Papers Published in the International Journal of Sediment Research Volume 36, No.2, 2021

Pages 165-334 (April 2021)

1. Experimental investigation of density current patterns using dynamic fractal analysis

Mohammad HOSSEINI, Mohammad Hadi FATTAHI, Saeid ESLAMIAN

Pages 165-176

2. Characteristics of sedimentation and channel adjustment linked to the Three Gorges Reservoir

Xiaoya TANG, Sichen TONG, Guoxian HUANG, Guangxiang XU, Xinghua LI, Kun LEI, Shiming YAO

Pages 177-189

3. Soil and water conservation measures improve soil carbon sequestration and soil quality under cashews

Gopal Ramdas MAHAJAN, Bappa DAS, Sandrasekaran MANIVANNAN, Begur Lakshminarasimha MANJUNATH, Ram Ratan VERMA, Sujeet DESAI, Rahul Mukund KULKARNI, Ashish Marotrao LATARE, Reshma SALE, Dayesh MURGAONKAR, Kiran Puna PATEL, Shaiesh MORAJKAR, Ashwini DESAI ·Natasha BARNES, Heena MULLA

Pages 190-206

4. Predicting soil erosion hazard in Lattakia Governorate (W Syria)

Mohammed SAFWAN, Khallouf ALAA, Alshiehabi OMRAN, Bao Pham QUOC, Thi Thuy Linh NGUYEN, Nam Thai VAN, Tran Anh DUONG, Hars á nyi ENDRE

Pages 207-220

5. Characteristic analysis of phospholipid fatty acids (PLFAs) in typical nutrient polluted lake sediment in Wuhan

Xia ZHANG, Qianru CHEN, Chuan WANG, Hongpei ZHANG, Yuqing ZHAO,

Liping ZHANG, Biyun LIU, Zhenbin WU, Qiaohong ZHOU

Pages 221-228

6. A laboratory investigation of bed-load transport of gravel sediments under dam break flow

Khabat KHOSRAVI, Amir Hooshang Nezamivand CHEGINI, James COOPER, Luca MAO, Mahmood HABIBNEJAD, Kaka SHAHEDI, Andrew BINNS

Pages 229-234

7. A new portable in situ flume for measuring critical shear stress on river beds

Cheng HE, James Nodwell TAYLOR, Quintin ROCHFORT, David NGUYEN

Pages 235-242

8. Evaluation of sediment contamination in the Red Sea coastal area combining multiple pollution indices and multivariate statistical techniques

Yousef Saeed SALEH

Pages 243-254

9. General velocity formula of boundary layer above mobile sediment bed induced by asymmetric waves

Xin CHEN, Minghong CHEN

Pages 255-267

10. Climatic and anthropogenic impacts on the decrease of sediment discharge to the Mediterranean coast from the largest river of Maghreb

Ali HADOUR, Gil MAH E′, Mohamed MEDDI

Pages 268-278

11. Numerical modeling of local scour at a submerged weir with a downstream slope using a coupled moving-mesh and masked-element approach

Xiaohui YAN, Colin David RENNIE, Abdolmajid MOHAMMADIAN

Pages 279-290

12. Risk analysis for clustered check dams due to heavy rainfall

Zuyu CHEN, Xieping HUANG, Shu YU, Wei CAO, Weiqin DANG, Yangqiang WANG

Pages 291-305

13. One-dimensional morphodynamic model for retrogressive erosion based on a sediment entrainment theory at high flow velocity

Zenghui WANG, Junqiang XIA, Meirong ZHOU, Shanshan DENG, Tao LI

Pages 306-316

14. Grain-size end-members and environmentally sensitive grain-size components: A comparative study in the mud shelf depocenters off southern Brazil

Michel Michaelovitch DE MAHIQUES, Samara Cazzoli Y GOYA, Maria Carolina da Silva Nogueira de MATOS, Rodrigo Augusto Udenal de OLIVEIRA, Bianca Sung Mi KIM, Paulo Alves de Lima FERREIRA, Rubens Cesar Lopes FIGUEIRA, Marcia Caruso B I′CEGO

Pages 317-327

15. Equilibrium relations for water and sediment transport in the Yellow River

Xujian CHEN, Yuqi AN, Zhihao ZHANG, Chunhong HU

Pages 328-334

1. Experimental investigation of density current patterns using dynamic fractal analysis

Mohammad HOSSEINI, Mohammad Hadi FATTAHI, Saeid ESLAMIAN

Pages 165-176

https://doi.org/10.1016/j.ijsrc.2020.09.001 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300962

Abstract: Density currents are caused by a difference in density, though low, of an entering fluid with the ambient fluid. This type of current is two-phased and found on riverbeds or in reservoirs behind dams, and is nonlinear in nature, complex, and sensitive to initial conditions. Fractal geometry is used as a powerful tool for studying complex natural phenomena. Using experimental studies and changes in inlet current conditions, the fractal and multi-fractal analyses of the interface between the density current and the ambient fluid were done. In addition, a search was made to find a possible connection between the nonlinear patterns. According to the results, with an increase in the inlet discharge and inlet density of the current the fractal dimension decreased. Further, the smaller the range of the singularity spectrum diagram was, i.e., the more it was less than 0.34, the lower the system's tendency was to be multi-fractal, and the system sensitive to large local changes. In the interface between the density current and the ambient fluid, using the fractal dimension-based Richardson number could improve experimental data by 12.4%. Moreover, with an increase in the Richardson number, the Reynolds number of the current decreased. Further, upon considering the fractal dimension, the Reynolds number improved by 23% and a good correlation with a coefficient of determination of 0.76.

Keywords: Density current; Fractal geometry; Richardson number; Multi-fractal analysis; Fluid interface

2. Characteristics of sedimentation and channel adjustment linked to the Three Gorges Reservoir

Xiaoya TANG, Sichen TONG, Guoxian HUANG, Guangxiang XU, Xinghua LI, Kun LEI, Shiming YAO

Pages 177-189

https://doi.org/10.1016/j.ijsrc.2020.10.003 https://www.sciencedirect.com/science/article/abs/pii/S1001627920301001

Abstract: Construction of large dams is attractive because of their great benefits in flood control, hydropower generation, water resources utilization, navigation improvement, etc. However, dam construction may bring some negative impacts on sediment transport and channel dynamics adjustments. Due to the effects of recent water and soil conservation projects, sediment retention in the newly constructed large upstream reservoirs, and other factors, the sedimentation in the Three Gorges Reservoir (TGR) is quite different from the amount previously predicted in the demonstration stage. Consequently, based on the measured data, characteristics of sedimentation and the related channel deformation in the TGR were analyzed. The results imply that sediment transport tended to be reduced after the Three Gorges Project (TGP). Sedimentation slowed dramatically after 2013 and indicated obvious seasonal characteristics. Due to the rising water level in the TGR in the flood season, the yearly sediment export ratio (Eratio) was prone to decrease. The water level near the dam site should be reasonably regulated according to the flow discharge to improve the sediment delivery capacity and reduce sedimentation in the TGR, and to try to avoid situations where the flood retention time is close to 444 h. The depositional belt was discontinuous in the TGR and was mainly distributed in the broad reaches, and only slight erosion or deposition occurred in the gorge reaches. Sedimentation in the broad and gorge reaches accounted for 93.8% and 6.2% of the total sedimentation, respectively. The estuarine reach located in the fluctuating backwater area experienced alternate erosion-deposition, with a slight accumulative deposition in the curved reach. Sedimentation mainly occurred in the perennial backwater area. The insight gained in this study can be conducive to directly understanding of large reservoir sedimentation and mechanism of channel adjustment in the reservoir region in the main channel of large river.

Keywords: Three Gorges Reservoir; Sedimentation characteristics; Channel adjustment; Reduced sediment load

3. Soil and water conservation measures improve soil carbon sequestration and soil quality under cashews

Pages 190-206

https://doi.org/10.1016/j.ijsrc.2020.07.009 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300810

Abstract: Land degradation is becoming a serious problem in the west coast region of India where one of the world's eight biodiversity hotspots, the ‘Western Ghats’, is present. Poor land management practices and high rainfall have led to increasing problems associated with land degradation. A long-term (13-year) experiment was done to evaluate the impact of soil and water conservation measures on soil carbon sequestration and soil quality at three different depths under cashew nut cultivation on a 19% slope. Five soil and water conservation measures - continuous contour trenches, staggered contour trenches, halfmoon terraces, semi-elliptical trenches, and graded trenches all with vegetative barriers of Stylosanthes scabra and Vetiveria zizanoides and control were evaluated for their influence on soil properties, carbon sequestration, and soil quality under cashews. The soil and water conservation measures improved significantly the soil organic carbon, soil organic carbon stock, carbon sequestration rate and microbial activity compared to the control condition (without any measures). Among the measures tested, continuous contour trenches with vegetative barriers outperformed the others with respect to soil organic carbon stock, sequestration rate, and microbial activity. The lower metabolic quotient with the measures compared to the control indicated alleviation of environmental stress on microbes. Using principal component analysis and a correlation matrix, a minimum dataset was identified as the soil available nitrogen, bulk density, basal soil respiration, soil pH, acid phosphatase activity, and soil available boron and these were the most important soil properties controlling the soil quality. Four soil quality indices using two summation methods (additive and weighted) and two scoring methods (linear and non-linear) were developed using the minimum dataset. A linear weighted soil quality index was able to statistically differentiate the effect of soil and water conservation measures from that of the control. The highest value of the soil quality index of 0.98 was achieved with continuous contour trenches with a vegetative barrier. The results of the study indicate that soil and water conservation measures for cashews are a potential strategy to improve the soil carbon sequestration and soil quality along with improving crop productivity and reducing the erosion losses.

Keywords: Land degradation; Microbial activity; Microbial biomass carbon; Minimum dataset; Soil erosion; Western Ghats

4. Predicting soil erosion hazard in Lattakia Governorate (W Syria)

Mohammed SAFWAN, Khallouf ALAA, Alshiehabi OMRAN, Bao Pham QUOC, Thi Thuy Linh NGUYEN, Nam Thai VAN, Tran Anh DUONG, Hars á nyi ENDRE

Pages 207-220

https://doi.org/10.1016/j.ijsrc.2020.06.005 https://www.sciencedirect.com/science/article/abs/pii/S100162792030069X Abstract: The main objective of this study is to predict soil erosion in the Lattakia Governorate (W Syria) using the Water Erosion Prediction Project model (WEPP) and to compare the result with that of the RUSLE. Field survey and data collection were carried out, and 44 soil samples were analyzed. In addition, all the necessary input files were prepared for use in the WEPP model and RUSLE. Results show that more than of 80% of the locations studied experience slight to moderate erosion (less than 5 t/ha/y), whereas the rest of the locations experience severe soil erosion hazard. Moreover, the volume of runoff estimated by the WEPP model is in the range of 51-321 mm, and the R² between the simulated soil erosion and the predicted runoff reached 0.68. Interestingly, the R²between the WEPP model and RUSLE is 0.56, which indicates a good correlation between the two models.

Keywords: Soil erosion; Run-off; WEPP; RUSLE; Syria

5. Characteristic analysis of phospholipid fatty acids (PLFAs) in typical nutrient polluted lake sediment in Wuhan

Xia ZHANG, Qianru CHEN, Chuan WANG, Hongpei ZHANG, Yuqing ZHAO,

Liping ZHANG, Biyun LIU, Zhenbin WU, Qiaohong ZHOU

Pages 221-228

https://doi.org/10.1016/j.ijsrc.2020.09.002 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300974 Abstract: The process of urbanization aggravates the endogenous pollution of urban lake sediment, and polluted sediment may seriously affect the quality of the water in lakes. At present, it is difficult to distinguish the difference between sediment that is heavily polluted by nitrogen (N) and phosphorus (P) when using an analysis based on a physicochemical index classification. The current study applied phospholipid fatty acid (PLFA) technology to further analyze the sediment characteristics from the perspective of microbiology. Surface sediment from five urban lakes that are heavily polluted with N and P in Wuhan were sampled. Statistical approaches were used to analyze the microbial community structure in the sampled sediment, and to determine the correlations between the microorganisms and physicochemical indices. The most severely polluted lake sediment had similar PLFA structures, the highest saturated fatty-acid content, and bacteria as the dominant microorganism. However, there were differences between the microbial biomass of the various sediment samples, which may have been related to the degree of N and P pollution. Analysis of the microbial diversity in the sediment samples indicated that the bacteria were experiencing starvation and nutrient pressure, which may have been due to the dissolved oxygen concentration of the heavily polluted lake sediment. A correlation analysis showed that the endogenous N and P had different effects on the microbes of the polluted sediment. A redundancy analysis (RDA) demonstrated that the N/P ratio had the greatest influence on the PLFA species, accounting for 83% of the cumulative interpretation. To effectively promote the role of sediment microorganisms on circulating elements, it is necessary to regulate the N/P ratio of the sediment to some extent. When the N/P ratio in sediment exceeds 6, N pollution should be prioritized.

Keywords: Lake sediment; Endogenous pollution; Phospholipid fatty acid (PLFA) analysis; Microbial population; N/P ratio

6. A laboratory investigation of bed-load transport of gravel sediments under dam break flow

Khabat KHOSRAVI, Amir Hooshang Nezamivand CHEGINI, James COOPER, Luca MAO, Mahmood HABIBNEJAD, Kaka SHAHEDI, Andrew BINNS

Pages 229-234

https://doi.org/10.1016/j.ijsrc.2020.08.005 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300949

Abstract: Dam break flows and resulting river bed erosion can have disastrous impacts on human safety, infrastructure, and environmental quality. However, there is a lack of research on the mobility of non-uniform sediment mixtures resulting from dam break flows and how these differ from uniform sized sediment. In this paper, laboratory flume experiments revealed that coarse and fine fractions in non-uniform sediment had a higher and a lower bed-load parameter, respectively, than uniform sediments of the same size. Thus, the finer fractions were more stable and the coarser fractions were more erodible in a nonuniform bed compared to a uniform-grained bed. These differences can be explained by the hiding and protrusion of these fractions, respectively. By investigating changes in mobility of the mixed-size fractions with reservoir water levels, the results revealed that at low water levels, when the coarser fractions were only just mobile, the bed-load parameter of the finer fractions was higher than the coarser fractions. The opposite was observed at a higher water level, when a significant proportion of the coarsest fractions was mobilized. The higher protrusion of these grains had an important effect on their mobility relative to the finer grains. The transported sediment on these mixed-sized beds was coarser than the initial bed sediment, and became coarser with an increase in reservoir water level.

Keywords: Dam break; Bed-load transport; Gravel; Laboratory flume

7. A new portable in situ flume for measuring critical shear stress on river beds

Cheng HE, James Nodwell TAYLOR, Quintin ROCHFORT, David NGUYEN

Pages 235-242

https://doi.org/10.1016/j.ijsrc.2020.08.004 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300937 Abstract: A new portable in situ flume (PISF) for measuring critical bed shear stress (CBSS) was developed in this study. The PISF consists of an open bottom sediment erosion chamber and an electrically-driven pump. Unlike most existing in situ flumes with similar designs, the new PISF does not rely on monitoring the flow conditions or particle density in the sediment erosion chamber; instead, it is a pre-calibrated flume. The calibration was performed by first determining CBSS of various selected sediment samples of known particle size and density (using the law of the wall), based on flow velocity-depth profiles measured in a 6 m straight open-channel flume using a Particle Image Velocimetry (PIV) system. These same particles of known CBSS were then used in the new in-situ flume under controlled lab conditions to obtain a series of calibration curves of CBSS vs. pump electrical power. A wide variety of particle types and sizes (simulated sediments) were used in this two-step calibration procedure to widen CBSS measurement range and simulate cohesive force effects. The size of the PISF is much smaller and more practical than other similar devices as lamellar flow conditions are not required and it can be applied to a wide range of sediment types including cohesive sediments.

Keywords: Sediment erosion; In situ flume; Critical bed shear stress; Particle image velocimetry; Law of the wall

8. Evaluation of sediment contamination in the Red Sea coastal area combining multiple pollution indices and multivariate statistical techniques

Yousef Saeed SALEH

Pages 243-254

https://doi.org/10.1016/j.ijsrc.2020.07.011 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300834

Abstract: In the recent years, the Red Sea coast of Yemen has been severely affected by intensive anthropogenic activities. The current study constitutes a thorough inquiry to evaluate the extent of heavy metals pollution in Yemen's Red Sea coast sediment and identifies the possible sources of pollution. The concentrations of five metals (copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), and nickel (Ni)) collected from nine sites along the Red Sea coast of Yemen were assessed using an atomic absorption spectrophotometer (ASS). Sediment quality indices, such as the sediment quality guidelines (SQGs), potential ecological risk (RI), contamination factor (CF), pollution load index (PLI), geoaccumulation index (I_geo), and modified degree of contamination (mCd) were computed. In addition, multivariate statistical techniques (principal component analysis (PCA), hierarchical cluster analysis, and Pearson's correlation analysis) were applied to identify the potential sources of metals. The mean concentrations of Cu, Zn, Cd, Pb, and Ni were 51.3, 61.9, 4.02, 9.9, and 33.4 mg/ kg dry wt, respectively. The spatial distribution revealed that the metals concentrations were high at the middle zone and low southward of Hodeida city. According to the SQGs, the adverse biological effects of metals were occasionally associated with Cu and Cd, frequently associated with Ni, and not expected to occur with Zn and Pb. The RI indicated that the sediment of the studied sites pose low (RI < 50) to considerable (100 RI < 200) ecological risk. The mean effect range-median quotient (M-ERM-Q) indicated that the combination of the studied metals had the toxicity probability of 21% at all studied sites. I_geo and CF indicated that the metals concentrations were in the descending order of: Zn > Ni > Pb > Cd > Cu, whereas the PLI and mCd indicated that Ras Isa (Site 5) and Urj village (Site 6) were the most polluted sites. PCA, cluster analysis, and correlation analysis found that Cd, Pb, and Ni mostly originated from anthropogenic sources while Cu and Zn were mainly derived from natural sources. Thus, it is evident that the intensive anthropogenic activities had negative influence on metals accumulation in the sediment of the Red Sea coast of Yemen leading to detrimental effects to the whole ecosystem. These comprehensive findings provide valuable information and data for future monitoring studies regarding heavy metals pollution and sediment quality at the Red Sea coast of Yemen.

Keywords: Red Sea; Heavy metals; Pollution; Spatial distribution; Sediment quality

9. General velocity formula of boundary layer above mobile sediment bed induced by asymmetric waves

Xin CHEN, Minghong CHEN

Pages 255-267

https://doi.org/10.1016/j.ijsrc.2020.07.002 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300743

Abstract: Sediment movement in the wave boundary layer above a mobile sediment bed is complex. A velocity formula for the boundary layer is proposed for sheet flow induced by asymmetric waves above a mobile sediment bed. The formula consists of a free stream velocity and a defect function which contains a phase-lead, boundary layer thickness and mobile sediment bed. Phase-lag of sediment movement is considered in the formula for the mobile sediment bed. The formula needs six dependent variables about asymmetric wave and sediment characteristics. Asymmetry effects on parameters (orbital amplitude, roughness height, bed shear stress, and boundary layer thickness) are properly considered such that the formula can yield velocity differences among onshore, offshore, acceleration, and deceleration stages. The formula estimates the net boundary layer velocity resulting from the mobile sediment bed and asymmetric boundary layer thickness. In addition, a non-constant phase-lead also contributes to the net boundary layer velocity in asymmetric oscillatory sheet flow. Results of the formula are as good as that of a two-phase numerical model. Sheet flow transport induced by asymmetric waves, and the offshore net sediment transport rate with a large phase-lag under velocity-skewed waves, can be adequately estimated by the formula with a power sediment concentration function.

Keywords: Asymmetric wave; Boundary layer; Mobile sediment bed; Sheet flow; Velocity formula

10. Climatic and anthropogenic impacts on the decrease of sediment discharge to the Mediterranean coast from the largest river of Maghreb

Ali HADOUR, Gil MAH E′, Mohamed MEDDI

Pages 268-278

https://doi.org/10.1016/j.ijsrc.2020.07.001 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300731

Abstract: The current study focuses on the issue of the decrease in sediment discharge to the Mediterranean Sea by the largest river in Algeria, the Wadi Cheliff (i.e. Cheliff River). This study clarifies the effect of climatic and anthropogenic factors on the changes in the sedimentary dynamics of the Cheliff River discharging to the sea. The data used (rainfall, water discharge, and sediment discharge) concern the Sidi Bel Attar gaging station on the Cheliff River, only 18 km from discharge to the Mediterranean Sea. A power-type statistical regression model was used to fill the 74.2% gap in Suspended Solids (SS) measurements in the establishment of a SS database for the period 1951-2012. The study results show that the transport of suspended sediment discharged to the sea is about 487 t/km2/yr. Statistical tests of breaks highlight that rainfall decreased by 26% and that water and sediment input to the sea declined from 74% to 63% for the period of 1981-2012. The correlation analysis shows a decrease in the contribution of rainfall on sediment and water input at the outlet equal to 77.9% and 77.8%, respectively, during the period of 1980-2012, compared to the period of 1968-1980. However, the double mass method reflects the contribution of factors other than rainfall to the decrease of sediment input to the sea. These other factors mainly include large dams, which intercepted about 71% of the total volume of sediment discharged to the sea during the period of 1968-2010. In addition the contribution of large dams to the reduction of sedimentary input to the sea is more important than that of the decrease in rainfall. The management of large dams also contributes to the increase in the sediment deficit to the sea through the prioritization of interception of sediment at the expense of releases, for socio-economic purposes, 68.4% of the Cheliff River discharge is diverted for human use. This has led to an increase in the mean water bed level at bankfull downstream, where the Cheliff River gave up 51% of its width to the floodplain between 1996 and 2009. In the light of the scarcity of sediment transport data in North Africa and in many other areas, the current study provides a reference framework for other studies: providing useful information for the study of the transfer of sediment from land to sea, and the links with the socio-economic needs.

Keywords: Sediment discharge; Cheliff River; Algeria; North Africa; Dams; Mediterranean Sea

11. Numerical modeling of local scour at a submerged weir with a downstream slope using a coupled moving-mesh and masked-element approach

Xiaohui YAN, Colin David RENNIE, Abdolmajid MOHAMMADIAN

Pages 279-290

https://doi.org/10.1016/j.ijsrc.2020.06.007 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300718

Abstract: This paper presents a model for local scour at submerged weirs with downstream slopes that uses a coupled moving-mesh and masked-element approach. In the developed model, the fluid-sediment interface is tracked using a moving-mesh technique, and the effects of the structure on the hydrodynamics and bed morphology are resolved using a masked-element technique. Compared to traditional sediment scour models, based on the moving-mesh technique, the present model has the advantage of allowing for a simpler setup of the computational grids and a larger-amplitude deformation. Laboratory experiments on local scour at a submerged weir with a downstream slope were conducted, which provided bed profiles at different time instants. The results obtained by the present model are compared to the experimental data. The comparisons demonstrate the performance of the model in satisfactorily predicting local scour at a submerged weir with a downstream slope. The model was further modified and employed to carry out additional computations to investigate the influence of various parameters and sub-models.

Keywords: Numerical modeling; Bed morphology; Submerged weir; Downstream slope; Moving-mesh and masked-element; Open FOAM

12. Risk analysis for clustered check dams due to heavy rainfall

Zuyu CHEN, Xieping HUANG, Shu YU, Wei CAO, Weiqin DANG, Yangqiang WANG

Pages 291-305

https://doi.org/10.1016/j.ijsrc.2020.06.001 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300652

Abstract: Check dams are commonly constructed around the world for alleviating soil erosion and preventing sedimentation of downstream rivers and reservoirs. Check dams are more vulnerable to failure due to their less stringent flood control standards compared to other dams. Determining the critical precipitation that will result in overtopping of a dam is a useful approach to assessing the risk of failure on a probabilistic basis and for providing early warning in case of an emergency. However, many check dams are built in groups, spreading in several tributaries in cascade forms, comprising a complex network. Determining the critical precipitation for dam overtopping requires a knowledge of its upstream dams on whether they survived or were overtopped during the same storm, while these upstream dams in turn need the information for their upstream dams. The current paper presents an approach of decomposing the dam cluster into (1) the heading dam, (2) border dams, and (3) intermediate dams. The algorithm begins with the border dams that have no upstream dams and proceeds with upgraded maps without the previous border dams until all the dams have been checked. It is believed that this approach is applicable for small-scale check dam systems where the time lag of flood routing can be neglected. As a pilot study, the current paper presents the analytical results for the Wangmaogou Check Dam System that has 22 dams connected in series and parallel. The algorithm clearly identified 7 surviving dams, with the remaining ones being overtopped for a storm of 179.6 mm in 12 h, which is associated with a return period of one in 200 years.

Keywords: Risk analysis; Check dam; Critical precipitation; Cascade dams

13. One-dimensional morphodynamic model for retrogressive erosion based on a sediment entrainment theory at high flow velocity

Zenghui WANG, Junqiang XIA, Meirong ZHOU, Shanshan DENG, Tao LI

Pages 306-316

https://doi.org/10.1016/j.ijsrc.2020.10.002 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300998

Abstract: Retrogressive erosion is a high-speed erosion process that usually occurs during the rapid release of stored water in reservoirs built on sandy rivers. Retrogressive erosion has been utilized in the practice of reservoir sedimentation control, but accurate prediction of the bed deformation process by numerical models has rarely been reported. The current study presents a one-dimensional morphodynamic model for simulating the evolution process of retrogressive erosion induced by high-velocity flows on steep slopes. The governing equations apply a Cartesian coordinate system with a vertically oriented z axis. The bed surface gradient and friction terms in the flow equations include correction factors to take account of the effects of high slope on flow movement. The net vertical sediment flux term in the sediment transport and bed deformation equations is calculated using an equation of erosion velocity. Particularly, this equation is based on an empirical relation between the sediment entrainment rate and the Shields parameter in contrast to the traditional sediment transport capacity, and the critical Shields parameter is modified by taking into account the permeability of the sediment layer and the stability of particles on a slope. The feedback of scoured sediment on the flow movement is considered by additional terms in the governing equations. Flume experiments of retrogressive erosion in literature were simulated to validate the model. The temporal variations of the longitudinal profiles of the free surface and channel bed and the sediment transport rate were well predicted. The algorithm calculating sediment entrainment in the proposed model also was validated for an experiment measuring entrainment rate from the literature. More importantly, it was found that the morphodynamic model using the sediment transport capacity equation predicts the trend of cumulative erosion contrary to the measurements, while results of the proposed model can follow a similar trend with the observed data in the retrogressive erosion process.

Keywords: Retrogressive erosion; Sediment entrainment; High slope; Morphodynamic model; Reservoir

14. Grain-size end-members and environmentally sensitive grain-size components: A comparative study in the mud shelf depocenters off southern Brazil

Pages 317-327

https://doi.org/10.1016/j.ijsrc.2020.07.004 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300767

Abstract: The current study aims to do a comparative analysis of the results obtained with two End-Member (EM) grain-size modeling techniques (AnalySize and BasEMMA) and the Environmental Sensitive Grain-Size (ESGS) modeling for sediment samples collected in the mudbelts of the southern Brazilian shelf. The methods were compared using grain-size data from the south Brazilian shelf, and the results are discussed here. It is the first time that the concept of ESGS, in its present form, is utilized outside China. The results show that despite its relative ease of use, the ESGS is not fully comparable to the EM analyses, and only two grain-size ESGS classes were recognized as analogous to EMs. The comparison of the AnalySize and Bas EMMA procedures also revealed significant differences between the techniques. A comparative analysis between the two EM techniques revealed advantages in the Bas EMMA, especially in the better correlation of the end-members with the original grain size distribution. The analysis of the geographical distribution of the EM abundances allowed point sources of sandy populations to be recognized as well as the contribution of the Rio de la Plata as a source of silty sediments to be inferred.

Keywords: Grain-size; End-member; Environmentally sensitive; Mudbelt; Continental shelf

15. Equilibrium relations for water and sediment transport in the Yellow River

Xujian CHEN, Yuqi AN, Zhihao ZHANG, Chunhong HU

Pages 328-334

https://doi.org/10.1016/j.ijsrc.2020.07.006 https://www.sciencedirect.com/science/article/abs/pii/S1001627920300780

Abstract: The equilibrium relations for water and sediment transport refer to the relative balance of sediment transport and the relative stability of river courses formed by the automatic adjustment of riverbeds. This is the theoretical basis for the comprehensive management of sediment in the Yellow River. Based on the theories of sediment carrying capacity and the delayed response of riverbed evolution, in this study, the equilibrium relations for water and sediment transport in the Yellow River are established. These relations include the equilibrium relationships between water and sediment transport and bankfull discharge in the upper and lower Yellow River and between water and sediment transport and the Tongguan elevation in the middle Yellow River. The results reveal that for the Ningmeng reach, the Tongguan reach, and the lower Yellow River, erosion and deposition in the riverbeds are adjusted automatically, and water and sediment transport can form highly constrained equilibrium relationships. These newly established equilibrium relationships can be applied to calculate the optimal spatial allocation scheme for sediment in the Yellow River.

Keywords: Yellow River; Water and sediment transport; Riverbed evolution; Bankfull discharge; Equilibrium relationship