Morphological reactions of schematic alluvial rivers: Long simulations with a 0-D model

Pages 295–304

M. Franzoia, M. Nones

 

Bedform development and its effect on bed stabilization and sediment transport based on a flume experiment with non-uniform sediment

Pages 305–312

Su-Chin Chen, Chia-Ning Yang, Ching-Ying Tsou

 

Study on the assessment of the comprehensive benefits of the utilization of sediment resources in reservoir areas

Pages 313–323

Jingmin Hou, Yuanjian Wang

 

Methodology for determination of correction factors in direct gamma spectrometric measurement of radionuclides in sediments

Pages 324–330

Esra Uyar, Alptuğ Özer Yüksel, Rufiyet Güven, Haluk Yücel

 

Particle size distribution of bed materials in the sandy river bed of alluvial rivers

ages 331–339

Luohao Zhang, Hongwu Zhang, Hongwu Tang, Chensu Zhao

 

A comparative study of three different learning algorithms applied to ANFIS for predicting daily suspended sediment concentration

Pages 340–350

Keivan Kaveh, Minh Duc Bui, Peter Rutschmann

 

The morphodynamic responses to deposition-promoting projects in island and reef coasts of the Zhoushan Archipelago, China

Pages 351–363

Qingzhi Hou, Zhili Wang, Yongjun Lu, Siping Mo

 

Reduction of local scour at river confluences using a collar

Pages 364–372

Nargess Amini, Behnam Balouchi, Mahmood Shafai Bejestan

 

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel—A case study on Sanmenxia Reservoir and the Lower Yellow River

Pages 373–383

Jianguo Chen, Wenhao Zhou, Shanshan Han, Gaohu Sun

 

Bed roughness and grain sorting- an experimental study over fine to medium sand beds

Pages 384–400

Barendra Purkait, Dipanjan Das Majumdar, Rajat Mazumder

 

Distribution characteristics of inertial sediment particles in the turbulent boundary layer of an open channel flow determined using Voronoï analysis

Pages 401–409

Xin Liu, Chunning Ji, Xiaoli Xu, Dong Xu, John J.R. Williams

 

Geochemical fractionation and ecological risks assessment of benthic sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean

Pages 410–420

Nsikak U. Benson, Essien D. Udosen, Joseph P. Essien, Winifred U. Anake, ... Abass A. Olajire

 

Modelling of resuspension due to fish activity: Mathematical modeling and annular flume experiments

Pages 421–431

Olya Skulovich, Catrina Cofalla, Caroline Ganal, Holger Schüttrumpf, Avi Ostfeld

 

Evaluation of phosphorus bioavailability in El Mex Bay and Lake Mariut sediments

Pages 432–441

Naglaa F. Soliman, Gehan M. El Zokm, Mohamed A. Okbah

 

Phosphorus fractions and sorption dynamics in the sediments of two Ca-SO4 water reservoirs in the central Argentine Andes

Pages 442–451

José Gabriel León, Fernando Luis Pedrozo, Pedro Félix Temporetti

 

Study on hydraulic characteristics of sabo dam with a flap structure for debris flow

Pages 452–464

Yeonjoong Kim, Hajime Nakagawa, Kenji Kawaike, Hao Zhang

 

Full papers are available at ScienceDirect:

http://www.sciencedirect.com/science/journal/10016279, with free access of the abstracts.

===============================================================

 

Morphological reactions of schematic alluvial rivers: Long simulations with a 0-D model

Pages 295–304

M. Franzoia, M. Nones

Abstract

The paper presents a 0-D model of an alluvial watercourse schematized in two connected reaches, evolving at the long time-scale and under the hypothesis of Local Uniform Flow. Each reach is defined by its geometry (constant length and width, time-changing slope) and grain-size composition of the bed, while the sediment transport is computed using a sediment rating curve. The slope evolution is provided by a 0-D mass balance and the evolution of the bed composition is computed by a 0-D Hirano equation. A system of differential equations, solved with a predictor-corrector scheme, is derived and applied to the schematic watercourse to simulate the morphological response to changing initial conditions, and the evolution towards long-term equilibrium conditions. Differently from a single-reach 0-D schematization with uniform grain-size, besides the simplifications adopted, the model proposed here simulates the behaviour of alluvial rivers in a physically-based way, showing a grain-size fining in the downstream direction accompanied by milder slopes, and a tendency to develop concave longitudinal profiles.

 

Bedform development and its effect on bed stabilization and sediment transport based on a flume experiment with non-uniform sediment

Pages 305–312

Su-Chin Chen, Chia-Ning Yang, Ching-Ying Tsou

Abstract

Non-uniform sediment deposited in a confined, steep mountain channel can alter the bed surface composition. This study evaluates the contribution of geometric and resistance parameters to bed stabilization and the reduction in sediment transport. Flume experiments were done under various hydraulic conditions with non-uniform bed material and no sediment supply from upstream. Results indicate that flume channels respond in a sequence of coarsening and with the formation of bedform-roughness features such as rapids, cascades, and steps. A bedform development coefficient is introduced and is shown to increase (i.e. vertical sinuosity develops) in response to increasing shear stress during the organization process. The bedform development coefficient also is positively correlated with the critical Shields number and Manning׳s roughness coefficient, suggesting the evolution of flow resistance with increasing bedform development. The sediment transport rate decreases with increasing bed shear stress and bedform development, further illustrating the effect of bed stabilization. An empirical sediment transport model for an equilibrium condition is proposed that uses the bedform development coefficient, relative particle submergence (i.e. the ratio of mean water depth and maximum sediment diameter), modified bed slope, and discharge. The model suggests bedform development can play a primary role in reducing sediment transport (increasing bed stabilization). The model is an extension of Lane׳s (1955) relation specifically adapted for mountain streams. These results explain the significance of bedform development in heightening flow resistance, stabilizing the bed, and reducing sediment transport in coarse, steep channels.

 

Study on the assessment of the comprehensive benefits of the utilization of sediment resources in reservoir areas

Pages 313–323

Jingmin Hou, Yuanjian Wang

Abstract

The utilization of sediment in reservoirs as resources is an efficient way to reduce reservoir sedimentation and turn disadvantage into benefit. Based on economic, social and ecological functions of sediment resources, this paper puts forward a two-layer, three-dimensional evaluation index system. It also establishes six direct and indirect indicators with their formulas to calculate the comprehensive benefits of sediment utilization in the Xixiayuan reservoir of the Yellow River with a volume of 2000 m3. The results show that social benefits would be more prominent, with the ecological benefits coming second. This demonstrates that the indirect public value of utilizing the sediment resources in the Yellow River Basin can be far greater than its direct economic value.

 

Methodology for determination of correction factors in direct gamma spectrometric measurement of radionuclides in sediments

Pages 324–330

Esra Uyar, Alptuğ Özer Yüksel, Rufiyet Güven, Haluk Yücel

Abstract

In this study, the practical methodologies are described for the determination of the factors for the self-absorption effect (Fs), spectral interferences (Fcsi), and true coincidence summing effects (Fcoi), which are used in direct gamma-spectrometric measurement of radionuclides such as 210Pb, 238U, 234Th, 226Ra, 214Pb, 228Ac, 208Tl, 214Bi, 137Cs and 40K in samples. To validate the applied methods, certified reference materials (CRMs) of lake and stream sediments were measured with an n-type Germanium (Ge) detector-calibrated using a multinuclide reference source. The highest self-absorption correction factors ranged from Fs = 1.44–2.10 for 46.5 keV peak (210Pb) and Fs = 1.25–1.60 for 63.3 keV peak (234Th) lying in the low energy region of the spectrum. The systematic influence was observed for 186.2 keV (226Ra) peak due to spectral interferences with the 235U contribution. For this peak, Fcsi is changed from 0.921 to 0.955. Additionally, the present study suggests that true coincidence summing (TCS) effects are not dominant, except for 208Tl and 214Bi for which Fcoi ranged from 1.179 to 1.192 an ranged from 1.140 to 1.151, respectively.

 

Particle size distribution of bed materials in the sandy river bed of alluvial rivers

ages 331–339

Luohao Zhang, Hongwu Zhang, Hongwu Tang, Chensu Zhao

Abstract

The particle size distribution of bed materials in the sandy river bed of alluvial rivers is important in the study of topics such as friction, river bed evolution, erosion, and siltation. It also can reflect the dependency relation between river bed sediment and flow intensity. In this paper, the critical pattern of sediment movement in the near-wall region of a sandy river bed was analyzed. According to the principle of momentum balance, the critical settling-rising condition of bed material in a sandy river bed was found to be instantaneous turbulent velocity equal to 2.7 times the sediment settling velocity in quiescent water. Based on a vertical instantaneous turbulent velocity with a Gaussian distribution, a theoretical relation for calculating the particle size distribution of bed materials in a sandy river bed without pre-known characteristic grain sizes was developed by solving a stochastic equation. The formula is verified using measured data, and the results show that the proposed formula was in accordance with the measured data. This study has theoretical significance and practical value for determining the bed material particle size distribution of the sandy bed of alluvial rivers.

 

A comparative study of three different learning algorithms applied to ANFIS for predicting daily suspended sediment concentration

Pages 340–350

Keivan Kaveh, Minh Duc Bui, Peter Rutschmann

Abstract

The modeling and prediction of suspended sediment in a river are key elements in global water recourses and environment policy and management. In the present study, an Adaptive Neuro-Fuzzy Inference System model trained with the Levenberg-Marquardt learning algorithm is considered for time series modeling of suspended sediment concentration in a river. The model is trained and validated using daily river discharge and suspended sediment concentration data from the Schuylkill River in the United States. The results of the proposed method are evaluated and compared with similar networks trained with the common Hybrid and Back-Propagation algorithms, which are widely used in the literature for prediction of suspended sediment concentration. Obtained results demonstrate that models trained with the Hybrid and Levenberg-Marquardt algorithms are comparable in terms of prediction accuracy. However, the networks trained with the Levenberg-Marquardt algorithm perform better than those trained with the Hybrid approach.

 

The morphodynamic responses to deposition-promoting projects in island and reef coasts of the Zhoushan Archipelago, China

Pages 351–363

Qingzhi Hou, Zhili Wang, Yongjun Lu, Siping Mo

Abstract

China׳s island and reef coasts are mainly distributed along the coasts of Zhejiang and Fujian provinces. These areas have favorable deep-water conditions and great development potential. The Zhoushan Archipelago is a typical island and reef coast. In the midst of the islands, there are many tidal channels with high water depth and high current velocity. Daishan Island is located on the northern part of the Zhoushan Archipelago. The sea north of Daishan Island can be characterized as having great water depth (generally between 10 and 20 m), high current velocity (the maximum measured value is about 2 m/s), and hyperconcentrated suspended sediment (annual average concentration under normal weather conditions is about 0.6 kg/m3). Sediment transport is influenced by the co-action of waves and currents. Land reclamation can ease the contradiction between the desire for development and the land resource shortage on island and reef coasts. Land reclamation generally starts from deposition-promoting projects on island and reef coasts with hyperconcentration of suspended sediment with the aim of reducing the reclamation cost. Based on the morphodynamic characteristics of the sea area near north of Daishan Island, a two-dimensional mathematical model was developed to analyze the co-action of current and waves and the model was verified for spring as well as neap tides in 2007 and 2012. The simulated values of tidal stages, tidal current velocities, tidal current directions, and suspended sediment concentration at 15 stations in 2007 and 9 stations in 2012 were in good agreement with the in-situ measured values. Furthermore, the simulated magnitude and pattern of erosion and sedimentation agreed well with the observations. This model was used to evaluate the effects of a proposed siltation scheme on the hydrodynamic environment and morphological change of the study area. The results of this study can inform the protection, development, and utilization of shoal-channels on island and reef coasts, as well provide a scientific basis for comprehensive maritime protection and development.

 

Reduction of local scour at river confluences using a collar

Pages 364–372

Nargess Amini, Behnam Balouchi, Mahmood Shafai Bejestan

Abstract

River confluences (RCs) are important features within river systems where the three dimensional (3D) flow structures and the downstream mixing of flows can cause deep scour holes. Despite this, few methods have been proposed to control scouring at RCs. In this study, application of a collar was experimentally examined for local scour control at the point where two rivers flow together. In particular, experimental tests were done with and without collar application at three different locations. The results reveal that the scour depth is directly proportional to the discharge ratio, i.e. the ratio of lateral discharge to that in the channel downstream of the confluence, and the densimetric Froude number (Frg). In addition, installation of a collar at RCs can decrease the scour depth up to 100%, thus completely avoiding the scour process. The results also show that by increasing the Frg the optimal installation location for a collar changes and moves towards the river bed level. Using a collar can also reduce the height of the point bar formed downstream of the confluence. The outcomes of the study allow derivation of an equation for predicting scour depth when a collar is applied as a countermeasure. The analysis of this equation shows that the estimates are mostly affected by the Frg.

 

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel—A case study on Sanmenxia Reservoir and the Lower Yellow River

Pages 373–383

Jianguo Chen, Wenhao Zhou, Shanshan Han, Gaohu Sun

Abstract

Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of retrogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accompanied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named”storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season” was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reservoirs in other large rivers carrying huge amounts of sediment.

 

Bed roughness and grain sorting- an experimental study over fine to medium sand beds

Pages 384–400

Barendra Purkait, Dipanjan Das Majumdar, Rajat Mazumder

Abstract

The relation between grain-size distribution of the bed and in suspension was critically examined under a uniform flow velocity of 50 cm/s over two beds: one of mainly fine sands and the other of medium sands. Two sections – one 2.85 m downstream and the other 6.35 m downstream in the experimental channel -were selected for sampling to study the grain-sorting pattern in the vertical direction along the direction of transport. The shape and type of the grain-size distribution pattern were critically studied with height above the bed. The change in the distribution pattern has been attributed to the change of local bed roughness causing scouring against the protruded relatively coarse grains on the bed. Such trends are important to predict the nature of river bed topography. The sand of Bed-1 initially exhibits a log-skew-Laplace distribution at different heights of suspension. The distribution pattern, however, changes but this changing pattern is not consistent along the upstream side. For Bed-2, which initially exhibits a log-normal distribution, the same pattern persists from the height of suspension at 5 cm up to 20 cm. Such consistency in log-normality is also observed at the downstream points of measurement. It is generally expected that the mean grain-size would reduce with increases of suspension height but the results of the experiments, in some occasions, differ significantly from the gradual fining upward trend. This result has been attributed to local changes of bed roughness arising from the protruded relatively coarse grains causing eddies, scouring, and turbulent phenomena which moves coarse particles higher in suspension adding a coarse tail to the distribution increasing the mean grain-size.

 

Distribution characteristics of inertial sediment particles in the turbulent boundary layer of an open channel flow determined using Voronoï analysis

Pages 401–409

Xin Liu, Chunning Ji, Xiaoli Xu, Dong Xu, John J.R. Williams

Abstract

This paper presents the numerical investigation of the distribution of inertial sediment particles in the turbulent boundary layer of an open channel flow with the particle Stokes number ranging from 0.6 to 20.4. The methodology is a combination of three numerical approaches, i.e. direct numerical simulation of turbulent flow, the point-particle immersed boundary method, and the discrete particle method. By applying the Voronoï analysis, the preferential concentration characteristics of sediment particles were investigated quantitatively. It was found that the normalized area of the Voronoï cells follows a log-normal particle distribution. The inertial sediment particles distributed unevenly in the turbulent boundary layer and the unevenness, governed by the particle Stokes number, was more significant as the particle Stokes number approaches unity. The inertial sediment particles in the turbulent boundary layer accumulated preferentially in streamwise-aligned streaky structures and this pattern was less significant with increasing particle Stokes number.

 

Geochemical fractionation and ecological risks assessment of benthic sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean

Pages 410–420

Nsikak U. Benson, Essien D. Udosen, Joseph P. Essien, Winifred U. Anake, ... Abass A. Olajire

Abstract

This study determines the pollution, fractionation, and ecological risks of sediment-bound heavy metals from coastal ecosystems off the Equatorial Atlantic Ocean. Contamination Factor (CF), pollution load index (PLI), and geoaccumulation index (Igeo) were used to assess the extent of the heavy metal pollution, while the potential ecological risk was evaluated using the risks assessment code (RAC) and Håkanson potential ecological risk. The analysis revealed concentrations (mg/g, dw) of the cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), and lead (Pb) in sediments for wet and dry seasons vary from 4.40–5.08, 14.80–21.09, 35.03–44.8, 2.14–2.28, and 172.24–196.39, respectively. The results also showed that the metal fractionation percentages in the residual, oxidizable, and reducible fractions are the most significant, while the exchangeable and carbonate bound trace metals are relatively low. The RAC values indicate no risk for Cd and Ni and low risk for other metals at all the studied sites during both seasons. Potential ecological risk analysis of the heavy metal concentrations indicates that Cd had high individual potential ecological risk, while the other metals have low risk at all investigated sites. The multi-elemental potential ecological risk indices (R1) indicate high ecological risk in all the ecosystems.

 

Modelling of resuspension due to fish activity: Mathematical modeling and annular flume experiments

Pages 421–431

Olya Skulovich, Catrina Cofalla, Caroline Ganal, Holger Schüttrumpf, Avi Ostfeld

Abstract

A spatially averaged numerical model was developed to describe the erosion of cohesive sediment. Together with known empirical relations, the model comprises a new formulation for resuspension due to fish activity. Experiments on erosion of natural sediments in the annular flume at Aachen University are used for model calibration. Empirical coefficients were evaluated with genetic algorithms to achieve the best agreement between the model results and the experimental data. The presented model shows sufficient flexibility to account for various sediment properties, including different sediment sources, natural and artificial contaminants, presence or absence of aquatic organisms, and results in an average coefficient of determination, R2 = 90.5% between the model results and the experimental data. Model validation allows it to be assumed that different contaminants affect bed properties differently. Fish activity plays an essential role in correct resuspension prediction. Further sediment erosion experiments with carefully chosen conditions will allow a more comprehensive model evaluation. The presented model is intended to serve as a building block in the development of a hydraulic-sediment-biota model within the W3-Hydro: Water Quality Event Detection for Urban Water Security and Urban Water Management Based on Hydrotoxicological Investigations project that aims to improve the knowledge concerning bioavailability, transport, fate, and effects of contaminants on the aquatic environment.

 

Evaluation of phosphorus bioavailability in El Mex Bay and Lake Mariut sediments

Pages 432–441

Naglaa F. Soliman, Gehan M. El Zokm, Mohamed A. Okbah

Abstract

Phosphorus (P) fractions and their bioavailability in the sediments from El Mex Bay and Lake Mariut in Egypt were investigated using different chemical extraction methods. Sodium bicarbonate (NaHCO3) extractable P (Olsen-P) was the largest fraction (14.42%), followed by algal available P (AAP) (3.56%), water soluble P (WSP) (0.79%), and readily desorbable P (RDP) (0.06%) for El Mex Bay. While AAP contributed 9.94% to total P in sediments from Lake Mariut, Olsen-P 8.53%, WSP 4.11%, and RDP 0.92%. Summation of the bioavailable P fractions didn’t exceed the sediment quality guidelines, and, therefore, P doesn’t represent a danger to marine organisms. Correlation coefficients showed that no apparent relations between total P (TP) and iron (Fe), aluminum (Al), and calcium (Ca) in the sediments. Furthermore, Fe:P ratio was less than 15 indicting that there was not enough Fe in surface sediments to bind to P at most of the sampling sites. The positive correlation between TP and organic matter (OM) for Lake Mariut and El Mex Bay sediments indicated that the organic matter content of the sediment was a useful predictor of the total phosphorus content. Data from this study constitute a baseline of phosphorus bioavailability in sediments from El Mex Bay and Lake Mariut and could be used as a reference for future studies on the changes of bioavailable and residual phosphorus fractions over time.

 

Phosphorus fractions and sorption dynamics in the sediments of two Ca-SO4 water reservoirs in the central Argentine Andes

Pages 442–451

José Gabriel León, Fernando Luis Pedrozo, Pedro Félix Temporetti

Abstract

Phosphorus (P) fractionation and sorption behavior were studied in the sediments of two calcium-sulfate (Ca-SO4: Ca2+170 mg L-1; SO42- 400 mg L-1) water reservoirs in the southern central Argentine Andes - El Carrizal Reservoir (ECR),which stratifies in summer and El Nihuil Reservoir (ENR),which is vertically mixed throughout the year. Sediment size classes reflected the lithology of both basins and the reservoirs relative location: ECR (downstream from a valley adjacent to a mountain environment) had higher clay proportions while the sand fraction was more important in ENR (just next to a mountain environment). In both reservoirs, the chemical composition revealed low alteration and calcium enrichment. Total P content was relatively high (1.1 – 1.6 mg P kg-1 dry weight) as expected from the contribution of marine formations. P fractionation was dominated by Ca-P (ECR, 69% and ENR, 63%) followed by organic-P (23%) in summer-anoxic ECR and by iron/aluminum (Fe/Al)-P (27%) in oxic ENR. Batch experiments showed that sorption behavior in ECR had a typical Langmuir isotherm plot while in ENR that model fitted only at low dissolved P values (<5 mg P L-1) and co-precipitation evidence was observed at higher P concentrations. It is proposed that lower Fe/Al-P content in anoxic (ECR) vs. oxic (ENR) sediments results from the P released from iron-bound phosphorus due to sulfate reduction-ferrous sulfide formation in an anoxic environment. This condition should enable ECR sediments to adsorb P into fresh oxidized iron, and ENR sediments to co-precipitate P with calcium due to Fe/Al-P saturation, as observed in batch experiments. This paper constitutes the first description of phosphorus content and dynamics in reservoir sediments in arid central western Argentina, where water sulfate concentrations are naturally high due to basin lithology.

 

Study on hydraulic characteristics of sabo dam with a flap structure for debris flow

Pages 452–464

Yeonjoong Kim, Hajime Nakagawa, Kenji Kawaike, Hao Zhang

Abstract

The front part of the flow is very important and complex in the case of debris flow where there is an accumulation of large boulders. It is important to control or dampen the energy of the frontal part of a debris flow for the safety of the downstream area because the impact pressure of debris flow is much greater than that of clear fluid. The main objective of this study is to analyze the hydraulic characteristics of the proposed dam (i.e. closed-type dam with flap). The vertical pressure distribution of this type is compared with conventional dam types. In the experiments, the total pressure associated with major debris flows was recorded in real time by a system consisting of four dynamic pressure sensors installed on different types of dam. The results from experimental data clearly show that the dam with the flap has advantages of capturing the debris flow with large boulders and controls the total pressure by flow circulation due to presence of the flap structure compared to a closed-type dam without flap. Furthermore, the empirical coefficients of hydrodynamic and solid collision models were proposed and compared with available coefficients.