Pub Date : 2025-07-29DOI: 10.1016/j.ijsrc.2025.07.006
Hao Hou , Wei Zhu , Cheng Lin , Huan Liu , Tao Liang , Jinyuan Xu
Fluid mud, characterized by a bulk density < 1.2 g/cm3, has various adverse environmental effects; furthermore, it can pose challenges for maritime navigation, as fluid mud is an important factor for determining the depth of navigation channels. Notably, the formation of fluid mud by mixing sand and clay is a complex process. Fluid mud typically occurs on the surface of sediment beds in river estuaries, where the confluence of freshwater and saltwater in such regions promotes particle flocculation. The current study is the first to document the occurrence of fluid mud in Lake Taihu, China. The formation mechanisms were investigated through a comprehensive field and laboratory characterization program. The presence of large flocs was confirmed through this program, prompting further investigation into the role of organic matter. The results indicated that polysaccharides played a crucial role in promoting the aggregation of inorganic particles into flocs. In Lake Taihu, cyanobacterial accumulation zones, which are rich in extracellular polymeric substances (EPS), were primarily found in downwind bays, which also served as the sediment deposition areas. Notably, flocs with a size of ∼80 μm contributed to the formation of highly loose fluid mud in the region, with the density varying from 1.09 to 1.13 g/cm3. Overall, the current study advances the current literature on hydrogeology and sedimentology, particularly with respect to the characterization and formation of fluid mud in lakes.
{"title":"Investigation into the existence and genesis of fluid mud in Lake Taihu, China","authors":"Hao Hou , Wei Zhu , Cheng Lin , Huan Liu , Tao Liang , Jinyuan Xu","doi":"10.1016/j.ijsrc.2025.07.006","DOIUrl":"10.1016/j.ijsrc.2025.07.006","url":null,"abstract":"<div><div>Fluid mud, characterized by a bulk density < 1.2 g/cm<sup>3</sup>, has various adverse environmental effects; furthermore, it can pose challenges for maritime navigation, as fluid mud is an important factor for determining the depth of navigation channels. Notably, the formation of fluid mud by mixing sand and clay is a complex process. Fluid mud typically occurs on the surface of sediment beds in river estuaries, where the confluence of freshwater and saltwater in such regions promotes particle flocculation. The current study is the first to document the occurrence of fluid mud in Lake Taihu, China. The formation mechanisms were investigated through a comprehensive field and laboratory characterization program. The presence of large flocs was confirmed through this program, prompting further investigation into the role of organic matter. The results indicated that polysaccharides played a crucial role in promoting the aggregation of inorganic particles into flocs. In Lake Taihu, cyanobacterial accumulation zones, which are rich in extracellular polymeric substances (EPS), were primarily found in downwind bays, which also served as the sediment deposition areas. Notably, flocs with a size of ∼80 μm contributed to the formation of highly loose fluid mud in the region, with the density varying from 1.09 to 1.13 g/cm<sup>3</sup>. Overall, the current study advances the current literature on hydrogeology and sedimentology, particularly with respect to the characterization and formation of fluid mud in lakes.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 890-897"},"PeriodicalIF":3.7,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486282","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The isotope tracing method provides a novel way to investigate the underlying mechanisms of water balance. This study focused on Taozi Lake in Changsha, a city in the subtropical monsoon region. We conducted continuous monitoring of meteorological factors and stable isotopes in precipitation and lake water samples and further employed the isotope mass balance model to estimate the evaporation to inflow ratio (E/I). The results revealed that the fitted slope of the lake water evaporation line (SLEL) was close to or even greater than the slope of the local meteoric water line (SLMWL) because of the inverse seasonal variations in precipitation isotopes and evaporation intensity. This led to significant depletion of stable isotopes in the water source. Conversely, the theoretical SLEL values derived from the Craig‒Gordon model provided a more accurate depiction of the evaporation enrichment processes of lake water and were more appropriate for identifying lake water sources. The E/I ratios exhibited seasonal variations, with the highest values occurring in autumn and the lowest values occurring in spring, reflecting the interplay between precipitation and evaporation. The interannual variability in the E/I ratios and lake water isotopes further underscored the lake's response to changing hydrometeorological conditions. The uncertainty in the E/I simulations was due primarily to the isotopic compositions of the inflow water and atmospheric vapor, followed by the relative humidity and surface water temperature. This study enhances our understanding of regional hydrological processes, particularly regarding lake water isotopes and simulations of lake water balance, while considering the uncertainties associated with the assumptions and input variables of the E/I ratio.
{"title":"Simulating the water balance of a small lake in the subtropical monsoon region via the stable isotopic technique","authors":"Meng Chen , Xinping Zhang , Xiong Xiao , Yong Zhang , Xuhong Zhan","doi":"10.1016/j.ijsrc.2025.07.007","DOIUrl":"10.1016/j.ijsrc.2025.07.007","url":null,"abstract":"<div><div>The isotope tracing method provides a novel way to investigate the underlying mechanisms of water balance. This study focused on Taozi Lake in Changsha, a city in the subtropical monsoon region. We conducted continuous monitoring of meteorological factors and stable isotopes in precipitation and lake water samples and further employed the isotope mass balance model to estimate the evaporation to inflow ratio (<em>E</em>/<em>I</em>). The results revealed that the fitted slope of the lake water evaporation line (<em>S</em><sub>LEL</sub>) was close to or even greater than the slope of the local meteoric water line (<em>S</em><sub>LMWL</sub>) because of the inverse seasonal variations in precipitation isotopes and evaporation intensity. This led to significant depletion of stable isotopes in the water source. Conversely, the theoretical <em>S</em><sub>LEL</sub> values derived from the Craig‒Gordon model provided a more accurate depiction of the evaporation enrichment processes of lake water and were more appropriate for identifying lake water sources. The <em>E</em>/<em>I</em> ratios exhibited seasonal variations, with the highest values occurring in autumn and the lowest values occurring in spring, reflecting the interplay between precipitation and evaporation. The interannual variability in the <em>E</em>/<em>I</em> ratios and lake water isotopes further underscored the lake's response to changing hydrometeorological conditions. The uncertainty in the <em>E</em>/<em>I</em> simulations was due primarily to the isotopic compositions of the inflow water and atmospheric vapor, followed by the relative humidity and surface water temperature. This study enhances our understanding of regional hydrological processes, particularly regarding lake water isotopes and simulations of lake water balance, while considering the uncertainties associated with the assumptions and input variables of the <em>E</em>/<em>I</em> ratio.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 898-910"},"PeriodicalIF":3.7,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486283","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-24DOI: 10.1016/j.ijsrc.2025.07.005
Fengling Yu , Junyang Ma , Zhaoquan Huang , Chengcheng Gao , Yishu Hou , Liangrong Zou , Dan Yu , Nengwang Chen , Siguang Liu , Tian Xia
Deep insight into the spatialtemporal composition and distribution dynamics of suspended particulate organic carbon (POC) and sedimentary total organic carbon (TOC) within the mountainous river-estuary-bay continuum provides us with a unique perspective for examining the impact of estuarine flow on the material cycle within the river-estuary-bay systems. In this study, we conducted a comparative analysis of the river-estuary-bay continuum of two subtropical mountainous rivers, the Jiulong River (JLR) and the Zhangjiang River (ZJR), southern China. Seasonal samples of suspended particles and surface sediments were collected from the lower river reaches, estuaries, and bay areas. Both suspended and sedimentary samples were analyzed for organic content and their isotopic signatures (δ13C), and C/N ratios. The results reveal notable differences between the two systems. The JLR system exhibits stronger seasonal and spatial variations in POC sources compared to the ZJR system. In contrast, the estuary and bay of the ZJR system show more pronounced marine POC signals than those of the JLR system. In the sediments of the estuary and bay, soil organic matter and C3 plants contribute to over 60 % of the total organic matter in the JLR system, whereas in the ZJR system, marine organic matter and soil are the two most significant contributors. This study identifies that estuarine hydraulic conditions control the provenance, dynamics, and fate of particulate organic matter (POM). River discharge plays a pivotal role in regulating the dispersion of terrestrial organic matter in the estuary; Estuarine circulation and the position of the turbidity maximum zone govern the temporal and spatial distribution of sedimentary organic matter. Moreover, high soil contribution to the estuarine and bay sediment organic matter suggests strong soil erosion of adjacent land, likely attributed to human activities. Our findings highlight the high sensitivity of POC composition and dynamics in these mountainous river-estuary-bay systems to changes in river discharge, tidal current, and maybe wave conditions. The results of this study will deepen our understanding of the dynamics and fate of POM from different sources within the mountainous river-estuary-bay continuum and provide vital information for the effective management of these highly dynamic and sensitive ecosystems.
{"title":"Sedimentary organic matters within the subtropical mountainous river-estuary-bay continuum: Provenances, fates and implications","authors":"Fengling Yu , Junyang Ma , Zhaoquan Huang , Chengcheng Gao , Yishu Hou , Liangrong Zou , Dan Yu , Nengwang Chen , Siguang Liu , Tian Xia","doi":"10.1016/j.ijsrc.2025.07.005","DOIUrl":"10.1016/j.ijsrc.2025.07.005","url":null,"abstract":"<div><div>Deep insight into the spatialtemporal composition and distribution dynamics of suspended particulate organic carbon (POC) and sedimentary total organic carbon (TOC) within the mountainous river-estuary-bay continuum provides us with a unique perspective for examining the impact of estuarine flow on the material cycle within the river-estuary-bay systems. In this study, we conducted a comparative analysis of the river-estuary-bay continuum of two subtropical mountainous rivers, the Jiulong River (JLR) and the Zhangjiang River (ZJR), southern China. Seasonal samples of suspended particles and surface sediments were collected from the lower river reaches, estuaries, and bay areas. Both suspended and sedimentary samples were analyzed for organic content and their isotopic signatures (δ<sup>13</sup>C), and C/N ratios. The results reveal notable differences between the two systems. The JLR system exhibits stronger seasonal and spatial variations in POC sources compared to the ZJR system. In contrast, the estuary and bay of the ZJR system show more pronounced marine POC signals than those of the JLR system. In the sediments of the estuary and bay, soil organic matter and C<sub>3</sub> plants contribute to over 60 % of the total organic matter in the JLR system, whereas in the ZJR system, marine organic matter and soil are the two most significant contributors. This study identifies that estuarine hydraulic conditions control the provenance, dynamics, and fate of particulate organic matter (POM). River discharge plays a pivotal role in regulating the dispersion of terrestrial organic matter in the estuary; Estuarine circulation and the position of the turbidity maximum zone govern the temporal and spatial distribution of sedimentary organic matter. Moreover, high soil contribution to the estuarine and bay sediment organic matter suggests strong soil erosion of adjacent land, likely attributed to human activities. Our findings highlight the high sensitivity of POC composition and dynamics in these mountainous river-estuary-bay systems to changes in river discharge, tidal current, and maybe wave conditions. The results of this study will deepen our understanding of the dynamics and fate of POM from different sources within the mountainous river-estuary-bay continuum and provide vital information for the effective management of these highly dynamic and sensitive ecosystems.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"41 1","pages":"Pages 72-82"},"PeriodicalIF":3.7,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-24DOI: 10.1016/j.ijsrc.2025.07.008
Morteza Movahhedi, Amir Reza Zarrati, Abbas Ghaedi Haghighi, Mohammad Hosain Sayad
Many experiments were done over a relatively wide range of effective parameters to determine the stable size of riprap stones around wing-wall abutments. The experiments involved five sizes of riprap stones, three abutment lengths, and various flow depths and velocities. The results of this study indicate that in the range of tested parameters, the most important factors influencing riprap instability are the upstream Froude number, the ratio of abutment length to flow depth, and the ratio of abutment width (thickness) to flow depth. Based on the experimental results, a relation for designing the stable size of riprap around wing-wall abutments is presented and compared with previous equations developed for different shapes of bridge abutments.
{"title":"Experimental study on riprap stable size around wing-wall abutments","authors":"Morteza Movahhedi, Amir Reza Zarrati, Abbas Ghaedi Haghighi, Mohammad Hosain Sayad","doi":"10.1016/j.ijsrc.2025.07.008","DOIUrl":"10.1016/j.ijsrc.2025.07.008","url":null,"abstract":"<div><div>Many experiments were done over a relatively wide range of effective parameters to determine the stable size of riprap stones around wing-wall abutments. The experiments involved five sizes of riprap stones, three abutment lengths, and various flow depths and velocities. The results of this study indicate that in the range of tested parameters, the most important factors influencing riprap instability are the upstream Froude number, the ratio of abutment length to flow depth, and the ratio of abutment width (thickness) to flow depth. Based on the experimental results, a relation for designing the stable size of riprap around wing-wall abutments is presented and compared with previous equations developed for different shapes of bridge abutments.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 911-918"},"PeriodicalIF":3.7,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486339","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-17DOI: 10.1016/j.ijsrc.2025.07.004
Huilan Zhang , Fangzheng Gu , Shaoqin Xia , Feng Li , Ping Wang , Linghan Wang , Di Zhang , Yanchong Duan , Qigang Chen
Understanding how bed roughness modulates hydrodynamic processes around vegetation is critical for predicting soil erosion patterns in sloped landscapes. Through flume experiments with high-frequency particle image velocimetry (PIV), this study quantifies the interactions between bed roughness (ks = 0.009, 0.25, 0.75, 1.55) and horseshoe vortex (HV) dynamics under overland flow conditions (ReD = 2627–3815). Time-averaged flow field analysis, based on vorticity and swirl strength methods, revealed that increasing surface roughness disrupted the HV system by reducing the number of vortices, decreasing the vorticity and swirl strength of the primary HV, and shifting its position closer to the bed. Statistical analysis of the instantaneous velocity components showed the emergence of bimodal probability density functions (PDFs) and joint probability density functions (JPDFs) in the near-wall region upstream of the cylinder, representing the backflow and downflow events. As roughness increased, the bimodal region decreased in size and shifted further from the cylinder. Linear stochastic estimation (LSE) was used to characterize the underlying flow modes, indicating that the backflow event was associated with the backflow mode, while the downflow event was linked to the zero-flow mode. Notably, roughness elements enhanced flow stagnation (zero-flow mode dominance > 60 %), suggesting a potential mechanism for erosion mitigation. These findings provide quantitative linkages between micro-scale hydrodynamics and landscape-scale erosion processes, informing the design of vegetation-based erosion control strategies through targeted roughness manipulation.
{"title":"Bed roughness effects on horseshoe vortex dynamics and soil erosion mechanisms in vegetated overland flows","authors":"Huilan Zhang , Fangzheng Gu , Shaoqin Xia , Feng Li , Ping Wang , Linghan Wang , Di Zhang , Yanchong Duan , Qigang Chen","doi":"10.1016/j.ijsrc.2025.07.004","DOIUrl":"10.1016/j.ijsrc.2025.07.004","url":null,"abstract":"<div><div>Understanding how bed roughness modulates hydrodynamic processes around vegetation is critical for predicting soil erosion patterns in sloped landscapes. Through flume experiments with high-frequency particle image velocimetry (PIV), this study quantifies the interactions between bed roughness (<em>k</em><sub><em>s</em></sub> = 0.009, 0.25, 0.75, 1.55) and horseshoe vortex (HV) dynamics under overland flow conditions (<em>Re</em><sub><em>D</em></sub> = 2627–3815). Time-averaged flow field analysis, based on vorticity and swirl strength methods, revealed that increasing surface roughness disrupted the HV system by reducing the number of vortices, decreasing the vorticity and swirl strength of the primary HV, and shifting its position closer to the bed. Statistical analysis of the instantaneous velocity components showed the emergence of bimodal probability density functions (PDFs) and joint probability density functions (JPDFs) in the near-wall region upstream of the cylinder, representing the backflow and downflow events. As roughness increased, the bimodal region decreased in size and shifted further from the cylinder. Linear stochastic estimation (LSE) was used to characterize the underlying flow modes, indicating that the backflow event was associated with the backflow mode, while the downflow event was linked to the zero-flow mode. Notably, roughness elements enhanced flow stagnation (zero-flow mode dominance > 60 %), suggesting a potential mechanism for erosion mitigation. These findings provide quantitative linkages between micro-scale hydrodynamics and landscape-scale erosion processes, informing the design of vegetation-based erosion control strategies through targeted roughness manipulation.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"41 1","pages":"Pages 110-124"},"PeriodicalIF":3.7,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929120","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-16DOI: 10.1016/j.ijsrc.2025.07.003
Hui Liang , Ruijing Jiang , Ronghua Liu , Jiyang Tian , Xingyao Pan , Zhuangxian Tian , Zhixian Cao
Rainfall-induced flash floods often trigger active sediment transport and substantial morphological changes, which in turn affect flood dynamics. Previous numerical studies have mostly overlooked the strong interactions between flow, sediment transport, and morphological evolution, and inevitably their impacts on flash flooding have remained poorly understood. Here a two-dimensional (2D) coupled shallow water hydro-sediment-morphodynamic (SHSM) model is applied to reconstruct an extreme flash flood in the Jiuyuan Gully catchment, Beijing, China, in July 2023. The impacts of sediment transport and morphological change on the flash flood are evaluated by comparing the results of a shallow water hydrodynamic (HD) model and the SHSM model. The SHSM model is shown to outperform the HD model in reproducing the observed maximum water levels, as sediment transport and morphological changes are explicitly taken into account. Bed load sediment prevails, while its transport rate may amount up to 30 kg/(m·s) in the flood conveyance channel and deviate from the transport capacity determined in line with local flows, as sediment entrainment is hindered by the concrete-lined bed. Aggradation in the flood conveyance channel is significant, reaching 3.0 m locally. Accordingly, the water level increases, leading to overbank flooding and extended inundation over the floodplains and adjacent areas. Consequently, flash flooding is exacerbated. The current findings highlight the critical role of morphological change induced by active sediment transport in modifying flash flooding, underscoring the significance of morphological change for practical flood warning and development of effective risk management strategies.
{"title":"Highly active sediment transport induces morphodynamic changes exacerbating flash flooding","authors":"Hui Liang , Ruijing Jiang , Ronghua Liu , Jiyang Tian , Xingyao Pan , Zhuangxian Tian , Zhixian Cao","doi":"10.1016/j.ijsrc.2025.07.003","DOIUrl":"10.1016/j.ijsrc.2025.07.003","url":null,"abstract":"<div><div>Rainfall-induced flash floods often trigger active sediment transport and substantial morphological changes, which in turn affect flood dynamics. Previous numerical studies have mostly overlooked the strong interactions between flow, sediment transport, and morphological evolution, and inevitably their impacts on flash flooding have remained poorly understood. Here a two-dimensional (2D) coupled shallow water hydro-sediment-morphodynamic (SHSM) model is applied to reconstruct an extreme flash flood in the Jiuyuan Gully catchment, Beijing, China, in July 2023. The impacts of sediment transport and morphological change on the flash flood are evaluated by comparing the results of a shallow water hydrodynamic (HD) model and the SHSM model. The SHSM model is shown to outperform the HD model in reproducing the observed maximum water levels, as sediment transport and morphological changes are explicitly taken into account. Bed load sediment prevails, while its transport rate may amount up to 30 kg/(m·s) in the flood conveyance channel and deviate from the transport capacity determined in line with local flows, as sediment entrainment is hindered by the concrete-lined bed. Aggradation in the flood conveyance channel is significant, reaching 3.0 m locally. Accordingly, the water level increases, leading to overbank flooding and extended inundation over the floodplains and adjacent areas. Consequently, flash flooding is exacerbated. The current findings highlight the critical role of morphological change induced by active sediment transport in modifying flash flooding, underscoring the significance of morphological change for practical flood warning and development of effective risk management strategies.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 935-953"},"PeriodicalIF":3.7,"publicationDate":"2025-07-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486338","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-11DOI: 10.1016/j.ijsrc.2025.07.001
Le Wang , Dayu Wang , Alan James Stewart Cuthbertson , Qingxia Chen , Jianzhao Guan , Lei Zhang , Hai Huang , Shanghong Zhang
Flocculation of cohesive sediments is widely observed in natural aquatic-sedimentary environments, such as river estuaries and nearshore coastal waters, where salinity, suspended sediment concentration and flow turbulence cause fine sediment particles to aggregate into larger flocs, resulting in intensified sedimentation. In contrast, there is currently very little evidence linking enhanced sedimentation, leading to significant storage loss within large freshwater reservoirs, specifically to fine sediment flocculation processes. Massive fine sediment volumes have been deposited in the Three Gorges Reservoir (TGR), China, which has been impounded over the past two decades. It has not yet been established what role, if any, fine sediment flocculation processes play a role in the amplified sedimentation rates that have been observed. The current study aims to test the hypothesis that fine sediment flocculation processes, which occur under prevalent hydrodynamic (i.e., turbulent shear rate G ≈ 4.67–227.39 s−1) and sedimentary (i.e., sediment concentration C ≈ 0.02–2.00 kg/m3) conditions in the TGR, play important roles in sedimentation rates during reservoir impoundment. A laboratory-based, experimental study was conducted within a new, bespoke Couette flow system designed specifically to mimic the environmental shear flow conditions experienced during impoundment. Sediment samples obtained directly from the TGR bed deposits were tested within this facility to ascertain their flocculation and settling behavior under controlled shear flows and sediment concentrations. A comprehensive analysis combining the sediment composition, measured aggregate/floc size distributions and their corresponding settling behavior collectively pointed to the occurrence of fine sediment flocculation within the TGR. By disentangling the individual influences of flow velocity and sediment concentration on floc size, the combined influence of the flocculation parameters C/G1/2 on floc size is fully revealed through experimental evidence, with a new empirical combined parameter, C0.44/G0.47, identified as being more appropriate for characterizing the variability in floc size under varying flow‒sediment conditions. The majority of flocs measured in the tests have a mean settling velocity nearly five times greater than that of the majority of primary fine sediment particles (i.e., with diameter D ≤ 29 μm) that comprise the sediment grain size distribution found in the TGR impoundment. This finding provides new evidence for the potential for flocculation-enhanced sedimentation rates occurring within the TGR and other similar large freshwater reservoirs, as dam construction disrupts the natural sediment continuity within the river system and inhibits the downstream transport of fine sediments.
{"title":"Experimental measurement of flocculation and settling behavior in fine sediments from the Three Gorges Reservoir, China","authors":"Le Wang , Dayu Wang , Alan James Stewart Cuthbertson , Qingxia Chen , Jianzhao Guan , Lei Zhang , Hai Huang , Shanghong Zhang","doi":"10.1016/j.ijsrc.2025.07.001","DOIUrl":"10.1016/j.ijsrc.2025.07.001","url":null,"abstract":"<div><div>Flocculation of cohesive sediments is widely observed in natural aquatic-sedimentary environments, such as river estuaries and nearshore coastal waters, where salinity, suspended sediment concentration and flow turbulence cause fine sediment particles to aggregate into larger flocs, resulting in intensified sedimentation. In contrast, there is currently very little evidence linking enhanced sedimentation, leading to significant storage loss within large freshwater reservoirs, specifically to fine sediment flocculation processes. Massive fine sediment volumes have been deposited in the Three Gorges Reservoir (TGR), China, which has been impounded over the past two decades. It has not yet been established what role, if any, fine sediment flocculation processes play a role in the amplified sedimentation rates that have been observed. The current study aims to test the hypothesis that fine sediment flocculation processes, which occur under prevalent hydrodynamic (i.e., turbulent shear rate <em>G</em> ≈ 4.67–227.39 s<sup>−1</sup>) and sedimentary (i.e., sediment concentration <em>C</em> ≈ 0.02–2.00 kg/m<sup>3</sup>) conditions in the TGR, play important roles in sedimentation rates during reservoir impoundment. A laboratory-based, experimental study was conducted within a new, bespoke Couette flow system designed specifically to mimic the environmental shear flow conditions experienced during impoundment. Sediment samples obtained directly from the TGR bed deposits were tested within this facility to ascertain their flocculation and settling behavior under controlled shear flows and sediment concentrations. A comprehensive analysis combining the sediment composition, measured aggregate/floc size distributions and their corresponding settling behavior collectively pointed to the occurrence of fine sediment flocculation within the TGR. By disentangling the individual influences of flow velocity and sediment concentration on floc size, the combined influence of the flocculation parameters <em>C</em>/<em>G</em><sup>1/2</sup> on floc size is fully revealed through experimental evidence, with a new empirical combined parameter, <em>C</em><sup>0.44</sup>/<em>G</em><sup>0.47</sup>, identified as being more appropriate for characterizing the variability in floc size under varying flow‒sediment conditions. The majority of flocs measured in the tests have a mean settling velocity nearly five times greater than that of the majority of primary fine sediment particles (i.e., with diameter <em>D</em> ≤ 29 μm) that comprise the sediment grain size distribution found in the TGR impoundment. This finding provides new evidence for the potential for flocculation-enhanced sedimentation rates occurring within the TGR and other similar large freshwater reservoirs, as dam construction disrupts the natural sediment continuity within the river system and inhibits the downstream transport of fine sediments.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 954-971"},"PeriodicalIF":3.7,"publicationDate":"2025-07-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486274","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-05DOI: 10.1016/j.ijsrc.2025.06.013
Misagh Parhizkar , Manuel Esteban Lucas-Borja , Pasquale Fabio Giuseppe Filianoti , Nikolaos Tziolas , Demetrio Antonio Zema
This study analyzed the effects of very intense rainfall (98 mm/h for 30 min) on soil left bare or treated with polyacrylamide, rice husk biochar and hydromulching. Rill morphometry, surface runoff and soil loss were measured in plots (100 cm × 50 cm) with three longitudinal slopes (10%, 17% and 28%). On the basis of these measurements, runoff and erosion were predicted via multiple linear equations for the experimental conditions. The effects of polyacrylamide application on surface runoff, soil loss and rill formation were not significant. In contrast, decreases in runoff generation and soil loss ((−40%)–55%) as well as rill widening and elongation ((−45%)–75%) were observed after the application of rice husk biochar and hydromulching. A multivariate statistical analysis revealed significant relationships among the soil hydrological, erosive and morphometric variables, as shown by coefficients of correlation greater than 0.78. Bare soils and plots treated with polyacrylamide on one side and those treated with rice husk biochar and hydromulching noticeably differ in their hydrological and morphological responses to intense rainfall. The multiple linear equations were accurate (R2 > 0.90) in predicting surface runoff and soil loss under all soil conditions. This study has several limitations (e.g., plot scale, simulated rainfall, and specific soil conditions). However, the results indicate the most suitable soil conservation techniques for specific rainfall intensities and conditions (excluding ecosystems subjected to deforestation). Moreover, this study provides multiple linear equations as hydrological tools to predict flood and erosion hazards in these areas.
{"title":"Variability in rill morphometry, surface runoff and erosion with soil conservation techniques (application of polyacrylamide and rice husk biochar and hydromulching) in deforested hillslopes under simulated rainfall","authors":"Misagh Parhizkar , Manuel Esteban Lucas-Borja , Pasquale Fabio Giuseppe Filianoti , Nikolaos Tziolas , Demetrio Antonio Zema","doi":"10.1016/j.ijsrc.2025.06.013","DOIUrl":"10.1016/j.ijsrc.2025.06.013","url":null,"abstract":"<div><div>This study analyzed the effects of very intense rainfall (98 mm/h for 30 min) on soil left bare or treated with polyacrylamide, rice husk biochar and hydromulching. Rill morphometry, surface runoff and soil loss were measured in plots (100 cm × 50 cm) with three longitudinal slopes (10%, 17% and 28%). On the basis of these measurements, runoff and erosion were predicted via multiple linear equations for the experimental conditions. The effects of polyacrylamide application on surface runoff, soil loss and rill formation were not significant. In contrast, decreases in runoff generation and soil loss ((−40%)–55%) as well as rill widening and elongation ((−45%)–75%) were observed after the application of rice husk biochar and hydromulching. A multivariate statistical analysis revealed significant relationships among the soil hydrological, erosive and morphometric variables, as shown by coefficients of correlation greater than 0.78. Bare soils and plots treated with polyacrylamide on one side and those treated with rice husk biochar and hydromulching noticeably differ in their hydrological and morphological responses to intense rainfall. The multiple linear equations were accurate (<em>R</em><sup>2</sup> > 0.90) in predicting surface runoff and soil loss under all soil conditions. This study has several limitations (e.g., plot scale, simulated rainfall, and specific soil conditions). However, the results indicate the most suitable soil conservation techniques for specific rainfall intensities and conditions (excluding ecosystems subjected to deforestation). Moreover, this study provides multiple linear equations as hydrological tools to predict flood and erosion hazards in these areas.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"40 6","pages":"Pages 857-868"},"PeriodicalIF":3.7,"publicationDate":"2025-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145486279","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-07-04DOI: 10.1016/j.ijsrc.2025.06.012
Zeyad Ayoob Sulaiman , Mena Ahmed Al Sawaf , Ahmed Shareef Hayder , Ahmed Moustafa Ahmed Moussa
Many fluvial systems have undergone significant changes in their morphology due to base level fall since the last glaciation. Channels in such transient fluvial systems continuously adjust their morphology and may still be incising until reaching a new equilibrium condition. This study examines morphometric change detection indices and techniques to quantify and analyze the recent variations in the channel properties of the lower portions of the Le Sueur and Maple Rivers, in response to upstream knickpoint migration. The results reveal that channel reaches upstream of the knickzones remain relatively stable, exhibiting low channel bed gradients and minimal morphological change. In contrast, the local channel gradient increases about ∼3 fold near the knickpoints and continues with predominantly high rates into the downstream direction. Together, the morphometric indices indicate that the channel geometry of the Maple and Le Sueur Rivers downstream of the knickpoints is actively adjusting to accommodate the rapid base level drop. Because of incomplete adjustment processes, both rivers experienced remarkable change in channel geometry between 2008 and 2015, albeit with differing adjustment patterns. In particular, the percentage change in channel properties along the knickzone reaches up to 120% for the channel cross-sectional area, 60% for the channel width, and 75% for the mean hydraulic depth. These changes are accompanied by a sharp increase in cross-sectional stream power and impose boundary shear stress along the knickzones which amplify sediment transport capacity and drive further modifications to channel size and shape. This study provides a quantitative framework for assessing geomorphic responses to base level drop and provides insights into the feedback mechanisms between hydraulic forces and channel morphology. The findings have broader implications for understanding channel evolution under non-equilibrium conditions and for guiding river management in similar fluvial systems.
{"title":"Characterizing changes in channel morphology associated with base level fall: Application on Le Sueur and Maple Rivers","authors":"Zeyad Ayoob Sulaiman , Mena Ahmed Al Sawaf , Ahmed Shareef Hayder , Ahmed Moustafa Ahmed Moussa","doi":"10.1016/j.ijsrc.2025.06.012","DOIUrl":"10.1016/j.ijsrc.2025.06.012","url":null,"abstract":"<div><div>Many fluvial systems have undergone significant changes in their morphology due to base level fall since the last glaciation. Channels in such transient fluvial systems continuously adjust their morphology and may still be incising until reaching a new equilibrium condition. This study examines morphometric change detection indices and techniques to quantify and analyze the recent variations in the channel properties of the lower portions of the Le Sueur and Maple Rivers, in response to upstream knickpoint migration. The results reveal that channel reaches upstream of the knickzones remain relatively stable, exhibiting low channel bed gradients and minimal morphological change. In contrast, the local channel gradient increases about ∼3 fold near the knickpoints and continues with predominantly high rates into the downstream direction. Together, the morphometric indices indicate that the channel geometry of the Maple and Le Sueur Rivers downstream of the knickpoints is actively adjusting to accommodate the rapid base level drop. Because of incomplete adjustment processes, both rivers experienced remarkable change in channel geometry between 2008 and 2015, albeit with differing adjustment patterns. In particular, the percentage change in channel properties along the knickzone reaches up to 120% for the channel cross-sectional area, 60% for the channel width, and 75% for the mean hydraulic depth. These changes are accompanied by a sharp increase in cross-sectional stream power and impose boundary shear stress along the knickzones which amplify sediment transport capacity and drive further modifications to channel size and shape. This study provides a quantitative framework for assessing geomorphic responses to base level drop and provides insights into the feedback mechanisms between hydraulic forces and channel morphology. The findings have broader implications for understanding channel evolution under non-equilibrium conditions and for guiding river management in similar fluvial systems.</div></div>","PeriodicalId":50290,"journal":{"name":"International Journal of Sediment Research","volume":"41 1","pages":"Pages 60-71"},"PeriodicalIF":3.7,"publicationDate":"2025-07-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145929049","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"环境科学与生态学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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