International Journal of Sediment Research
Volume 33, Issue 3
Pages 221-370 (September 2018)
Towards a universal optimization of the performance of sand storage dams in arid and semi-arid areas by systematically minimizing vulnerability to siltation: A case study in Makueni, Kenya
Josep de Trincheria, Walter Filho Leal, Ralf Otterpohl
Pages 221-233
Analytical approach for sheet flow transport in purely acceleration-skewed oscillatory flow
Xin Chen, Fujun Wang, Xuelin Tang
Pages 234-242
Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water
Chung Rak Song, Jinwon Kim, James Tyler Kidd, Alexander Cheng, David Admiraal
Pages 243-249
Phosphorus fractionation and release characteristics of sediment in the Saemangeum Reservoir for seasonal change
Dong-Heui Kwak, Young-Tae Jeon, Young Duck Hur
Pages 250-261
Multigene genetic programming for sediment transport modeling in sewers for conditions of non-deposition with a bed deposit
Mir Jafar Sadegh Safari, Ali Danandeh Mehr
Pages 262-270
Wide river or narrow river: Future river training strategy for Lower Yellow River under global change
Xiaonan Li, Deyu Zhong, Y. Joseph Zhang, Yanjun Wang, ... Hongwu Zhang
Pages 271-284
An isotopic model for the origin of autochthonous organic matter contained in the bottom sediments of a reservoir
Piotr Koszelnik, Renata Gruca-Rokosz, Lilianna Bartoszek
Pages 285-293
Assessment of heavy metal pollution from the sediment of Tupilipalem Coast, southeast coast of India
Sreenivasulu Ganugapenta, Jayaraju Nadimikeri, Sundara Raja Reddy Balam Chinnapolla, Lakshmanna Ballari, ... Lakshmi Prasad Tella
Pages 294-302
Characteristics and influencing factors of sediment deposition-scour in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River, China
Bo Yao, Qingquan Liu
Pages 303-312
Sheet flow hydrodynamics over a non-uniform sand bed channel
Anurag Sharma, Bimlesh Kumar
Pages 313-326
Enhanced bed load sediment transport by unsteady flows in a degrading channel
Zhijing Li, Honglu Qian, Zhixian Cao, Huaihan Liu, ... Penghui Hu
Pages 327-339
Soil and onsite nutrient conservation potential of aromatic grasses at field scale under a shifting cultivated, degraded catchment in Eastern Ghats, India
Partha Pratim Adhikary, Hunsur Chikkanarasimhaiah Hombegowda, Dhananjay Barman, Madegowda Madhu
Pages 340-350
Flow fields and particle trajectories beneath a tidal bore: A numerical study
Adrien Berchet, Bruno Simon, Anthony Beaudoin, Pierre Lubin, ... Serge Huberson
Pages 351-370
==================================================
Sreenivasulu Ganugapenta, Jayaraju Nadimikeri, Sundara Raja Reddy Balam Chinnapolla, Lakshmanna Ballari, Rajasekhar Madiga, Nirmala K, Lakshmi Prasad Tella,
Assessment of heavy metal pollution from the sediment of Tupilipalem Coast, southeast coast of India,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 294-302,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.02.004.
(http://www.sciencedirect.com/science/article/pii/S1001627916300919)
Abstract: Sediment from twelve stations was sampled from the Tupilipalem Coast, southeast coast of India, and the presence of a set of heavy metals was established including iron (Fe), manganese (Mn), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), zinc (Zn) and cadmium (Cd). The heavy metals were assessed by factor analysis, the results of which showed positive and/or negative correlations among Fe, Mn, Cr, Cu, Ni, Pb, Zn, and Cd. Factor analysis also indicated that heavy metals in the sediments of the study area have different natural and anthropogenic sources. Similarly, a sediment pollution assessment was done using the Geoaccumulation Index (Igeo), Enrichment Factor (EF), and Pollution Load Index (PLI). The Geoaccumulation Index indicated that the surface sediment of the Tupilipalem Coast was extremely contaminated with Fe, Mn, Cr, Cu, Ni, Pb, and Zn. The calculation of enrichment factors showed a significant enrichment with respect to Pb, Zn, and Cd and a moderate enrichment with Cr, Cu, and Ni. The falling trend of average contents’ enrichment factors is Cd> Pb> Zn> Cu> Cr> Ni> Mn> Fe. The PLI values of the Cd show higher (>1) values due to the influence of distinct external sources like agricultural runoff, industrial activities, and other anthropogenic inputs. Ninety two percent of heavy metals under study showed the highest concentrations at station TP-5 where the Buckingham Canal and other agricultural and aquacultural effluents connect with the Bay of Bengal. This location is the second inlet which is periodically closed and it seemed that these parts of the study area are heavily affected by anthropogenic pollution.
Keywords: Factor analysis; Geo accumulation index; Enrichment factor; Pollution load index; Heavy metal pollution; East coast of India
Xin Chen, Fujun Wang, Xuelin Tang,
Analytical approach for sheet flow transport in purely acceleration-skewed oscillatory flow,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 234-242,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.05.001.
(http://www.sciencedirect.com/science/article/pii/S1001627917303591)
Abstract: An instantaneous analytical approach is developed to predict sheet flow transport in purely acceleration-skewed oscillatory flow. The approach is derived from exponential approximations of velocity and concentration profiles above a mobile seabed, and it particularly considers factors of phase lead; phase lag (i.e. phase residual and phase shift); acceleration modification; and asymmetries in shear stress, roughness height, and boundary layer development. The approach can predict net boundary layer flow above a mobile seabed, and can revert to the classical bedload model. Instantaneous and net sediment transport rates are studied using the approach. The instantaneous sediment transport rate in an onshore flow stage can be approximated by a power function of velocity in which the exponent is confirmed to range between 1 and 5 with a decrease in the phase residual. The net sediment transport rate predicted using the approach is validated using a considerable amount of measured data, and compared with existing instantaneous and half-period type models that consider the phase lag or acceleration modification. For the net sediment transport rate in purely acceleration-skewed oscillatory flow, the phase residual is less important than the acceleration-skewed boundary layer difference between onshore and offshore acceleration stages.
Keywords: Analytical approach; Sheet flow; Acceleration-skewed oscillatory flow; Phase lag; Boundary layer flow
Bo Yao, Qingquan Liu,
Characteristics and influencing factors of sediment deposition-scour in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River, China,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 303-312,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.03.003.
(http://www.sciencedirect.com/science/article/pii/S1001627918300921)
Abstract: The annual changes of sediment deposition-scour on the riverbed in the Sanhuhekou-Toudaoguai Reach of the upper Yellow River during the years 1952–2010 were investigated based on runoff and sediment transport observations from the Sanhuhekou and Toudaoguai hydrological stations. Multiple influencing factors such as reservoir operations, tributary inflows, as well as runoff and sediment loads from the Shidakongdui area were analyzed. The results show that even though the sediment loads from the major sources, the Shidakongdui area as well as the upstream tributaries such as the Qingshui River and the Zuli River have reduced especially since the 2000s as a result of enhanced water-soil conservation measures and improvement of vegetation cover, the study reach was still generally in a status of cumulative aggradation. This is mainly due to the joint operations of the Liujiaxia Reservoir and the Longyangxia Reservoir, which significantly reduced the annual runoff and sediment loads at the Sanhuhekou Crosssection. The reservoirs also remarkably altered the summer flood characteristics of the study reach, inducing the shape of the annual flow curve changing from a ‘single-peak’ into a ‘double-peak’. These alternations sharply decreased the sediment transport capacity of flooding in the summer flood season which yields more than 90% of the sediment loads, leading to an unbalanced relation between the water and sediment. In addition, the estimated incoming sediment coefficient of the Sanhuhekou Crosssection ranged from 0.003 to 0.014?kg s/m6, of which 0.004?kg s/m6 was suggested as a rough critical value to determine the scour or deposition status of the study reach.
Keywords: Upper Yellow River; Sanhuhekou-Toudaoguai Reach; Sediment deposition; Incoming sediment coefficient; Runoff; Sediment loads
Xiaonan Li, Deyu Zhong, Y. Joseph Zhang, Yanjun Wang, Yongqiang Wang, Hongwu Zhang,
Wide river or narrow river: Future river training strategy for Lower Yellow River under global change,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 271-284,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.04.001.
(http://www.sciencedirect.com/science/article/pii/S1001627916301275)
Abstract: The choice of a river training strategy is extremely important for the Lower Yellow River (LYR). Currently, the wide-river training strategy applies in the training of the LYR. However, remarkable changes in the hydrological processes in the Yellow River basin, as well as immediate pressure from socio-economic development in the Yellow River basin, make it necessary to consider if there is a possibility to change the river training strategy from wide-river training to narrow-river training. This research investigates the impacts of different river training strategies on the LYR through numerical simulations. A one-dimensional (1-D) model was used to simulate the fluvial processes for the future 50 years and a three-dimensional (3-D) model was applied to study typical floods. The study focused on river morphology, the results show that if the present decreasing trend in both water discharge and sediment load persists, the deposition rate in the LYR will further decrease no matter what strategy is applied. Especially, narrow-river training can achieve the aim to increase the sediment transport capacity in the LYR compared with wide-river training. However, if the incoming water and sediment load recovers to the mean level of the last century, main channel shrinkage due to sedimentation inevitably occurs for both wide-river and narrow-river training. Most importantly, this study shows that narrow-river training reduces the deposition amount over the whole LYR, but it provides little help in alleviating the development of the “suspended river”. Instead, narrow-river training can cause aggradation in the transitional reach where the river pattern changes from highly wandering to meandering, further worsening the “hump deposition” there. Because of uncertainty regarding future changes in hydrological processes in the Yellow River basin, and the lack of feasible engineering measures to mitigate “suspended river” and “hump deposition” problems in the LYR, caution should be exercised with respect to changes in the river training strategy for the LYR.
Keywords: Lower Yellow River; River training; Water‐sediment interactions; Numerical modeling; Hump deposition
Josep de Trincheria, Walter Filho Leal, Ralf Otterpohl,
Towards a universal optimization of the performance of sand storage dams in arid and semi-arid areas by systematically minimizing vulnerability to siltation: A case study in Makueni, Kenya,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 221-233,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.05.002.
(http://www.sciencedirect.com/science/article/pii/S1001627917300276)
Abstract: Sand storage dams are hydraulic retention structures that increase the volume of coarse sediments in seasonal sandy streams by exclusively blocking the bedload transport during runoff events. However, siltation of fine grain particles, which are transported as part of the suspended load, is a major factor causing sand storage dams to perform poorly. Therefore, this study aimed to evaluate the hydrological performance and cost-efficiency of 30 sand storage dams. This study also aimed to increase the understanding of critical factors which may affect the performance and lead to siltation of sand storage reservoirs. The analysis was based on a physical survey of 30 sand storage dams that were built in one-stage in southeastern Kenya. Most of the study sites had the capacity to produce sand. However, the reservoirs suffered from severe siltation, which caused generalized low annual yields, reduced supply capacities, and low cost-efficiency. It is argued that the main factors for the poor performance were the high inter- and intra-annual variability of bedload transport, which coupled with the construction of one-stage spillways, led to siltation of the reservoirs. Thus, large volumes of fine grain particles accumulated in the reservoirs during runoff events with bedload layer heights lower than the height of the one-stage spillways. To systematically maximize the robustness to the inherent variability of bedload transport, and ensure optimal performance levels by systematically minimizing siltation, spillways should be built in stages of reduced height. Thus, the lower the stage height, the higher the probability of maximizing the accumulation of coarse sediment. It is estimated that a multi-stage construction process with stage heights of 20?cm would have produced a performance 26 times higher. This implies that the 30 reservoirs would have had the capacity to supply 8516 people as compared to the current supply capacity of 330 people. Improvements in the performance of sand storage dams can greatly assist attempts to link this technology with income-generating activities for agropastoralists in arid and semi-arid areas.
Keywords: Bedload transport variability; Spillway; Multi-stage construction
Partha Pratim Adhikary, Hunsur Chikkanarasimhaiah Hombegowda, Dhananjay Barman, Madegowda Madhu,
Soil and onsite nutrient conservation potential of aromatic grasses at field scale under a shifting cultivated, degraded catchment in Eastern Ghats, India,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 340-350,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.01.002.
(http://www.sciencedirect.com/science/article/pii/S1001627918300179)
Abstract: Land degradation due to soil erosion is a global problem, especially on cultivated hill slopes. Economically important aromatic grasses can protect degraded hill slopes more effectively than field crops, but little information is available on their performance. This study quantifies runoff, sediment yield, enrichment ratios of soil and nutrients, and sediment-associated organic carbon and nutrients losses under three aromatic grass species: citronella (Cymbopogon nardus), lemon (Cymbopogon flexuosus), and palmarosa (Cymbopogon martini), compared with a traditional field crop, finger millet (Eleusine coracana) grown at three land slopes (4%, 8%, and 12%). It was observed that the degree of slope and type of grass both significantly influenced runoff generation. Runoff and sediment yield (SY) were significantly higher at 12% slope than at 8% and 4% slopes. Relation between rainfall and runoff were significant for all the grass species (p < 0.05). Palmarosa, lemon, and citronella grass reduced the SY by 10, 54, and 60%, respectively, over finger millet. SY was also significantly related to rainfall for all the treatments (p < 0.05). The threshold runoff values to produce SY were higher for aromatic grasses compared to finger millet. Enrichment of clay, silt, sand, soil organic carbon (SOC), available nitrogen (N), phosphorus (P) and potassium (K) in the sediment were not significantly different between slopes but differed significantly between aromatic grasses and finger millet. Sediment associated nutrient load varied inversely with SY mainly because of the nutrient dissolution effect of high runoff volume. Annual loss of SOC and nutrients varied from 84.7–156.8?kg?ha-1 y-1 for SOC, 4.38–9.18?kg?ha-1 y-1 for available N, 0.35–0.75?kg?ha-1 y-1 for available P, and 2.22–5.22?kg?ha-1 y-1 for available K, with the lowest values for citronella and highest for finger millet. The study found that the aromatic grasses have greater environmental conservation values than finger millet on steep degraded land.
Keywords: Aromatic grass; Enrichment ratio; Nutrient loss; Runoff; Sediment yield
Chung Rak Song, Jinwon Kim, James Tyler Kidd, Alexander Cheng, David Admiraal,
Effect of thickness of planar nozzles on erosion depth of levee soils subjected to plunging water,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 243-249,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.04.010.
(http://www.sciencedirect.com/science/article/pii/S100162791630138X)
Abstract: In this study, the effect of the thickness of a planar jet on the erosion depth when the jet impinges on a surface composed of cohesive soil was analytically and numerically evaluated. The results showed that the erosion depth was practically independent of the nozzle thickness for erosion depths shallower than the potential core length (i.e. the region of the jet in which the central flow velocity is the same as the nozzle velocity). The relation between nozzle thickness and erosion depth was non-linear with continuously variable slope for erosion depths deeper than the potential core length. Finally, the relation was approximately linear when the erosion depth converged to the equilibrium erosion depth. The findings of this study indicate that direct and fast prediction of the erosion depth in the field is possible using the data from a small scale soil erosion test with similar flow velocities.
Keywords: Nozzle thickness; Levee erosion; Erosion depth; Plunging water; Planar nozzle
Mir Jafar Sadegh Safari, Ali Danandeh Mehr,
Multigene genetic programming for sediment transport modeling in sewers for conditions of non-deposition with a bed deposit,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 262-270,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.04.007.
(http://www.sciencedirect.com/science/article/pii/S1001627917300252)
Abstract: It is known that construction of large sewers based on consideration of flow with non-deposition without a bed deposit is not economical. Sewer design based on consideration of flow with non-deposition with a bed deposit reduces channel bed slope and construction cost in which the presence of a small depth of sediment deposition on the bed increases the sediment transport capacity of the flow. This paper suggests a new Pareto-optimal model developed by the multigene genetic programming (MGGP) technique to estimate particle Froude number (Frp) in large sewers with conditions of sediment deposition on the bed. To this end, four data sets including wide ranges of sediment size and concentration, deposit thickness, and pipe size are used. On the basis of different statistical performance indices, the efficiency of the proposed Pareto-optimal MGGP model is compared to those of the best MGGP model developed in the current study as well as the conventional regression models available in the literature. The results indicate the higher efficiency of the MGGP-based models for Frp estimation in the case of no additional deposition onto a bed with a sediment deposit. Inasmuch as the Pareto-optimal MGGP model utilizes a lower number of input parameters to yield comparatively higher performance than the conventional regression models, it can be used as a parsimonious model for self-cleansing design of large sewers in practice.
Keywords: Bed load; Bed deposition; Non-deposition; Multigene genetic programming; Sediment transport; Sewer
Dong-Heui Kwak, Young-Tae Jeon, Young Duck Hur,
Phosphorus fractionation and release characteristics of sediment in the Saemangeum Reservoir for seasonal change,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 250-261,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.04.008.
(http://www.sciencedirect.com/science/article/pii/S1001627917300616)
Abstract: Periodical algal blooms result in deposition and release of phosphorus (P) from the sediment into the water. Therefore, during seasonal changes when algal particles begin to settle to the bottom, understanding the behavior and distribution characteristics of the P in sediment is the most important key to manage the water quality of the Saemangeum Reservoir. In this study, the variation of water quality and sediment composition including chlorophyll-a (Chl-a) and P was investigated to determine the interaction between water and sediment. The study focused primarily on algal particle sedimentation that affects the P release and mineralization of sediment. The Chl-a concentration in water showed a sharp decline in October when the algae began to die in the fall, and afterward the concentration of chemical oxygen demand (COD) and total P (TP) in the sediment increased due to the sedimentation of decaying algal particles in November. During the same period of time, the readily bio-available P (RAP) in the sediment showed a drastic increase in the upper region where the Chl-a concentration of water was high. In sequence, the high RAP zone shifted from the upper region to the lower region in the early winter. The RAP shift was considered to be derived from the physical flow of the overlying water from which the decomposing algae settled on the surface of the sediment. The Saemangeum Reservoir was constructed recently; therefore, all the types of inorganic P fractions except soluble reactive phosphorus (SRP) that exist on the bottom surface of the lake and the marsh's sediment layer were not sufficient to significantly influence the overlying water. On the other hand, the released P from the algae was distinct and sensitive to the seasonal change. In conclusion, the algal particle sedimentation was important to control eutrophication rather than P release from the mineralized inorganic P of the sediment surface layer in the Seamangeum Reservoir.
Keywords: Algal bloom; Fractionation; Phosphorus; Water management; Release; Sediment
Adrien Berchet, Bruno Simon, Anthony Beaudoin, Pierre Lubin, Germain Rousseaux, Serge Huberson,
Flow fields and particle trajectories beneath a tidal bore: A numerical study,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 351-370,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.03.001.
(http://www.sciencedirect.com/science/article/pii/S1001627916301524)
Abstract: Tidal bores may appear in some estuaries when the tides quickly reach a high level. This phenomenon is rare but has a strong impact during its short duration: i.e. the river bed is significantly eroded and sediments are then transported. In this paper, the trajectories of suspended particles induced by this flow are numerically studied. Four undular bores with Froude numbers between 1.1 and 1.2 are studied. Despite similar Froude numbers, various initial flow conditions were selected to produce or not an inversion of the flow direction during the bore passage. The particle trajectories associated with each distinct flow configuration are presented and analyzed. These trajectories, estimated by solving the Maxey-Riley equation, appear to be very different even though the Froude numbers of flows are similar. These observations are important because the Froude number is often used to characterize a tidal bore as it describes well the free surface, however, it cannot describe the sediment transport. Finally, Chen's model of wave-current interactions is adapted to fit the cases studied and is applied to the four bores simulated. The results highlight that this latter model can reproduce the observed trajectories and dissociate their different components. From this model, it is shown that the inertial and Basset history effects can be neglected compared to the gravity and flow entrainment effects due to the viscous drag when one wants to determine the long-term trajectories of suspended particles.
Keywords: Tidal bores; Sediment transport; Trajectories; Physical modeling; Numerical modeling
Zhijing Li, Honglu Qian, Zhixian Cao, Huaihan Liu, Gareth Pender, Penghui Hu,
Enhanced bed load sediment transport by unsteady flows in a degrading channel,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 327-339,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.03.002.
(http://www.sciencedirect.com/science/article/pii/S1001627916300725)
Abstract: Laboratory flume experiments were done to investigate bed load sediment transport by both steady and unsteady flows in a degrading channel. The bed, respectively composed of uniform sand, uniform gravel, or sand-gravel mixtures, always undergoes bulk degradation. It is found that both uniform and non-uniform bed load transport is enhanced greatly by unsteady flows as compared to their volume-equivalent steady flows. This enhancement effect is evaluated by means of an enhancement factor, which is shown to be larger with a coarser bed and lower discharges. Also, the fractional transport rates of gravel and sand in non-uniform sand-gravel mixtures are compared with their uniform counterparts under both steady and unsteady flows. The sand is found to be able to greatly promote the transport of gravel, whilst the gravel considerably hinders the transport of sand. Particularly, the promoting and hindering impacts are more pronounced at lower discharges and tend to be weakened by flow unsteadiness.
Keywords: Bed load; Gravel; Sand; Unsteady flow; Enhancement effect
Piotr Koszelnik, Renata Gruca-Rokosz, Lilianna Bartoszek,
An isotopic model for the origin of autochthonous organic matter contained in the bottom sediments of a reservoir,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 285-293,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2017.10.002.
(http://www.sciencedirect.com/science/article/pii/S1001627917300136)
Abstract: Geochemical analysis of surface sediment samples collected in 2005 and 2006 was used to evaluate the potential sources of the organic matter present in sediments of southeast Poland's Solina Reservoir. Statistical analysis of sediment variables (carbon to nitrogen ratio, and the carbon 13 and nitrogen 15 isotope ratios) determined for the organic fraction indicated significant spatial variability with respect to sources of organic matter. A binary mixing model was developed from literature sources to predict the relative contributions of allochthonous and autochthonous production to sediment organic matter. Autochthonous production was shown to account for 60–75% of bulk sedimentation in the lacustrine parts of the reservoir, near the dam. In contrast, autochthonous production accounted for only 25% of sedimentation in the riverine zone receiving stream inputs. Statistical analysis identified the δ15N of organic matter as the best predictor of the source of organic matter. Multiple regression analysis indicated that two water-quality variables (nitrate and dissolved silica) were significantly related to the δ15N signature of organic matter. This led to a conclusion that limnetic nitrate and dissolved silica concentrations were regulating organic matter production in the Solina Reservoir.
Keywords: Reservoir; Bottom sediments; Organic matter; Stable isotope
Anurag Sharma, Bimlesh Kumar,
Sheet flow hydrodynamics over a non-uniform sand bed channel,
International Journal of Sediment Research,
Volume 33, Issue 3,
2018,
Pages 313-326,
ISSN 1001-6279,
https://doi.org/10.1016/j.ijsrc.2018.01.004.
(http://www.sciencedirect.com/science/article/pii/S1001627918300295)
Abstract: The current study experimentally investigates the flow characteristics and temporal variations in the sheet flow profile of a non-uniform sand bed channel. Experiments were done to explore turbulent structures in the presence of a sheet flow layer with and without seepage. The turbulent events, such as stream wise velocity, Reynolds shear stresses, and turbulence intensities were found to be increasing and vertical velocity was found decreasing with a sheet layer. The presence of a sheet layer also effects the turbulent energy production and energy dissipation. All the turbulence parameters with and without a sheet layer have also been influenced by the presence of downward seepage. The rate of sheet flow movement is increased with seepage, owing to increased turbulence with seepage. The current study used wavelet analysis on temporally lagged spatial bed elevation profiles obtained from a set of laboratory experiments and synchronized the wavelet coefficients with bed elevation fluctuation at different spatial scales. A spatial cross correlation analysis at multiple scales, based on the wavelet coefficients, has been done on these bed elevation datasets to observe the effect of downward seepage on the dynamic behavior of sheet flow at different length scales. It is found that seepage increases average bed celerity and also increases the celerity of sheet flow of similar length scales. This increase in the celerity has been hypothesized as the increase of sheet flow movement as well as the increase in turbulent parameters with seepage, which destabilizes the bed particles resulting in a disruption in the continuous propagation pattern of the sheet flow. The increase of sheet flow celerity with seepage is confirmed from the saturation level of the wavelet power spectra of the bed elevation series. The presence of seepage also affects the non-uniformity of collective sheet material.
Keywords: Sheet flow; Non-uniform sand; Turbulence; Seepage