Search

As a prerequisite and foundation for studying the evolution mechanism of river channels, an in-depth understanding of the cross-sectional morphology adjustment is required. As a starting point, it is crucial to systematically summarize and generalize the research findings on channel morphological adjustment obtained to date, particularly in the context of the significant changes in the water and sediment conditions of large rivers that have occurred worldwide. This paper provides a comprehensive review of the research findings on the three following aspects of the Lower Yellow River: the transverse distribution of overbank flow velocity, the transverse distribution of suspended sediment concentration, and the morphological adjustment of the river cross-section. There are various equations available to predict the lateral depth–average flow velocity distribution. These equations are classified into the two following categories: empirical and theoretical formulas. Theoretical formulas are obtained through consideration of the cross-sectional morphology, accounting for inertial force terms caused by secondary flow, and momentum transfer between the main channel and its floodplain. Similarly, empirical equations and theoretical formulas for sediment concentration transverse distribution are also summarized, given the different influencing factors and assumptions. We also discuss the morphological adjustment of river cross-sections based on the analysis of measured data, mathematical model calculation, and the physical model test. In particular, we propose the idea of revealing channel cross-section morphology evolution mechanisms from the theoretical level of water and sediment movement and distribution. This review aims to enhance understanding of overbank flow, sediment transport, and channel morphology in the Lower Yellow River and may also serve to some extent as a reference for the evolution and management of channels in other rivers. [ABSTRACT FROM AUTHOR]

Releasing experimental floods as part of environmental flow programs aims to restore river beds by moving and restoring sediments to improve hydromorphological conditions of the river. However, it remains a challenge to understand how flood release characteristics affect channel morphology, sediment transport, and hydrodynamics. In this study, field surveys and a 2D hydro‐morphodynamic and sediment transport numerical model were used to determine how differences in flood magnitude and falling limb alter hydrogeomorphic conditions within a 4 km reach of the lower Spöl River. The model was constrained by drone flight‐derived high‐resolution digital elevation models and two field‐measured flood releases. The highest flood magnitude of 40 m3/s resulted in 2,700 m3 of total sediment transport, 2,000 m3 of net total volumetric change and 16 900 m2 more wetted area after the flood. The same flood, simulated with an increase in falling limb slope, resulted in a decrease in the duration of full sediment mobility and a corresponding reduction of 8% in net total volumetric change and 5.3% in the total wetted area. Contrastingly, the lowest flood magnitude of 25 m3/s produced 130% lower total sediment transport, 105% lower net total volumetric changes and 10% less wetted area after the flood. Overall, we show that hydro‐morphodynamic modelling of river erosion and deposition combined with spatially rich topographic datasets are extremely useful in forming designed environmental flood scenarios to optimise sediment transport and thus hydrogeomorphic changes to set environmental flows. We contend that scenario modelling is necessary to help water managers optimise the amount of water allocated to environmental flows and to simultaneously restore and maintain riverine dynamics in heavily modified rivers. [ABSTRACT FROM AUTHOR]

Our research introduces the river regulation effects on three sections of the upper and middle Odra River (south-western Poland), with differently channelized parts. In the upper and lower reaches, the river was straightened, narrowed, and trained with groins, whereas in the middle section, it was also impounded by numerous barrages. The discharge duration (DD) and water stage duration (WSD) curves for water-gauge stations from these river sections were analyzed to recognize changes in river flows and channel morphology since the mid-20th century. This analysis is supplemented by an examination of repeated surveys of the gauge cross sections of the river, annual precipitation totals in its catchment, and their relationship to the variation of the North Atlantic Oscillation (NAO) index. Our findings provide new hydrological insights for the region. The three river sections exhibited different patterns of the adjustment of the channel morphology to the river channelization: upper section was typified by channel incision, middle section by channel stability, and lower section by channel incision in its upper part and vertical stability of the channel bed in the lower part. Barrages in the middle section stabilized water stages in a wide range of hydrological conditions. Annual precipitation totals and river run-off did not change systematically over the study period. The variation in precipitation totals was inversely related to annual values of the NAO index. The study confirms the usefulness of DD/WSD curves to analyze changes in river run-off and the vertical position of the channel bed. [ABSTRACT FROM AUTHOR]

The Three Outlets Channel (TOC) consisting of three anabranching rivers formed due to natural avulsion by extremely high floods, is the primary water–sediment channel connecting the Jingjiang in the middle Yangtze River and Dongting Lake (the second largest freshwater lake in China). Since the impoundment of the Three Gorges Reservoir (TGR) in 2003, the decreasing diversion of runoff and sediment load of the TOC has an impact on the hydrological connectivity of the river–lake relation. Nonetheless, it lacks complete understanding on the diversion of runoff and sediment load, erosion and deposition amount, and the calculation method of diversion runoff in the TOC. We used remote sensing images, hydrological data, and channel topography to analyze the change in runoff and sediment load, channel morphology, local erosion and deposition amounts. The main results show that: (i) Meander cutoffs of the Lower Jingjiang accelerated the reduction process of the Ouchi River's runoff and sediment load and the increase in the number of dry days. After the impoundment of the TGR, the diversion of sediment load of the TOC was greatly affected, but the decreasing trend of the runoff diversion slowed down. (ii) The morphological change of the inlet zone of Ouchi River is larger than that of Songzi River and Hudu River. The morphological evolution of the inlet area led to the change in the diversion of runoff and sediment load of the TOC. (iii) In the dry season, the water level drop in the inlet zone of the TOC leads to a decrease in the diversion discharge. Therefore, considering the water level drop and channel width adjustment in the inlet zone, five empirical formulae for the diversion discharge of the five hydrological stations in the TOC are proposed. These empirical formulae can be used as a short-term forecast for future changes in the hydrologic regime and the dynamics of the Jingjiang–Dongting Lake relation. [ABSTRACT FROM AUTHOR]

This paper presents a numerical model study on the ice cover effect on bank stability in non-cohesive alluvial channels. The model consists of a coupled two-dimensional finite element unsteady hydrodynamic model with bank erosion and mass failure processes for open water and ice-covered conditions. The associated morphological change is modeled with non-equilibrium sediment transport, including the side slope effect on bed load transport. The model adopts two sets of repose angles for emerged and submerged bank materials in analyzing non-cohesive bank mass collapses and redistributions. The model is validated with published laboratory experiments on bank retreat caused by dam-break flow and equilibrium cross-section evolution and showed improvements over existing numerical models. Simulated results showed that the ice cover caused larger bank retreats and bed depositions and slower channel cross-sectional change due to the reduced bed shear stress and the increased flow depth. Article Highlights: A bank stability model is developed by coupling the unsteady hydrodynamics, non-equilibrium sediment transport, and bank erosion and mass failure processes. The model is validated with published laboratory experiments and other models. The ice-covered flow causes larger riverbank retreats and slower cross-sectional changes than that of the open channel flow. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms controlling downstream water‐level variations after the operation of the Three Gorges Dam is important for riverine flood and drought management. However, our quantitative understanding of the multiple controls of river morphology, vegetation, and floodplain resistance on water levels in the Middle Yangtze River (MYR) remains limited. Here, we analyze changes in river channels and floodplain resistance in the MYR using 450 cross‐sectional profiles as well as data on discharge, water levels, sediment, and satellite images from 2003 to 2015. Results show an overall decline in low‐flow water‐levels (at a given small discharge) due to severe incisions of low‐flow channels caused by a sharp reduction of ∼90% in sediment loads from 1950–2002 to 2003–2020. In contrast, high‐flow water‐levels (at a given large discharge) display minor changes. Our analysis shows that the notably increased floodplain resistance due to vegetation growth is likely the dominant factor elevating flood water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profiles. Our findings further the understanding of downstream geomorphic response to dam operation and their impacts on water levels and have important implications for riverine flood management in dammed river systems. Key Points: Hungry‐water‐driven channel erosion causes the sharp reduction in low‐flow water‐levelsFloodplain resistance increase dominates the minor change in high‐flow water‐levels, followed by riverbed coarsening and greater fluctuations in the river longitudinal profileFloodplain resistance increase mainly caused by vegetation expansion in floodplain and channel bars due to the reduced floodplain submerged frequency [ABSTRACT FROM AUTHOR]

A better understanding of how vegetation influences alluvial channels could improve (a) assessments of channel stability and flood risks, (b) applications of vegetation as a river management tool, and (c) predictions of channel responses to climate change and other human impacts. We take advantage of a natural field experiment in the semi‐arid to arid Henry Mountains, Utah, USA: large spatial differences in bed and bank vegetation are found along some alluvial channels due to localized perennial springs caused by aquicludes in the underlying bedrock. Airborne LiDAR topography and flood modeling are used to constrain channel morphology, vegetation density, and flow velocity at different flood discharges for three spring‐fed reaches along intermittently flowing streams. The spatial distribution of vegetation quantitatively influences both the magnitude and direction of channel adjustment. Reaches with abundant bed vegetation are significantly wider (by an average of ≈50%), with shallower flows and lower velocities, than reaches with little bed vegetation. Reaches with dense channel bank vegetation are ≈25% narrower and ≈25% deeper than sparsely vegetated reaches. We interpret that sediment grain size influences the spatial distribution of vegetation within spring reaches, but that bank vegetation may be more important than grain size for "threshold" width adjustments. Widths, depths, and velocities are fairly insensitive to whether local hydraulic roughness is parameterized in terms of local vegetation density or is assumed spatially constant, suggesting that the underlying "bare earth" topography of the channel bed and banks exerts more control on local flow than does local vegetation density in this landscape. Plain Language Summary: Vegetation is found almost everywhere on Earth's surface and varies with regional climate rather than over short distances. It is therefore difficult to isolate vegetation influences on river channel dimensions from other controls such as flood discharge or sediment grain size, or to predict how climate change may drive river change. We isolate vegetation controls by studying river channels with large natural variations in vegetation due to localized groundwater springs. We use high‐resolution topographic data (collected using lasers shot from airplanes) to measure how much vegetation is found along and in channels, and we use computer models to calculate the width, depth, and velocity of flow at different flood discharges. We find that vegetation can cause channels to either be narrower or wider, depending on whether more vegetation is located on channel beds or banks, and we quantify the magnitude of these effects. Key Points: Groundwater‐fed springs in dryland landscapes provide an opportunity to isolate effects of vegetation on channel morphodynamicsVegetation can drive channel widening or narrowing, depending on whether the vegetation is focused on the channel bed or banksAt‐a‐station hydraulic geometry exponents are relatively insensitive to vegetation density in our data [ABSTRACT FROM AUTHOR]

Twenty-four years (1999–2022) of channel change is assessed using specific-gage analysis based on the United States Geological Survey (USGS) rating curve calibration data from thirteen sites (drainage area < 500 km2) to understand the sensitivity of discharge-specific stage (DSS) or its inverse, stage-specific channel capacity (SSCC) to streamflow regimes, hydroclimatological history, and land use in small Piedmont watersheds of North Carolina, USA. We compare observed channel changes to common streamflow and flood metrics, Atlantic Multi-decadal Oscillation Index (AMOI), and land use/land cover data using regression and correlation techniques to suggest drivers of change and infer sensitivity. In addition to interannual variability, our results at most sites reveal three coherent periods of DSS/SSCC variation at the sub-decadal scale as well as multidecadal trend variation. The magnitudes and frequencies of these changes indicative of potential sensitivity vary substantially amongst sites. The trendlines from the DSS plots for the full length of record indicate that six sites showed increased specific stage while the remaining seven sites showed either reduced or a near-zero change in specific stage. Coefficients of determination relating specific stage and the index of AMO are low (R2 = 0.14—0.38) with both positive and negative relationships exhibited. Multiple regression, coefficients of determination relating specific stage and average monthly discharge are more variable, ranging from 0.18 to 0.94. Both positive and negative correlations (r ≤ 0.7) are found between specific stage and basin land use/land cover intensity indices, although few are significant at 95 % confidence interval. Both qualitative observations and correlation analyses support inferences that drought and persistent low mean discharge conditions tend to increase discharge-specific stage values (decreasing SSCC), by aggradation of the bed and/or lower banks. At our sites, this may be responsible for a sub-decadal trend of increasing specific stage between roughly 2013 and 2018, followed by ongoing reductions over the subsequent period. • Changes in discharge-specific stage were analyzed for 13 small stream channels. • Several channels exhibited similar coherent patterns of change over 24 years. • Correlations with annual and monthly streamflow were low to moderate. • Correlations with the Atlantic Multidecadal Oscillation were also low to moderate. • Watershed land use/land cover influences were apparent at some sites. [ABSTRACT FROM AUTHOR]

Summary: Changes in bed topography that build and maintain channel morphology are driven by the displacements of individual particles, either though their entrainment or deposition. However, the linkages between these topographic changes and individual grain displacements have not been comprehensively addressed, as many historical tracer studies have not included coincident topographic data. In this study, we compare the movements of bedload tracers to the differences in repeat topographic surveys across four gravel‐bed river reaches. To do this, we apply a 1‐D Bayesian survival process model to the starting and ending locations of tracers. This model estimates downstream trapping probabilities, which represent the likelihood that a given segment of channel will "trap" an entrained particle. We then adapt this model to estimate downstream trapping probabilities using digital elevation models of difference and compare the results. The estimates from the tracer and topographic trapping models showed general alignment, meaning that tracers were preferentially trapped in segments that experienced deposition along the channel. Thus, tracers in this study were able to identify downstream differences in bedload transport. The comparison also highlighted that tracer‐estimated trapping probabilities were larger than topographically estimated ones. This supports previous observations that sediment travel distances estimated using tracers are shorter than those estimated using morphological methods. We find that the differences between these two estimates vary systematically across study environments. These variations are attributable to either study design (i.e., tracers being larger than the median size of the sediment that deforms the bed) or differences in compensating scour and fill. We explore potential causes for differences in compensating scour and fill, including hydrograph shape, sediment delivery regime, channel deformation style, and channel width, highlighting that morphodynamics needs to be considered in designing bedload tracer studies. [ABSTRACT FROM AUTHOR]

Transverse drainages are prominent landscape features in active foreland thrust-and-fold belts. Understanding their response to folding processes is pivotal for comprehending landscape evolution and erosion-deformation interactions within the foreland. Here, we focus on the extensively developed transverse drainages across the Tugerming anticline in the southern Tian Shan foreland. Based on fold topography, drainage patterns, and various morphometric indices, we conducted a detailed geomorphological analysis of the Tugerming anticline. Our results suggest that the Tugerming fold laterally grows towards both ends, exhibiting notable segmentation along its strike. The westward lateral fold growth is characterized by interactions between the Tugerming anticline and two adjacent anticlines (Yiqikelike and Tuziluoke). At its eastern termination, lacking nearby folds, the Tugerming anticline laterally propagates without other adjacent folds, resulting in an elongated, gentle termination. Additionally, the hinterland catchment controls sediment and water flux of foreland transverse rivers, and its size has a significant influence on both channel morphology and river-fold interactions of the Tugerming anticline. Among the transverse rivers studied, those with large hinterland catchments (>80 km2) were dominated by braided river channels. In these cases, rivers respond to changes in channel gradient due to fold growth primarily through aggradation and degradation processes. Conversely, rivers with limited hinterland catchments (<80 km2) or originating within the fold, show a prevalence of incised meander channels. Moreover, channels accommodate gradient changes induced by the growing fold, primarily altering channel morphology, including channel sinuosity, slope, and width-to-height ratio. Our study reveals the significance of considering the hinterland catchment size in interpreting river-fold interactions and associated channel morphology within foreland transverse drainages. • We study transverse drainages in the Tugerming anticline in South Tian Shan foreland. • Geomorphic indices suggest lateral growth of the Tugerming fold towards both ends. • The lateral fold growth exhibits significant along-strike segmentation characters. • Hinterland catchment sizes affect channel morphology and river-fold interaction. [ABSTRACT FROM AUTHOR]

Barak River is highly meandering rivers flowing through the alluvial plains of Assam in India. However, due to dynamic system, it is found that channel being subjected to regular shifting which creates uncertainty to the habitants residing nearby the river. Therefore, it is anticipated to carry out a study regarding changes in channel morphology and prediction of centerline channel migration during 1984–2030, using multiperiod Landsat remote sensing images along with autoregressive integrated moving average model (ARIMA). From morphometric analysis, it was found that the mean value of meander length (ML), meander width (MB), and meander ratio (MR) indicates an increasing trend, while sinuosity (C), wavelength (λ), and radius of curvature (RC) show a decreasing trend. The outcome of ARIMA model specifies that channel shifting of mid-line is going to change suddenly either to rightward or leftward directions. Throughout the whole alluvial part of the Barak River, rightward side is recognized as major concern. Observed and predicted values have shown a good R2 value (R2 = 0.89 and R2 = 0.88) at CS-30 and CS-18 respectively. Also, lowest RMSE is observed at CS-12 and highest RMSE is observed at CS-21. Finally predicted values were generated for the estimation of centerline channel shifting between two time intervals (2017–2023 and 2023–2030), which shows that the channel shifting of the river basin will occur at many regions particularly at critical sections. Overall, the findings of this study could be used further in river training works and in understanding the future dynamics of channel. [ABSTRACT FROM AUTHOR]

Patch‐burn grazing (PBG) can promote terrestrial heterogeneity and biodiversity, but can temporarily increase stream nutrients and ecosystem metabolism, and alter macroinvertebrate assemblages. The impacts of grazing on stream channel morphology and post‐PBG recovery patterns are unclear.We assessed the influence of grazing in PBG managed grassland streams in Missouri, USA, and subsequent recovery when grazing ceased for 2 years. We hypothesized that grazing would degrade water quality, stream biotic integrity and channel morphology, but that riparian fencing would mitigate these effects. We predicted that biological and chemical variables in unfenced streams would return to pre‐PBG levels within 2 years after grazing ceased, but channel morphology would not.Six small headwater streams (two in ungrazed control watersheds, two in PBG watersheds with 10 m fenced riparian zones and two in PBG unfenced) were sampled over 7 years; 2 years before PBG, 3 years during PBG and 2 years post‐PBG. We sampled macroinvertebrates and water chemistry monthly when water was present and surveyed channel morphology at least once each study period.During grazing, unfenced watersheds showed the greatest changes in channel width, depth and area. During the post‐PBG period, one of the two unfenced watersheds showed partial recovery of channel morphology. Although grazing increased concentrations of nutrients and chlorophyll‐a, concentrations returned to pre‐PBG conditions after grazing ceased, indicating recovery. Very fine organic sediments increased in the unfenced watersheds compared to the control during grazing but recovered afterwards. Contributions of Chironomidae to total invertebrate abundance increased in the unfenced watersheds during grazing, and then decreased during the post‐PBG period.Riparian fencing mostly mitigated effects of grazing on the streams. Unfenced streams were resilient to effects of grazing in a PBG managed grassland, with most metrics recovering within 2 years after grazing ceased, except for channel morphology.Synthesis and applications. Grazing in a patch‐burn grazed managed grassland coupled with riparian fencing could be an effective conservation tool for land managers of prairies, with relatively modest influences on stream water quality and biotic integrity. Persistent changes in stream channel morphology and effects of longer periods of grazing deserve further research. [ABSTRACT FROM AUTHOR]

The area between the river and its surrounding vegetation constitutes the riparian zone which produces woody debris (WD) that modifies the fluvial dynamics. The WD is constituted by branches and trunks deposited in the river channel. One of the ways that WD can modify the geomorphology of the river is to form steps and pools (step-pool system). In this way, the objective of the present study was to perform a literature review on woody debris in rivers and, to identify the main focus used in research on the occurrence and monitoring of these materials. It was observed that the WD can be found as individual pieces or forming accumulations, and that there is a tendency among the researchers to analyze the diameter and length of the pieces, obtaining the total volume in length of river. There is a gap regarding the woody debris management in Brazil, because only one biome (Atlantic Forest) was included in the few researches carried out. The knowledge of WD dynamics can be surely used in the future in the watersheds management and for rivers renaturalization. [ABSTRACT FROM AUTHOR]

A history of land clearance and riparian tree and wood management has resulted in limited riparian woodland and wood along British rivers. However, river management approaches are now being promoted that 'work with natural processes' to reduce flood risk through measures intended to restore, protect and emulate the natural function of catchments, rivers, estuaries and coasts. Wood has started to be reintroduced into river channels during river restoration and natural flood management activities, but this needs to be undertaken using appropriate quantities, locations and designs that mimic natural tree‐wood features. This paper reviews the knowledge that is needed to support wood reintroduction activities including (i) the characteristics of the riparian tree species and wood that are present; (ii) the importance of river size relative to that of trees and wood pieces; and (iii) the way trees, wood and geomorphic processes interact across rivers and floodplains of different energy and style. [ABSTRACT FROM AUTHOR]

The present paper utilizes entropy to investigate variability in the surface areas of sandbars distribution of the Brahmaputra River, India. The intensity entropy disorder index (IDI) was computed for the dry and the post‐monsoon season for a selected reach of the river. The planform disorder index (PDI) was computed to represent the annual scale planform change due to seasonal flood. Finally, annual monsoon and peak flood stream power were evaluated and related to PDI. The results showed that the intensity disorder index followed a decreasing trend in dry and post‐monsoon seasons; tending towards lower deviation from a uniform distribution. It was noted that except for extreme flood years the PDI trend correlated well with monsoonal stream power. Distinctive trends in stream power were also observed in the present study. © 2018 John Wiley & Sons, Ltd. The present study utilizes entropy method to investigate variability in sandbars distribution of the Brahmaputra River, India. [ABSTRACT FROM AUTHOR]

In this paper we analyse the recent geomorphological evolution of the River Ñuble, an unmodified wandering river in the Mediterranean region of Chile, highlighting the relation between the observed hydroclimatic trends in the region and the morphology of the river. The work documents the recent changes (2003–2016) in channel morphology (i.e., narrowing, simplification, vegetation encroachment) and, in particular, how the river has progressively reduced its geomorphic activity during the last decade. Changes have been detected using aerial imagery and quantified by means of a series of channel form indices that allow tracking the geomorphological evolution of an 8-km river segment. The catchment has experienced a clear decrease in the frequency and magnitude of flood events, although this fact is not fully supported by a generalized reduction in the analysed rainfall series. We relate the observed river relaxation and the associated channel changes with the reported period of low hydroclimatic activity, which follows a humid period that occurred in the Pacific region during the 1970s and 1980s, connected to the PDO (Pacific Decadal Oscillations) that particularly affected the northern and the central parts of Chile. Altogether, this resulted in generalized river stability and a simplification of the drainage pattern of the channel. In absence of river training practices and other major changes in the catchment, the reduction of formative discharges appears thus to be the main control of the recent evolution of this gravel-bed river. [ABSTRACT FROM AUTHOR]

Geomorphic diversity at a variety of spatial and temporal scales has been studied in the western Ganga plains (WGP), India, to isolate the dominating factors at each scale that have the potential to cause major geomorphic change. The Ganga River and its major tributaries draining the WGP have been investigated in terms of longitudinal, cross-sectional, and planform morphology to assess the influence of potential controls such as climate, geology, topography, land use, hydrology, and sediment transport. These data were then compared with those from the rivers draining the eastern Ganga plains (EGP) to understand the geomorphic diversity across the Ganga plains and the causal factors. Our investigations suggest that in-channel geomorphic diversity over decadal scale in rivers with low width-to-depth ( W / D ) ratio is caused by periodic incision/aggradation, but it is driven by channel avulsion in rivers characterized by high W / D ratio. Similarly, planform (reach-scale) parameters such as sinuosity and braid-channel-ratio are influenced by intrinsic factors such as changes in hydrological conditions and morphodynamics (cutoffs, small-scale avulsion) that are in turn impacted by natural and human-induced factors. Finally, we have isolated the climatic and hydrologic effects on the longitudinal profile concavity of alluvial trunk channels in tectonically stable and unstable landscapes. We demonstrate that the rivers flowing through a tectonically stable landscape are graded in nature where higher discharge tends to create more concave longitudinal profiles compared to those in tectonically unstable landscape at 10 3 -year scale. [ABSTRACT FROM AUTHOR]

Wood accumulations are important morphological agents forming the character of high-gradient streams in the Moravskoslezské Beskydy Mts. The aim of the research is to define both the extent and character of the impact of wood accumulations on the streams. A total of 126 accumulations have been identified of the total wood volume of 503 m3 that is unevenly distributed within the studied streambeds. The wood volume in the studied streambeds is particularly dependent on the age and species composition of vegetation, channel morphology, and the geological bedrock resistance to the action of the stream, especially in forced alluvial reaches. The research revealed the deposition of fine-grained material immediately upstream of the wood accumulations, creating gravel bars and capturing fine organic debris. On the other hand, immediately downstream of the accumulations fine-grained fractions are carried away and coarser material is deposited, creating pools and plunge pools, evorsion potholes and bank scours. The research further showed a low intensity of the transport of woody material through the streambeds. The accumulations usually occur in the place where the stream has been dammed by a fallen tree member or in structurally predisposed streambed segments. As a result, discontinuities in energy and material flow occur that help to increase the streambed heterogeneity. [ABSTRACT FROM AUTHOR]

Studies involving river corridor needs a clear cut and an integrated basin management approach because it helps in improving or maintaining water quality, protecting wetlands, enhancing river restoration decision etc. Hence, this study seeks to identify major landuse types within the River Ona Corridor; examine the impact of these landuse types within the River Ona corridor on its channel morphology and understand the risk being posed by these landuse types. The study is designed by selecting two reaches of six times the average width from each of the four major landuse types that exist along the river corridor. This study revealed that along the downstream section of Eleyele Dam of River Ona, natural forest stabilizes river channel banks, thereby presenting a narrow and shallow width and depth respectively but the widest of all is found within the agricultural zones. [ABSTRACT FROM AUTHOR]

Mediterranean rivers are hotspots for biodiversity, and riverine species are adapted to regular physical perturbations that affect channel morphology during flashy rainfall-runoff events. Dams alter flow regimes, changing flood magnitude and frequency; they also interrupt the continuity of sediment transport. Changes in both flood and sediment transport regimes affect downstream channel dynamics and the ecological functioning of fluvial systems. This paper examines the effects of flow regulation on bed disturbance, invertebrate assemblages and their biological traits in a Mediterranean river (the Siurana, NE Iberian Peninsula). Results are put in the broader context of the whole Ebro river catchment. The Siurana Reservoir causes a complete inversion of the seasonal flow regime and reduces flood magnitude notably. Upstream from the reservoir, torrential floods mobilize surface and subsurface bed materials, regularly disturbing the physical habitat; downstream, geomorphological activity in the channel is almost nonexistent. Altogether, damming causes significant differences in taxonomic composition of the benthic invertebrate communities; density and biomass increase notably below the dam although diversity decreases. At the broader scale taxa with active aerial dispersal traits dominate unregulated reaches in areas with marked Mediterranean hydro-climatic regimes, whereas reaches with more stable regimes are characterized by fully aquatic detritivore species. [ABSTRACT FROM AUTHOR]

The Biała River, Polish Carpathians, was considerably modified by channelization and channel incision in the twentieth century. To restore the Biała, establishing an erodible corridor was proposed in two river sections located in its mountain and foothill course. In these sections, longer, unmanaged channel reaches alternate with short, channelized reaches; and channel narrowing and incision increases in the downstream direction. In June 2010 an 80-year flood occurred on the river; and this study aims at determining its effects on physical habitat conditions for river biota, channel morphology, and valley-floor infrastructure. Surveys of 10 pairs of closely located, unmanaged and channelized cross sections, performed in 2009 and in the late summer 2010, allowed us to assess the flood-induced changes to physical habitat conditions. A comparison of channel planforms determined before (2009) and after (2012) the flood provided information on the degree of channel widening as well as changes in the width of particular elements of the river's active zone in eight stretches of the Biała. The impact of the flood on valley-floor infrastructure was confronted with the degree of river widening in unmanaged and channelized river reaches. Before the flood, unmanaged cross sections were typified by finer bed material and greater lateral variability in depth-averaged and near-bed flow velocity than channelized cross sections. The flood tended to equalize habitat conditions in both types of river cross sections, obliterating differences (in particular physical habitat parameters) between channelized and unmanaged channel reaches. River widening mostly reflected an increase in the area of channel bars, whereas the widening of low-flow channels was less pronounced. A comparison of channel planform from 2009 and 2012 indicated that intense channel incision typical of downstream sections limited river widening by the flood. Active channel width increased by half in the unmanaged cross sections and by one-third in the channelized cross sections. However, damage to the valley-floor infrastructure was practically limited to the channelized river reaches with reinforced channel banks. This indicates incompetent management of riparian areas rather than the degree of river widening as a principal reason for the economic losses during the flood. [ABSTRACT FROM AUTHOR]

Dunes of the lowermost Mississippi River (LmMR) in USA and the lowermost Yangtze River (LmYR) in China have been recently investigated in some reaches. Yet, our understanding of dune formation in large lowland alluvial rivers is still limited. This study compared characteristics of dunes in an 8-km long reach in the LmMR and a 35-km long reach of the LmYR to discern similarity and difference in dune development. The primary goal of the study was to assess morphological responses of dunes to natural factors and human interventions in these two world's large rivers. Multi-beam bathymetric measurements in the river reaches were used to quantify dune length, height, stoss and lee angles. The results showed that both the LmMR and LmYR had large (10–100 m in length), medium (5–10 m in length), and small dunes (0.6–5 m in length), but very large dunes (dune length >100 m) only developed in the LmYR. Large dunes were predominant, amounting to 88.4% in the LmMR and 54% in the LmYR. There was a close correlation between dune height and dune wavelength in both the LmMR and LmYR. Significant differences (p < 0.0001) in dune size, geometry (height/wavelength), and symmetrical characteristic (stoss slope/lee slope) were found between the LmMR and the LmYR. On average, dunes in the LmYR were longer and taller (20.08 m and 0.91m) than those in the LmMR (17.62 m and 0.87 m), which was likely owing to the human activities in the LmYR and the backwater effects in the LmMR, as well as the influence of river discharge and flow strength. Little difference was found in dune roughness between the LmMR and the LmYR, indicating that the flow resistance is similar in the two regions. The findings suggest that human activities are the dominant factor affecting dune morphology in large lowland rivers. • Dunes in the lowermost Yangtze River were larger than those in the lowermost Mississippi River. • Significant differences in dune characteristics were found between the two world's large rivers. • Human activities are the dominant factor affecting dune morphology in large lowland rivers. [ABSTRACT FROM AUTHOR]

Regional climate, geology, vegetation, and land use influence hydrogeomorphic processes, which influence stream channel form and the recruitment and transport of wood in streams. We studied relationships between channel morphology and frequencies of large in-channel wood in three upland ecoregions of eastern Oklahoma where streams contain high fish diversity and valuable sport fisheries. We surveyed 138 streams for wood within the Boston Mountains ( n = 30), Ozark Highlands ( n = 30), and Ouachita Mountain ( n = 78) ecoregions. Our study investigated whether (1) the frequency of large wood differed among ecoregions; (2) channel morphology influenced the distribution of large wood within and among ecoregions; and (3) a relationship existed between the frequency and size of trees in the riparian zone and the frequency of large wood within and among ecoregions. The frequency of single large wood pieces did not differ among ecoregions or vary with drainage area. However, the presence of one or more wood accumulation (2 to 4 pieces) increased with drainage area and increased at a higher rate in the Boston Mountains and Ozark Highlands than in the Ouachita Mountains. The frequency of single wood pieces decreased in narrower channels with larger substrates but increased in larger stream channels overall. No association existed between riparian tree density and in-channel wood in study reaches. We discuss these results in the context of wood recruitment and transport, and highlight key questions that remain regarding wood in eastern Oklahoma streams. [ABSTRACT FROM AUTHOR]

Accurate estimation of flow resistance is crucial for flood routing, flow discharge and velocity estimation, and engineering design. Various empirical and semiempirical flow resistance models have been developed during the past century; however, a universal flow resistance model for varying types of rivers has remained difficult to be achieved to date. In this study, hydrometric data sets from six stations in the lower Yellow River during 1958–1959 are used to calibrate three empirical flow resistance models (Eqs. (5)–(7)) and evaluate their predictability. A group of statistical measures have been used to evaluate the goodness of fit of these models, including root mean square error ( RMSE ), coefficient of determination ( CD ), the Nash coefficient ( NA ), mean relative error ( MRE ), mean symmetry error ( MSE ), percentage of data with a relative error ≤ 50% and 25% ( P 50 , P 25 ), and percentage of data with overestimated error ( POE ). Three model selection criterions are also employed to assess the model predictability: Akaike information criterion ( AIC ), Bayesian information criterion ( BIC ), and a modified model selection criterion ( MSC ). The results show that mean flow depth ( d ) and water surface slope ( S ) can only explain a small proportion of variance in flow resistance. When channel width ( w ) and suspended sediment concentration ( SSC ) are involved, the new model (7) achieves a better performance than the previous ones. The MRE of model (7) is generally < 20%, which is apparently better than that reported by previous studies. This model is validated using the data sets from the corresponding stations during 1965–1966, and the results show larger uncertainties than the calibrating model. This probably resulted from the temporal shift of dominant controls caused by channel change resulting from varying flow regime. With the advancements of earth observation techniques, information about channel width, mean flow depth, and suspended sediment concentration can be effectively extracted from multisource satellite images. We expect that the empirical methods developed in this study can be used as an effective surrogate in estimation of flow resistance in the large sand-bed rivers like the lower Yellow River. [ABSTRACT FROM AUTHOR]

Dunes are present in nearly all fluvial channels and are vital in understanding sediment transport, deposition, and flow conditions during floods of rivers and estuaries. This information is pertinent for helping developing management practices to reduce risks in river transportation and engineering. Although a few recent studies have investigated the micromorphology of a portion of the Yangtze River estuary in China, our understanding of dune development in this large estuary is incomplete. It is also poorly understood how the development and characteristics of these dunes have been associated with human activities in the upper reach of the Yangtze River and two large-scale engineering projects in the estuarine zone. This study analyzed the feature in micromorphology of the entire Yangtze River estuary bed over the past three years and assessed the morphological response of the dunes to recent human activities. In 2012, 2014, and 2015, multi-beam bathymetric measurements were conducted on the channel surface of the Yangtze River estuary. The images were analyzed to characterize the subaqueous dunes and detect their changes over time. Bottom sediment samples were collected for grain size analysis to assess the physical properties of the dunes. We found that dunes in the Yangtze River estuary can be classified in four major classes: very large dunes, large dunes, medium dunes, and small dunes. Large dunes were predominant, amounting to 51.5%. There was a large area of dunes developed in the middle and upper reaches of the Yangtze River estuary and in the Hengsha Passage. A small area of dunes was observed for the first time in the turbidity maximum zone of the Yangtze River estuary. These dunes varied from 0.12 to 3.12 m in height with a wide range of wavelength from 2.83 to 127.89 m, yielding a range in height to wavelength of 0.003--0.136. Sharp leeside slope angles suggest that the steep slopes of asymmetrical dunes in the middle and upper reaches, and the turbidity maximum zone of the Yangtze River estuary face predominantly towards tides because of the ebb-dominated currents. Sharp windward slope angles in the lower reach of the North Passage show the influence of flood-dominated currents on dunes. It is likely that the scale of dunes will increase in the future in the South Channel because of a sharp decline of sediment discharge caused by recent human activities. [ABSTRACT FROM AUTHOR]

Flows in ephemeral channels in semiarid areas are only occasional, and channel changes are episodic; but the flash floods can be devastating and have major geomorphological impacts. Data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels. For this purpose nine reaches of river channel in three catchments in SE Spain – the Nogalte, Torrealvilla, and Salada – have been sites for measurement of flows and their effects over the period 1997–2012. The sites encompass a range of channel size, channel morphology, substrate, vegetation, and position within the catchments. A major difference is between schist and marl bedrock areas. Peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events. Over the 16-year period, an average of 0.5 flow events per year has been recorded at the schist sites, and an average of one per year at the marl sites; but occurrence has been highly variable from year to year. Threshold daily rainfall for channel flow is mostly 15–20 mm, but higher rainfalls do not always produce flow. One to two major floods have occurred in each of the catchments in the period, including the extreme flood event of September 2012 in the Nogalte catchment. Measured morphological changes have occurred between 2 and 10 times at the monitored sites. The same size flow can have differing effects depending on the state of the system. Low flow can mobilise sediment without producing much morphological change. The long-term trajectory of the reaches and the sediment substrate has a major influence on response to events. Channel change is governed by threshold values of hydraulic conditions. The measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in management. [ABSTRACT FROM AUTHOR]

As part of an hierarchical, multi-scale, hydromorphological framework for European rivers that has been developed within the REFORM project, a procedure for classifying rivers has been devised. The procedure includes components that categorise river channel morphology, floodplain morphology, flow regime, and groundwater-surface water interactions, and is designed for operational use in the context of river management. Channel morphology is classified at a first level by a basic river typology interpreted using remotely sensed images, and at a second level by an extended river typology that integrates information from field observations. Floodplains are classified by adopting the Nanson and Croke typology with specific reference to the types of floodplain that are most likely to be encountered widely across Europe. Nine flow regime types are identified using a series of hydrological indicators. Finally, where groundwater has a significant influence on river flows, a range of potential groundwater-surface water interactions are identified reflecting the morphological river type and its geological and climatic setting. Within the REFORM project, the river typology has been tested using case studies representative of a wide variety of European catchment conditions. Four case studies are used to illustrate the classification procedure and to discuss its main strengths and limitations. [ABSTRACT FROM AUTHOR]

Comprehensive field survey of the physiographic context and channel morphology is a key to distinguish characteristic hydrogeomorphic reaches of a watercourse. In this analysis field data were collected during seasonal campaigns following a field survey protocol developed in the Polish Carpathian Mountains. Complementary information was conducted from cartographic materials and digital elevation model to map diverse sections of the semi-natural Váralja Stream in the Eastern Mecsek Mountains. Geological, geomorphological and anthropogenic effects had to be considered as decisive factors in recent fluvial development, with emphasis on the sediment transport influenced by woody debris. A total of 12 hydrogeomorphic reaches were identified along the stream by interpreting the spatial arrangement of channel forms and analysing the characteristics of the watershed environment. The mapped reaches are connected with transitional zones of different length. Step systems are typical on the upper reach of the stream, but they were found to be the result of the geological composition and structure of the region. It was also proven that woody debris accumulations, made up of tree trunks, branches and roots have significant influence on the channel evolution of the Váralja stream. Even though the presented field survey instructions were field-tested in alpine catchments the conducted research confirmed the applicability of such workflow in low mountainous environment. Furthermore, the results on the hydrogeomorphic conditions of this small watershed with intense relief provide useful information for understanding the flash floods occurring in the region. [ABSTRACT FROM AUTHOR]

Gravel-bed rivers featuring a near dynamic equilibrium state usually display a good correspondence between geomorphological and riparian community gradients, whereas long-term human alterations may disrupt these patterns. The aim of this study was to investigate the distribution of woody riparian vegetation on three geomorphic units - floodplains, bars, and islands along the Piave River, a gravel-bed river located in Northern Italy suffering from various degrees of human pressure and disturbances. A total of 214 plots (4 × 4 m) along three cross sections in each of two sub-reaches of the river were surveyed in order to identify the different morphological units, dendrological characteristics of standing plants, and species composition. Three riparian woody communities, with decreasing woody species richness and tree size, were identified by cluster analysis: Alnion incanae ( n = 58), Salicion eleagni ( n = 52), and Rhamno-Prunetea ( n = 27). The first was significantly associated with floodplains and the others with bars. No community showed a relatively stronger association with islands. Linear mixed models showed that the three geomorphic units significantly differed in mean elevation, fine sediment depth, and geomorphic persistence, but not all Tukey contrasts were significant, and absolute differences in mean elevation above talweg were quite small (<25 cm). Moreover, the three woody communities were not always related to corresponding geomorphological gradients, which reflected the river's complex history of channel adjustments. Most notably, mean grain size did not differ between either geomorphic or vegetation units. This study therefore indicates that riparian woody vegetation along altered gravel-bed rivers may differ substantially from those characterizing near-equilibrium river systems. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The morphological analysis of Bashistha and Bahini-Bharalu river channels has been carried out through the measurements of channel geometry (channel width, channel depth, bed width, wetted perimeter, hydraulic radius), channel fluid dynamics (water discharge, velocity) and downstream hydraulic geometry (relationships among independent and dependent channel variables). The study has been carried out in seven cross sections along the Bashistha river and in eight cross sections along the Bahini-Bharalu river. The cross sectional shapes and sizes of both the rivers are analyzed from the cross sectional profiles. The fluvio-geomorphic behaviour of the rivers are analyzed by the study of their hydraulic geometry. [ABSTRACT FROM AUTHOR]

Excess fine sediments in streambeds are among the most pervasive causes of degradation in streams of the United States. Simple criteria for acceptable streambed fines are elusive because streambed fines and biotic tolerances vary widely in the absence of human disturbances. In response to the need for sediment benchmarks that are protective of minimum aquatic life uses under the Clean Water Act, we undertook a case study using surveys of sediment, physical habitat, and macroinvertebrates from New Mexico streams. Our approach uses weight of evidence to develop suggested benchmarks for protective levels of surficial bedded sediments <0.06 mm (silt and finer) and <2.0 mm (sand and finer). We grouped streams into three ecoregions that were expected to produce similar naturally occurring streambed textures and patterns of response to human disturbances. Within ecoregions, we employed stressor response models to estimate fine sediment percentages and bed stability that are tolerated by resident macroinvertebrates. We then compared individual stream sediment data with distributions among least-disturbed reference sites to determine deviation from natural conditions, accounting for natural variability across ecoregion, gradient, and drainage area. This approach for developing benchmark values could be applied more widely to provide a solid basis for developing bedded sediment criteria and other protective management strategies in other regions. [ABSTRACT FROM AUTHOR]

The paper outlines changes in the channel morphology of the Ropa riverbed over the last six years, taking into account the role of large floods and the Klimkówka water reservoir in shaping the morphology of the riverbed. The analysis was based on annual geodetic measurements of the Ropa riverbed conducted between 2009-2014. The research was carried out in four cross profiles of the riverbed located upstream (1 profile) and downstream (3 profiles) of the reservoir. In order to recognise the direction and scale of morphology changes of the riverbed, additional analyses of water levels in the Ropa River was performed in the analysed multiannual period. The conducted analysis led to the conclusion that floods with extremely large discharges are the key factor causing the deepening of the riverbed downstream from the reservoir. It can be up to about 70 cm deep during a single event. The reservoir is just one additional factor of many which shape the direction and scale of changes to the riverbed. A significant role in modifying the riverbed morphology upstream from the reservoir is played by river control works, which diminish the effects of sediment accumulation occurring on this section. [ABSTRACT FROM AUTHOR]

Abstract: A detailed measurement of 93 channel reaches that were classified with an adjusted Montgomery–Buffington (1997) reach-scale system provided comprehensive information of approximately 9 at-a-reach parameters: the channel gradient, the bankfull width, the bankfull depth, d 90, the percentage of resistant rocks in the bed sediment, the number of pieces of large woody debris, valley confinement, direct sediment inputs and the presence of fluvial accumulations in the stream channel. In addition, the quantified intensity of sediment transport (i.e. ratio between sediment supply and transport capacity in longitudinal stream profiles) during flood events has been estimated by the one-dimensional bedload transport model (TOMSED), which was validated in two local streams. The principal component analysis of the at-a-reach parameters did not reveal significant groups of channel-reach morphologies; thus, the selected parameters that exclude sediment transport dynamics within stream longitudinal profile cannot reliably distinguish or predict individual channel reach morphologies. Nevertheless, the channel gradient represented the most significant single explanatory variable for stepped-bed morphologies. The addition of bedload transport parameters demonstrated that limited sediment supply streams and streams with limited transport capacities featured different successions of the channel reach morphologies in terms of the channel gradient and, subsequently, the fluvial continuity. The bedrock-cascades and step-pools were significant for the first case, whereas cascade and step-rapid morphology often occurred in higher sediment supply conditions. [Copyright &y& Elsevier]

ABSTRACT Accurate mapping of water surface boundaries in rivers is an important step for monitoring water stages, estimating discharge, flood extent, and geomorphic response to changing hydrologic conditions, and assessing riverine habitat. Nonetheless, it is a challenging task in spatially and spectrally heterogeneous river environments, commonly characterized by high spatiotemporal variations in morphology, bed material, and bank cover. In this study, we investigate the influence of channel morphology and bank characteristics on the delineation of water surface boundaries in rivers using high spatial resolution passive remote sensing and a template-matching (object-based) algorithm, and compare its efficacy with that of Support Vector Machine (SVM) (pixel-based) algorithm. We perform a detailed quantitative evaluation of boundary-delineation accuracy using spatially explicit error maps in tandem with the spatial maps of geomorphic and bank classes. Results show that template matching is more successful than SVM in delineating water surface boundaries in river sections with spatially challenging geomorphic landforms (e.g. sediment bar structures, partially submerged sediment deposits) and shallow water conditions. However, overall delineation accuracy by SVM is higher than that of template matching (without iterative hierarchical learning). Vegetation and water indices, especially when combined with texture information, improve the accuracy of template matching, for example, in river sections with overhanging trees and shadows - the two most problematic conditions in water surface boundary delineation. By identifying the influence of channel morphology and bank characteristics on water surface boundary mapping, this study helps determine river sections with higher uncertainty in delineation. In turn, the most suitable methods and data sets can be selectively utilized to improve geomorphic/hydraulic characterization. The methodology developed here can also be applied to similar studies on other geomorphic landforms including floodplains, wetlands, lakes, and coastlines. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Beaver dams in streams are generally considered to increase bed elevation through in-channel sediment storage, thus, reintroductions of beaver are increasingly employed as a restoration tool to repair incised stream channels. Here we consider hydrologic and geomorphic characteristics of the study stream in relation to in-channel sediment storage promoted by beaver dams. We also document the persistence of sediment in the channel following breaching of dams. Nine reaches, containing 46 cross-sections, were investigated on Odell Creek at Red Rock Lakes National Wildlife Refuge, Centennial Valley, Montana. Odell Creek has a snowmelt-dominated hydrograph and peak flows between 2 and 10m3 s−1. Odell Creek flows down a fluvial fan with a decreasing gradient (0.018–0.004), but is confined between terraces along most of its length, and displays a mostly single-thread, variably sinuous channel. The study reaches represent the overall downstream decrease in gradient and sediment size, and include three stages of beaver damming: (1) active; (2) built and breached in the last decade; and (3) undammed. In-channel sediment characteristics and storage were investigated using pebble counts, fine-sediment depth measurements, sediment mapping and surveys of dam breaches. Upstream of dams, deposition of fine (≤2mm) sediment is promoted by reduced water surface slope, shear stress and velocity, with volumes ranging from 48 to 182m3. High flows, however, can readily transport suspended sediment over active dams. Variations in bed-sediment texture and channel morphology associated with active dams create substantial discontinuities in downstream trends and add to overall channel heterogeneity. Observations of abandoned dam sites and dam breaches revealed that most sediment stored above beaver dams is quickly evacuated following a breach. Nonetheless, dam remnants trap some sediment, promote meandering and facilitate floodplain development. Persistence of beaver dam sediment within the main channel on Odell Creek is limited by frequent breaching (<1–5years), so in-channel sediment storage because of damming has not caused measurable channel aggradation over the study period. Enhanced overbank flow by dams, however, likely increases fine-grained floodplain sedimentation and riparian habitat. Contrasts between beaver-damming impacts on Odell Creek and other stream systems of different scales suggest a high sensitivity to hydrologic, geomorphic, and environmental controls, complicating predictions of the longer-term effects of beaver restoration. [Copyright &y& Elsevier]

Highlights: [•] A conceptual model for river ice types and river ice processes is presented. [•] The model can be used for any channel type and size, in any cold region setting. [•] The model distinguishes steep from low-gradient river ice types and processes. [•] The channel morphology is used as a versatile channel and river ice type indicator. [ABSTRACT FROM AUTHOR]

ABSTRACT Urbanization through the addition of impervious cover can alter catchment hydrology, often resulting in increased peak flows during floods. This phenomenon and the resulting impact on stream channel morphology is well documented in temperate climatic regions, but not well documented in the humid tropics where urbanization is rapidly occurring. This study investigates the long-term effects of urbanization on channel morphology in the humid sub-tropical region of Puerto Rico, an area characterized by frequent high-magnitude flows, and steep coarse-grained rivers. Grain size, low-flow channel roughness, and the hydraulic geometry of streams across a land-use gradient that ranges from pristine forest to high density urbanized catchments are compared. In areas that have been urbanized for several decades changes in channel features were measurable, but were smaller than those reported for comparable temperate streams. Decades of development has resulted in increased fine sediment and anthropogenic debris in urbanized catchments. Materials of anthropogenic origin comprise an average of 6% of the bed material in streams with catchments with 15% or greater impervious cover. At-a-station hydraulic geometry shows that velocity makes up a larger component of discharge for rural channels, while depth contributes a larger component of discharge in urban catchments. The average bank-full cross-sectional area of urbanized reaches was 1.5 times larger than comparable forested reaches, and less than the world average increase of 2.5. On average, stream width at bank-full height did not change with urbanization while the world average increase is 1.5 times. Overall, this study indicates that the morphologic changes that occur in response to urban runoff are less in channels that are already subject to frequent large magnitude storms. Furthermore, this study suggests that developing regions in the humid tropics shouldn't rely on temperate analogues to determine the magnitude of impact of urbanization on stream morphology. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The article presents the results of research on morphological changes of the Carpathian river Ropa caused by high flood events. The analysis was based on the surveys of river cross-profiles located above (1 profile) and below (3 profiles) the Klimkówka Reservoir that were performed in 2009 and 2010. Data on the discharges and water stages of the Ropa River at the gauging station at Szymbark (near Gorlice) were also used in the study. Attention was paid to the possible role of the Klimkówka Reservoir in the transformation of the morphology of the Ropa River channel. [ABSTRACT FROM AUTHOR]

Bunte, Kristin, John P. Potyondy, Kurt W. Swingle, and Steven R. Abt, 2012. Spatial Variability of Pool-Tail Fines in Mountain Gravel-Bed Stream Affects Grid-Count Results. Journal of the American Water Resources Association (JAWRA) 48(3): 530-545. DOI: 10.1111/j.1752-1688.2011.00629.x Abstract: Fine sediment (<2 and <6 mm) particles underlying a 49-intersection grid placed on a streambed at 25, 50, and 75% of the wetted pool-tail width are commonly counted to assess the status and trend of aquatic ecosystems or to monitor changes in the supply of fines in mountain gravel-bed streams. However, results vary even when crews perform nearly identical procedures. This study hypothesized that spatial variability of pool-tail fines affects grid-count results and that a sampling scheme can be optimized for precision and accuracy. Grid counts taken at seven evenly spaced locations across the wetted width of 10 pool tails in a pool-riffle study stream indicated a bankward fining trend with secondary peaks of fines within the stream center. Sampling locations close to the waterlines harbored more than twice as many fines as central locations. Most of the five grid-count schemes derived from the seven sampled locations produced significantly different results. Compared with sampling at all seven locations, schemes that focus near waterlines overpredicted fines, while those that focus on the center underpredicted them. Variability of fines among pool tails was the highest within a broad band along the waterlines; hence, focusing sampling there yielded the most variable results. The scheme sampling at 25, 50, and 75% of the wetted width had the lowest precision and moderate accuracy. Accuracy and precision of grid-count results can be greatly improved by sampling at seven even-spaced locations across the pool tail. [ABSTRACT FROM AUTHOR]

Bunte, Kristin, John P. Potyondy, Kurt W. Swingle, and Steven R. Abt, 2012. Spatial Variability of Pool-Tail Fines in Mountain Gravel-Bed Stream Affects Grid-Count Results. Journal of the American Water Resources Association (JAWRA) 48(3): 530-545. DOI: 10.1111/j.1752-1688.2011.00629.x Abstract: Fine sediment (<2 and <6 mm) particles underlying a 49-intersection grid placed on a streambed at 25, 50, and 75% of the wetted pool-tail width are commonly counted to assess the status and trend of aquatic ecosystems or to monitor changes in the supply of fines in mountain gravel-bed streams. However, results vary even when crews perform nearly identical procedures. This study hypothesized that spatial variability of pool-tail fines affects grid-count results and that a sampling scheme can be optimized for precision and accuracy. Grid counts taken at seven evenly spaced locations across the wetted width of 10 pool tails in a pool-riffle study stream indicated a bankward fining trend with secondary peaks of fines within the stream center. Sampling locations close to the waterlines harbored more than twice as many fines as central locations. Most of the five grid-count schemes derived from the seven sampled locations produced significantly different results. Compared with sampling at all seven locations, schemes that focus near waterlines overpredicted fines, while those that focus on the center underpredicted them. Variability of fines among pool tails was the highest within a broad band along the waterlines; hence, focusing sampling there yielded the most variable results. The scheme sampling at 25, 50, and 75% of the wetted width had the lowest precision and moderate accuracy. Accuracy and precision of grid-count results can be greatly improved by sampling at seven even-spaced locations across the pool tail. [ABSTRACT FROM AUTHOR]

We examine the morphology and dynamics features of the river channels within the basin of the lower reaches of the Amur river on spawning grounds. We report evidence that the spawning grounds tend to occur at definite elements of the river channel as well as data on particle-size composition of alluvial deposits in autumn chum salmon (keta) spawning stretches. Factors having a negative influence on the preservation of spawning grounds have been identified. [ABSTRACT FROM AUTHOR]

Abstract: We examined the role of bed sediment size, bank materials, riparian vegetation, and discharge on channel form along a 10-km reach of the Upper Tualatin River, encompassing both gravel and sand-bed reaches. Statistical correlations and analyses of downstream changes of channel morphology reveal that bank materials and bed sediment are the dominant controls on channel cross section form. A rapid downstream reduction in bed sediment size in the gravel-bed channel is followed by an abrupt transition to a narrower, deeper, and less sinuous sand-bed channel with more cohesive bank materials. The simultaneous reductions in channel slope, bed sediment size, and width-to-depth ratio indicate the channel crosses a geomorphic threshold to maintain continuity in sediment transport. This gravel-to-sand transition and associated change in channel form are induced by a break in valley slope and an increase in bank resistance from cohesive bank materials. Bank materials, measured as the average percent silt and clay in banks, are a primary influence on channel form within both subreaches but demonstrate a greater influence on channel width and vertical stability in the gravel-bed channel and on channel depth and lateral stability in the sand-bed channel. Riparian vegetation at current densities and compositions is not a significant control on contemporary channel cross section form and may be responding to the bank and channel stability provided by cohesive bank materials in the laterally dynamic gravel-bed channel. [ABSTRACT FROM AUTHOR]

The article discusses the river meander bend morphology of the Dane River in Lithuania. It states that most bends show an autogenic sequence that fits with the qualitative models of meander development and have increased the rates of erosion and bankline movement. It also mentions that the changes of meander morphology was due to the formation and sequence of development of the mid-channel bars.

The article presents a study regarding the digital elevation models (DEMs) extraction of river channels and banks in a riparian forest, which is a new approach in digital photogrammetry. It introduces a method to capture and assess the photogrammetric data using a camera placed 10m above through a unipod. It involves the generation of DEMs through the process of using software and statistical filters. Results of the study reveal supplementary DEM checkpoints during the overall station survey.

Abstract: Small, low order channels located in wet meadows along the Mogollon Rim of northern Arizona that receive the bulk of their flow from spring discharge exhibit a morphology that differs markedly from channels that receive the bulk of their flow from runoff. These small, spring-dominated channels generally have dense vegetation cover, vertical (or near vertical) banks with flat channel beds that are armored with clasts up to 60 mm. Clasts armoring the spring-dominated channels become mobile at 45 to 85% of the bankfull depth. The lack of fine-grained material in the bed of the spring-dominated channels reflects the small drainage size, lack of fine grain input from the spring, and winnowing affect of the consistent discharge. Minor amounts of large woody debris were present in some of the spring-dominated channels, however, unlike previous studies it does not appear to play a role in the spring-dominated channel morphology. Sinuosity values for spring-dominated channels averaged 1.19, while the average sinuosity values for the runoff-dominated channels, 1.08, were significantly lower. Measured width-to-depth ratios averaged 2.4 in the spring-dominated channels, much lower than the average ratio of 11.6 found for the runoff-dominated channels. The standard deviation of width-to-depth ratios was higher for runoff-dominated channels, reflecting a more variable channel profile. A third channel type, here referred to as hybrid channels, receive significant flow from both springs and runoff. These channels have characteristics that fall between spring-dominated and runoff-dominated channels. Elevation, gradient, organic matter content, and sediment grain size distribution of the wet meadows in which the channels are formed do not exhibit significant differences between channel types, suggesting that these factors are not responsible for the observed differences in channel morphologies. The major differences in controls on the channel morphology found between the spring-dominated and runoff-dominated channels are the discharge regime and the sediment input. The hydrology unique to the spring-dominated channels and the lack of fine-grained sediment input combine to create the observed differences. [Copyright &y& Elsevier]

Abstract: Measurements of two small streams in northeastern Vermont, collected in 1966 and 2004–2005, document considerable change in channel width following a period of passive reforestation. Channel widths of several tributaries to Sleepers River in Danville, VT, USA, were previously measured in 1966 when the area had a diverse patchwork of forested and nonforested riparian vegetation. Nearly 40 years later, we remeasured bed widths and surveyed large woody debris (LWD) in two of these tributaries, along 500 m of upper Pope Brook and along nearly the entire length (3 km) of an unnamed tributary (W12). Following the longitudinal survey, we collected detailed channel and riparian information for nine reaches along the same two streams. Four reaches had reforested since 1966; two reaches remained nonforested. The other three reaches have been forested since at least the 1940s. Results show that reforested reaches were significantly wider than as measured in 1966, and they are more incised than all other forested and nonforested reaches. Visual observations, cross-sectional surveys, and LWD characteristics indicate that reforested reaches continue to change in response to riparian reforestation. The three reaches with the oldest forest were widest for a given drainage area, and the nonforested reaches were substantially narrower. Our observations culminated in a conceptual model that describes a multiphase process of incision, widening, and recovery following riparian reforestation of nonforested areas. Results from this case study may help inform stream restoration efforts by providing insight into potentially unanticipated changes in channel size associated with the replanting of forested riparian buffers adjacent to small streams. [Copyright &y& Elsevier]

Although the geomorphic and ecological importance of large wood in streams and rivers is well recognized, most studies consider only dead wood in channels. However, we have observed that living parts of trees are often found within active channels and that this "livewood" shares functions with both instream dead wood and live riparian trees, while also providing some functions unique to living woody material within a channel. We describe the mechanisms that produce livewood and illustrate its characteristics and influences on riparian and stream ecosystems with examples from Europe, North America, and New Zealand. We hypothesize that, compared with dead wood in channels, livewood (a) persists longer because of greater stability and greater resistance to decay, and (b) imparts greater structural complexity (with associated hydraulic roughness and retentiveness). The phenomenon of livewood implies that a broader range of tree species and sizes than previously considered may contribute functionally important wood to channels. We encourage the study of livewood in a range of forest-stream ecosystems to test our hypotheses and further our understanding of how forests interact with rivers and streams. [ABSTRACT FROM AUTHOR]

The article presents a study which describes a geostatistical framework that is specifically designed for analysis of river channel topography. The approach incorporates geomorphic concepts into a modular kriging procedure that can be customized to meet the objectives of specific applications in different types of river. The authors of the study use a modular approach that includes an algorithm for transforming the coordinates of data and prediction locations to a channel-centered coordinate system, different methods of representing the trend component of topographic variation and search strategies that incorporate geomorphic information.

Historical records indicate that gray wolves (Canis Iupus) were extirpated from the upper Gallatin River Basin in the early 1900s. Following the removal of these large carnivores, elk (Cervis elaphus) began to increasingly browse streamside vegetation in the winter range, causing widespread loss of formerly extensive willow (Salix spp.) communities. Historical aerial photographs and chronosequences of ground photographs were used to characterize general changes in vegetation and channel morphology over time. In August of 2004, riparian vegetation and channel cross-sections were surveyed along three reaches of the upper Gallatin River. Reach A was located upstream of the elk winter range (control reach) whereas reaches B and C (treatment reaches) were located within the elk winter range. Willow cover on floodplains averaged 85 per cent for reach A, but only 26 per cent and 5 per cent for reaches B and C, respectively. The average return period of calculated bankfull discharges was 31 yrs for reach A but increased to 324 yrs and 106 yrs for reaches B and C, respectively. The long-term loss of streamside vegetation allowed channels to generally increase in hydraulic capacity (via increases in width, incision or both) and decrease their hydrologic connectivity with adjacent floodplains. This study documents, perhaps for the first time, the resultant impacts to riparian vegetation functions and stream channel characteristics following the extirpation of a large mammalian carnivore. [ABSTRACT FROM AUTHOR]

Relations between changes in bed morphology and heavy metal concentrations were investigated in the Mala Panew River channel in southern Poland. Samples of bed sediments were collected at ten locations 12 times during two years. Concentrations of cadmium, zinc and lead in the river sediments are among the highest in Poland and in silt-clay fraction it reaches 600, 4000 and 500 ppm, respectively. At most channel locations, migration of one or two sand bars was observed. Usually a dead water zone, which was a particularly important sink for fine, strongly polluted organic sediments, appeared in front of the bar. Here, also the highest heavy metal concentrations occurred. The dead water existed usually for several months until it was destroyed by a flood or filled with sand sediments in the case of the bar front accretion. As a result, a marked drop of metal concentrations, accompanied by higher flow velocities, followed in a relatively short period. [ABSTRACT FROM AUTHOR]