Numerical Investigation of the Combined Slot Effect on the Erosion Pattern Around a Combination of Spur Dikes in Series

Modifying the river course for flood control, prevention of bed erosion, bank protection, and the regulation of river width are among the goals of spur dikes incorporation. The common spur dikes have simple (I), L and T geometrical shapes. The present research has been conducted to reduce the scour depth in front of the spurs dikes and improve the sedimentation conditions for the LTT combination of spur dikes in series by investigating different combinations of slots in the body of the spur dike; using numerical methods. The slot dimension was taken equal to 10% of the effective area of the spur dike body. Finally, the (LS-W-Wi, TS-W, TS-W-Wi) combination contained the slots in the web and wing of the first and third spur dike also the slot at the web of the middle spur dike was found as the best combination of slots. This combination conducted to reduce the scour depth about 6.8% and increase the deposition about 52% comparing by the spurs dikes without slots. Reducing the scour depth and increasing the sedimentation rate of materials between the spurs dikes. Also, the maximum scour depth decreases up to 20%. The results revealed that the presence of slots in spur dike structures and their different positions have complicated and considerable influences on the form and morphology of the erodible bed which could be the topic for further researches.

Seasonal Tidal Dynamics in the Qiantang Estuary: The Importance of Morphological Evolution

Despite the increasing number of studies on the river-tide interactions in estuaries, less attention has been paid to the role of seasonal morphological changes on tidal regime. This study analyzes the seasonal interplay of river and tide in the Qiantang Estuary, China, particularly focusing on the influences of the active morphological evolution induced by the seasonal variation of river discharge. The study is based on the high and low water levels at three representative stations along the estuary and daily river discharge through 2015, an intermediate flow year in which a typical river flood occurred, as well as the bathymetric data measured in April, July and November, 2015. The results show strong seasonal variations of the water level in addition to the spring-neap variation. These variations are obviously due to the interaction between river discharge and tide but can only be fully explained by including the effect of morphological changes. Two types of the influences of the variation of the river discharge on the tidal dynamics in the estuary can be distinguished: one is immediately induced by the high flow and the other continues for a much longer period because of the bed erosion and the following bed recovery. Tidal range in the upper reach can be doubled after the flood because of bed erosion and then decrease under normal discharge periods due to sediment accumulation. Over a relatively short term such as a month or a spring-neap tidal cycle, there exist good relationships between the tidal range, tidal amplification in the upper reach and the tidal range at the mouth, and between the hydraulic head over the upper and lower reaches. Such relationships are unclear if all data over the whole year are considered together, mainly because of the active morphological evolution.

Nails Involvement in Winiwarter-Buerger Disease

<b><i>Introduction:</i></b> Buerger disease, or thromboangiitis obliterans, is an inflammatory and occlusive process involving small and medium size arteries and veins, which generally affects the lower limbs of young adult male with the habit of smoking. <b><i>Case Presentation:</i></b> This paper reports 2 patients who developed nail lesions as the first sign of Buerger disease. <b><i>Conclusion:</i></b> Signs and symptoms of Buerger’s disease are secondary to the inflammatory process and arterial occlusion which results in severe ischemia. Involvement of nails is not common, but we found 2 different clinical features which have not been previously reported in the literature: chronic paronychia, and proximal leukonychia or onycholysis and nail bed erosion.

Hydrodynamic Performance of A-Jacks Concrete Armor Units in Riverbeds around Downstream in Flip Buckets

The jet flipped from flip buckets hits the dam’s downstream side as a free jet with an immense amount of energy, leading to bed erosion. Erosion of river bed materials downstream of dams could affect the performance of dams or power plants by altering the tailwater depth, rendering proper designs of controlling structures or erosion reduction methods highly indispensable in this regard. Hence, the hydrodynamic performance of A-Jacks concrete armor units in controlling scour was examined in this study. A-Jacks armors are applicable as a flexible protection without environmental risks often for bed erosion control. The desirable functionality of A-Jacks armors depends on the flow hydrodynamic parameters such as velocity profile variations ( U / U B ), the Reynolds stresses ( τ u ′ w ′ and τ v ′ w ′ ), and the skin friction coefficient ( C f ) created as a consequence of using A-Jacks armors on beds. The size of A-Jacks elements can have a role in increasing the flow turbulence to a certain depth so that after the impact of the flow with A-Jacks armor, the vortices’ intensity as well as the shear stress affecting the bed gradually decreases. The results of the numerical model suggest that the surge in the flow turbulence energy dissipation downstream of flip buckets significantly mitigates the underlying conditions of scouring phenomena, which is evidence of A-Jacks armors’ acceptable performance in scaling down scour depths.

Numerical Investigation of a Flash Flood Process that Occurred in Zhongdu River, Sichuan, China

In 2018, a flash flood occurred in the Zhongdu river, which lies in Yibin, Sichuan province of China. The flood caused many casualties and significant damage to people living nearby. Due to the difficulty in predicting where and when flash floods will happen, it is nearly impossible to set up monitors in advance to detect the floods in detail. Field investigations are usually carried out to study the flood propagation and disaster-causing mechanism after the flood’s happening. The field studies take the relic left by the flash flood to deduce the peak level, peak discharge, bed erosion, etc. and further revel the mechanism between water and sediment transport during the flash flood This kind of relic-based study will generate bigger errors in regions with great bed deformation. In this study, we come up with numerical simulations to investigate the flash flood that happened in the Zhongdu river. The simulations are based on two-dimensional shallow water models coupled with sediment transport and bed deformation models. Based on the real water level and discharge profile measured by a hydrometric station nearby, the numerical simulation reproduced the flash flood in the valley. The results show the flood coverage, water level variation, and velocity distribution during the flood. The simulation offers great help in studying the damage-causing process. Furthermore, simulations without considering sediment transport are also carried out to study the impact of bed erosion and sedimentation. The study proved that, without considering bed deformation, the flood may be greatly underestimated, and the sediment lying in the valley has great impact on flood power.

Multidecadal Analysis of an Engineered River System Reveals Challenges for Model-Based Design of Human Interventions

Hydraulic models were used in practice to predict the effect of human intervention during extreme conditions. However, the accuracy of such predictions remains untested. In this study, we compare a simulated trend in water levels covering a twenty-year period of large-scale human intervention with a thirty-year observational record. The results show that the observed water levels display a linearly decreasing trend attributed to channel bed erosion. A deviation from this trend, which would be an indication of the effect of human intervention, was not observed. We propose that the most likely explanation for this is that any effect observable at lower discharge is hidden in the uncertainty of the rating curve. Given the inherent uncertainties associated with making predictions about a changing system for conditions with a low period of return, we argue that model uncertainty should be considered in intervention design.

Numerical Investigation of the Inland Transport Impact on the Bed Erosion and Transport of Suspended Sediment: Propulsive System and Confinement Effect

For competitive reasons, inland ships as maritime ships are increasingly larger with powerful propulsive systems. The impact of this evolution on the environment is multiple. One of the major impacts is the erosion of the channel bed and the sediment suspension. This erosion phenomenon is essentially caused by the turbulent flow around the ship generated by its movement as well as its propulsive system. Hence, for a better prediction and understanding of this phenomenon, it is indispensable to simulate with great precision the flow around the ship hull and the induced shear stress at the bottom. Different ways were used in the past to estimate the shear stress at the waterway bottom. Some of these ways are empirical, analytical and numerical using shallow water models. In the present work to study the erosion phenomenon caused by the inland transport, a sedimentary transport model was developed and implemented in the Computational Fluid Dynamics (CFD) model (Fluent) as external code. The coupled model was firstly verified and validated using measurements. The validated model was subsequently used to assess the influence of several parameters: depth (h) to draught (T) ratio, ship advance ratio (J), ship speed and sediment size (d50). The first results show clearly that the coupled model behaves correctly and gives very satisfactory results. The impact of each parameter was compared and analyzed.

MODELING AND FIELD OBSERVATIONS OF CHANNEL PROCESSES OF THE SIBERIAN RIVERS. OB RIVER AT BARNAUL CITY SITE AS A CASE STUDY

Computer simulation of channel morphodynamic for the section of a large river in real unsteady hydrological conditions is conducted. The Ob river channel section at Barnaul city is investigated. At the site considered the channel processes cause serious hazard to some important structures such as the municipal water intake and the power line. The time of modeling covers the period from the flood peak to the low water stage. The simulation is implemented by means of Delft3D program suite. The sediment transport is calculated by two types of Van Rijn’s formula (1984 and 1993). The simulation results are verified by the field data collected at the study site over the same time period. These results show poor agreement with the field data. The river bed erosion spatial pattern modeled differs from the real one significantly. Probably a reason of this discrepancy is that the formula used can’t estimate the sediment transport value correctly.

Numerical study on the effect of edge scouring on stability of soft mattress in the Yangtze estuary

&lt;p&gt;&lt;strong&gt;Abstract: &lt;/strong&gt;In the Yangtze River Estuary deep-water channel regulation project, soft mattresses have been widely used to reduce bed erosion and thus improve stability of bridges/piers/levees/dikes. However, soft mattresses are also subject to failure due to the continuous and gradual scour in their edges, which have been a major risk for their stability. Here we report a preliminary numerical study on this issue. Firstly, a depth-averaged two-dimensional hydro-sediment-morphodynamic model is applied to simulate edge scour process for the submerged dike of the Jiangyanansha in the Yangtze estuary. For this purpose, physically-based sediment erosion parameterization is proposed to take account of the effect of the soft mattresses. Compared with the inner area of the soft mattress, only the edge area has stronger erodibility. Numerical comparative studies indicate that a scouring pit may develop to the vicinity of the submerged dike without the protection of the soft mattress, whereas under the protection of the soft mattress, the scouring pit can be largely controlled. Nevertheless, as the scouring process continues, the pit region and depth increase, which may finally lead to failure of the soft mattress. Finally, full 3D high-resolution simulations of the near-bed flow structure with/without edge scour are conducted using flow3D to shed light on the failure mechanisms of the soft mattresses.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; submerged dikes, soft mattress, erodibility, Yangtze estuary, edge scour, flow structure&lt;/p&gt;