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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]

Understanding flow-sediment interactions is important for comprehending river functioning. Fine sediment accumulation processes, in particular, have key implications for ecosystem health. However, the amount of fines generated by intragravel flows and later accumulated in gravel streambeds may have been underestimated, as the hydraulic-related driving transport mechanisms in play are not clearly identified. Specifically, the relative contribution of fines from upper vs. lower sediment layers in gravel beds is not well understood. By recreating flooded and dewatered conditions in an experimental flume filled with natural sediment, we estimated such contributions by observing and collecting intragravel transported fines that were later accumulated into a void in the middle of the sediment matrix. Near-bed transport in the upper sediment layers (named Brinkman load ) during flooded conditions accounted for most (90%) of the accumulated fines. Intragravel transport in the lower sediment layers (named Interstitial load ) was the sole source of transport and accumulation during dewatered conditions with steeper hydraulic gradients. Interstitial load accounted for 10% of the total transport during flooded conditions. Although small, such estimations demonstrate that hydraulic-gradient transport in the lower sediment layers occurs in spite of the contradicting analytical assessments. We provide a case study to challenge the traditional approaches of assessing intragravel transport, and a useful framework to understand the origin and relative contribution of fine sediment accumulation in gravel beds. Such knowledge will be highly useful for the design of monitoring programs aiding river management, particularly in regulated rivers. [ABSTRACT FROM AUTHOR]

Fine sediment processes in gravel beds may have significant impacts to overall river ecosystem function. In addition to gravitational deposition, horizontal intragravel transport has been recognized to influence fine sediment accumulation. However, the specific hydraulic mechanisms and origin of fine sediment movement are not clearly identified. The purpose of this study was to investigate key hydraulic drivers and patterns of fine sediment accumulation. Using a conceptual framework to set the scene, we implemented an experimental setup in a gravel lateral bar subject to irregular flow fluctuations in the Kiewa River (Australia). We installed nine sets of sediment collector pairs and piezometers into the gravel. Each pair included one horizontally and one horizontally-vertically perforated collector. Mid-range, rather than peak flows, covering the site in water drove fine sediment deposited in the collectors. We estimated horizontal contribution to final deposition as 59%. Such contribution resulted from shear stresses > 3 N m − 2 promoting streamwise near-bed turbulence at the water-sediment interface during flooded conditions. Despite high subsurface hydraulic gradients, intragravel transport in the lower sediment layers via Darcy flow did not show any influence to fine sediment deposition. Our findings contribute to an improved understanding of fine sediment accumulation processes, key for overall river ecosystem functioning, particularly in regulated rivers. [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]

Channel changes in meandering rivers naturally exhibit complex behaviour, and understanding the river dynamics can be challenging in environments also subject to cumulative human impacts. Planform changes were analysed on four reaches of the lower course of the Peixe River, Brazil, at decadal scales over the period 1962–2008 from aerial photographs and satellite imagery, complemented by a historical map from 1907. Analysis of the spatial and temporal patterns of channel change mechanisms and morphometry of bends and of the sinuosity and morphodynamic variations of the reaches demonstrates major changes in planform characteristics. Sinuosity in all reaches decreased from ~ 2.6 to ~ 1.7, average wavelength of bends has increased from ~ 200 to ~ 500 m, and the planform has become much simpler. Changes have been progressive from downstream to upstream, with higher intensities of processes, particularly cutoffs first in downstream reaches then more recently in upstream reaches. It is suggested that channel changes represent a morphological adjustment to human interventions, such as reservoir construction and land use. However, evidence of the autogenic behaviour of meanders is highlighted in which the existence of compound meanders reveals control over the spatial variation in the reaches. The results suggest that geomorphic thresholds associated with the compound meander formation and the bend evolution should be considered, even in impacted meandering rivers, because they exert primary controls on the spatial-temporal adjustment of channels. [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]

The 2008 eruption of Chaitén volcano in southern Chile severely impacted several densely forested river catchments by supplying excess pyroclastic sediment to the channel networks. Our aim is to substantiate whether and how channel geometry and forest stands changed in the Rayas River following the sudden input of pyroclastic sediment. We measured the resulting changes to channel geometry and riparian forest stands along 17.6 km of the impacted gravel-bed Rayas River (294 km 2 ) from multiple high-resolution satellite images, aerial photographs, and fieldwork to quantify yield volume characteristics of the forest stands. Limited channel changes during the last 60 years before the eruption reflect a dynamic equilibrium condition of the river corridor, despite the high annual precipitation and the sediment supply from Chaitén and Michinmahuida volcanoes in the headwaters. Images taken in 1945, 2004, and 2005 show that total size of the vegetated channel islands nearly doubled between 1945 and 2004 and remained unchanged between 2004 and 2005. Pyroclastic sediment entering the Rayas River after the 2008 eruption caused only minor average channel widening (7%), but killed all island vegetation in the study reach. Substantial shifts in the size distribution of in-channel vegetation patches reflect losses in total island area of 46% from 2005 to 2009 and an additional 34% from 2009 to 2012. The estimated pulsed release of organic carbon into the channel, mainly in the form of large wood from obliterated island and floodplain forests, was 78–400 tC/km/y and surpasses most documented yields from small mountainous catchments with similar rainfall, forest cover, and disturbance history, while making up between 20% and 60% of the annual carbon burial rate of fluvial sediments in the northern Patagonian fjords. We conclude that the carbon footprint of the 2008 Chaitén eruption on the Rayas River was more significant than the measured geomorphic impacts on channel geometry for the first five years following disturbance. The modest post-eruptive geomorphic response in this river is a poor indicator of its biogeochemical response. [ABSTRACT FROM AUTHOR]

Abstract: Fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades. Fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development. This paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to: conceptual models; fluvial features and environments being studied; tools used by fluvial geomorphologists; geomorphic specialty groups within professional societies; journals in which fluvial geomorphic research is published; and textbooks of fluvial geomorphology. During this half century, fluvial geomorphology broadened considerably in scope, from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range, to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient, substrate composition, and grain size. The array of tools for making basic observations, analyzing data, and disseminating research results also expanded considerably during this period, as did the diversity of the fluvial geomorphic community. [Copyright &y& Elsevier]

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: Predictions of river channel form under current conditions or in response to environmental or management changes and the rapid comparison of different channel reaches are important tasks in river management. River classification is a common and valuable framework to address these aims but may suffer from the necessity to force a continuum of channel morphology into discrete groups. More generally, the scope to test the ability of predictive tools has been limited because of a shortage of field data. In this study, we used principal component analysis (PCA) to identify the main sources of variation among river reaches in England and Wales based on a set of 20 variables expected to correlate with channel morphology. The PCA scores were then used to predict the distributions of a wide range of hydromorphic features based on >4000 reaches surveyed in the River Habitat Survey baseline. For comparison, the predictive ability of three pairs of variables (channel slope–discharge, slope–catchment area, and specific power–catchment area) was also tested. The PCA identified specific stream power, channel size and groundwater input as the main sources of variation among reaches. Regression models using PCA scores or paired variables were effective predictors of a range of channel characteristics, including predominant substrate, flow biotopes, and channel vegetation. Channel cross sections and anthropogenic modifications were less predictable. All of the approaches permitted simple plots of river reaches and quantitative comparisons of the (dis)similarity among individual reaches, whilst the paired variables also minimised the data requirements. Our work reiterates the value of simple, paired variables as a basis for rapidly comparing river reaches and, for the first time, quantifies the predictive ability of these approaches across a wide range of channel characteristics at a national scale. Principal component analysis provides a valuable exploratory tool for identifying the main sources of variation in complex, multivariate data from which a simplified version (e.g., specific power and area) could be adopted. [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: Particles of fine sediment can clog interstitial pore spaces of coarser grained sediment in river beds and thereby impede the exchange of water, dissolved constituents, and particulate matter with consequent ecological impacts. The extent to which fine sediment reduces connectivity between the stream bed and overlying channel is a function, in part, of sediment residence time. Short residence times imply frequent exchange of matter and reduced impact of fine sediment on stream bed habitat, while long residence times indicate that with respect to fine sediment delivery, the stream bed is more isolated from the overlying channel. Here we present a novel technique to quantify the residence time of river bed sediment at various depths over annual and decadal timescales using the fallout radionuclides (FRNs) 7Be (t 1/2 =53days) and 210Pbex (t 1/2 =22.3years). We placed mesh cylinders filled with 7Be-free sediment into a stream bed to quantify the capture of 7Be-tagged particles in the absence of scour and fill. We also took cores to the depth of refusal in alluvial sediment in unregulated and regulated rivers in Vermont and New Hampshire. Sampled watershed areas ranged from 29 to 410km2, and core depths ranged from 19 to 77cm. The 210Pbex activity profiles of cores show that bed sediment is exchanged to the depth of refusal at decadal timescales. In contrast, 7Be activity profiles indicate that fine sediment infiltrating into the bed had residence times ranging from 4 to >300days in unregulated rivers. Cores from a regulated river are notably different—subsurface sediment residence times were always longer than in unregulated rivers at comparable depths, likely owing to restriction of bed mobilization and clogging of bed material by fine sediment. These results suggest that filtration can be an important component of bed material delivery to stream beds, but filtration does not deliver material as deeply into the bed as scour and fill. We find that fallout radionuclides provide direct measurements of time and depth scales of active exchange of particulate matter, which are key controls on hyporheic function. [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: This paper presents data compiled from aerial photography, General Land Office maps (GLOs), and discharge data from the central Platte River in Nebraska that quantify and provide a new understanding of channel evolution and abandonment in a braided stream. Analyses of aerial photographs and GLOs in ArcMap™ show that channel area decreased by an average of 46% from 1938 to 2006 and that channel widths in 1858 were an average of 539% greater than in 2006. Annual discharge during 1942–2006 does not show a clear long-term relationship with the decrease in channel width and area. Rather, stabilization through vegetation of bars and channel banks is cited as the major contributing factor to channel shrinkage and the development of an anabranching system within the boundaries of the 1858 channel. The stabilization of anabranches and the encroachment of vegetation onto banks, abandoned channels, and islands have significantly impacted the riparian ecosystem as mobile sandy bars gradually disappeared. Annual aerial photographs of the Platte River from 1984 to 2001 show that the river responds to year-to-year changes in mean discharge through the formation and disappearance of in-channel features such as medium-size transverse bars, large transverse bars, open channels, exposed channel surfaces, laterally accreted surfaces, and vegetated channel islands. Vegetated channel islands and stable anabranches also increased during 1984–2009. Significant change has also occurred since the beginning of the twentieth century on the Wood River, a local tributary to the Platte River. The Wood River experienced a long-term increase in sinuosity after it occupied the abandoned North Channel of the Platte River, which last experienced major sediment transport 350±50years ago, according to an optically stimulated luminescence date. The modern Wood River is also superimposed on a prehistoric meandering pattern with significantly greater meander amplitude. We present the first channel abandonment model to account for the gradual abandonment of the Platte River braided stream system and its evolution from a braided to an anabranching system: in stage 1, the channel prominently features macroform bars comprising downstream-migrating foresets; in stage 2, downstream-migrating dunes are deposited over channel bed features; and in stage 3, there is a shift from a braided stream to a stream dominated by anabranches and only channel bed features (e.g., three-dimensional dunes) are present. Our new model characterizes the features expected to be found in abandoned braided channels, as well as more temporary features that form and are destroyed through successive stages of abandonment. [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: Fluvial erosion of peat deposits occurs in many environmental settings; however, the erosion and transport of large peat blocks by river channels has received relatively little attention. This paper describes the sedimentary significance and potential palaeoenvironmental interpretation of peat blocks in alluvial river systems. Evidence is presented from a number of field studies of upland river systems in northern England that illustrate a range of peat block forms and sedimentary features that are briefly compared with examples of peat blocks preserved in gravel stratigraphy. We show that peat blocks are an important geomorphological and sedimentological component of upland rivers draining eroding peatland catchments. They are of widespread occurrence and contribute significantly to river channel roughness and channel sedimentation. A variety of common sedimentary features can be observed including, shadow, crescent, perched, armoured, drape, embedded (part buried), cluster, and step forms. Peat blocks tend to be deposited on channel margins and bar tops and can be used as “maximum” stage indicator for major floods. The role of peat blocks in controlling sedimentation varies with channel width. In narrow channels where the size of the peat block approximates the channel width, blocks become jammed in the channel and exert a primary control on channel sedimentation. In wider channels, blocks tend to occur in isolation or in small clusters and are of only secondary importance in controlling sedimentation. Residence times of peat blocks varies from short periods of temporary deposition (days to months) to much longer timescales (months to years) with some blocks becoming permanently incorporated into the sedimentary record. The sedimentary characteristics of contemporary buried peat blocks have much in common with blocks preserved in alluvial gravel stratigraphy. This offers the potential for using these features for palaeoenvironmental reconstruction. Peat blocks in many ways are analogous to other low density geological materials (ice blocks, woody debris, and some volcanic sediments), and recognising the special sedimentological characteristics of this suite of materials is important as they are not always adequately characterised using conventional hydraulic relationships. [Copyright &y& Elsevier]

Abstract: Forced riffle-pools occur in gravel-bed rivers where a large nonalluvial element leads to local scour and deposition. To manage rivers where this type of morphology is found and to specify restoration measures that mimic this process, more field data on sediment mobility in forced riffle-pools is needed. The objectives of this study are to describe the spatial variability of sediment mobility and deposition in a developing forced riffle-pool and to use high-resolution flow velocity measurements to explain the observed dynamics. The field site is a forced riffle-pool in Moras Creek, a 6-m-wide gravel-bed stream with a 1.2% bed slope in Quebec, Canada. Topography and the movement of sediment particles equipped with Passive Integrated Transponder (PIT) tags are surveyed through a series of competent floods. Bed shear stress is estimated from near-bed measurements of time-averaged velocity and turbulent kinetic energy. The sediment transport regime of the creek is characterized by partial mobility, exponential distributions of path lengths, and a negative relation between particle size and path length. Full mobility occurs in the center of the pool and over the exit slope where flow is accelerated from the constriction of flow during two events above the bankfull discharge. Partial mobility occurs during the same events over the entrance slope to the pool. Lateral gradients of deposition and mobility suggest that the majority of sediment in motion is routed over the side bar at the entrance to the pool. High levels of turbulence intensity that occur as a result of flow deceleration may explain the removal of finer sediments from the head of the pool. [ABSTRACT FROM AUTHOR]

Abstract: The recent evolution of the Adra River delta in southeastern Spain has been reconstructed from historical maps, aerial photographs, and submarine multibeam bathymetric data. We have distinguished three main evolutionary stages whose development took place as a direct response to the main anthropic and natural influences on the river system. The first stage (4000BC to 1872AD) represents the natural behavior of the deltaic system with negligible anthropic influence. This long stage is characterized by coastline advance with the formation of a small asymmetric triangular delta in the natural river mouth and a typical prodeltaic deposit. In contrast, the second and third stages are characterized by anthropic interventions in the catchment and the river mouth, which heavily modified the natural dynamics of the deltaic system. The second stage (1872AD to 1972AD) coincided with damming of the natural river channel very close to its mouth and the construction of two successive artificial channels to deviate the river flow. The coastal dynamics changed during this second stage with erosion of the original delta and the formation of a new, asymmetrical delta at the mouth of the artificial channels. This younger eastern delta comprises two infralittoral wedges in the submarine realm, which recorded changes of lateral redistribution processes and enhanced influence of energetic events and can only be explained if the sediment supply from the river source was reduced during this period. The third stage (1972AD to present-day) started with the damming of the trunk river in the central sector of the catchment, thus drastically reducing sediment flow to the coastal realm and triggering general erosion and coastline retreat. [Copyright &y& Elsevier]

Abstract: In 2000 and 2003 before the closure of 3-Gorges Dam, numerous sediment samples were taken from the middle-lower Yangtze River channel to examine sediment transport processes and associated hydromorphological nature of the river. Analytical results show that the riverbeds consist mostly of medium to coarse sands and gravelly sands, and fine sand occurs locally, especially near the river coast. The results further indicate a downstream fining trend in riverbed sediment from Yichang to the river mouth, totaling about 1900 km long with 12 sediment zones (I-XII). These were identified as alternate coarse- and fine-grained sediment on the riverbed, although the zonation of I–III below Three-Gorges Dam site is weaker. The mode of sediment transport in the river is dominated by saltation (20–80%), followed by bed-load transport with 3–15%; transport by suspension is quite low. Grain-sizes associated with hydrological parameters have greater values in the Jingjiang Reaches (from Yichang to Chenglingji; unit stream power: 5–18 N m−1s−1, boundary shear stress: 14 Nm−2 and mean flow velocity: 2–3.2 ms−1), whereas the values obtained from Chenglingji downstream are considerably low (<5 N m−1s−1, 1–4 Nm−2 and <0.7–1.5 ms−1). These values, when compared with on-site measured velocity of the ADP flow column, revealed the erosive riverbed sediment transport in the Jingjiang Reaches, and the accumulative riverbed transport downstream, from Wuhan to the river coast. Hydrological parameters together with distribution of grain-sizes indicate a coarsening riverbed in the Jingjiang river, largely because damming peaked since the last half-century. This corroborates the weakening sediment zonation in the Jingjiang Reaches, which is expected to extend further downstream towards the river coast in response to the potential impact of 3-Gorges Dam in the coming decades. [Copyright &y& Elsevier]

Abstract: Dams disturb in the fluvial dynamics by changing the natural cycle of the rivers, interfering with the transport-deposition processes and affecting river ecology. The Brazilian part of the Paraná Basin has the largest hydrometrical power potential of the country with more than 150 hydroelectric power dams that transformed the Paraná River and its tributaries in a succession of lakes. This research aims to analyze the changes in certain fluvial variables in the last natural downstream reach of the Upper Paraná River after closure of the Porto Primavera Dam. Data acquired before and after dam construction showed changes in water discharge, bank erosion, flood pulse, bed load grain size discharge, concentration of suspended load and bedform morphology and size. Those alterations generated changes in river ecology especially on fish reproduction, benthic community, and rotifers variety and density. A review of the obscure regional literature, generally in Portuguese, is also presented. [Copyright &y& Elsevier]

Abstract: This paper examines the characteristics of historical floods and associated monsoon precipitation in the Yangtze Catchment, with specific attention given to the middle and lower Yangtze basin. Based on in situ field observations and historical discharge, flood duration, and land-use information, etc, we propose a number of flood characteristics of the basin: 1) floods have occurred more frequently after 1950s, however, changes in discharge can only partially explain the occurrence of the floods; 2) spectral analysis on the annual mean water discharge during 1860–1985 in Hankou hydrological gauging station of the middle Yangtze River reveals 16.4-year and 2.5-year flood recurrences, which become shortened from what has been recorded in the Chinese historical literature on millennial time scale; 3) floods after 1950s tend to have higher water levels (both mean and peak) and longer duration than before, but with remarkably limited inundation area; and 4) a series of flood waves generated by monsoon precipitation in 1998, initiated from the middle Yangtze, highlights the basin-wide climate hazards with a recurrence of around 60 years. Intensifying anthropogenic activity in the last century, including deforestation, dyking, and lake–coast reclamation etc. that results directly in riverbeds aggradation and shrinkage of lake water area in the middle Yangtze basin, are the key causes for recently human-induced floods in the basin. Threatened land property in the basin reminds us to harmonize with the river and provide more space for flooding. [Copyright &y& Elsevier]

Abstract: The rivers of coastal Maine flow through mainstem lakes and long low-gradient reaches that break the continuum of bedload transport expected in nonparaglacial landscapes. Stream erosion of glacial deposits supplies coarse sediment to these systems. The land use history includes intensive timber harvest and associated dam construction, which may have altered the frequency of substrate-mobilizing events. These watersheds are vital habitat for the last remaining wild anadromous Atlantic salmon in the United States. Future adjustments in channel morphology and habitat quality (via natural stream processes or restoration projects) depend on erosion, transport, and deposition of coarse sediment. These factors motivate our study of competence at four sites in the Sheepscot and Narraguagus watersheds. Three of the four sites behaved roughly similarly, with particle entrainment during intervals that include winter ice and spring flood conditions, and relatively minor bed mobilization during moderate floods in the summer and fall (with a recurrence interval of 2–3 years). The fourth site, on the Sheepscot River mainstem, exhibits more vigorous entrainment of marked particles and more complex three-dimensional channel morphology. This contrast is partially due to local geomorphic conditions that favor high shear stresses (particularly relatively steep gradient), but also likely to nourishment of the bedload saltation system by recruitment from an eroding glacial deposit upstream. Our results suggest that the frequency and magnitude of bedload transport are reach specific, depending on factors including local channel geometry, upstream sediment supply and transport, and formation of anchor ice. This presents a challenge for stream practitioners in this region: different reaches may require contrasting management strategies. Our results underscore the importance of understanding channel processes at a given site and assessing conditions upstream and downstream as a prerequisite for conducting habitat restoration projects. [Copyright &y& Elsevier]

Abstract: The geological and meteorological setting of the Jianghan–Dongting lake area leads to high precipitation and siltation, but poor water discharge, thus the area is frequently flooded. In the past the river–lake relationship of the Middle Yangtze has been variable but has deteriorated recently under increasing human influence. The Jianghan Plain of the Middle Yangtze becomes a waterlogged lowland under the constant threat of flooding from the perched Jingjiang River. Due to siltation and land reclamation the Dongting Lake has lost most of its regulatory function for the river and has become increasingly vulnerable to flood disasters. The Middle Yangtze River has been undergoing siltation, resulting from a downstream decline of sediment transport capacity, resulting in the elevation of the flood level above the lowlands. Heightening of the levees has caused further siltation of the channel. The Three Gorges Reservoir will provide a buffering period of 50–80 years, during which much of the silt will be trapped in the reservoir and scouring downstream may occur. We should utilize this period to work out an overall resolution to the problem. Construction of a water and silt diversion project in the Honghu Lake and surrounding areas may resolve this problem in the dangerous Chenglingji–Wuhan Segment of the Yangtze. Widening the canals connecting the Middle Yangtze and Han Rivers may function as a discharge-dividing channel of the Yangtze, which may prove to be beneficial. [Copyright &y& Elsevier]

Abstract: This study examines the characteristics of sediment rating parameters recorded at various gauging stations in the Yangtze Basin in relation to their controls. Our findings indicate that the parameters are associated with river channel morphology of the selected reaches. High b-values (>1.600) and low log(a) values (<−4.000) occur in the upper course of the steep rock-confined river, characterizing high unit stream power flows. Low b-values (<0.900) and high log(a) values (>−1.000) occur in the middle and lower Yangtze River associated with meandering reaches over low gradients, and can be taken to imply aggradation in these reaches with low stream power. Higher b-values (0.900–1.600) and lower log(a)-values (−4.000 to −1.000) characterize the reaches between Yichang and Xinchang, immediately below the Three Gorges. These values indicate channel erosion and bed instability that result from changes in channel gradient from the upstream steep valley to downstream low slope flood plain settings. Differences in channel morphology accompany these changes. Confined, V-shaped valleys occur upstream and are replaced downstream by broad U-shaped channels. The middle and lower Yangtze shows an apparent increase in channel instability over the past 40 years. This inference is based on sediment rating parameters from various gauging stations that record increasing b-values against decreasing log(a)-values over that time. Analysis of the sediment load data also reveals a strong correlation between changes in sediment rating curve parameters and reduction of annual sediment budget (4.70×108 t to 3.50×108 t/year, from the 1950s to 1990s), largely due to the damming of the Yangtze and sediment load depletion through siltation in the Dongting Lake. Short-term deviations from the general trends in the sediment rating parameters are related to hydroclimatic events. Extreme low b-values and high log(a)-values signify the major flood years, while the reverse indicates drought events. When compared with rivers from other climate settings, it is evident that the wide range of values of the Yangtze rating parameters reflects the huge discharge driven by the monsoon precipitation regime of eastern China. [Copyright &y& Elsevier]

The timescale required for a river channel to reach new equilibrium conditions following a disturbance presumably depends on channel substrate size, and previous field studies have suggested that gravel-bed channels should reach equilibrium more quickly than sand-bed channels. To estimate the relative timescale difference between sand-bed and gravel-bed rivers responding to base-level lowering, we developed a simple scaling approximation. Equilibrium timescales derived from these equations for sand-bed rivers were found to be approximately half of those for gravel-bed rivers. While gravel-bed channels do not need to transport as much sediment to reach equilibrium conditions as sand-bed channels, transport of sediment is more rapid in sand-bed channels leading to quicker equilibration. [Copyright &y& Elsevier]

Along the eastern margin of the Qinghai–Tibet Plateau, there are frequent occurrences of strong tectonic movement and large-scale landslides. River blockages often occur in deep-cut river valleys, forming large-scale dammed lakes. In this study, a ~26.5 m thick lacustrine sedimentary profile that underlying the modern riverbed of the Yalong River is reported. Here, 14C dating results show that lacustrine deposition began at ~25 ka and continued till ~10 ka, mainly during the Last Glacial Maximum. Paleoclimatic indicators, such as particle size, magnetic susceptibility, and spore-pollen combination, were used to reconstruct the evolution process of the paleoenvironment in the study area, revealing that a paleo-flood event occurred at ~19 ka. The Tongzilin dammed lake contains an excellent record of the geomorphic evolution of the lower reaches of the Yalong River during the Last Glacial Maximum. Before 25 ka, the Yalong River experienced strong downcutting to form a deep valley, which created the space conditions for the formation of the dammed lake; from 25 to 10 ka, the dammed lake remained relatively stable, with dominating accumulation; and after 10 ka, the dammed lake broke and the river continued to downcut. • A dammed lake deposition during the LGM was found buried in the modern riverbed of the Yalong River. • Through 14C dating, the chronological framework of this lacustrine deposit was established. • Tongzilin dammed lake is controlled by climate and structure during the LGM. • The evolution of fluvial geomorphology in the lower reaches of Yalong River is well recorded in Tongzilin dammed lake. [ABSTRACT FROM AUTHOR]

Avulsions are rare events that cause major realignments to fluvial systems and hold potential for significant societal consequences. We present a case study of an avulsion in a minimally-aggrading landscape that was influenced by long-term human modifications to a fluvial environment that was initially setup for an avulsion during regional Pleistocene deglaciation. The 2006 Suncook River avulsion in New Hampshire, USA, is a valuable example because minimal environmental management took place for a decade following the event, allowing natural processes to dominate initial fluvial responses. Geospatial data collected during this period allow for the evaluation of the short- and long-term morphological evolution of a river that experienced an avulsion. We review data from technical reports on the event and present a new synthesis of aerial imagery and topographic data highlighting key geomorphic features associated with the avulsion. These features include headcutting and widening associated with a 0.6-km long channel created by the avulsion. Downstream of the avulsion site, extensive channel filling, deposition of meter-scale sand sheets on floodplain surfaces, and development of a cutoff channel were major manifestations of the event. The initial setup for the avulsion can be traced to Pleistocene deglaciation, when glaciofluvial ridges deposited in the valley blocked a more direct route for the river and shifted the channel towards an area of shallow bedrock. Human modifications to the channel—including mill dam construction, floodplain narrowing, road development, and gravel mining—contributed to the avulsion setup by increasing superelevation and undermining the glaciofluvial deposits that had directed the river during the Holocene. The avulsion was triggered by a ~50-yr flood event following a 70-yr interval with no major floods but marked by continued human modification to the landscape. The unusual nature of the event combined with the wealth of available geospatial and hydrologic data make the Suncook River system an attractive target for future studies that can examine avulsion processes in greater detail. • Case study of 2006 Suncook River avulsion in New Hampshire, USA • Avulsion setup through combination of regional deglaciation and human impacts • Triggered by ~50-year flood event that followed several decades of low-intensity floods • Avulsion incised floodplain and glaciogenic sediments to create new channel. • Sediment wave caused downstream channel filling and significant overbank deposition. [ABSTRACT FROM AUTHOR]

The tectonic and fluvial setting of the Rhine-Meuse river system in the Lower Rhine Embayment rift system is exceptionally well known. The 19th century, pre-regulation river courses of three rivers are used to study a postulated sinuosity response to faulting. The fault-perpendicular Meuse River shows patterns of sinuosity changes at different spatial scales. The large-scale (>5 km) sinuosity changes are related mainly to the faulting-induced changes of the subsurface lithology, determining the bed and bank characteristics. However, at a smaller scale, some fault-related channel sinuosity anomalies are observed. The fault-parallel Roer River shows sinuosity changes related to a normal, non-tectonic longitudinal gradient change. Sinuosity patterns of the Rhine River are predominantly related to lithological differences and reduced incision rates. Sinuosity can thus be an indicator of tectonic motions, but gradient, subsurface lithology and river bank composition determine sinuosity as well. Therefore, a sinuosity change is no proof for fault activity. On the other hand, the absence of a sinuosity change does not imply inactivity of a fault at geological time-scales. • Sinuosity patterns in the Lower Rhine Embayment are studied for tectonic forcing. • Morphometric analysis are performed on river channels of the Meuse, Roer and Rhine. • The Meuse River is (indirectly) controlled by tectonics on a block-scale. • The relation between fault motions, river gradient and sinuosity is not straightforward. • A sinuosity change alone is no proof for fault activity. [ABSTRACT FROM AUTHOR]

Identifying and understanding functional process domains (sensu Montgomery, 1999) in rivers is paramount for linking the physical habitat template to ecosystem structure and function. To date, efforts to do this have been rare, especially in large rivers, as they require appropriate tools for quantifying habitat heterogeneity with fine-scale resolution across broad spatial extents. In this study, we used side-scan sonar technology to map riverbed substrate at six sites in the Yellowstone and Missouri rivers. Substrate maps were then analyzed and visualized using geospatial analysis to relate fine-grained spatial substrate patterns to process domain structure. Our findings revealed two distinct nested domains of substrate patchiness, suggesting that different factors are responsible for shaping patterns of substrate at different scales. Although small-scale patchiness in substrate was likely driven by internal, or autogenic, physical processes, patterns at larger segment extents (>3 km) were often driven by abrupt transitions in habitat related to exogenous factors such as lateral erosion of talus, tributary inputs, and bank armoring. Additionally, we found that heterogeneity in benthic substrate increased with spatial extent at all of our study sites; however, this relationship was lower in the Missouri River, which is altered by impoundment. Our study represents one of the first efforts to relate benthic habitat heterogeneity to nested process domain structure in large riverscapes, and offers a unique perspective for linking landscape processes, geomorphological habitat heterogeneity, and biological structure and function in large rivers. [ABSTRACT FROM AUTHOR]

Whereas the geomorphic effects of in-channel mining have been widely documented, very few studies have focused on recovery trajectories after mining ended. This paper describes and quantifies the channel adjustment of extended and over-widened mining pits located in a low energy gravel-bed river, and identifies the factors that control their recovery rate. The study was based on aerial photographs and LiDAR analysis, grain-size sampling, bedload computation and geophysical measurements made during ground penetrating radar (GPR) and electrical resistivity tomography (ERT) surveys. We describe the spatio-temporal changes in the morphology of former pits as well as the current surficial longitudinal grain-size pattern in pits and in neighbouring upstream and downstream reaches. Our results show a wide range of geomorphic readjustments. Between 23 and 47 yr after the end of mining, the mining reaches have still not yet fully recovered. The planimetric recovery rate is closely correlated with the ratio of the volume deposited in the pits to their original volume. Finally, the infilled material is only partly composed of bedload and the mainly sandy fine sediments play a primary role in the recovery process. The abundance of sand, controlled by the lithology of the watershed, explains the unexpectedly high recovery rates of some pits despite the low energy of the river. • Characterisation of morphological and grain-size recovery of former in-channel pits • Adjustment still underway 27–47 years after mining stopped • Recovery rate controlled by pit volume, the volume of sediment supplied and pit trap efficiency • The sand load plays an essential role in recovery processes • Catchment lithology also crucial in recovery [ABSTRACT FROM AUTHOR]

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]

The transport of coarse material strongly controls the stability and evolution of mountain fluvial systems but, despite this, bedload dynamics are not yet fully understood especially in mountain streams. In this sense, particular attention was paid on the bedload magnitude (volume) expressed at event-scale and on the long-term, while few studies were focused on when and how the transport of the coarse material occurs. The aim of this work was to investigate the bedload mobility in the Rio Cordon, a mountain stream characterized by cascade and step-pool morphologies with a rough streambed. Here, the critical conditions for initiation of motion, transport distance and virtual velocity expressed by the coarse streambed material were assessed and their relationships with hydraulic forcing conditions and grain size were analyzed. To this end, a monitoring program based on bedload tracing was maintained over 7 years, allowing to analyze the bedload mobility during persistent high frequency/low magnitude flow conditions. To investigate the bedload mobility, 250 tracers were released between 2011 and 2012 and their propagation along study site was monitored until 2018. Overall, 14 tracer inventories were realized, determining 1697 tracer localizations. During the study period, the bedload dispersion resulted well described by the peak discharge magnitude (Q p , q p and ω p − ω c), while no significant relationships were observed with duration of competent flow (t over) and effective runoff volume (ER). Transport distance and tracer grain size were negatively correlated, whereas virtual velocity increased with increasing particle size. In this sense, the propagation velocity seems to be affected by the high frequency flows that, on the one hand triggered mobilization of the coarser tracers only through limited and impulsive events and, on the other hand favored a slowdown on the finer particles due to bedforms disturbance. Compared to other study sites, the Rio Cordon exhibited accentuated threshold conditions with lower transport distance and virtual velocity, confirming that steep mountain streams are generally influenced by a reduced transport efficiency due to protruding bedforms and macro-roughness that cause a pronounced energy dissipation. Interestingly, such condition seems to have progressively reduced from under- to near-bankfull flows. The results were compared to the bedload mobility observed in the Rio Cordon during 1993–1998, enabling to quantitatively assess how the bedload dispersion varied between a setting of stable armouring layer with protruding bedforms (2012–2018) and a partial alteration of these (1993–1998). An evident difference was observed in terms of transport distance, while critical conditions did not significantly change. Lastly, the long-term bedload tracing investigation highlighted that a certain legacy on the transport efficiency was produced by the persistent high frequency flow conditions. Over the study period, a general decrease of transport distance was observed that could be explained by a progressive stabilization of streambed material. Previous studies suggested that such condition can be interrupted by high magnitude/low frequency floods. • Bedload mobility was investigated over 7 years in a steep mountain stream. • Mobility of the coarse material was well described by peak discharge magnitude. • Influence of armour layer and protruding bedforms on bedload mobility was assessed. • A legacy on the transport efficiency was induced by the high frequency flows. [ABSTRACT FROM AUTHOR]

Human activities are known to impact the physical template of river channels. These impacts can result from deliberate, direct modifications as well as via indirect processes linked to broadscale landscape change. This study examined changes in the physical template of the Barwon-Darling River, a dryland river in southeastern Australia. Historical longitudinal profiles from the late 1800s were compared with contemporary profiles derived from high-definition, side scanning sonar. Comparisons focused on characterising waterhole features as they are a critical biophysical component of dryland rivers. The use of historical data presented several challenges related to small sample size and suspected sampling bias in the historical survey. However, this study demonstrates that these issues are not insurmountable providing the limitations and uncertainties with the data are acknowledged and data analyses are limited to parameters that can distinguish genuine landscape change. The findings revealed a dramatic change in the physical template of the Barwon-Darling River over a 120-yr period. Waterhole depths and distances between waterholes have been altered significantly. The magnitude and trajectory of change was found to be scale-dependent, with the greatest observable change aligned with the presence or absence of low-level weirs. Waterholes influenced by low-level weirs have increased in depth because of localised impoundment, whilst the distance between deep waterholes (>4 m in depth) has declined substantially. In contrast, the maximum depths of waterholes located outside the influence of weir pools has declined by 1.6 m and the distance between deep waterholes has more than doubled in several reaches. These declines are likely to be caused by sediment accumulation in waterholes associated with anthropogenic increases in sediment flux and a decline in the river's capacity to entrain and transport sediment throughout the system. • Waterhole depths and distances between waterholes have been altered over 120 years. • The trajectory and rate of change is aligned with low level-weir occurrence. • Maximum waterhole depths declined substantially in non-weir pool locations. • Distances between deep waterholes have doubled in several non-weir pool locations. • Historical data can be valuable if data limitations are acknowledged. [ABSTRACT FROM AUTHOR]

This paper documents ranges of streambed and bank erosion observed across suburban northern Kentucky via time-series surveys at 61 stream monitoring sites from the last ~10 yr. Average erosion rates in streams draining undeveloped watersheds (<5% total impervious area, TIA) were nominal: 0.5 cm/yr of incision (range of −5.8 to 11 cm/yr) and 1.0 cm/yr of widening (range of −58 to 20 cm/yr). By contrast, streams draining developed watersheds (>5% TIA) averaged 1.5 cm/yr of incision (range of −9.2 to 36 cm/yr) and 9.4 cm/yr of widening (range of −11 to 61 cm/yr). The suburban streams also followed predictable patterns of evolution consistent with the "classic" Channel Evolution Model (CEM) of Schumm et al. (1984) , with the initial incision period (Stage 2) coinciding with bed coarsening followed by widening (Stage 3). Out of 45 sites draining >5% TIA, only four were in a state of dynamic equilibrium (Stage 1), two of which were attributable to stabilization via stream restoration and another was attributable to an upstream stormwater retrofit that substantially restricted erosive discharges. The other stable suburban site drained a watershed that was only 6.5% TIA and was just upstream of a reach undergoing incision and headcutting, implying that it would likely be experiencing incision (Stage 2) soon. Although the suburban sites spanned a gradient of development age and extent, >90% fell into unstable CEM categories (Stages 2 through 4), with only one site exhibiting features emblematic of potential geomorphic recovery (Stage 4 trending to Stage 5), attributable to an upstream stormwater retrofit. This case study underscores the predictable nature of long-term channel instability in gravel/cobble streams draining conventionally-developed suburban watersheds in support of more mechanistically based stormwater management strategies tailored to prevent the geomorphic degradation commonly associated with the urban stream syndrome. [ABSTRACT FROM AUTHOR]