Showing papers on "Stream power published in 2021"

Predicting river channel pattern based on stream power, bed material and bank strength:

Abstract: Rivers exhibit a wide variety of channel patterns, and predicting changes in channel pattern is important in order to foresee river responses to climate change and river restoration. Many discrimin...

Response of soil detachment capacity to landscape positions in hilly and gully regions of the Loess Plateau

Abstract: Landscape position may impact soil detachment capacity (Dc) by overland flow through the imposing influences on soil properties and plant roots. Nonetheless, little knowledge existed with regard to the response of Dc to landscape position. Therefore, this study was conducted to detect the response of Dc to landscape positions and identify the primary influencing factors in hilly and gully regions of the Loess Plateau. 540 undisturbed soil samples taken from six landscape positions were subjected to scour in a hydraulic flume to determine Dc. The results demonstrated that Dc of the top ridge was the maximum (1.13 kg m−2 s−1), while Dc of the footslope was the minimum (0.0026 kg m−2 s−1). The landscape positions significantly influenced Dc, presenting a regularly decreasing trend from the top to the bottom. Dc increased with stream power (ω) by a power function. Power function was better than linear function for predicting of Dc. The partial least square regression analysis showed that soil organic matter, water stable aggregate (WSA), root mass density (RMD), and soil cohesion (Coh) dominated the variations in Dc. Significant negative relationships were detected between these primary factors and Dc. Landscape position affected Coh, WSA and RMD, which in turn controlled the regular change of Dc with landscape position. Dc of six landscape positions could be satisfactorily estimated by ω, WSA, and RMD (r2 = 0.81; NSE = 0.81). The results are helpful to understand the vertical changes in soil erosion intensity in small watershed scale.

Hydromorphological evaluation of the river training impact on a multi-thread river system (Belá River, Carpathians, Slovakia).

Abstract: The paper evaluates the impact of river training works designed to address problems associated with flooding on the braided-wandering Bela River in Slovakian Carpathians. This impact was investigated after the flood event in July 2018 on 11 river reaches where the river engineering and management intervention was applied. We analyzed its impact by spatio-temporal variations in river morphology (12 channel parameters) and changes in cross-section and hydraulic parameters (flow velocity, shear stress, stream power, W/D ratio) between pre- and post-flood management periods. The research hypotheses related to decreasing geodiversity in managed river reaches, a rapid increase in flow velocity during an extreme flood in river reaches where there is no sufficient floodplain inundation due to artificially high banks built by river training works, and increasing erosive force in the channel zone thanks to river management intervention were confirmed. The intervention in the braidplain area of the Bela River resulted in an undesirable simplification of the river pattern, loss of geomorphic diversity, loss of channel-floodplain connectivity, and disturbance and restraint of hydromorphological continuity. Identification of main conflicts of the Bela River management is important for clarifying the different approaches of stakeholders in the study area and aims to provide an objective illustration of their consequences. The presented analyses could help in future management issues as well as in the more critical decision-making process in vulnerable and rare braided river systems on the present when we are losing so many natural rivers by human decisions.

Geomorphic Analysis, Morphometric-based Prioritization and Tectonic Implications in Chite Lui River, Northeast India

Abstract: River morphometry is a useful approach in basin analysis which helps to interprets fluvially originated landforms. The aim of the present work is to evaluate the morphometric and morphotectonic parameters along with prioritization for soil erosion and water availability in Chite Lui watershed. Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) is a useful approach to find out soil erosion and ground water potential zone with an aim to achieve successful management of a watershed. It helps to examine the susceptibility zone in watershed. The present paper documents the delineation of 14 sub-watersheds in Chite Lui River at 3rd order stream. Its prioritization has been performed using several morphometric parameters namely drainage density, elongation ratio and many other parameters using Analytical Hierarchical Process (AHP). Sub-watersheds are ranked from 1–14 based on soil erosion and groundwater potential zones. The Chite Lui watershed is a fifth order drainage basin with a total area of 52.7 km2. The tectonic parameters of the watershed as the asymmetry value is 34%, indicates the structural control over the area either by uplift or tilting. The hypsometric integral value is 0.5 and the valley width height ratio is 0.05 which also suggest tectonic activity in the area. Sinuosity related many parameters along with geomorphic indices like stream power index (SPI), stream gradient index (SL) and topographic wetness index (TWI) were also calculated to suggest the watershed health. The present paper shows that the morphometric analysis is highly relevant and efficient in delineating susceptibility zones.

Hydrological, geomorphic and sedimentological responses of an alpine basin to a severe weather event (Vaia storm)

Abstract: To achieve a reliable analysis of the impacts induced in mountain basins by large and infrequent floods, all their main components, from the spatial-temporal distribution of meteorological agents to the hydrological, geomorphic and sedimentological response should be considered. Comprehensive study of the hydro-geomorphic responses is extremely valuable to increase the awareness of large floods, especially, in highly populated mountain areas. Such type of investigation requires a solid and wide dataset, which is why only few studies had the chance to describe the response in such a holistic way. This work comprehensively analyzed the high magnitude/low frequency Vaia event, a severe storm that affected northeastern Italy in October 2018 and thus the Rio Cordon study basin. The 80 h precipitation registered in the basin showed a total rainfall equal to 29.8% of the mean annual precipitation. The temporal distribution of rainfall presented two phases, i.e., a first characterized by moderate but persistent precipitation and a second more intense, exhibiting recurrence intervals over 50 years. A combination of indirect methods permitted the reconstruction of the hydraulic forcing acted in the Rio Cordon. Despite the implicit uncertainty, these methods clearly highlighted the high magnitude expressed by October 2018 flood, which generated a unit peak discharge equal to 3.3 m3 s−1 km−2 and a peak of unit stream power of 3865 W m−2, i.e., the highest hydraulic forcing conditions ever observed in 34 years. In terms of geomorphic changes, the use of pre- and post-event LiDAR data stressed out a moderate response of the hillslopes, where the (re)activation of the sediment sources was limited. Only few of these acted as sediment supplier to the main channel. The channel network instead, exhibited an evident response, with the Rio Cordon severely altered by wide lateral widening, deep streambed incision and armouring removal. The hydraulic and geomorphic forcing generated by October 2018 flood caused extensive streambed remobilization and boulder mobility that, in turn, induced the transport of a massive sediment volume. In this sense, the match between bedload observed and bedload predicted suggested the outstanding hydraulic forcing occurred and the quasi-unlimited supply conditions acted during the flood. The long-lasting monitoring program maintained in the Rio Cordon basin provided the rare opportunity to compare two high magnitude/low frequency floods and their induced effects. The September 1994 and October 2018 events were caused by different rainfall conditions, which resulted in different hydrological- and, especially, geomorphic- and sedimentological-responses. Particularly, the October 2018 flood induced an unprecedented alteration on the fluvial system, the effects of which could persist over the long-term.

Upscaling Sediment-Flux-Dependent Fluvial Bedrock Incision to Long Timescales

Abstract: Fluvial bedrock incision is driven by the impact of moving bedload particles. Mechanistic, sediment-flux-dependent incision models have been proposed, but the stream power incision model (SPIM) is ...

Exploring rainfall kinetic energy induced erosion behavior and sediment sorting for a coarse-textured granite derived soil of south China

Abstract: Screen covering is a widely used soil conservation practice to control water erosion in coarse-textured soil areas. A better understanding of the effects of screen covers at reducing rainfall kinetic energy (KE) on the erosion behavior will improve erosion prediction and control measures development. The objective of this study was to investigate and quantify the effects of rainfall KE on the soil loss and sediment sorting for developing a prediction model in a coarse-textured soil. A series of rainfall simulation experiments were conducted in three horizons of a coarse-textured soil under five rainfall KEs (628, 443, 324, 231, and 110 J m−2 h-1) which were obtained by covering the soil surface with wire screens of different apertures at a coincident intensity of 90 mm h-1. The results showed that the increase in rainfall KE increased runoff rate and soil erosion rate. The soil erosion rate also increased with depth of the soil layer exposed to the soil surface. Based on the soil clay content, a power relationship could describe the relationships between soil erosion rate and geometric mean diameter of sediment and stream power. With increasing rainfall KE and runoff duration, although the percentage of clay- and silt-sized particles in the sediment decreased, both were still higher than the content in the original soil. The enrichment of fine particles in runoff produced a coarsening layer on the slope surface, which might restrain the subsequent erosion in situ. The observed large preferential loss of clay- and silt-sized particles by erosion emphasizes the importance of sediment sorting for subsequent erosion in these coarse-textured soils. These results suggest that the relationship of rainfall KE to erosion should be considered for practical and effective estimation and prediction of the potential erosiveness of rainstorms.

An integrated approach for evaluating the flash flood risk and potential erosion using the hydrologic indices and morpho-tectonic parameters

Abstract: An arid climate and lacking adequate flood management systems are the main reasons for flash flood events in arid and semi-arid areas. The study area is a part of the Sinai Peninsula in Egypt, Wadi Gharandal subjected to several flooded events during the past decades. The present study incorporated hydrologic indices and morpho-tectonic parameters to identify the potential sediment accumulation and erosion. Integration of hydrologic indices, stream power index, sediment transport, and topographic wetness indices with morpho-tectonic parameters to produce and detect erosion and sedimentation associated with flash floods is the main objective. Consequently, the geographic information system (GIS) and the fuzzy k-means clustering algorithm were implemented for spatial data classification and management. The applied method revealed that the hydrologic and morphometric parameters play major roles in flash flood contributing factors. The low slope areas are associated with low run-off connected with a high sediment accumulation. Conversely, a high level of erosion is encountered in the steeper slope areas. Furthermore, terrain and lithology are decisive in sediment accumulation and erosion risk in the study area. The present study demonstrates the hydrologic and morpho-tectonic parameters with remote sensing data set are efficient tools in evaluating flash floods, potential erosion, and management, supporting the urban planner for future development.

How to Quantify the Dynamics of Single (Straight or Sinuous) and Multiple (Anabranching) Channels from Imagery for River Restoration

Abstract: Since the 2000s, European rivers have undergone restoration works to give them back a little more ‘freedom space’ and consolidate the hydro-sedimentary continuum and biological continuity as required by the Water Framework Directive (WFD). In high-energy rivers, suppression of lateral constraints (embankment removal) leads to geomorphological readjustments in the modification of both the active-channel length and active-channel width. The article provides a new methodological development to overcome the shortcomings of traditional methods (based on diachronic cross-section analysis) unable to simultaneously take into account these geometric adjustments after active-channel restoration. It allows us to follow and precisely quantify the geomorphological changes of the active channel faced to the stakes (i.e., structures or urbanized, recreation or agricultural areas) in the floodplain. The methodology proposes three new indicators (distance from active channel to stakes or floodplain margins as indicator 1; distance from stakes to active channel as indicator 2; diachronic distance as indicator 3) and a metric analysis grid in the 2D Euclidean space. It is applied to the Clamoux River (order 4, Strahler; bankfull, specific stream power: 280 W/m2) in the Aude watershed (Mediterranean France). The paper shows the full potential of this methodological protocol to be able to meet managers’ expectations as closely as possible within the framework of the multi-annual active-channel monitoring.

Geomorphic controls on the diversity and patterns of fluvial forms along longitudinal profiles

Abstract: A mix of catchment-scale controls operate to determine geomorphic river diversity in a catchment. These are contextualised here as imposed and flux controls. Imposed controls do not adjust over geomorphic timeframes and produce the environmental setting in which a river functions. Flux controls are dynamic interactions between flow and sediment that heavily influence geomorphic river diversity. We measure and statistically analyse the network scale mix of imposed and flux controls occurring along longitudinal profiles of various shape. We use this to explain the diversity, pattern and sequence of river types at different positions in a catchment. Using the Richmond River catchment, New South Wales, Australia, as our case study we analyse the imposed controls of slope and valley bottom width and the flux controls of bed material size and gross stream power for five river types, ranging from confined continuous rivers in headwaters to laterally unconfined discontinuous rivers in lowland plains. We find that slope and gross stream power are strong, positively correlated controls on all river types, but act most strongly on rivers with continuous channels. In contrast, bed material size is a dominant control on rivers with discontinuous channels. Slope and gross stream power are also critical for determining the downstream pattern of river types along longitudinal profiles. However, the relationship between these controls is complex as not all rivers are influenced by these controls in the same way. Understanding the mix and patterns of controls operating along longitudinal profiles can be used to explain the variability and pattern of river types we see in the landscape.

Stream power index for networks (SPIN) toolbox for decision support in urbanizing watersheds

Abstract: Urbanization typically leads to erosion and instability in rivers, and many management and restoration strategies have been developed to dampen the worst impacts. Stream power, defined as the rate of energy expenditure in a river, is a promising metric for analyzing cumulative effects. In this paper we describe a spatial decision support system called the Stream Power Index for Networks (SPIN) toolbox that can be used to assess urban river stability at a watershed scale. The objectives of the paper are to: a) describe the toolbox algorithms and procedures and b) demonstrate the utility of the approach. SPIN is written in Python and packaged as an ArcGIS toolbox. The toolbox combines existing landscape analysis algorithms with new algorithms to model river confluences, channel sinuosity, and threshold sediment particle sizes. Data can also be ingested from a standard hydraulic model. Two case studies demonstrate use of the toolbox to: i) anticipate current morphology; ii) predict urban morphologic change; and iii) analyze the benefits for stormwater management and channel restoration scenarios on channel stability.

Semi-automating the calculation of catchment scale geomorphic controls on river diversity using publically available datasets

Abstract: The global availability of Digital Elevation Models (DEMs) has enabled rapid, catchment scale geomorphic analysis of river systems. In this paper, we present a semi-automated GIS approach to quickly and accurately extract catchment scale geomorphic controls: slope, gross stream power and valley bottom width, and import bed material texture data along a drainage network. To enable rapid applicability of this approach, we provide the workflow for calculating elevation, slope, contributing catchment area and gross stream power embedded within ArcGIS toolkit, ArcGIS ModelBuilder and Python script as supplementary data . We also present an approach for disaggregating the drainage network and deciding the most appropriate reach length over which to calculate slope based on catchment topography. We demonstrate the importance of investigating DEM quality prior to use, strategic selection of the flow accumulation algorithm, and validation of the drainage network output using aerial imagery.

Changes in the hydrological regime and channel morphology as the effects of dams and bridges in the Barakar River, India

Abstract: The anthropogenic activities affect the river channel as well as the whole system in different magnitudes and dimensions. Barakar River, the main tributary to the Damodar River in eastern India, is modified by several engineering structures. Hydrological parameters, such as monthly discharge, peak flow discharge and geomorphological factors, such as gradient, width–depth ratio, grain size, braid–channel ratio, sinuosity ratio, riffle-pool sequence, and stream power are taken into consideration to highlight the significant alterations of the river due to dam and bridge construction. The alterations are assessed with the help of hydrological data, satellite images, and digital elevation data along with field survey. The downstream section of the dams, the river is characterised by high braiding, sinuous, total and unit stream power along with the presence of a box-shaped bedrock channel, high gradient, bed coarsening and armouring due to the release of high-velocity sediment-free ‘hungry water’. In the upstream reach, the grain size decreases towards the dam, and it increases suddenly with poor sorting at the immediate downstream regime of the dam. The effects of bridges on the Barakar river morphology include an increase of gradient, width and depth of the river channel at the downstream of the bridges. The construction of bridges influences riffle-pool sequences. Thereby, the pool depth spacing is greater than the riffle crest spacing. However, the integration of natural as well as human-induced factors can be the best approach to understand the anthropogenic alteration of the river. Moreover, construction of some check dams at the upper section of the tributaries of the Barakar River can be very effective for morphological stability.

Modeling glacial and fluvial landform evolution at large scales using a stream-power approach

Abstract: . Modeling glacial landform evolution is more challenging than modeling fluvial landform evolution. While several numerical models of large-scale fluvial erosion are available, there are only a few models of glacial erosion, and their application over long time spans requires a high numerical effort. In this paper, a simple formulation of glacial erosion which is similar to the fluvial stream-power model is presented. The model reproduces the occurrence of overdeepenings, hanging valleys, and steps at confluences at least qualitatively. Beyond this, it allows for a seamless coupling to fluvial erosion and sediment transport. The recently published direct numerical scheme for fluvial erosion and sediment transport can be applied to the entire domain, where the numerical effort is only moderately higher than for a purely fluvial system. Simulations over several million years on lattices of several million nodes can be performed on standard PCs. An open-source implementation is freely available as a part of the landform evolution model OpenLEM.

Small hydropower dam site suitability modelling in upper Benue river watershed, Nigeria

Abstract: Small hydropower (SHP) is one of the most critical renewable energy that is well adapted to the rural localities in less developed countries across the world. Most rural communities in Nigeria are off the national power grid and are bedevilled by an inconsistent supply of electricity. The one possible panacea to the rural energy crisis is harnessing the terrain and abundant rivers and streams within their domain. This study aimed to identify and select suitable sites for the SHP dam in the upper Benue river watershed. Ten thematic layers, land use, precipitation, geology, soil, slope, elevation, stream power index, topographic wetness index, drainage density, and flow, were integrated with Geographic information system and Analytical hierarchy process. A composite suitability map created revealed that 7.5% of the watershed is of a very high suitable class, while 17.5% of the watershed is of a very low suitable class. To select an ideal location, a semi-automatic approach was developed to identify narrow valleys by intersecting contour with stream order and the suitability layer. Eighteen (18) potential dam sites were identified after a query operation was done. The developed method was validated using field data which were correlated with the model output using t-Test; paired two samples for the mean. A strong Pearson correlation of 0.71 between the field data and the semi-automatic approach was observed. The approach offers good prospects for dam site selection. Based on a field survey, the potential dam sites are feasible economically and technically for SHP dam construction that will provide cheap renewable energy to millions of inhabitants in the watershed.

Uncertainty analysis of the HEC-RAS results in hydraulic simulation of Karoon River flow by Monte-Carlo approach

Abstract: Introduction The roughness parameter in hydraulic modelling of natural river and channel flows is not measurable easily and accurate point determination of roughness coefficient, its spatial and temporal variations includes several uncertainties that acts as the main source of error and uncertainties in hydraulic modeling. These drawbacks restricts the applicability of hydraulic modelling in river engineering projects, flood control and management, re-habitation and river restoration. Due to the uncertainties in rating curve, stage, top water width, stream power, shear stress, Froude number and velocity. Because of these drawbacks, in the current study uncertainty analysis by Monte-Carlo Simulation (MCS) combined with HEC-RAS model. Methodology In the current study uncertainty analysis, by Monte-Carlo Simulation (MCS) combined with HEC-RAS model is used to study a 105 km reach of Karoon River from Mollasani to Farsiat as shown in Fig. 1. The model is calibrated and verified using two year daily data of river flow and stage levels in Ahvaz station at the middle of the river reach. A computational control module is developed and combined with computational core of HEC-RAS to perform MCS automatically and the flowchart of modeling strategy and uncertainty analysis is presented in Fig.2. The MCS approach is coupled with computational core of HEC-RAS model by developing a subprogram that create and modifies the input files of HEC-RAS, run it automatically based on random samples of n Manning, and extracting the results of HEC-RAS model in each execution for further analysis in an automatic procedure. By using probability distribution of Manning roughness, 3000 simulations performed and graphical and quantitative indices used to evaluate the uncertainties of model results. In order to refine proper MCS from non-proper ones, the NSE>0.75 index is used to objectively sample n Manning from uncertainty analysis. The uncertainty analysis of proper MCS evaluated by 5 and 95% uncertainty bounds. The uncertainty analysis of model results are evaluated based on the six parameters of water surface elevation, top width of water, flow velocity, Froude number, stream power and shear stress in 3000 runs of peak flow and mean flow discharges respectively and quantified by two indices of 95PPU and d-factor. Results and Discussion The calibration and verification results of the HEC-RAS model in Figs 3-4 shows that in the calibration data set the R2 and RMSE of model in discharge are 0.94 and 21 (m3/s); and 093 and 0.6 (m) for water stage respectively. These values in the verification stage were 0.94 and 25.2(m3/s) for discharge; and 0.91 and 0.1(m) for water stage respectively. The results in 105 km length of Karoon River reveals high level of uncertainties with d-factor greater than 1 up to 11 in peak discharge of 3000 and mean daily discharge of 457 m3/s. These results revealed that using conditional evaluations based on NSE>0.75 reduced the uncertainty of d-factor in results of rating curve, stage, top water width, stream power, shear stress, Froude number and velocity. The d-factor of water stage reduced from 2 to 0.07 in peak discharge, and from 0.96 to 0.02 in average flows. These uncertainty reductions in top width of water were 2.5 to 0.19 in peak discharge and 1.3 to 0.078 in average flows of Karoon river. The highest uncertainty of HEC-RAS model results observed in water velocity and Froude number with di-factor 10.85 and 7.44 in peak discharge respectively. This trend of uncertainty reduction observed for water velocity, Froude number, stream power and shear stress along the river, as provided in Tables 1-3. The spectral responses of hydraulic parameters in model result that presented in Figs 5-10, indicate that although the HEC-RAS model produced high uncertainty values, especially in the complex domain of Karoon river, but these uncertainties dos not deviates the hydraulic patters of river flow in the study reach. The peak and maximum values and the zones of high vales of parameters, show high level of uncertainty than the small or moderate hydraulic situations. These indicates the inherent uncertainty in model results that causes high extents of spectral responses for model simulations. The provided findings necessitates the accurate determination of roughness coefficient according to its spatial and dynamic variations along the river reach. Conclusion The uncertainty results revealed high level of latent uncertainties in HEC-RAS model results and probabilistic analysis of models results is required for river re-habitation and management practices of large rivers such as Karoon River to provide certain and reliable results. The presented methodology and framer in the current study that uses automatic control and automation of HEC-RAS runs, strengths the modeling capability of one dimensional river flows for probabilistic analysis and automatic calibration of this mode.

Morphological controls on Hortonian surface runoff: An interpretation of steady-state energy patterns, maximum power states and dissipation regimes within a thermodynamic framework

Abstract: . Recent developments in hydrology have led to a new perspective on runoff processes, extending beyond the classical mass dynamics of water in a catchment. For instance, stream flow has been analysed in a thermodynamic framework, which allows the incorporation of two additional physical laws and enhances our understanding of catchments as open environmental systems. Related investigations suggested that energetic extremal principles might constrain hydrological processes, because the latter are associated with conversions and dissipation of free energy. Here we expand this thermodynamic perspective by exploring how hillslope structures at the macro- and microscale control the free energy balance of Hortonian overland flow. We put special emphasis on the transitions of surface runoff processes at the hillslope scale, as hillslopes energetically behave distinctly different in comparison to fluvial systems. To this end, we develop a general theory of surface runoff and of the related conversion of geopotential energy gradients into other forms of energy, particularly kinetic energy as the driver of erosion and sediment transport. We then use this framework at a macroscopic scale to analyse how combinations of typical hillslopes profiles and width distributions control the spatial patterns of steady-state stream power and energy dissipation along the flow path. At the microscale, we analyse flow concentration in rills and its influence on the distribution of energy and dissipation in space. Therefore, we develop a new numerical method for the Catflow model, which allows a dynamical separation of Hortonian surface runoff between a rill- and a sheet flow domain. We calibrated the new Catflow-Rill model to rainfall simulation experiments and observed overland flow in the Weiherbach catchment and found evidence that flow accumulation in rills serves as a means to redistribute energy gradients in space, therefore minimizing energy expenditure along the flow path, while also maximizing overall power of the system. Our results indicate that laminar sheet flow and turbulent rill flow on hillslopes develop to a dynamic equilibrium that corresponds to a maximum power state, and that the transition of flow from one domain into the other is marked by an energy maximum in space.

Bedrock river erosion through dipping layered rocks: quantifying erodibility through kinematic wave speed

Abstract: . Landscape morphology reflects drivers such as tectonics and climate but is also modulated by underlying rock properties. While geomorphologists may attempt to quantify the influence of rock strength through direct comparisons of landscape morphology and rock strength metrics, recent work has shown that the contact migration resulting from the presence of mixed lithologies may hinder such an approach. Indeed, this work counterintuitively suggests that channel slopes within weaker units can sometimes be higher than channel slopes within stronger units. Here, we expand upon previous work with 1-D stream power numerical models in which we have created a system for quantifying contact migration over time. Although previous studies have developed theories for bedrock rivers incising through layered stratigraphy, we can now scrutinize these theories with contact migration rates measured in our models. Our results show that previously developed theory is generally robust and that contact migration rates reflect the pattern of kinematic wave speed across the profile. Furthermore, we have developed and tested a new approach for estimating kinematic wave speeds. This approach utilizes channel steepness, a known base-level fall rate, and contact dips. Importantly, we demonstrate how this new approach can be combined with previous work to estimate erodibility values. We demonstrate this approach by accurately estimating the erodibility values used in our numerical models. After this demonstration, we use our approach to estimate erodibility values for a stream near Hanksville, UT. Because we show in our numerical models that one can estimate the erodibility of the unit with lower steepness, the erodibilities we estimate for this stream in Utah are likely representative of mudstone and/or siltstone. The methods we have developed can be applied to streams with temporally constant base-level fall, opening new avenues of research within the field of geomorphology.

Predicting the sediment transport capacity from flow condition and particle size in the presence of vegetation cover

Abstract: The sediment transport capacity plays a pivotal role in erosion research, and is usually predicted using hydraulic variables. The transport capacity and hydraulic variables are affected by vegetation cover. Our understanding of the effect of vegetation cover, including the size, density, and arrangement of vegetation stems, on the relationship between the sediment transport capacity and hydraulic variables were rather limited. The objectives of this study were to investigate the effect vegetation stem cover on the relationship between hydraulic variables and the sediment transport capacity and to derive an equation for predicting the sediment transport capacity in the presence of vegetation cover. Five data sets from 288 flume experiments with a wide range of discharge (0.25–2 × 10−3 m3 s−1), slope (8.8–42.3%), median sediment diameter (0.11–1.16 × 10−3 m), stem cover (0–30%), stem diameter (2–36 mm), and stem arrangement (bead, tessellation, zigzag, random, and banding) were compiled for this study. Extensive regression analysis has shown that the sediment transport capacity could be expressed as a power function of flow velocity, shear stress, stream power, or unit stream power. Predictors of the sediment transport capacity were ranked from the unit stream power as the strongest, followed by the stream power, flow velocity, and the shear stress. Vegetation stem cover had no apparent and direct effect on the relationship between hydraulic variables and the sediment transport capacity so long as the unit stream power or stream power was used as its predictor. Vegetation cover became a significant factor only when the shear stress was used to predict the sediment transport capacity. Finally, a new equation involving the slope gradient, flow velocity, and median sediment diameter in a nondimensional form was shown to be a superior predictor of the sediment transport capacity with the Nash–Sutcliffe coefficient of efficiency of 0.92. The product of slope and flow velocity, that is, the unit stream power, captures the effect of vegetation stem cover and surface roughness and was shown to be an effective predictor of the transport capacity in the presence of vegetation cover.