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Stormwater management in urban environments typically involves regulation of release rates of stored water from control structures to mitigate enhanced peak flows that can cause damaging flooding. The extent to which this mitigation influences stream geomorphic stability remains largely unexplored. Moreover, few, if any, studies have examined how instability is related to hydraulic effects of in-channel structures within urban stream systems. This paper assesses the potential for channel instability under existing conditions in two urban streams in Cook County, Illinois using a stream-power modeling approach. It also evaluates the impact of watershed-specific release rates intended to mitigate flooding from future development on instability potential. The analysis utilizes hydrologic and hydraulic modeling to estimate stream power per unit area for 2-year and 50-year storm events for both the existing base condition and for four release-rate scenarios. Stream power exceeding the critical power required to mobilize channel bed material is integrated over time to determine excess work. Results show that the spatial distribution of excess work for the base condition varies by more than nine orders of magnitude within individual reaches, confirming high potential for instability. Release-rate scenarios both increase and decrease the magnitude of excess work relative to the base conditions within specific reaches of the two streams but do not alter substantially the high variability in excess work. The results demonstrate that instability potential in these urban fluvial systems is governed primarily by spatial variability in hydraulic properties associated with fragmentation of the streams by multiple in-channel structures. [ABSTRACT FROM AUTHOR]

River channels, riparian and floodplain forms and dynamics are all influenced strongly by biological processes. However, the influence of macroinvertebrates on entrainment and transport of river sediments remains poorly understood. We use an energy‐based approach to explore the capacity of benthic animals to move surficial, gravel‐bed particles in field and laboratory settings and use the results to assess the relative significance of biological and physical benthic processes. Our results showed that in 11 British gravel‐bed rivers, the maximum energy content (i.e., calorific content) of macroinvertebrate communities generally matched the flow energy associated with median discharges and, at multiple sites, exceeded that of the 10‐year return interval flood. A series of laboratory experiments used to estimate the minimum energy expended by signal crayfish (Pacifastacus leniusculus) when performing geomorphic work established that crayfish move gravel particles at energy levels below that expected of the flow, complicating direct comparisons of the capacity for macroinvertebrates and fluvial flows to influence bed mobility. Our findings suggest that the influence of macroinvertebrate communities in either promoting or suppressing, the mobilisation of the bed may be large compared to equivalent values of fluvial energy. Based on these findings, we conclude that in the gravel‐bed rivers studied, the macroinvertebrate community's potential to perform geomorphic work matches or exceeds the stream power during most of the year. Although our study examined biological and fluvial energy systems separately, it is important to recognise that in nature, these systems are highly interactive. It follows that utilising the energy framework presented in this paper could lead to rapid advances in both fluvial biogeomorphology and river management and restoration. [ABSTRACT FROM AUTHOR]

A knickzone is defined as a waterfall or an oversteepened fluvial reach encompassing a series of waterfalls. Knickzones are remarkable landforms in that they may represent diametrically opposed conditions: either rapid upstream propagation of base-level fall or a condition of stability and stalled response to base-level fall. Knickzones on the Hawaiian islands exhibit evidence of both behaviours, and in this study, we explore whether this dichotomy can be explained by a threshold stream power for river incision. Topographic analysis shows that the transition between fluvial hanging valleys, where no measurable upstream retreat from the stream junction or coastline has occurred, and knickzones that have retreated or formed upstream of their outlet can be defined by a range of catchment sizes from ~0.5 to 6 km². This transition is present on all volcanoes in our analysis regardless of significant base-level fall, and there is no clear trend of drainage area above knickzones with volcano age. To explain these observations, we hypothesize that knickzones form or stabilize where maximum unit stream power (ωm) does not exceed the critical unit stream power required to incise bedrock (ωc). Using estimates of a maximum possible flood discharge as a function of drainage area to calculate ωm, we show that drainage areas above knickzones are well described by the theoretical prediction that incision stalls when ωm ≤ ωc, where ωc falls in a narrow range from 14 to 40 kW/m². Furthermore, we demonstrate that knickzone positions are largely insensitive to mean climate conditions, likely reflecting the fact that extreme flood events are either insensitive or inversely correlated with mean annual rainfall. [ABSTRACT FROM AUTHOR]

Round mesas up to 500 m high occur in Martian outflow channels. Mesas in Ravi and Elaver Valles occur in deepest parts of the channels where the most intense megaflood erosion occurred. I theorize that Noachian basalts poured into craters which acted as lava traps, similar to Kilauean lava lakes. Subsequent flood basalts buried the infilled craters. Hesperian megafloods stripped away hundreds of meters of basalts, exhuming erosion‐resistant strata. Lava solidification theory is explored to assess the role of cooling in governing the structure and strength of the Martian basalts. The postulated lava lakes that formed the Ravi Vallis mesas would have needed millennia to cool. The larger Elaver Vallis mesa may have needed up to 20,000 years to solidify. Long cooling times led to coarse, doleritic mineral textures and reduced numbers of cooling joints, greatly increasing bulk rock strength and resistance to hydrodynamic erosion. Using rock mechanics theory, cores of exhumed lava‐filled craters would have bulk rock strengths at least 5 to 30 times greater than more highly fractured basalts. Discharge hydrographs for the Morella Crater breach flood that carved Elaver Vallis peak at ∼2.1 × 107 m3 s−1. Stream power per unit streambed area ranged up to >150,000 W m−2 as the breach grew in size. The calculations provide an envelope of power sufficient to erode hundreds of meters of basalts, but not great enough to remove the large mesa. Thus the legacy of an ancient, lava‐filled crater is a high mesa on the floor of Elaver Vallis. Plain Language Summary: Flat‐topped hills stand as high as 500 m on the floors of huge river channels on Mars. These mesas should have been eroded away by the powerful floods that carved these deep channels. I propose that the mesas were once craters that were overrun and filled in by lavas. The result was deep lava lakes that took thousands of years to cool. The slow cooling reduced the number of fractures that could form in the rock, making it much stronger and able to withstand the tremendous power of floods. Thinner lava flows had covered the area before the craters formed. They had many fractures because they cooled quickly. They were then more intensely fractured by the asteroid impacts that formed the craters. Powerful floods eroded away these highly fractured rocks, leaving the strong centers of the former lava lakes as high mesas. One of these mesas stands in a channel that was eroded when a large lake in Morella Crater breached the crater's rim. That special condition made it possible to calculate how the flood power changed over time. Round mesas in other channels may have been formed within a similar range of flood power. Key Points: Mesas up to 500 m high exist on the floors of outflow channels where megaflood erosion had stripped away hundreds of meters of basaltsI propose that these mesas were Noachian‐age craters that were overrun and deeply filled by basalt flows, then later exhumed by megafloodsLava physics & rock mechanics reveal that slow cooling of these lava lakes led to minimal fractures, greatly adding to bulk rock strength [ABSTRACT FROM AUTHOR]

Soil erosion and the consequent loss of nutrients have consistently been significant factors contributing to land degradation and nonpoint source pollution. While runoff serves as the primary carrier for nutrient loss, the hydraulic processes governing the mechanisms of nutrient loss remain not entirely clear. This paper aims to investigate the impacts of rainfall intensity and the slope gradient on hydraulic parameters, soil loss rates, and ammonia nitrogen loss rates, with the objective of determining the optimal hydraulic parameters for more accurate predictions of soil erosion and nutrient loss rates. A series of simulated rainfall experiments with three rainfall intensities (25, 50, and 75 mm min−1) and four slope gradients (8.7%, 17.6%, 26.8%, and 36.4%) were conducted on a 5 m × 10 m slope. The results indicated that the flow velocity, shear stress, stream power, unit stream power, and unit energy all increased with the increase in slope gradient or rainfall intensity. The water depth decreased with an increase in the slope gradient but increased with an increase in the rainfall intensity. Laminar flow occurred in all experiments (Reynolds number < 500). Only the overland flow under a 25 mm h−1 rainfall intensity and 8.7% slope gradient was subcritical flow (Froude number < 1). Hydraulic parameters, the soil loss rate, and ammonia nitrogen loss rate could be all expressed as the product of rainfall intensity and slope power function, with R2 ranging from 0.949 to 0.997. The average soil loss rate and process soil erosion rate could both be fitted using the power function of hydraulic parameters, with the optimal fitting parameter being stream power (R2 = 0.980 and 0.909). The average ammonia nitrogen loss rate exhibited a linear relationship with the hydraulic parameters, and the optimal fitting parameter was also stream power (R2 = 0.933). However, there were relatively low correlations between hydrodynamic parameters and the ammonia nitrogen loss rate (R2 = 0.450–0587). Our results contribute to a deeper understanding of the hydraulic processes involved in nutrient loss. [ABSTRACT FROM AUTHOR]

The Mississippi River channel from New Orleans to the Gulf of Mexico (GOM) is a key deep draft navigation channel and an active deltaic lobe. Natural and engineered lateral exits from this reach into adjacent receiving basins historically has provided mineral sediment for wetland accretion in the face of rising relative sea level and supported estuarine‐coastal food webs. However, our analysis indicates water losses from the channel have increased by 25% since 2004 due to (1) bank failures during large floods since 2012 that have created several large exit channels downriver of the flood protection levee, and (2) the opening of an engineered diversion at West Bay in 2004. This has resulted in a 60%–80% loss in stream power in the lowermost navigation channel that is accompanied by net shoaling between 2012 and 2022 and an increased dredging need. Our 2022 survey in the GOM exit passes indicates that only 20% of the freshwater, 5% of the total suspended sediment (2% of the sand) at New Orleans now reaches the GOM: this supports previous research indicating the delta front is retreating after centuries of progradation. Together these results indicate that (1) river containment and the sustainability of the navigation channel is threatened, (2) sediment load reaching the seaward end of the delta may be insufficient to avoid major degradation, and (3) the increased freshwater flux into adjacent shallow coastal water bodies has unknown implications for coastal hypoxia and food webs, including commercial species (e.g., oysters) and marine mammals. Future acceleration in sea level rise rates and tropical storm frequency/intensity would likely worsen these trends. [ABSTRACT FROM AUTHOR]

In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of 240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p < 0.001) and depth (p < 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., streambank erosion) to watershed loads and is critical to account for interannual sediment and TP export. [ABSTRACT FROM AUTHOR]

Study region: The Three Gorges Reservoir area (TGR), China Study focus: Soil erosion on purple soil hillslope and its negative effects are deleterious to the ecological environment of the TGR. Sheet erosion is the initial form of the slope erosion, which is notably impacted by land degradation, polyacrylamide (PAM) is commonly applied for soil and water conservation purpose, while the sheet erosion on purple soil hillslope treated with PAM remains unclear. New hydrological insights for the region: The findings suggested that the sheet erosion and runoff rate increased as the rainfall intensity was increased and the slope gradient was decreased with increasing PAM application rate until reaching minimum values at 0.80 g m−2, and these quantities increased afterward. The single and combined impacts of the PAM application rate, rainfall intensity and slope gradient on erosion and runoff were significant. The slope gradient, rainfall intensity and PAM application rate also influenced the hydrodynamic parameters, and the stream power was the optimal parameter for describing the sheet erosion. An equation encompassing the rainfall intensity, slope gradient and PAM application rate was used for sheet erosion rate prediction with high accuracy relative to the stream power and PAM application rate. These results could be helpful to better understand sheet erosion on purple soil slopes treated with PAM and offer fundamental guidelines for soil and water conservation in the TGR.

In recent decades, the number of rainfall-induced landslides has increased significantly in many parts of Malaysia, especially in the urbanized and hilly areas. The disturbance of hilly morphology as a result of human activities has increased the potential for erosion on man-made slopes, especially during extreme rainfall during rain events. Most hilly areas in Malaysia are covered by a thick layer of soil, which is known to have a significant impact on soil erosion. However, little is known about how soil erosion and rainfall could be the driving force behind landslide initiation, especially on stabilized slopes. Therefore, this study focuses on the soil detachment rate of landslides triggered by rainfall at different rainfall intensities. A sandbox model is used to represent real slope conditions. The relationship between the soil detachment capacity, soil properties (water content, slope, clay layers and soil compaction), hydraulic parameters (flow shear stress and stream power) and rainfall intensities (low, medium and high) was investigated. The results showed that the hydraulic parameters and the rainfall intensity are directly proportional to the detachment rate of the soil. Water content and slope show a higher soil detachment rate and a lower critical flow shear stress than other soil properties. It can be concluded that high saturation and steep slope increase the risk of soil erosion because the cohesion and friction of the soil are significantly reduced, leading to a weakening of the soil structure at the surface. The results of this study can feed into the existing analysis of slope stability and formulate the onset of a landslide triggered by rainfall, especially in eroded soils. [ABSTRACT FROM AUTHOR]

Investigation of spatial susceptibility of debris flow is a basis for carrying out geological hazard prevention and developing ecological restoration plans. It is difficult to efficiently and accurately identify potential debris flow gullies on a large spatial scale simply by relying on field surveys combined with remote sensing observations or debris flow simulations with small watersheds as units. Taking the Jinsha River Basin of China as an example, we propose a quantitative scheme to describe the intensity of extrinsic forces by calculating the stream power gradient (ω). We extracted gullies prone to debris flow, assuming that there is no spatial heterogeneity in the provenance supply conditions based on the fundamental understanding that debris flow is a high-energy gravity flow. In the situation where the threshold (ω=1×10−4 W/m²) is the mutational site of the gradient change trend of the relation curve between the number of debris flow gullies and ω value, a total of about 32 thousand debris flow gullies with lengths of more than 200 m were found. In the middle and lower reaches of the basin, these gullies are located within a 30-kilometer buffer zone along the Jinsha and Yalong Rivers, and there is a power function relationship between the number of debris flow gullies and the width of a buffer zone. However, extreme weather events are likely to increase in the future under global warming, and these areas should be the critical prevention areas of debris flow disasters, especially the cascade reservoir area. The results of this study provide a lattice data set of spatial locations of the gullies prone to debris flow and the stream power gradients in the Jinsha River basin, which can be used to retrieve the exact location of the high-energy gullies and can also be used as the basic data for the study of related geological hazards and surface processes in general.

Bedload transport is highly variable, and we address the issue of what value(s) of the transport rate a formula is expected to predict by incorporating two metrics of variance in an elementary scale correlation between the transport rate and stream power. The first captures uncertainty in the empirical relation we develop to describe the efficiency of the bedload transport process, and the second acknowledges that different patterns of transport are experienced under similar hydraulic conditions. Our simple, generalized expression explicitly applies to rivers in which there is always a high availability of mobile sediment on the bed, and we demonstrate that it provides a realistic portrayal of the observed range of transport rates in rivers with a sporadically mobile gravel armour and a characteristic bedload size that is approximately the same as that of the substrate. Accepting that the transport rate is influenced by the nature of the material available at the bed surface which is, in turn, moderated by antecedent flows, we suggest that if effort in the field is required to apply our methodology it should be expended on characterizing the sizes available on the bed between floods, rather than observing active transport during individual events. [ABSTRACT FROM AUTHOR]

A variety of stream power‐based approaches for predicting catchment‐scale alluvial channel adjustment have been developed. There is an international interest in applying these to inform river catchment management. However, there is some uncertainty regarding their ability to make consistently accurate predictions. This study evaluates the performance of a range of stream power indices for predicting observed channel adjustment. Remotely sensed data were used to generate 33 different stream power indices every 50 m across the networks of five test catchments. The performances of the indices were evaluated by comparing them against observations of erosion and deposition‐dominated channels extracted from the UK's River Habitat Survey (RHS) database. A selection of metrics for evaluating the performance of the indices were calculated. The key finding from this study is that the stream power indices were poorly associated with the observations of alluvial channel adjustment. It is not clear whether this poor association is due to limitations with stream power indices or the suitability of the RHS observations. However, this is not the first study to find a weak association between stream power and observed adjustment. Therefore, caution is recommended to anyone hoping to take advantage of the practicability of stream power indices until further testing is applied using alternative observation datasets. An additional finding from this study is the inconsistency of outcomes between different measures of model performance. It is recommended that future studies also employ multiple model performance measures rather than relying on accuracy alone. [ABSTRACT FROM AUTHOR]

Neck cutoff is a sudden phenomenon that occurs during the evolution of meandering rivers, but its process and mechanism remain unclear. In this investigation, the neck-narrowing process before cutoff, the formation of a new river, and the appropriate conditions for cutoff under constant and variable discharges were studied using experimental methods in a laboratory flume. The results indicated that bank erosion upstream and downstream of the neck was the main factor that triggered cutoff, regardless of whether the discharge changed. The sinuosity of the model river was approximately 7, the ratio of the neck width to the average river width reached approximately 0.43, and the experimental material was nonuniform natural sand. Under the conditions that the unit width discharge ranged from 0.0039 to 0.0069 m2/s and the longitudinal gradient was 1‰, neck cutoff could occur after sufficient bank erosion. When neck cutoff was imminent, the sinuosity of the channel increased and the channel rotated downstream. After neck cutoff, the formation of a new river experienced three stages, namely, the short-term longitudinal scouring stage, the long-term horizontal widening stage, and the long-term transverse widening and normal slow development stage. The discharge resulting in neck scouring was the effective discharge contributing to the cutoff, and this discharge directly affected the cutoff time and position. We attempted to explain the factors leading to neck cutoff from an energy consumption perspective. Neck cutoff was a sudden phenomenon that occurred when the energy consumption of a meandering river increased to its maximum value upon entry to the recession stage from the relative equilibrium stage. To a certain extent, this study is significant in understanding river evolution and neck cutoff. [ABSTRACT FROM AUTHOR]

Study region: Eighteen main rivers in Taiwan. Study focus: The concept of total stream power (TSP) or specific stream power (SSP) has been investigated previously as an index for assessing the status of a river channel. Here, we introduce a new diagram called the “stream power loop” to review variations in fluvial conditions, morphology, and sediment transport potential from river source to estuary. Because of its physical basis, the loop diagram reflects fluvial morphology and watershed conditions. Additionally, we present a spiral diagram that depicts variations in the spatial gradients of TSP and SSP. The gradient implied the sediment transport trend, which from upstream to downstream changes gradually from scouring to siltation in ideal conditions. The loop and spiral diagrams provide an overview of the fluvial system. New hydrological insights for the region: The loop diagram applications in Taiwan categorized the rivers into three types: simple loop, maple-leaf loop, and complex loop. Diverse geology increases the likelihood of large tributaries and abrupt changes in terrain, both of which affect the components of stream power–discharge and slope. The scatter distribution of all the data aggregated from the 18 rivers showed a shrinking radius and a counter-clockwise spiral pathway, passing through the mountain river zone, the braided river zone, and finally to the straight & meandering river zone. The result supported the concept of stream power loop and indicated that stream power loop can interpret the status of the river systems.

Soil erosion and the consequent loss of nutrients have consistently been significant factors contributing to land degradation and nonpoint source pollution. While runoff serves as the primary carrier for nutrient loss, the hydraulic processes governing the mechanisms of nutrient loss remain not entirely clear. This paper aims to investigate the impacts of rainfall intensity and the slope gradient on hydraulic parameters, soil loss rates, and ammonia nitrogen loss rates, with the objective of determining the optimal hydraulic parameters for more accurate predictions of soil erosion and nutrient loss rates. A series of simulated rainfall experiments with three rainfall intensities (25, 50, and 75 mm min−1) and four slope gradients (8.7%, 17.6%, 26.8%, and 36.4%) were conducted on a 5 m × 10 m slope. The results indicated that the flow velocity, shear stress, stream power, unit stream power, and unit energy all increased with the increase in slope gradient or rainfall intensity. The water depth decreased with an increase in the slope gradient but increased with an increase in the rainfall intensity. Laminar flow occurred in all experiments (Reynolds number < 500). Only the overland flow under a 25 mm h−1 rainfall intensity and 8.7% slope gradient was subcritical flow (Froude number < 1). Hydraulic parameters, the soil loss rate, and ammonia nitrogen loss rate could be all expressed as the product of rainfall intensity and slope power function, with R2 ranging from 0.949 to 0.997. The average soil loss rate and process soil erosion rate could both be fitted using the power function of hydraulic parameters, with the optimal fitting parameter being stream power (R2 = 0.980 and 0.909). The average ammonia nitrogen loss rate exhibited a linear relationship with the hydraulic parameters, and the optimal fitting parameter was also stream power (R2 = 0.933). However, there were relatively low correlations between hydrodynamic parameters and the ammonia nitrogen loss rate (R2 = 0.450–0587). Our results contribute to a deeper understanding of the hydraulic processes involved in nutrient loss.

Lowland rivers across the world are characterized by accumulation of sediment due to a decrease in the channel slope. Despite the antiquity of the topography, the lowland part of the west‐flowing rivers of Western Ghat, India is characterized by poorly developed floodplains except for the southern part of the Ghat. This poses a question of the sediment transportation and deposition capacity in these lowland rivers, which in turn governs geomorphic characteristics. In this study, we adapted a novel method to integrate hydrological model‐derived discharge estimates, channel slope estimates from digital elevation models, bankfull channel width estimates from high‐resolution Google Earth satellite images and field observations. We modelled the downstream distribution of total stream power (Ω), specific stream power (ω) and shear stress (τb) for four west‐flowing river systems from different lithological and climatic settings. The 75th percentile discharge from monthly time series data was used in modelling to assess channel processes. The peak values of Ω are distributed all along the longitudinal profile, whereas the peak values of ω and τb are consistently higher in the escarpment. Scaling relationships between hydrogeomorphic parameters were also established to understand the inherent controls on the distribution of these driving parameters. We inferred that ω is sufficient to transport large grain sizes even in the low‐gradient lowland stretches. Hence sediments are mostly absent in the channel, and floodplains are not well developed. Despite having a low gradient, the lowland coastal rivers can efficiently evacuate most of the eroded sediments to the offshore region. Finally, the lithological control is manifested by the variability of channel width regulating the sediment transport in the coastal rivers of the Western Ghat. [ABSTRACT FROM AUTHOR]

In a river cross section or segment that has attained an equilibrium flow regime, the relationship between geometric (river depth, width, hydraulic radius, bed slope, etc.) and/or hydraulic (velocity, roughness, shear stress, etc.) factors in relation to the river's equilibrium discharge (i.e., flows of fixed nominal return period or at bankfull depth) is termed hydraulic geometry (HG). HG relations have been proposed from a multitude of approaches: empirical, statistical, physically based, and extremal. Furthermore, multiple extremal hypotheses exist, depending on the variable to be optimized (maximized or minimized). In this study, we (1) present a unified framework by invoking the principle of maximum entropy (or, equivalently, Laplace's law of insufficient reason), that is, assuming that individual contributions by geometric and hydraulic factors to HG through the optimization of extremal hypotheses (Froude number, frictional resistance, mobility index, stream power, sediment flux, etc.) presumably stem from equiprobable contributions of these factors—in other words, entropy is maximized; (2) enumerate 26 combinations (groups of sizes two to five) of the five basic HG variables, namely depth, width, slope, velocity, and friction, and analyze their interrelations; and (3) relax our initial equiprobability assumption by plugging in a scaling (weighting) parameter and show that 11 special cases of the 26 unique combinations lead to reasonable approximations of benchmark empirical results in the literature in at least one instance for each of the five extremal hypotheses considered here. The benefits of the unified framework include providing a theoretical basis to bring together various hypotheses that result in HG relations and providing an analytical way to quantify (or explain) epistemic uncertainty therein. Ultimately, this unified framework improves our understanding of HG and provides an analytical framework for improving predictions of river flows. [ABSTRACT FROM AUTHOR]

The variations in hydrodynamic parameters at different polysaccharides rates and the relationships between sheet erosion modulus and hydrodynamic parameters were analyzed to reveal the hydrodynamic mechanism of sheet erosion on loessial slopes. Artificially simulated rainfall experiments were carried out under three slope gradients (10°, 15°, and 20°), three rainfall intensities (1.0, 1.5, and 2.0 mm·min−1), and four dry-spreading rates of polysaccharides (0, 1, 3, and 5 g·m−2). The results showed that (1) four hydrodynamic parameters (flow velocity, shear stress, stream power, and unit stream power) all increased with both rainfall intensities and slope gradients at four rates of polysaccharides. (2) Polysaccharides could effectively reduce hydrodynamic parameters. In contrast to the bare slope, the average flow velocity, shear stress, stream power, and unit stream power diminished by 27.11~41.18%, 9.53~18.67%, 31.82~50.24%, and 27.11~41.18%, respectively. (3) Polysaccharides could effectively reduce the growth rate of the sheet erosion modulus with hydrodynamic parameters, and there were few differences among the different rates (1, 3, and 5 g·m−2). The increasing rates of the sheet erosion modulus with flow velocity, shear stress, stream power, and unit stream power were 14.0~65.7%, 14.8~33.9%, 7.8~23.7%, and 9.7~29.5%, respectively. (4) At different polysaccharides rates, the relationships between sheet erosion modulus and hydrodynamic parameters were all in logarithmic functions. Moreover, flow velocity (R2 ≥ 0.920) and stream power (R2 ≥ 0.876) were better hydrodynamic parameters than shear stress (R2 ≥ 0.598) or unit stream power (R2 ≥ 0.537). Polysaccharides decreased the hydrodynamic parameters and the response rates of sheet erosion to hydrodynamics. [ABSTRACT FROM AUTHOR]

Meandering rivers are among the most dynamic Earth-surface systems, which generally appear in fertile valleys, the most valuable lands for agriculture and human settlement. Landsat time series and morphological parameters are complementary tools for exploring river dynamics. Karun River is the most effluent and largest meandering river in Iran, which keeps the Karun's basin economy, agriculture, and industrial sections alive; hence, investigating morphological changes in this river is essential. The morphological characteristics of Karun have undergone considerable changes over time due to several tectonic, hydrological, hydraulic, and anthropogenic factors. This study has identified and analyzed morphological changes in Karun River using a time series of Landsat imagery from 1985–2015. On that basis, morphological dynamics, including the river's active channel width, meander's neck length, water flow length, sinuosity index, and Cornice central angle, were quantitatively investigated. Additionally, the correlation between the stream power and morphological factors was explored using the data adopted from the hydrometric stations. The results show that the dominant pattern of the Karun River, due to the sinuosity coefficient, is meandering, and the majority of the river falls in the category of developed meander rivers. Moreover, the number of arteries reduced in an anabranch pattern, and the river has been migrating towards the downstream and eastern sides since 1985. This phenomenon disposes a change in the future that can be hazardous to the croplands and demands specific considerations for catchment management. [ABSTRACT FROM AUTHOR]

Streambed aggradation and degradation are ways in which a stream will respond to changes in the incoming flow and sediment loads. Several environmental and societal problems are attributed to these channel bed adjustments. Prior studies have extensively used stream power to discern dominant channel processes and establish threshold limits required to trigger channel modifications. However, these studies were constrained by limited datasets and the scope of the applications. The current study used a large dataset of streambed median grain size (D50) across the contiguous U.S. in conjunction with a screening tool to assess the streambed stability for channel erosion and deposition potential. Analysis at the Physiographic Province level indicated major geomorphic changes are highly likely to occur in the Blue Ridge and Pacific Border provinces. Deposition-dominated streams are prominent in the Central Lowland, Great Plains, and Coastal Plain, whereas the Colorado Plateaus and Wyoming Basin have the highest percentage of stable channels. Smoothed spatial maps of stream power indicated the prevalence of high stream power in the Northeast and Pacific Northwest regions of the U.S. Comparison of channel erosion and deposition predictions using the stream power map with actual field calculated aggradation and degradation results yielded a 55% prediction accuracy. Further analysis based on the stream order revealed the association of higher stream power with lower stream orders. [ABSTRACT FROM AUTHOR]

In-channel storage of both fine sediment and sediment-bound phosphorus has been recognized as potentially large contributors to respective watershed loads, yet they are rarely quantified in the field. In this field-based study, we quantified and characterized in-channel fine sediment and total phosphorus (TP) storage within a third-order stream. We hypothesized storage to be significant within the context of watershed-scale sediment and TP loads and that storage trends are influenced by channel characteristics and hydraulics. In May 2015, the volume of stored in-channel sediment was estimated within a 13.5 km stretch of Walnut Creek, an alluvial stream draining an agriculturally dominated watershed in Jasper County, Iowa, USA. Storage volume was estimated in-field through a series of240 transects which were stratified across reaches of the varying channel and hydraulic conditions (e.g., sinuosity, stream power). Overall storage volume was broken down into feature classes (e.g., point bars) based on in-channel depositional processes. Following in-field quantification, feature class sediment samples were collected and analyzed for physical properties (e.g., bulk density) and TP concentration. Physical and chemical analyses, coupled with in-field volume estimation, allowed for watershed-scale masses of in-channel sediment and TP to be calculated and then placed within the context of respective annual loads. Sediment and TP were estimated to be stored at ~2.7 Mg m-1 and 0.7 kg m-1, respectively. Sinuous reaches exhibited significantly greater sediment storage volume (p < 0.001) and depth (p < 0.001) versus straight reaches. Reach sinuosity exhibited a significant positive correlation (p = 0.03) with storage mass and represented the most effective storage predictor. The majority of storage mass (72%) was represented by colluvial material accumulations at the streambank toe. Loose bed sediment was the second greatest contributor to storage mass (18%), with the remaining feature classes (e.g., bars) representing a combined ~10%. Sediment storage mass was ~3.25 times greater than the watershed suspended sediment load for 2015. The TP mass was found to be nearly equal to the respective watershed load for 2015. In-channel sediment and TP storage masses within Walnut Creek were found to be significant in comparison to respective annual loads, and thus storage is expected to play a significant role in respective watershed routing, loading, and the overall budgets of these parameters. Though challenging, quantification of in-channel fine sediment and TP storage is necessary to relate source contributions (e.g., stream- bank erosion) to watershed loads and is critical to account for interannual sediment and TP export. [ABSTRACT FROM AUTHOR]

In recent decades, the number of rainfall-induced landslides has increased significantly in many parts of Malaysia, especially in the urbanized and hilly areas. The disturbance of hilly morphology as a result of human activities has increased the potential for erosion on man-made slopes, especially during extreme rainfall during rain events. Most hilly areas in Malaysia are covered by a thick layer of soil, which is known to have a significant impact on soil erosion. However, little is known about how soil erosion and rainfall could be the driving force behind landslide initiation, especially on stabilized slopes. Therefore, this study focuses on the soil detachment rate of landslides triggered by rainfall at different rainfall intensities. A sandbox model is used to represent real slope conditions. The relationship between the soil detachment capacity, soil properties (water content, slope, clay layers and soil compaction), hydraulic parameters (flow shear stress and stream power) and rainfall intensities (low, medium and high) was investigated. The results showed that the hydraulic parameters and the rainfall intensity are directly proportional to the detachment rate of the soil. Water content and slope show a higher soil detachment rate and a lower critical flow shear stress than other soil properties. It can be concluded that high saturation and steep slope increase the risk of soil erosion because the cohesion and friction of the soil are significantly reduced, leading to a weakening of the soil structure at the surface. The results of this study can feed into the existing analysis of slope stability and formulate the onset of a landslide triggered by rainfall, especially in eroded soils.

The quantification of bedload sediment transport in rivers is possible from statistics of individual particle displacements. However, there is a lack of empirical basis for a universal relation between particle displacement distance and hydraulic drivers. Previous work suggests that a simple linear relation exists between the energy of a flood and the mean travel distance of bedload particles. Such a relation would be advantageous, but a consistent model able to collapse the data from different rivers has not been developed. Here, we develop a predictive relation from a unique data set collected in three watersheds from a single region but contrasting hydrologic regimes due to urbanization and storm water management. Additional data from two rivers from outside the region are used to validate the model. We show that the mean of an exponential distribution of surface particle travel displacements can be reliably predicted from either the cumulative discharge or stream power exceeding the mobilization threshold, which is calibrated using field data. The strength of the relation decreases after large flood events that appear to cause tracer burial due to vertical mixing. This result indicates that the relation is most applicable for the entrainment phase of transport in which tracers are dispersing over the bed surface. Tracer movements become more challenging to predict over a long series of events due to burial and eventual tracer slowdown, but the relation remains valid for the particles located on the bed surface, making it suitable for analyzing the impact of climate and landscape changes over time. Plain Language Summary: Coarse (bedload) sediment transport models are notoriously challenging to build because of how many different factors affect the movement of individual grains in rivers. Many different models have been proposed that relate the strength of the flow to the distance sediment grains travel in a particular river. However, a universal model that applies across all rivers has not been built. We propose that a large portion of the variation between models is due to inconsistency in how flow strength and grain movements are measured and calculated between studies. Following a consistent methodology that aims to minimize many of the complexities of bedload transport, we developed a model between the flow energy in a flood and the distance coarse grains travel that applies to three rivers with very different hydrologic settings. We use data from two additional rivers in different parts of the world to further demonstrate the success of the model. The universality of this model makes it ideal for analyzing the impact of climate change and land‐use change on sediment transport. The results provide some evidence of a universal relation between flow and sediment transport and call for a more thoughtful and consistent methodological approach between studies. Key Points: Mean tracer travel lengths normalized by the channel width can be modeled as a linear function of the cumulative excess stream powerA consistent tracer data set analysis methodology allows for a collapse of the model between rivers with different hydrologic regimesTransition between entrainment and diffusion bedload transport regimes due to tracer burial is confirmed using a field data set [ABSTRACT FROM AUTHOR]

In near-field remote sensing, noncontact methods (radars) that measure stage and surface water velocity have the potential to supplement traditional bridge scour monitoring tools because they are safer to access and are less likely to be damaged compared with in-stream sensors. The objective of this study was to evaluate the use of radars for monitoring the hydraulic conditions that contribute to bridge–pier scour in gravel-bed channels. Measurements collected with a radar were also leveraged along with minimal field measurements to evaluate whether time-integrated stream power per unit area (Ω) was correlated with observed scour depth at a scour-critical bridge in Colorado. The results of this study showed that (1) there was close agreement between radar-based and U.S. Geological Survey streamgage-based measurements of stage and discharge, indicating that radars may be viable tools for monitoring flow conditions that lead to bridge pier scour; (2) Ω and pier scour depth were correlated, indicating that radar-derived Ω measurements may be used to estimate scour depth in real time and predict scour depth based on the measured trajectory of Ω. The approach presented in this study is intended to supplement, rather than replace, existing high-fidelity scour monitoring techniques and provide data quickly in information-poor areas. [ABSTRACT FROM AUTHOR]

Selective removal of particles and nutrients by water erosion is a key factor in soil erosion studies. Most agricultural soils are located on gentle slopes where fertility is high; however, until now, the main attention on sediment transport mechanisms was paid to high-slope gradients, where soil erosion is intense, but soils are less productive. Despite the importance of sediment size distribution (SSD) and transport mechanisms under unsteady-state conditions, few studies have been done on this issue. Higher sediment concentrations in the early stages of the runoff indicate the need to deal with unsteady-state conditions. To address this issue, sheet erosion experiments were done using a 0.2 m by 1 m tilting flume under controlled laboratory conditions. Six inflow rates (75, 100, 125, 150, 175, and 200 mL/s) were applied on two contrasting soils, including an adjacent agricultural soil and a not cultivated soil (namely Cropland soil and Control soil, respectively) at two low slope gradients (1.5% and 2%). No rill formation was observed during the experiments. The sediment-laden runoff was sampled during unsteady-state flow to determine the SSDs and sediment transport mechanisms of eroded particles for unsteady-state conditions. The results indicated different trends in the selective removal of sediment particles depending on hydraulic conditions and soil aggregate size. The contribution of suspension-saltation (SS) to the total sediment load for the Cropland and Control soils varied from 22% to 68% and from 35% to 59%, respectively, while up to 78% and 65% of soil particles were transported by bed load (BL), respectively. However, SS and BL indicated a reverse trend with stream power. The Cropland soil showed a single peak in the SSD at low stream powers because of the selective removal of fine particles (0.042 mm), whereas the SSD was shifted to a bimodal distribution at higher stream powers with the selective depletion of both fine (≤ 0.084 mm) and coarse (1.5 mm) particles. The Control soil experienced a unimodal SSD in a range of sizes between 0.109 and 0.175 mm for all stream powers. The findings of the current study highlight the need for further study on the erosion of low-slope agricultural soils, where small stream powers can remove fine and fertile soil particles. [ABSTRACT FROM AUTHOR]

The fragment of an ancient document dating back about a thousand years reveals, probably for the first time, the use of the term "bridle" (= reins to direct the horse) in the field of river hydraulics. The discovery seems to confirm what we ourselves demonstrated a few years ago in the pages of this journal, namely that the analogy between the stream and the horse finds its origin in the geographical enclave where the tradition and culture of ancient Greece are best preserved, as in Aspromonte. To confirm this, the use of the word λουρίον (meaning leather strip, as are the reins used to control the horse's strength) to indicate the presence of a river control work appears particularly relevant. This attests to how the animal and natural association, horse and stream precisely, was established as a relic of archaic Greek literature. [ABSTRACT FROM AUTHOR]

The sinuosity of alluvial meandering rivers gives insight of variations in channel morphology and point bar scale. However, it is currently unclear if a quantitative relationship exists between the sinuosity and various channel characters such as the channel width, valley slope, discharge, and sediment grain size. In this work, an empirical approach was used to study the sinuosity variation for alluvial meandering rivers with scroll bars. The empirical dataset of the present study includes a literature survey and ten new alluvial meandering rivers with scroll bars. The average sinuosity of the study rivers was re-measured using the centerline digitized from a series of satellite imageries. The results indicate that the average sinuosity of rivers with scroll bars changes according to the equation below, in a form related to the potential specific stream power: P = 1.22 ω 0.09 where P is sinuosity and ω is potential specific stream power. According to this empirical equation, the potential specific stream power has a positive relationship with the sinuosity for meandering rivers with scroll bars. Additionally, the grain size of the channel bed determines the maximum sinuosity, which can be expressed as: P max = 1.22 ∗ 900 10 D 50 0.42 0.09 where Pmax is the maximum sinuosity and D50 is median grain size. We suggest that if the stream power keeps increasing when the sinuosity reaches the maximum limit, chute channels and chute bars will develop. [ABSTRACT FROM AUTHOR]

Neck cutoff is a sudden phenomenon that occurs during the evolution of meandering rivers, but its process and mechanism remain unclear. In this investigation, the neck-narrowing process before cutoff, the formation of a new river, and the appropriate conditions for cutoff under constant and variable discharges were studied using experimental methods in a laboratory flume. The results indicated that bank erosion upstream and downstream of the neck was the main factor that triggered cutoff, regardless of whether the discharge changed. The sinuosity of the model river was approximately 7, the ratio of the neck width to the average river width reached approximately 0.43, and the experimental material was nonuniform natural sand. Under the conditions that the unit width discharge ranged from 0.0039 to 0.0069 m2/s and the longitudinal gradient was 1‰, neck cutoff could occur after sufficient bank erosion. When neck cutoff was imminent, the sinuosity of the channel increased and the channel rotated downstream. After neck cutoff, the formation of a new river experienced three stages, namely, the short-term longitudinal scouring stage, the long-term horizontal widening stage, and the long-term transverse widening and normal slow development stage. The discharge resulting in neck scouring was the effective discharge contributing to the cutoff, and this discharge directly affected the cutoff time and position. We attempted to explain the factors leading to neck cutoff from an energy consumption perspective. Neck cutoff was a sudden phenomenon that occurred when the energy consumption of a meandering river increased to its maximum value upon entry to the recession stage from the relative equilibrium stage. To a certain extent, this study is significant in understanding river evolution and neck cutoff.

The advent of 2D hydraulic modelling has improved our understanding of flood hydraulics, thresholds, and dynamic effects on floodplain geomorphology and riparian vegetation at the morphological-unit scale. Hydraulic concepts of bed shear stress, stream power maxima, and energy (cumulative stream power) have been used to characterize floods and define their geomorphic effectiveness. These hydraulic concepts were developed in the context of reach-averaged, 1D hydraulic analyses, but their application to 2D model results is problematic due to differences in the treatment of energy losses in 1D and 2D analyses. Here we present methods for estimating total and boundary resistance from 2D modelling of an extreme flood on a subtropical river. Hydraulic model results are correlated with observations of the flood impacts on floodplain geomorphology and the riparian vegetation to identify thresholds and compute variants of flood energy. Comparison of LiDAR data in 2011 and 2014 shows that the 2011 flood produced 2-4 m of erosion on floodplain bars that were previously forested or grass-covered. Deposition on flood levees, dunes, and chute bars was up to 3.4 m thick. Various hydraulic metrics were trialled as candidates for thresholds of vegetation disturbance. The accuracy of thresholds using metrics extracted at the flood peak (i.e. boundary resistance and stream power maxima) was similar to that using energy as a threshold. Disturbance to forest and grass on vegetated bars was associated with stream powers of >834 W/m2 and unit flows of >26 m2/s, respectively. Correlation of the hydraulic metrics with erosion and deposition depths showed no substantial improvement in using flood energy compared to metrics extracted at the flood peak for describing erosion and deposition. The extent of vegetation disturbances and morphological adjustments was limited for this extreme flood, and further 2D studies are needed to compare disturbance thresholds across different environments. [ABSTRACT FROM AUTHOR]

Streambed aggradation and degradation are ways in which a stream will respond to changes in the incoming flow and sediment loads. Several environmental and societal problems are attributed to these channel bed adjustments. Prior studies have extensively used stream power to discern dominant channel processes and establish threshold limits required to trigger channel modifications. However, these studies were constrained by limited datasets and the scope of the applications. The current study used a large dataset of streambed median grain size (D50) across the contiguous U.S. in conjunction with a screening tool to assess the streambed stability for channel erosion and deposition potential. Analysis at the Physiographic Province level indicated major geomorphic changes are highly likely to occur in the Blue Ridge and Pacific Border provinces. Deposition-dominated streams are prominent in the Central Lowland, Great Plains, and Coastal Plain, whereas the Colorado Plateaus and Wyoming Basin have the highest percentage of stable channels. Smoothed spatial maps of stream power indicated the prevalence of high stream power in the Northeast and Pacific Northwest regions of the U.S. Comparison of channel erosion and deposition predictions using the stream power map with actual field calculated aggradation and degradation results yielded a 55% prediction accuracy. Further analysis based on the stream order revealed the association of higher stream power with lower stream orders.

Meandering rivers are among the most dynamic Earth-surface systems, which generally appear in fertile valleys, the most valuable lands for agriculture and human settlement. Landsat time series and morphological parameters are complementary tools for exploring river dynamics. Karun River is the most effluent and largest meandering river in Iran, which keeps the Karun’s basin economy, agriculture, and industrial sections alive; hence, investigating morphological changes in this river is essential. The morphological characteristics of Karun have undergone considerable changes over time due to several tectonic, hydrological, hydraulic, and anthropogenic factors. This study has identified and analyzed morphological changes in Karun River using a time series of Landsat imagery from 1985–2015. On that basis, morphological dynamics, including the river’s active channel width, meander’s neck length, water flow length, sinuosity index, and Cornice central angle, were quantitatively investigated. Additionally, the correlation between the stream power and morphological factors was explored using the data adopted from the hydrometric stations. The results show that the dominant pattern of the Karun River, due to the sinuosity coefficient, is meandering, and the majority of the river falls in the category of developed meander rivers. Moreover, the number of arteries reduced in an anabranch pattern, and the river has been migrating towards the downstream and eastern sides since 1985. This phenomenon disposes a change in the future that can be hazardous to the croplands and demands specific considerations for catchment management.

Sediment selectivity during transport may provide basic information for evaluating on-site and off-site impacts of the soil erosion. Limited information is, however, available on the selectivity of sediments in rill erosion, particularly in the rainfed furrows. Toward this, the sediment selectivity was investigated in three soil textures (loam, loamy sand sand clay loam) under 10% slope using 90 mm.h-1 rainfall intensity for 40 min. Soil samples were passed from a 10 mm sieve and packed in to the erosion flume with 0.4m × 4 m in dimensions. Particles size distribution (PSD) was determined in the sediments (PSDs) and compared with the original soil PSD (PSDo). The proportion of PSDs and PSDo was stated as PSDs/PSDo to show the selectivity of soil particles by rill erosion. Based on the results, all three soils appeared as the coarse particles (coarse sand and very coarse sand) in sediments with the PSDs/PSDo>1, indicating the higher selectivity of these particles by rill erosion. Loamy sand was the most susceptible soil to rill erosion among the studied soils, which generated a higher runoff (0.0035 m2.s-1) and sediment load (0.1 kg.m-1.s-1) during rainfall. The PSDs of this soil were similar to those of the original soil PSD. This study revealed that the stability of aggregates could be regarded as the major soil factor controlling rill erosion rate and the sediment selectivity in the semi-arid soils. With an increase in the water-stable aggregates, soil infiltration rate and as a consequence, shear stress of flow could be decreased in the rills.

Landscape evolution models that invert topography for rock uplift can improve our understanding of both tectonic and geomorphic processes when properly constrained with data. Here we present a flexible, data‐driven Bayesian approach to invert fluvial topography for tectonic and geomorphic model parameters and apply it to a case study, the uplifting footwall of the Corinth Rift, Greece. We invert transient river profiles and up‐flexed marine terraces to resolve seven unknown parameters in a regional‐to‐flexural uplift tectonic model and the stream power incision model. The best‐fit tectonic parameters are consistent with independent data and predict block uplift rates of ∼0.1 mm yr−1 that changed to flexural uplift rates of ∼1.6 mm yr−1 at ∼0.6 Ma, as the master normal fault initiated. Similarly, the best‐fit geomorphic parameters predict sediment flux consistent with the offshore record and erodibility consistent with previous studies. However, the drainage area exponent, m, of ∼2, and slope exponent, n, of ∼7, are unusually high, indicating a threshold channel steepness where fluvial topography is largely insensitive to rock uplift rate >0.05 mm yr−1. Analysis indicates channels narrow to accommodate enhanced uplift rates, but channel narrowing only partially explains our results, suggesting that other processes not accounted for in the generic stream power model are also relevant to bedrock river incision in Corinth. Our results help clarify the tectonic and geomorphic evolution of the Corinth Rift, have important implications for studies that invert topography for rock uplift histories, and provide insight into potential limitations of some long‐term river incision models. Plain Language Summary: Landscapes are influenced by many factors, including climate, land motion, and the strength of rocks. To understand and reproduce the evolution of landscapes, scientists use numerical models to approximate the physics that shape topography. Armed with these mathematical techniques, it is, in principle, possible to "unwind" the current landscape to understand the history of past events and processes that shaped it. In this work, we present models that use data from rivers and uplifted fossil beaches to understand the history of vertical land movement and the physical processes that gave rise to a well‐known site in the north of the Peloponnese, Greece. Our results provide specific insight into the study area and, more generally, have important implications for the processes that erode and transport sediment from continental settings. Our models are flexible and can include other types of data that may be important in other sites. Our findings highlight several key questions that merit further research to understand the processes that control the long‐term evolution of continental landscapes. Key Points: We present a new Bayesian approach to simultaneously invert river profiles and marine terraces for tectonic and geomorphic model parametersThis approach is applied to the Corinth Rift and offers new insights into the rift's recent (< 1 Myr) tectonic and geomorphic historyThe tectonic parameters are consistent with existing studies, and the geomorphic parameters suggest a threshold channel steepness index [ABSTRACT FROM AUTHOR]

In near-field remote sensing, noncontact methods (radars) that measure stage and surface water velocity have the potential to supplement traditional bridge scour monitoring tools because they are safer to access and are less likely to be damaged compared with in-stream sensors. The objective of this study was to evaluate the use of radars for monitoring the hydraulic conditions that contribute to bridge–pier scour in gravel-bed channels. Measurements collected with a radar were also leveraged along with minimal field measurements to evaluate whether time-integrated stream power per unit area (Ω) was correlated with observed scour depth at a scour-critical bridge in Colorado. The results of this study showed that (1) there was close agreement between radar-based and U.S. Geological Survey streamgage-based measurements of stage and discharge, indicating that radars may be viable tools for monitoring flow conditions that lead to bridge pier scour; (2) Ω and pier scour depth were correlated, indicating that radar-derived Ω measurements may be used to estimate scour depth in real time and predict scour depth based on the measured trajectory of Ω. The approach presented in this study is intended to supplement, rather than replace, existing high-fidelity scour monitoring techniques and provide data quickly in information-poor areas.

In order to determine erosion- limited conditions and the suitability of hydraulic parameters in sheet erosion of loess gentle slope, simulated rainfall test was used in this study, under condition of 60 mm/ h rainfall intensity, 3 slopes (7. 5°, 10°, 15°) and 2 slope lengths (5 m and 10 m), to verify the feasibility of sediment concentration as a characterization parameter to determine the erosion-limited conditions in the process of sheet erosion, and to propose an evaluation method to test the suitability of the relationship between hydraulic parameters and sediment yield. The test results showed that sheet erosion process could be divided into three erosion stages; transport-limited stage, de tachment-limited stage I and detachment- limited stage II according to the change of sediment concentration with run off, and the amount of erosion in detachment-limited stage I was dominant absolutely. For the suitability of hydraulic parameters, both stream power and Reynolds number could well characterize the relationship with sediment yield, while flow shear stress and Froude number could not effectively reflect the relationship with sediment yield. In differ ent erosion- limited stages, steam power and Reynolds number have different relationship with sediment yield. In the transport-limited stage and detachment-limited stage II, steam power and Reynolds number showed exponential and linear positive correlation with sediment yield, respectively. In the detachment-limited stage I, stream power and Reynolds number had a linear negative correlation with sediment yield, but the interaction was not unique, with dif ferent slope length and Reynolds number critical value. That is, in the transport-limited stage and detachment-limited stage II, the relationship between stream power, the Reynolds number and the sediment yield was not affected by the effect of slope length; in the detachment-limited stage I, the joint influence of slope length and the critical value of Reynolds number should be considered simultaneously. The results of this study can provide valuable information for a better understand of the complexity of sheet erosion process. [ABSTRACT FROM AUTHOR]

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This study has hypothesized that for many rivers the trade‐off between flow accumulation and the decrease in slope along channel length means that stream power increases downstream and, moreover, that given the low slope angles in headwater and low‐order streams, they would have insufficient stream power to erode let alone transport sediment. The study considered the stream power profile, the particle travel distances and the application of the Hjulström curve based on the velocity profile of nine, large UK catchments. The study showed that: Some rivers never showed a maximum in their longitudinal stream power profile, implying that some rivers never develop a deposition zone before they discharge at the tidal limit.Particle travel distances during a bankfull discharge event showed that for some rivers 91% of the upper main channel would not be cleared of sediment. Furthermore, while some rivers could transport a 2 mm particle their entire length in one bankfull event, for another river it would take 89 such events.The Hjulström curve shows that for three of the study rivers the upper 20 km of the river was not capable of eroding a 2 μm particle.The study has shown that for all rivers studied, erosion is focused downstream and deposition upstream. Many UK rivers have a dead zone where, on time scales of the order of centuries, no erosion or transport occurs and erosion only occurs in the lower courses of the channel where discharge rather than slope dominates – we propose these as underpowered rivers. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd [ABSTRACT FROM AUTHOR]

Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s-1 to 0.0456 m3 s-1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.

Purpose: The degree of the river channel change, and particularly the amount of transported sediment, defines the geomorphic effectiveness of a flood event. This study aims to improve the level of understanding of the control exerted by the streamflow and the flow energy on the sediment flux regimes during flood events, which are ranked depending on their geomorphic effectiveness. Materials and methods: The study focused on the Trotuș River, Eastern Carpathians, Romania. Two data sources were used: gauging stations (discharge and suspended sediment load) and field observations (grain size, channel bed slope and channel width corresponding to bankfull discharge). The bedload sediment transport was estimated using the Bedload Assessment for Gravel-bed Streams (BAGS) program. The parameters and variables taken into consideration (magnitude, duration, stream power, total energy expenditure, total sediment load) were statistically analysed for each flood event. Results and discussion: Just 15% of the total 76 investigated flood events ranked in the class which includes the flood events with the highest geomorphic effectiveness. Of the 41 × 106 t of sediment carried through the four gauging stations during flood events, approximately 74% was transported at stream power values above 300 W m−2. In the years with type B flood events, the sediment flux was much higher than the multiannual average value. Changes of the sediment rating curves were documented at all gauging stations subsequent to major flood events. Clockwise loops accounted for the highest percentages in all types of flood events. Major flood events generate significant changes in river channels, which are subsequently reflected in the sediment regime. Conclusions: The main cause of the changes occurring in the sediment regime likely lies in the channel adjustments subsequent to flood events. This investigation introduces a methodology for ranking flood events depending on their magnitude, duration, stream power and transported sediment. [ABSTRACT FROM AUTHOR]

The 2010 dam breach and consequent anomalous flood event on the Cedar River in Nebraska, USA provided an opportunity to study the following objectives: (1) evaluate the impact of an extreme flood event on streambank retreat along a 45 km stretch relative to the average annual retreat; (2) quantify the changes in streambank retreat for each km segment downstream of the breach; and (3) examine the influence of riparian vegetation and radius of curvature on meander bank erosion rate. During the hydrologic event, discharge peaked at nearly three times greater than the next highest recorded rate and equated to a return period of 2,000 years. Aerial images and ArcGIS were utilized to calculate the average annual streambank retreat for each year during the preflood (2006–2010), flood (2010), and postflood (2010–2016) periods. The 2010 flood period had a significantly higher average annual streambank retreat of 2,820 m2/km/yr than the preflood and postflood periods, which, respectively, measured 576 and 384 m2/km/yr. From 2006 to 2016, 29% of all streambank erosion was from this one extreme flood event, thus demonstrating the impact that one extreme flood event can have on streambank retreat and the geomorphology of a stream system. Research Impact Statement: From 2006 to 2016, 29% of all Cedar River streambank erosion was from one extreme flood event, demonstrating the impact one such event can have on streambank retreat and geomorphology of a stream system. [ABSTRACT FROM AUTHOR]

Understanding the evolution of the fluvial geomorphology in an orogenic belt provides valuable insight into the relationship between upper crustal deformation and surface processes. The upper Lancang-Mekong River is in an area experiencing both uplift and erosion. The related processes provide a steady sediment supply to the lower reaches of the river and play an important role in the regional environmental changes. The Xiaohei (Weiyuan) River Basin is an important sub-basin in this area, which is characterized by large-scale topographic fluctuations, active tectonics and erosion, and anthropogenic activities. These different factors introduce numerous complexities to the local surface processes. In this study, we investigate and quantify the controls of geomorphic evolution of the Xiaohei River Basin. We located and mapped the main knick-zones within the channels and examined the main genetic factors, such as faults and stratigraphic differences. The results show that the areas with the lowest uplift rates are characterized by a low steepness index and are located in the southeastern part of the basin. The stream power of the mainstream increases downstream, with an average value of ~122 W/m. The erosional activity of the various stream channels is intense. Overall, the basin tends to expansion, with only local instances of inward contraction. Our analysis confirms that a number of the geomorphic evolutionary characteristics of the Xiaohei River Basin are transient. In addition, the future potential for the increasing the number of dams and the hydropower development in the basin may weaken the expansion trend of the basin over a long period of time. [ABSTRACT FROM AUTHOR]

The construction of dams significantly alters flow and sediment regimes with subsequent deleterious effects on the morphological and ecological character of rivers. Effective experimental floods can ameliorate the downstream geomorphic impacts of dams. The traditional view is that large floods are required to perform effective geomorphic work, and the geomorphic outcomes of small floods are often overlooked. Many river restoration frameworks do not consider small floods. Yet, there is evidence that the hydrological characteristics that ameliorate specific geomorphic impacts in a river are unique to each river, and a customised approach to setting the right mix of floods (including small experimental floods) is needed. In this study, we modify an existing flood effectiveness model developed for large floods, for determining the geomorphic effectiveness of small floods in a highly regulated Australian river. Two flood classes were added to the model (medium peak stream power and moderate total energy expenditure), and the flood power characteristics were rescaled to reflect the relative difference in the magnitude of the small floods and the magnitude of the geomorphic work performed. Using a step‐wise approach, this customised model determined the geomorphic effectiveness of small floods. The best flood for ameliorating the geomorphic impacts of flow regulation had medium to long duration (10 to 51 days), high peak unit stream power (77 to 123 Wm−2) and moderate to large total energy expenditure (78,600 to 342,320 × 103 J). This approach to determining flood effectiveness for small floods is applicable to other geomorphically impacted river channels downstream of dams and can be used to inform experimental flood releases for geomorphic outcomes. [ABSTRACT FROM AUTHOR]

On 2 September 2018, an intense rainstorm swept Mengdong Town in Yunnan Province of China, inducing a serious landslide and debris flow disaster with 10 deaths and 11 missing. Image interpretation, field survey, and slope stability analysis were used to examine the characteristics and initiation mechanism of this hazard. A total of 1774 landslide scars were identified, the area of which occupied 8.26% of the study region. Due to the spatial inhomogeneity of precipitation, these scars mainly concentrated along valleys in the lower part of the study area. Besides, well-forested hillslopes were more prone to landslides, indicating the limited role of trees in stabilizing slopes in extreme rainfall events. The initiation of landslides is mainly attributed to the week cohesion of the saturated clayey sand beneath the root zone, where the tensile resistance of roots was absent, and the increase of positive pore water pressure. Additionally, 288 landslide scars were situated adjacent to roads, demonstrating that the road construction activity had intensified the landslide disaster. Owing to the relatively low mobility of landslides, a considerable portion of landslide debris deposited on the valley floor in smaller watersheds (< 6.03 hm2), while the remaining portion entered high-order channels. In these channels, where stream power was relatively large, the woody debris and soil carried by landslides were entrained by streamflow, and debris flows were formed. Moreover, the magnitude of debris flow was amplified by the vertical and lateral erosion of the stream channel. [ABSTRACT FROM AUTHOR]

Few studies have been done regarding the role of the raindrop in the hydrodinamic mechanism of soil erosion. In this study, rainfall simulation experiments were conducted to evaluate the role of raindrop in runoff discharge, sediment concentration and hydraulic properties of flow under four slope gradients (5, 10, 15 and 20%) in a clay soil using a 90 mm.h-1 rainfall intensity to reach the steady state flow. Soil sample was packed into the erosion flume with 0.3m× 0.4m × 4 m in dimensions and tested under two soil surface conditions: one with raindrop impact and one without raindrop impact. The results showed that runoff discharge, sediment concentration, flow depth, shear stress, stream power, Reynolds number and runoff velocity under without raindrop impact condition were significantly lower than those in the condition with the raindrop impact with a factor of 0.62 to 3.54, 0.08 to 11.83, 0.91 to 0.96, 0.26 to 3.25, 0.52 to 4.45, and 0.36 to 3.27, 0.23 to 0.79 times, respectively; on the other hand, the Darcy Wysbach, Chezy and Manning coefficients were increased significantly under without raindrop impact (P<0.01). Flow velocity was the key hydraulic parameter strongly affecting the hydraulic properties. These findings indicated the importance of raindrop impact in the detachment rate of soil particles through the change of the hydraulic characteristics. This study also revealed the key role of raindrop impact on the runoff hydraulic characteristics, as well as particle detachments rate in rills. Information about the role of raindrop impact is a substantial step in modeling the rill erosion. Therefore, elimination of raindrops impact, especially in the steep slopes, with the conservation of natural vegetation cover can sufficiently prevent runoff production as well as the particle detachment rate. [ABSTRACT FROM AUTHOR]

Water flow direction and velocity affect and controls erosion, transport and deposition of sediment in rivers, reservoirs and different hydraulic structures. One of the main structures affected is pumping stations within the dams wherein the velocity distribution near the station intake is disturbed. The two‐dimensional (2‐D) HEC‐RAS 5.01 model was utilized to study, analyse and evaluate the effects of pumping rates and flow depth on the flow velocity distribution, flow stream power and their effects in the Mosul Dam reservoir. The pumping station was considered as a case study. The station is suffering from sediment accumulation around, and in, its intake and suction pipes. The main inflow sources to the reservoir are the Tigris River and run‐off from the valleys within its basin. The reservoir was divided into two parts for the present study, including the upper part near the pumping station (analysed as a two‐dimensional zone), while the lower part was analysed as a one‐dimensional flow to reduce the simulation period computation time (1986–2011). Different operation plans (i.e. pumping rate and water depth) were considered. The results of the depth‐averaged velocity model indicated that when the pumping station was working at a range from the designed full capacity (100% to 25% of its full capacity), the maximum flow velocity increased from 75 to 4 times the normal velocity when there is no pumping dependent on pumping rate and flow depth. For the same operation plans, the flow stream power varied from around zero values to 400 times at full pumping capacity and low flow depth. For sediment routing along the reservoir, the considered statistical criteria indicated the model performance in estimating the total sediment load deposition and invert bed level is much better than in the case of erosion and deposition areas for different considered bed sections of the reservoir. [ABSTRACT FROM AUTHOR]