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yes / A two dimensional (2D) RNG k-ε sediment model including the effects of secondary currents is developed to simulate sediment transport and bed deformation in rivers with continuous bends. Nonuniform suspended and bedload sediment transports and variation of effective bed material size distribution are included in the model. A semi-coupled scheme for sediment model is proposed, which can be used for simulating both the long- and short-term sediment transport whenever riverbed changes. The model is applied to simulate the flow and sediment transport in the Shapotou reservoir in the upper reach of the Yellow River which is a typical natural river reach with continuous bends. River bed deformations caused by suspended and bedload sediment transport are investigated. Good agreement between the numerically simulated results and the field measurements is obtained, indicating that the model is capable of simulating the sediment transport and predicting the bed deformation of rivers having continuous bends with reasonable accuracy. / the Major Research Plan Project, National Natural Science Foundation of China(Grant No.: 91230111 and 51279071); National Key BasicResearch Development Program of China (973 Program, Grant No.: 2010CB429002);Project of Science and Technology of Colleges in Ningxia, China (Grant No.:NGY2012097)

Yes / Based on the Lagrangian approach, this study proposes a random displacement model (RDM) to predict the concentration of suspended sediment in vegetated steady open channel flow. Validation of the method was conducted by comparing the simulated results by using the RDM with available experimental measurements for uniform open-channel flows. The method is further validated with the classical Rouse formula. To simulate the important vertical dispersion caused by vegetation in the sediment-laden open channel flow, a new integrated sediment diffusion coefficient is introduced in this study, which is equal to a coefficient multiplying the turbulent diffusion coefficient. As such, the RDM approach for sandy flow with vegetation was established for predicting the suspended sediment concentration in low-sediment-concentration flow with both the emergent and submerged vegetation. The study shows that the value of for submerged vegetation flow is larger than that for emergent vegetation flow. The simulated result using the RDM is in good agreement with the available experimental data, indicating that the proposed sediment diffusion coefficient model can be accurately used to investigate the sediment concentration in vegetated steady open channel flow. / National Natural Science Foundation (No. 51439007, 11672213, and 11872285); Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project No: 2018HLG01)

Yes / Ice cover formed on an alluvial channel can significantly alter the flow characteristics, such as the vertical distributions of streamwise velocity and shear stress, and hence the water and sediment transport process. The vertical profile of the suspended sediment concentration in the ice-covered alluvial channels with steady uniform flows is investigated in this study. To calculate the suspended sediment concentration, we are based on the Schmidt O’Brien equation and deduce an analytical model that employs an existing eddy viscosity model and a modified formula of the sediment fall velocity considering the common effects of the upper and lower boundaries. The proposed analytical model is then validated by using available experimental data reported in the literature. The predicted accuracy of the proposed model is evaluated through error statistics by comparing to previous modeled results. The relative concentration profiles of the suspended sediment are subsequently simulated by applying the validated analytical model with different characteristic parameters. Results show that the relative concentration decreases with the increase of both the ice cover roughness and the sediment fall velocity. The uniformity of the relative concentration distribution is closely related to the value of the proportionality parameter σ, revealing the physical mechanism that the more prominent the turbulent diffusion effect is, the more uniform the relative concentration profile is. / This work was supported by the National Natural Science Foundation of China (grant 604 numbers 52020105006 and 11872285) and the Open Funding of State Key Laboratory of Water Resources and Hydropower Engineering Science (WRHES), Wuhan University (Project number 2018HLG01).

Yes / This paper reviews existing studies relating to the assessment of sediment concentration profiles within various flow conditions due to their importance in representing pollutant propagation. The effects of sediment particle size, flow depth, and velocity were considered, as well as the eddy viscosity and Rouse number influence on the drag of the particle. It is also widely considered that there is a minimum threshold velocity required to increase sediment concentration within a flow above the washload. The bursting effect has also been investigated within this review, in which it presents the mechanism for sediment to be entrained within the flow at low average velocities. A review of the existing state-of-the-art literature has shown there are many variables to consider, i.e., particle density, flow velocity, and turbulence, when assessing the suspended sediment characteristics within flow; this outcome further evidences the complexity of suspended sediment transport modelling.

Sediment, an integral part of rivers and watersheds, is eroded from, stored in, and transported through various watershed components. Rivers often receive sediment in the form of episodic, discrete pulses from a variety of natural and anthropogenic processes, this sediment can be transported downstream along the bed or suspended in the water column. Most sediment measurements are focused on the component suspended in the water column. Recent advances in data collection techniques have substantially increased both the resolution and spatial scale of data on suspended sediment dynamics, which is helpful in linking small, site-scale measurements of transport processes in the field with large-scale modeling efforts. Part of this research evaluates the accuracy of the latest laser diffraction instrument for suspended-sediment measurement in rivers, LISST-SL2 for measuring suspended sediment concentration (SSC), particle size distribution (PSD), and velocity by comparing to concurrent physical samples analyzed in a lab for SSC and PSD, and velocity measured using an acoustic Doppler current profiler (ADCP) at 11 sites in Washington and Virginia during 2018-2020. Another part of this work employs a 1-D river network, bed material transport model to investigate the magnitude, timing, and persistence of downstream changes due to the introduction of sediment pulses in a linear river network. We specifically focus on comparing bed responses between mixed and uniform grain size sediment pulses. Then the model capability is utilized to explore the control of hydrograph structure on debris flow sediment transport through a more complex river network at different time horizons. Another part of this work investigates the effect of differences in spatial distribution of debris flow sediment input to the network by analyzing corresponding tributary and mainstem characteristics. Based on an extensive dataset, our results highlight the need for a correction of the raw LISST-SL2 measurements to improve the estimation of effective density and particle size distribution with the help of a physical sample. Simulation results from the river network model show that bed response is primarily influenced by the sediment-pulse grain size and distribution. Intermediate mixed-size pulses are likely to have the largest downstream impact because finer sizes translate quickly and coarser sizes (median bed gravel size and larger) disperse slowly. Furthermore, a mixed-size pulse, with a smaller median grain size than the bed, increases bed mobility more than a uniform-size pulse. While investigating the hydrologic control on debris flow simulation, this study finds that differences between transport by a 30-year daily hydrograph and simplified hydrographs were greatest in the first few years, but errors decreased to around 10% after 10 years. Our simulation results highlight that the sequence of flows (initial high/low flow) is less important for transport of finer sediment. We show that such network-scale modeling can quantitatively identify geomorphically significant network characteristics for efficient transport from tributaries to the mainstem, and eventually to the outlet. Results suggest that watershed area and slope characteristics are important to predict aggradation hotspots in a network. However, to predict aggradation and fluvial geomorphic responses to variations in sediment supply from river network characteristics more confidently, more widespread (in several other river networks) model applications with field validation would be useful. This work has important implications for river management, as it allows us to better predict geomorphically significant tributaries and potential impact on downstream locations, which are important for river biodiversity. Model results lead the way to use of simplified flow hydrographs for different timescales, which is crucial in large-scale modeling as it is often restricted by computational capacity. Finally, given the ability for reliable quantification of a high-resolution time-series of different suspended-sediment characteristics, in-stream laser diffraction offers great potential to advance our understanding of suspended-sediment transport. / Doctor of Philosophy / Rivers receive sediment from different natural and human sources, and water moves this sediment in various ways. These ways include along the bottom of the stream or suspended in the water. Quantifying suspended sediment in streams is an important step to estimate the threat to riverine environments as suspended sediments not only carry chemicals and pollutants, but also interact with the river bottom to affect the characteristics of streams. Measurement of suspended-sediment concentration and particle-size is critical for many engineering, ecological, and river-structure issues, but obtaining an accurate measurement of sediment quantity in a river is challenging. The recent advancement of a laser diffraction instrument allows us to obtain frequent measurements of suspended-sediment concentration and particle size by volume. We applied the most recent such instrument at 11 sites in Washington and Virginia during 2018-2020, along with concurrent water samples to measure suspended-sediment concentration and particle size by mass in a laboratory. Our analysis suggests that at least one supporting physical mass measurement be obtained to improve the estimation from laser measurement. Beside this site-scale measurement, we apply a large-scale river network model to estimate how sediment moves along the bed of rivers at large spatial extents. We simulate how this added sediment results in downstream changes in the amount of sediment in the river channel. We compare observed changes in the elevation of the stream bottom and sediment accumulation rates in a downstream lake to model results. Then we investigate the magnitude, timing, and persistence of downstream changes due to the introduction of added sediment by comparing the changes against a baseline condition (without the added sediment). We find that the added sediment that is half as large as on the river bottom and with a range of sizes are likely to affect the largest downstream changes because smaller sizes move quickly and larger sizes move slowly. Furthermore, added sediment that is smaller than on the river bottom and with a range of sizes help more sediment on the river bottom move than if that sediment addition all had the same particle size. We also employ this model to explore the effect of flow variation and river characteristics on sediment movement. Comparing between a 30-year flow record and simplified flow records, we show that results from simplified flow records vary initially, but errors decrease after 10 years. That is, both flow records result in similar sediment movement in the long-term. In terms of aggradation from added sediment, results show that the characteristics of elevation change of the river bottom play a vital role along with the contributing landscape area. This work has important implications for river management, as it not only allows us to accurately measure suspended sediment with an advanced instrument, but also better understand how rivers and aquatic habitat are affected by variations in added sediment.

Os processos hidrossedimentológicos são complexos e dependem de diversos fatores. Entendê-los requer alto grau de especialização de mão de obra, além da utilização de equipamentos e técnicas ainda incipientes no país. O monitoramento hidrossedimentológico com dados confiáveis de concentração de sedimentos em suspensão pode ser problemático quando são empregados métodos convencionais, pois geralmente os mesmos apresentam medições com quantidade de postos e frequências inferiores aos desejáveis, limitando estudos e a gestão de recursos hídricos quando se trata de reservatórios. Nesse contexto, esta dissertação apresenta um estudo realizado no reservatório da Pequena Central Hidrelétrica Mogi-Guaçu (SP) na qual realizou-se a correlação dos dados de concentração de sedimentos em suspensão mensuradas com dispositivo automático (LISST-100X) e por amostragem convencional (Garrafa Van Dorn). Por meio de regressões lineares e testes estatísticos avaliou-se a eficiência da técnica de difração à laser, e se estimaram as concentrações de sedimentos em suspensão para as duas campanhas realizadas. Analisando os resultados obtidos, confirmou-se estatisticamente que dentre todos os cenários de regressões lineares adotados, o modelo que divide o reservatório em setores apresentou melhores estimativas de concentração, inferindo-se que a concentração do sedimento em suspensão possui um comportamento característico ao segmento do reservatório de Mogi-Guaçu. Notou-se também, a redução da concentração entre as duas campanhas realizadas, decorrente principalmente pela redução da velocidade do fluxo d\'água. Desse modo, a sonda LISST-100X, se mostrou viável para o estudo de caso. Ressalta-se que a utilização desta sonda possibilitou a obtenção de um número maior de dados do que os obtidos por meio do emprego de técnica convencional, possibilitando uma análise mais completa do reservatório e reduzindo significativamente o trabalho de campo, laboratório e escritório. / Hydrosedimentological processes are complex and depend on many factors and understanding them requires a high degree of labor specialization, as well as the use of equipment and techniques still incipient in Brazil. The hydrosedimentological monitoring with reliable sediment concentration data may be problematic when conventional methods are used. Its measurements are usually undertaken at a number of stations and frequencies below the desired ones, which limit studies and the management of water resources of reservoirs. This dissertation reports on a study on the Mogi-Guaçu (SP) Small Hydroelectric Plant reservoir and the correlation between the suspended sediment sample data measured by an automatic device (LISST-100X) and conventional sampling conducted by a Van Dorn sampler. The laser diffraction efficiency was evaluated by linear regression and statistical tests and the concentration of suspended sediment was estimated for the two campaigns. The results show the model that divides the reservoir into sectors provided better estimates of concentration and the concentration of suspended sediment exhibited a characteristic behavior for the segment of Mogi-Guaçu reservoir. A reduction in the concentration, caused mainly by a decrease in the water flow speed, was also observed between the two campaigns and laser diffraction proved feasible for the case study. This methodology enables the obtaining of a larger amount of data than that achieved by conventional techniques, a more complete analysis of the shell and significant reductions in the field, laboratory and office work.

Usualmente la producción de sedimentos en suspensión (Qss) de un río es calculada utilizando datos de caudales medios diarios o mensuales. Considerando que la mayor Qss ocurre durante los eventos de lluvias y también que los caudales medios no son capaces de representar adecuadamente los máximos caudales, principalmente en zonas de alta variabilidad climática, la forma usual de cálculo de Qss puede subestimar esta producción. En este sentido, esta investigación buscó analizar la influencia de la variabilidad temporal de los datos de caudales en el cálculo de la producción de sedimentos. Adicionalmente fue analizada el uso de diferentes tipos de curvas de sedimentos: (i) para todo el periodo de estudio, (ii) por años hidrológicos y (iii) asociación por épocas características (húmedas, semi-húmedas y secas). El estudio fue realizado en la subcuenca del río Torata, ubicada en una zona semiárida al sur del Perú, entre 2100 y 5200 m de altitud con pendiente promedio de 21.0% y alta variabilidad climática, en especial la precipitación que se ve reflejado en los caudales, ya que en un lapso de horas puede variar de 4 a 34 m3/s. El error entre la descarga prevista y estimada para el periodo de estudio (2001-2012) utilizando los diferentes tipos de curvas fue (i) -65.85%, (ii) -15.36% y (iii) -8.74%, presentando mejora en el coeficiente de eficiencia de Nash-Sutcliffe de 0.248 para 0.500. Los resultados mostraron que la diferencia entre la descarga de sedimentos en suspensión total para el periodo calculado con caudales medias mensuales y diarias fue de -92% y -62%, ambos en comparación de producción para valores medios horarios. También fue constatado que el 99.7% de la producción de sedimentos ocurre en temporada de lluvias, inclusive, un único evento de lluvia llegó a producir 80% de la producción anual. Los resultados de esta investigación ponen en manifiesto la importancia de utilizar registros de caudales con escalas pequeñas de tiempo (minutos, horas), que puedan representar la alta variabilidad de los caudales característicos de zonas semiáridas. / The usual methods that calculate the suspended sediment flux (Qss) of rivers employ discharge mean values daily or monthly. As most of the sediments are transported during overflow events and a mean value smooths the flood peak discharge, mainly in high climatic variability areas, the usual method to evaluate the Qss might underestimate the production of river sediments. This paper reports on an analysis of the gauge influence of temporal variability on the sediment yield estimation. Additionally, the use of different types of sediment rate curves was analyzed for (i) the whole time-series data, (ii) per hydrological year, and (iii) per hydrological pattern characterization (flood, intermediary and drought). A study case was conducted in the Torata river sub-catchment, a Peruvian semi-arid area located between altitudes of 2100 and 5200 meters and whose average slope is 21%. The high climatic variability is expressed by the huge river flow amplitude, which ranges from 4 to 34 m3/s in a few hours. The errors for the sediment yield from 2001 to 2012 estimated by the different sediment rating curves were (i) -65,85%, (ii) -15,36% and (iii) -8,74%, with a 0,248 to 0,500 Nash-Sutcliffe efficiency coefficient improvement. The differences between the sediment yield in total suspension for the period calculated monthly and daily were -92% y and -62%, respectively, in comparison with the production for hourly average values. Results show that 99,7% of the sediment are produced during the flood season and a single overflow event could represent 80% of the annual sediment discharge flow. This research highlights the importance of collecting and using discharge data of a short time interval (minutes or hours) to compute and represent the overflow peaks typical of semiarid regions.