presented conceptual connectivity framework on geomorphic change in human-impacted fluvial systems a cautionary note is flagged regarding the need (i) to include and to systematically conceptualise the role of different types of human agency in altering connectivity relationships in geomorphic systems and (ii) to integrate notions of human-environment interactions to connectivity concepts in geomorphology to better explain causes and trajectories of landscape change. Geomorphic response of fluvial systems to human disturbance is shown to be determined by system-specific boundary conditions (incl. system history, related legacy effects and lag times), vegetation dynamics and human-induced functional relationships (i.e. feedback mechanisms) between the different spatial dimensions of connectivity. It is further demonstrated how changes in social systems can trigger a process-response feedback loop between social and geomorphic systems that further governs the trajectory of landscape change in coupled human-geomorphic systems. [ABSTRACT FROM AUTHOR]

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: 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: The Pleistocene deposits of the valley of the River Piedra (NE Spain) are represented by thick tufas with small amounts of detrital material; the development of these deposits correlates with marine isotopic stages 9, 7, 6, and 5. The sedimentary scenario in which they formed mostly corresponded to stepped fluvial systems with barrage-cascade and associated dammed areas separated by low gradient fluvial stretches. Mapping and determining the sedimentology and chronology of these deposits distinguished two main episodes of fluvial diffluence that originated as a result of the temporary blockage of the river — a consequence of the vertical growth of tufa barrages in the main channel. In both episodes, water spilt out toward a secondary course from areas upstream of barrages where the water level surpassed the height of the divide between the main and secondary course. As a consequence, extensive and distinct tufa deposits with very varied facies formed over a gently inclined area toward and, indeed, within the secondary course. The hydrology of this secondary course was episodic, fed only by surface water. The two diffluence episodes detected occurred during MIS 7 and 7–6 and were interrupted by incision events, reflected by detrital deposits at the base of each tufa sedimentation stage in the main channel. Incision, which caused the breakage of the barrages, allowed water to again flow through the main channel. No evidence of diffluence was seen in any younger (MIS 5 to present-day) tufa deposits. The proposed diffluence model might help explain other carbonate fluvial systems in which (1) tufas appear in areas with no permanent water supply, and (2) tufas are absent over extensive areas despite conditions favourable to their formation. [Copyright &y& Elsevier]

Abstract: Natural hazard and risk assessments are predicated on a detailed understanding of the relationship between frequency and magnitude of the hazardous process under investigation. When information is sought from the deep past (i.e., several thousand years), continuous event records do not exist and the researcher has to rely on proxy data to develop the frequency–magnitude (F–M) model. Such work is often prohibitively expensive and few well-researched examples for mass movement are available worldwide. The Cheekye fan is a desirable location for land development and has a depth and breadth of previous research unprecedented on any debris-flow fan in Canada. We pursued two principal strains of research to formulate a reliable F–M relationship. The first focuses on stratigraphic analyses combined with radiometric dating and dendrochronology to reconstruct a comprehensive picture of Holocene debris-flow activity. The second approach examines hydrological limitations of rock avalanche evolution into debris flows through either entrainment of saturated sediments or by failure of a landslide-generated dam and upstream impoundment. We thus hypothesize that debris flows from Cheekye River can be separated into two quasi-homogenous populations: those that are typically triggered by relatively small debris avalanches, slumps, or rock falls or simply by progressive bulking of in-stream erodible sediments; and those that are thought to result from transformation of rock avalanches. Our work suggests that debris flows exceeding some 3 million m3 in volume are unlikely to reach the Cheekye fan as a result of limited water available to fully fluidize a rock avalanche. This analysis has also demonstrated that in order to arrive at reasonable estimates for the frequency and magnitude of debris flows on a complex alluvial fan significant multidisciplinary efforts are required. Without the significant precursor investigations and the additional efforts of this study, life and property may be jeopardized or the design of debris-flow mitigation may be subject to considerable and unquantifiable error. [Copyright &y& Elsevier]

Abstract: Railroads and roads are ubiquitous features in the river corridors of the United States. However, their impact on hydrologic, geomorphic, and ecological processes in fluvial and riparian landscapes has not been systematically explored at regional or continental extents. This study documents the geographic distribution of roads and railroads in the alluvial floodplains of the continental United States and the regional variability of their potential impacts on lateral connectivity and resultant channel and floodplain structure and function. We use national scale data sets and GIS analysis to derive data on stream–transportation network interactions in two broad categories: (1) crossing impacts, such as bridges and culverts, and (2) impacts where transportation infrastructure acts as a longitudinal dam along the stream channel, causing lateral floodplain disconnection. Potential stream crossing impacts are greatest in regions with long histories of road and railroad development and relatively low relief, such as the Mid-Atlantic, New England, and the Lower Mississippi and Ohio Valleys. Potential lateral disconnections are more prevalent in rugged regions such as the Western U.S. and Appalachians where transportation routes follow river corridors along valley bottoms. Based on these results, we develop a conceptual model that suggests that the area of lateral disconnection due to transportation infrastructure should be most extensive in mid-sized alluvial valleys in relatively rugged settings. The result of this disconnection is the disruption of the long-term, cut-and-fill alluviation and of the shorter-term flood and flow pulse processes that create and maintain ecosystem function in river landscapes. The tremendous extent of transportation infrastructure in alluvial valleys documented in this study suggests a revision to H.B.N. Hynes'' statement that the valley rules the stream. Instead, it appears that in modern landscapes of the U.S. the valley rules the transportation network — and the transportation network rules the stream. [Copyright &y& Elsevier]

Abstract: Changes in bed morphology and sedimentology at stream confluences in relation to specific hydrological events have not been documented extensively. Moreover, few, if any, studies have investigated the effect of net hydrological conditions on channel change at a confluence over a period of many years. Repeat cross section surveys and sampling of bed material at a small, asymmetrical stream confluence reveal the short-term effects of hydrological variability on bed morphology and spatial patterns of bed material texture. Survey data over a 15-year period illustrate the long-term response of channel morphology at the confluence to net hydrological conditions. Results confirm that this confluence is a dynamic fluvial environment, involving shifts in the zone of scour and repeated deposition and erosion of a bar complex at the downstream junction corner as the discharge ratio changes in response to hydrological variability in the tributary streams. Persistent faster runoff-response times of the lateral tributary compared to the main stem have resulted in long-term net erosion of the channel bank opposite this tributary. The documented morphological and sedimentological changes are consistent with and can be explained by results of experimental studies and by past investigations at this confluence that have documented changes in patterns of mean flow structure and turbulence in response to variation in the discharge ratio of contributing streams. [Copyright &y& Elsevier]

Abstract: Bankfull channel width is a fundamental measure of stream size and a key parameter of interest for many applications in hydrology, fluvial geomorphology, and stream ecology. We developed downstream hydraulic geometry relationships for bankfull channel width w as a function of drainage area A, w = α A β, (DHGwA) for nine aggregate ecoregions comprising the conterminous United States using 1588 sites from the U.S. Environmental Protection Agency''s National Wadeable Streams Assessment (WSA), including 1152 sites from a randomized probability survey sample. Sampled stream reaches ranged from 1 to 75 m in bankfull width and 1 to 10,000 km2 in drainage area. The DHGwA exponent β, which expresses the rate at which bankfull stream width scales with drainage area, fell into three distinct clusters ranging from 0.22 to 0.38. Width increases more rapidly with basin area in the humid Eastern Highlands (encompassing the Northern and Southern Appalachians and the Ozark Mountains) and the Upper Midwest (Great Lakes region) than for the West (both mountainous and xeric areas), the southeastern Coastal Plain, and the Northern Plains (the Dakotas and Montana). Stream width increases least rapidly with basin area in the Temperate Plains (cornbelt) and Southern Plains (Great Prairies) in the heartland. The coefficient of determination (r 2) was least in the noncoastal plains (0.36–0.41) and greatest in the Appalachians and Upper Midwest (0.68–0.77). DHGwA equations differed between streams with dominantly fine bed material (silt/sand) and those with dominantly coarse bed material (gravel/cobble/boulder) in six of the nine analysis regions. Where DHGwA equations varied by sediment size, fine-bedded streams were consistently narrower than coarse-bedded streams. Within the Western Mountains ecoregion, where there were sufficient sites to develop DHGwA relationships at a finer spatial scale, α and β ranged from 1.23 to 3.79 and 0.23 to 0.40, respectively, with r 2 >0.50 for 10 of 13 subregions (range: 0.36 to 0.92). Enhanced DHG equations incorporating additional data for three landscape variables that can be derived from GIS—mean annual precipitation, elevation, and mean reach slope—significantly improved equation fit and predictive value in several regions, most notably the Western Mountains and the Temperate Plains. Channel width was also related to human disturbance. We examined the influence of human disturbance on channel width using several indices of local and basinwide disturbance. Contrary to our expectations, the data suggest that the dominant response of channel width to human disturbance in the United States is a reduction in bankfull width in streams with greater disturbance, particularly in the Western Mountains (where population density, road density, agricultural land use, and local riparian disturbance were all negatively related to channel width) and in the Appalachians and New England (where urban and agricultural land cover and riparian disturbance were all negatively associated with channel width). [Copyright &y& Elsevier]

Abstract: Confluence dynamics in the Ganga–Ramganga valley in the western Ganga plains of India has been studied through systematic mapping of channel configuration using multi-date remote sensing images and topographic sheets for a period spanning nearly 100 years (1911–2000). The study has been supplemented with a detailed analysis of the channel morphology, hydrology and sediment transport characteristics of the different rivers. Our study indicates that new confluences have been created during this period and that the confluence points have moved both upstream and downstream on a historical time scale. Apart from major avulsions, other processes that have controlled the confluence movements include river capture, cut-offs and aggradation in the confluence area. River capture occurs through lateral bank erosion and migration, encroachment by the master stream and beheading of smaller rivers resulting in upstream movement of the confluence point. Another process which influences the upstream migration of the confluence is an increase in sinuosity of one of the channels near the confluence and then a cut-off. Aggradation in the confluence area and local avulsions of the primary channel in a multi-channel system seem to be the major process controlling the downstream movement of the confluence point. Analysis of channel morphology, hydrology and sediment budget for the study period supports our interpretations. [Copyright &y& Elsevier]

Abstract: A sharp decrease in total suspended solids (TSS) concentration has occurred in the Mekong River after the closure of the Manwan Dam in China in 1993, the first of a planned cascade of eight dams. This paper describes the upstream developments on the Mekong River, concentrating on the effects of hydropower dams and reservoirs. The reservoir-related changes in total suspended solids, suspended sediment concentration (SSC), and hydrology have been analyzed, and the impacts of such possible changes on the Lower Mekong Basin discussed. The theoretical trapping efficiency of the proposed dams has been computed and the amount of sediment to be trapped in the reservoirs estimated. The reservoir trapping of sediments and the changing of natural flow patterns will impact the countries downstream in this international river basin. Both positive and negative possible effects of such impacts have been reviewed, based on the available data from the Mekong and studies on other basins. [Copyright &y& Elsevier]

Abstract: The Kent River flows from semi-arid headwaters in the agricultural (wheatbelt) region of Western Australia to a wetter and forested lower-catchment. It is set in an atypical fluvial environment, with rainfall decreasing inland towards a low-relief upper catchment. Replacement of native deep-rooted perennial vegetation with shallow-rooted seasonal crops has altered the hydrology of the upper catchment. Clearing for agriculture has also increased recharge of regional groundwater systems causing groundwater to rise and mobilise salt stores. This has increased stream salinity which has degradation riparian vegetation and decreased flow resistance. Elevated groundwater has also affected streamflow, increasing flow duration and annual discharge. The altered hydrological regime has affected geomorphic stability, resulting in channel responses that include incision and removal of uncohesive material. Channel response is variable, showing a high dependence on channel morphotype, channel boundary material and severity of salinity (degree of vegetation degradation). Response in confined reaches bounded by sandy material has been characterised by minor lateral bank erosion. In the fine-grained, wider, low-gradient reaches, mid-channel islands have been stripped of sandy sediment where vegetation has degraded. Following an initial period of high erosion rates in these reaches, the channel is now slowly adjusting to a new set of boundary conditions. The variable response has significant implications for management of salt affected rivers in southwestern Australia. [Copyright &y& Elsevier]

Abstract: Spontaneous, autogenic self-organization has been described in numerous geomorphic systems, but it has not been investigated in detail with respect to coarse bedforms in general or step-pools in particular. In this paper, we review the spatial organization of step-pool systems and present example evidence of step-pool development as an autogenic self-organization process. We then outline the mathematical language for defining spatially divergent self-organization and test these ideas using two unique field examples from Oregon (Andrews Experimental Forest) and California (Baxter Creek), where step-pools developed from planar beds in artificially manipulated channels. Results show that step-pool development is consistent with a spatially divergent self-organization phenomenon. Entropy increases as initially undifferentiated planar channels diverge into steps and pools, then declines when a series of steps and pools of consistent size and spacing is established, signifying stability in the system. The self-organization process is accompanied by increasing flow resistance and decreasing slope (through increasing the “vertical sinuosity” of the step-pool profile and creation of low- or negative gradient pool areas), suggesting a minimization of stream power. The self-adjustment of the step-pool bed profile over time represents another manifestation of a general process that results in rhythmic patterns on the surface of Earth. [Copyright &y& Elsevier]

Abstract: Historical and modern scientific contexts are provided for the 2006 Binghamton Geomorphology Symposium on the Human Role in Changing Fluvial Systems. The 2006 symposium provides a synthesis of research concerned with human impacts on fluvial systems — including hydrologic and geomorphic changes to watersheds — while also commemorating the 50th anniversary of the 1955 Man''s Role in Changing the Face of the Earth Symposium [Thomas, Jr., W. L. (Ed.), 1956a. Man''s Role in Changing the Face of the Earth. Univ. Chicago Press, Chicago. 1193 pp]. This paper examines the 1955 symposium from the perspective of human impacts on rivers, reviews current inquiry on anthropogenic interactions in fluvial systems, and anticipates future directions in this field. Although the 1955 symposium did not have an explicit geomorphic focus, it set the stage for many subsequent anthropogeomorphic studies. The 1955 conference provided guidance to geomorphologists by recommending and practicing interdisciplinary scholarship, through the use of diverse methodologies applied at extensive temporal and geographical scales, and through its insistence on an integrated understanding of human interactions with nature. Since 1956, research on human impacts to fluvial systems has been influenced by fundamental changes in why the research is done, what is studied, how river studies are conducted, and who does the research. Rationales for river research are now driven to a greater degree by institutional needs, environmental regulations, and aquatic restoration. New techniques include a host of dating, spatial imaging, and ground measurement methods that can be coupled with analytical functions and digital models. These new methods have led to a greater understanding of channel change, variations across multiple temporal and spatial scales, and integrated watershed perspectives; all changes that are reflected by the papers in this volume. These new methods also bring a set of technical demands for the training of geomorphologists. The 2006 Binghamton Geomorphology Symposium complements the 1956 symposium by providing a more specific and updated view of river systems coupled with human interactions. The symposium focuses on linkages between human land use, structures, and channel modification with geomorphology, hydrology, and ecology. The emergence of sustainability as a central policy guideline in environmental management should generate greater interest in geomorphic perspectives, especially as they pertain to human activities. The lack of theories of anthropogeomorphic change, however, presents a challenge for the next generation of geomorphologists in this rapidly growing subfield. [Copyright &y& Elsevier]

Abstract: The hydrology and geomorphology of large rivers in America reflect the pervasive influence of an extensive water control infrastructure including more than 75,000 dams. One hundred thirty-seven of the very large dams, each storing 1.2 km3 (106 acre feet) of water or more, alter the flows of every large river in the country. The hydrologic effects of these very large dams emerge from an analysis of the stream gage records of 72 river reaches organized into 36 pairs. One member of each pair is an unregulated reach above a dam, whereas the other is a regulated reach downstream from the same structure. Comparison of the regulated and unregulated reaches shows that very large dams, on average, reduce annual peak discharges 67% (in some individual cases up to 90%), decrease the ratio of annual maximum/mean flow 60%, decrease the range of daily discharges 64%, increase the number of reversals in discharge by 34%, and reduce the daily rates of ramping as much as 60%. Dams alter the timing of high and low flows and change the timing of the yearly maximum and minimum flows, in some cases by as much as half a year. Regional variation in rivers, dams, and responses are substantial: rivers in the Great Plains and Ozark/Ouachita regions have annual maximum/mean flow ratios that are 7 times greater than ratios for rivers in the Pacific Northwest. At the same time, the ratio of storage capacity/mean annual water yield for dams is greatest for Interior Western, Ozark/Ouachita and Great Plains rivers and least for Pacific Northwest streams. Thus, in many cases those rivers with the highest annual variability have the greatest potential impact from dams because structures can exert substantial control over downstream hydrology. The hydrologic changes by dams have fostered dramatic geomorphic differences between regulated and unregulated reaches. When compared to similar unregulated reaches, regulated reaches have 32% larger low flow channels, 50% smaller high flow channels, 79% less active flood plain area, and 3.6 times more inactive flood plain area. Dams also affect the area of active areas, the functional surfaces that are functionally connected to the present regime of the river. Regulated reaches have active areas that are 72 smaller than the active areas of similar unregulated reaches. The geomorphic complexity (number of separate functional surfaces per unit of channel length) is 37% less in regulated reaches. Reductions in the size of hydrologically active functional surfaces are greatest in rivers in the Great Plains and least in Eastern streams. The largest differences in geomorphic complexity are in interior western rivers. The shrunken, simplified geomorphology of regulated large rivers has had direct effects on riparian ecology, producing spatially smaller, less diverse riparian ecosystems compared to the larger, more complex ecosystems along unregulated reaches of rivers. [Copyright &y& Elsevier]

Abstract: The Brahmaputra River finds its origin in the Chema Yundung glacier of Tibet and flows through India and Bangladesh. The slope of the river decreases suddenly in front of the Himalayas and results in the deposition of sediment and a braided channel pattern. It flows through Assam, India, along a valley comprising its own Recent alluvium. In Assam the basin receives 300 cm mean annual rainfall, 66–85% of which occurs in the monsoon period from June through September. Mean annual discharge at Pandu for 1955–1990 is 16,682.24 m3 s− 1. Average monthly discharge is highest in July (19%) and lowest in February (2%). Most hydrographs exhibit multiple flood peaks occurring at different times from June to September. The mean annual suspended sediment load is 402 million tons and average monthly sediment discharge is highest in June (19.05%) and lowest in January (1.02%). The bed load at Pandu was found to be 5–15% of the total load of the river. Three kinds of major geomorphic units are found in the basin. The river bed of the Brahmaputra shows four topographic levels, with increasing height and vegetation. The single first order primary channels of this braided river split into two or more smaller second order channels separated by bars and islands. The second order channels are of three kinds. The maximum length and width of the bars in the area under study are 18.43 km and 6.17 km, respectively. The Brahmaputra channel is characterised by mid-channel bars, side bars, tributary mouth bars and unit bars. The geometry of meandering tributary rivers shows that the relationship between meander wavelength and bend radius is most linear. The Brahmaputra had been undergoing overall aggradation by about 16 cm during 1971 to 1979. The channel of the Brahmaputra River has been migrating because of channel widening and avulsion. The meandering tributaries change because of neck cut-off and progressive shifting at the meander bends. The braiding index of the Brahmaputra has been increasing from 6.11 in 1912–1928 to 8.33 in 1996. During the twentieth century, the total amount of bank area lost from erosion was 868 km2. Maximum rate of shift of the north bank to south resulting in erosion was 227.5 m/year and maximum rate of shift of the south bank to north resulting in accretion was 331.56 m/year. Shear failure of upper bank and liquefaction of clayey-silt materials are two main causes of bank erosion. [Copyright &y& Elsevier]

Abstract: This paper presents an overview of tropical river systems around the world and identifies major knowledge gaps. We focus particularly on the rivers draining the wet and wet–dry tropics with annual rainfall of more than 700 mm/year. The size of the analyzed river basins varies from 104 to 6×106 km2. The tropical rivers across the globe drain a variety of geologic–geomorphologic settings: (a) orogenic mountains belts, (b) sedimentary and basaltic plateau/platforms, (c) cratonic areas, (d) lowland plains in sedimentary basins and (e) mixed terrain. All of them show clearly high but variable peak discharges during the rainy season and a period of low flow when rainfall decreases. Some tropical rivers show two flood peaks, a principal and a secondary one, during the year. We computed the intensity of floods and discharge variability in tropical rivers. The relationship between sediment yield and average water discharge for orogenic continental rivers of South America and Asia was also plotted. Insular Asian rivers show lower values of sediment yield related to mean annual discharge than continental orogenic rivers of Asia and South America. Rivers draining platforms or cratonic areas in savanna and wet tropical climates are characterized by low sediment yields. Tropical rivers exhibit a large variety of channel form. In most cases, and particularly in large basins, rivers exhibit a transition from one form to another so that traditional definitions of straight, meandering and braided may be difficult to apply. In general, it is more useful to apply the terminology of single and multi-channel systems or complex anabranching systems at least for selected regional segments. Present-day knowledge of tropical systems and its potential application to improve interpretation of older alluvial sequences and facies models are briefly discussed. Human impact and river management issues including land use changes, mining, dams, interbasin water transference as well as flood hazards are some of the daunting problems in tropical river basins today. [Copyright &y& Elsevier]

Anabranching river systems are now regarded as a separate class in river classifications owing to their distinctive morphological/hydrological characteristics and fluvial processes. A better understanding of anabranching rivers still needs detailed data from different environmental and geographical settings. This paper presents a detailed account of an anabranching river system from the Himalayan foreland basin. The Baghmati river system from north Bihar Plains, eastern India provides a typical example of an anabranching river system located in the interfan area between the Kosi and the Gandak megafans. The river system is braided in upstream reaches and meandering in downstream reaches, but the midstream anabranching reach is characterized by low width–depth ratio (11–16), gentle gradient (0.00018–0.00015), variable peak discharge, frequent flooding and high sediment load. The anabranching in the midstream reaches is a response to its inability to transport high sediment load due to gentle channel slope and dominance of aggradation process. The development of anabranches is related to rapid and frequent avulsions of the river channels with eight major avulsions observed in the 30-km-wide floodplain in the last 230 years. The decadal scale avulsion history of the Baghmati river system makes it ‘hyperavulsive’ and the major causative factors for such channel instability are sedimentological readjustments and active tectonics in the basin area. [Copyright &y& Elsevier]