Bed Level Research Articles

Pre-modelling as a tool for optimizing morphodynamical numerical simulations

ABSTRACT The present study proposes, systematizes and validates a new, robust hot-start approach to numerical hydro-morphodynamic modelling, aiming to improve the quality of the interpolated bathymetrical data used in the referred models for representing river channels. This approach works by criteriously removing the small scale systemic errors in a channel’s bathymetry which often obfuscate the behaviour of fluvial morphodynamics, thereby improving the accuracy of the interpolated bed level along the modelling grid and the intelligibility of morphodynamical simulations. The pre-modelling approach was demonstrated using data from a case study in Portugal. The improvements obtained in terms of the quality of the morphology were both qualitatively and quantitatively assessed. Pre-modelling was proven to produce, at least, small improvements regarding the overall bed level accuracy (∼5% reduction in mean error) and significant benefits to the overall intelligibility of the results (with up to 22% reduction in the spatial entropy of morphodynamics and up to 55% increase in the agreement between theoretical and simulated values for each different scenario).

New features of the cerebral hemodynamics of brain arteries in patients with HIV-infection in Uzbekistan

We aim to study the cerebral hemodynamic indices of the brain arteries in HIV-infected patients. 56 HIV-infected patients were examined, with verified serological and clinical diagnosis, whose average age was 35.7 ± 1.3 years, among which there were 31 (55.4%) men and 25 (44.6%) women. The state of cerebral hemodynamics and vascular reactivity of the cerebral arteries was studied using standard techniques using sensors of 2, 4, 8 MHz on the Spectromed-300 device (Russia). Cerebral hemodynamic disorders in patients according to the Doppler study showed a decrease in blood flow velocity in the ICA by 24.5 and 33.9%, in the MCA by 25.4 and 34.5%, in the PA - by 24.3 and 44.7%, in OA - by 21.7 and 32.6% (groups 1 and 4, respectively) in relation to the indicators in the control group. There were also signs of an increase in vascular tone in all investigated vessels, according to an increase in the pulsation index (Pi) and circulatory resistance (Ri), on average, 1.5 and 2.3 times in group 1; 1.8 and 2.75 times in 4 groups. An increase in vascular tone suggests the inadequate functioning of dilatatory mechanisms at the capillary bed level, which indicates stress in the mechanisms of adaptation of cerebral vessels, which, if not corrected, can lead to their breakdown and development of dyscirculatory processes in the CNS in HIV-infected patients already at the preclinical stages of the disease.

Physical model of scour at the toe of rock armoured structures

Toe structures are a common feature in coastal rock armoured structures, both safeguarding the structure against scour at the toe and providing support to the armour layer. The toe structure itself is often comprised of rocks as well. Hence, generally some form of scour protection, such as a filter layer or a geotextile, is applied underneath the toe structure. Currently, there is a lack of available methods to judge the necessity of these kinds of costly scour protection measures underneath the toe structure. In this paper, a unique data set from physical model tests of scour at the toe of rock armoured structures is presented. The bed level change is measured by a laser scanner across the entirety of the sand bed, including underneath the structure. Additionally, the temporal development of the scour at the glass wall of the flume is measured using an innovative combination of video imagery and a deep learning algorithm. The sand diameter is not varied in the physical model tests. In all tests, scour was observed both in front of the structure and underneath the structure. Two expressions have been derived that give estimates for both kinds of scour, and thus can give insight into the necessity of scour protection underneath the toe structure.

A model for simulation of debris flow sedimentation in slit detention-dam reservoirs

Debris flow is a natural phenomenon that requires appropriate structural measures such as detention dams to reduce hazards resulting from it. The objective of this paper is to present a two-dimensional numerical model to investigate debris flow deposition in the reservoir of the detention slit dams. The governing equations include shallow water equations considering the bed level variation, sediment continuity, and debris-flow transport equations. Shallow water equations were discretized using the MacCormack scheme and then Banihabib Scheme was applied for solving sediment continuity equation. The governing equations were solved in an iterative procedure and as a result, flow properties and bed level variations were obtained in silt dam reservoir. The model performance was evaluated against experimental and numerical models in two aspects including the outflow hydrograph and reservoir bed level variations or trapping efficiency. The model performed quite well in outflow hydrograph simulation, and the comparison of the bed level variations or trapping efficiency illustrated that the simulated values were acceptable. A sensitivity analysis of the parameters was carried out to analyze the influence of parameters variation on outflow and sedimentation volume. The results of this sensitivity analysis revealed sedimentation is more sensitive to the parameter variation than outflow hydrograph. Generally, the proposed numerical method can provide insights on the debris flow deposition in slit dam reservoir, which could be useful for slit dam design.

Optimum Design for Controlling the Scouring on Bridge Piers

The scouring around bridge pier can be considered the most important reasons of bridge failure. Therefore, we investigated by using physical models of piers and we used single pier with square collar , circular collar and interaction of two piers in laboratory channel, its width 1 m and applied three velocities (0.1, 0.08, and 0.07) m/sec. This experimental investigation was made to choose the optimum shape and location of collar of single pier and comparing it with the interaction of two piers, the results showed that both square and circular collar decrease the scour depth, but the square collar is more effective of reducing scouring and the best location at bed level for single pier, comparing the results of single pier with the interaction of two piers, the interaction of two piers without any countermeasure reduced scour depth about 58%.

Beach response to breakwater layouts of drainage pipe outlets during beach nourishment

Managing drainage pipes to optimize beach nourishment is a complex problem. In this study, the ‘salient’ landform is explored as a feasible plan that considers beach nourishment and breakwater geometry of the drainage pipe outlets. The XBeach model was used to establish an idealized model for analyzing the beach response to three typical breakwater layouts (straight, landward convex, and seaward convex). The seaward convex breakwater layout was found to be the most effective option because it can accumulate the largest volume of sediment behind the structure. The seaward convex layout was also used to analyze the beach response to incident wave angles ranging from 0° (normal to the shore) to 60°. As the incident wave angle increases, the volume of sand salient accumulated in the leeward of the breakwater and the flow speed in the cross-show direction gradually decrease, while the wave height and the flow speed in the along shore direction gradually increase. However, there is a critical angle of approximately 50° at which opposite trends of changes in bed level, wave height and Eulerian flow occur.

A Comparative Study of Comprehensive Modeling Systems for Sediment Transport in a Curved Open Channel

In recent decades, a variety of morphodynamic model systems have been developed to improve our understanding of sediment transport and the resulting changes in riverbed topography. Despite progress in the description of physical processes, the degree of accuracy of morphodynamic model results remains difficult to assess and are also less than for hydrodynamics alone. In this paper, three different 2D morphodynamic systems have been applied to simulate a complex hydrodynamic and morphodynamic situation. These model systems were validated using data of sediment sorting and bed deformation conducted in a 180° channel bend under unsteady-flow conditions. The calculations obtained by each modeling system were compared with the available observed data. The simulated results showed that all applied morphodynamic models could precisely calculate the bed level changes and the areas of deposition and scour. However, the models are not efficient enough to predict the distribution of the mean grain size in the channel bend.

Effect of Sediment Load Boundary Conditions in Predicting Sediment Delta of Tarbela Reservoir in Pakistan

Setting precise sediment load boundary conditions plays a central role in robust modeling of sedimentation in reservoirs. In the presented study, we modeled sediment transport in Tarbela Reservoir using sediment rating curves (SRC) and wavelet artificial neural networks (WA-ANNs) for setting sediment load boundary conditions in the HEC-RAS 1D numerical model. The reconstruction performance of SRC for finding the missing sediment sampling data was at R2 = 0.655 and NSE = 0.635. The same performance using WA-ANNs was at R2 = 0.771 and NSE = 0.771. As the WA-ANNs have better ability to model non-linear sediment transport behavior in the Upper Indus River, the reconstructed missing suspended sediment load data were more accurate. Therefore, using more accurately-reconstructed sediment load boundary conditions in HEC-RAS, the model was better morphodynamically calibrated with R2 = 0.980 and NSE = 0.979. Using SRC-based sediment load boundary conditions, the HEC-RAS model was calibrated with R2 = 0.959 and NSE = 0.943. Both models validated the delta movement in the Tarbela Reservoir with R2 = 0.968, NSE = 0.959 and R2 = 0.950, NSE = 0.893 using WA-ANN and SRC estimates, respectively. Unlike SRC, WA-ANN-based boundary conditions provided stable simulations in HEC-RAS. In addition, WA-ANN-predicted sediment load also suggested a decrease in supply of sediment significantly to the Tarbela Reservoir in the future due to intra-annual shifting of flows from summer to pre- and post-winter. Therefore, our future predictions also suggested the stability of the sediment delta. As the WA-ANN-based sediment load boundary conditions precisely represented the physics of sediment transport, the modeling concept could very likely be used to study bed level changes in reservoirs/rivers elsewhere in the world.

Scour at river bridge piers: real-time vulnerability assessment through the continuous monitoring of a bridge over the river Po, Italy

Bridge failures are not uncommon during floods. Therefore, the assessment of bridge vulnerability is crucial to help a bridge’s administration take the best decisions during emergencies (i.e. closing the bridge). The first step to achieve this is to implement a monitoring system providing needed information to develop scenarios based on administration response time. The proposed system seeks a real-time evaluation of the loads acting on the bridge. Wind and water contributions, debris accumulation upstream of piers and river bed level are evaluated by specific devices. The most difficult measurement is the identification of the riverbed position in close proximity to piers. Scour model predictions are still far from robust and accurate and no standard devices are available to measure it. Unfortunately, the main reason for bridge failure is scour around bridge piers, called local scour. A monitoring system was developed for this purpose and installed on a critical bridge over the river Po in Italy, as a result of the cooperation between the Politecnico di Milano and the Province of Mantova. The aim was to measure the main parameters for a proper evaluation of the bridge’s vulnerability. The paper’s focus is twofold: to show long-term data and all the phases needed to assess bridge safety. The first aspect, not so common in the literature, is useful to understand the temporal evolution of the environment around the bridge. The second one provides a roadmap for risk assessment and management decisions relying on the widely available database. With regard to this second topic, another paper describing the overall strategy has already been published. The main focus here is on potential implementation, with an emphasis on the available data.

The heterogeneity of mudflat erodibility

The prediction of the erosion of mudflats is hampered by inaccurate estimates of the erodibility distribution of the sediment bed. To investigate how erodibility varies in space and what the vertical distribution over the sediment depth is, comprehensive observations of the sediment properties, hydrodynamics and bed-level changes were conducted on an intertidal flat in the Western Scheldt Estuary, the Netherlands. The erosion potential on a mudflat is determined by the critical shear stress for erosion (τe), erosion rate coefficient (M) and local hydrodynamic conditions. A clear difference in hydrodynamic forcing was observed, leading to significant bed level variations at the low water line, where erosion often occurs during very shallow water condition, and a nearly constant bed level at the upper part. The erosion parameters τe and M could be determined over a sediment bed of 12 cm at the low water line. The erosion coefficient M can be considered constant with depth, although there is a large spreading. A clear vertical variation of τe was found: τe increased significantly downward from 0.10 Pa at the sediment surface to 1.13 Pa at 12 cm below the surface. Additionally, there was a strong indication that the presence of diatoms enhanced τe in the upper 2 mm of sediment by five times of the abiotic τe (from 0.09 Pa to 0.46 Pa). These findings lead to the following improvement for predicting morphological changes of tidal mudflats: (1) very shallow conditions should be better simulated, (2) the vertical distribution of τe should be considered. Otherwise, erosion rates can be overestimated, especially during extreme events, because exposure of the deeper well-consolidated layer likely occurs; and (3) an appropriate description of the effect of diatoms should be considered as part of the bottom boundary condition.

Evaluation of Cross-Shore Profile Behavior in Medium-Term Timescales Using XBeach: A Case Study of Zarabad Fishery Harbor, Iran

Among the numerous problems that decrease the capability of a harbor in the country, seasonal sedimentation is identified as a major problem for many fishery harbors. In 2007, Zarabad Fishery Harbor conditions were also identified as critical due to the large volume of sand accumulation and consequent closure of its entrance. Numerical modeling of coastal bed level change was implemented to provide insight into the typical response of the Zarabad beach to regular wave attacks, and to obtain an operational and validated model for the site. Advanced numerical models employed to predict coastal evolution at a variety of time and spatial scales usually include many free parameters that require calibration to the available field data. The XBeach numerical model was selected for its capacity to accurately model hydrodynamic and morphological processes over a two-dimensional domain. It comprises about 250 model settings that approximately 150 of these settings relate to physical and numerical Behavior and the other 100 are case-specific parameters. In this research, 11 parameters are adopted to optimize the model prediction efficiency for Zarabad Fishery Harbor area. For calibration and validation stages, two cross-shore profiles and two medium-term time periods are selected. The model showed great promise in predicting the evolution of cross-shore profiles under water, but as expected, the dry part results showed major errors. XBeach proved to be an operational tool to predict cross-shore profiles in the area, in such timescales. Although, more tests are needed to utilize the model in longer time periods with regard to the duration of simulations.

Servo-Controlled versus Protocol Driven Therapeutic Body Cooling on Transport

Background: Early initiation of therapeutic hypothermia (TH) for the treatment of Hypoxic Ischemic Encephalopathy (HIE) in term newborns has shown to improve outcomes. Many infants require transport into tertiary hospitals. The Tecotherm-Neo provides servo-controlled cooling compared to protocol driven use of various cooling agents. SMART Aim: By January, 2017, a protocol to recognize, initiate, and therapeutically cool infants during transport using the Tecotherm will be developed and implemented with a target temperature goal of 33-34° Celsius. Setting: Our NICU is a 71 bed Level 3 NICU that services a 100-mile …

Standardization of Handoff from the Transport Team to the Neonatal Intensive Care Unit. A Quality Improvement Project

Background: The handoff or transfer of patient care from one team to another has been associated with communication failures. Handoff failures affect patient outcome, increase the cost of medical care and affect patient, family and healthcare provider satisfaction. The risk of handoff failure increases as the number of providers and institution increases, this places transported patients at an specially high risk. Arkansas Children's Hospital (ACH) has a 100 bed Level IV neonatal intensive care unit (NICU). All patients are outborn and are transported almost exclusively by the ACH transport team. …

Effect of Soil Non-Uniformity on Scour for Circular Compound Bridge Piers

Bridge piers having a varying foundation diameter are known as compound bridge piers. In India for the construction of road and railway bridges circular compound bridge piers are mostly adopted. In past studies it has been concluded that 60-70% of bridge failure occurs because of scour around bridge pier across a river due to flowing water. Most of the past studies were done on the uniform bridge pier and a very few studies has been carried out so far on scour around compound bridge piers. For economical design of bridge pier foundation there is a need to determine the scour depth. In the present study, an experimental investigation has been carried out for computation of time variant change of scour depth for two different models of circular compound bridge piers over non-uniform soil for all possible cases of position of footing with respect to level of the bed, i.e., I. Footing at the level of bed, and II. Footing below the level of bed (1cm, 2cm, 3cm and 4cm) for non-uniform sediments

Effects on Scour for Different Foundation Geometry of Compound Circular Bridge Piers

This experimental study examines the variation of scour depth with time of Clearwater scour condition around compound circular bridge piers for steady flow conditions. Most of the circular bridge piers are resting on the bigger diameter caissons known as the compound circular bridge piers and are widely used in India for construction of road and railways bridge across the rivers. In past studies, it has been observed that most bridge failure occurs because of scouring due to flowing water around a bridge pier across a river. Most of the past studies were done on the uniform bridge pier and a very few studies have been done so far on scouring around non-uniform bridge piers. Estimation of scour depth is required for the economical and a sound design of bridge pier foundation. In present study, an experimental investigation has been done in a tilting flume for computation of rate of change of depth of scour with time at two different models of compound circular bridge piers by varying the foundation top position with respect to level of bed, i.e., 1. The foundation top at the level of bed, and 2. The foundation top below the level of bed (viz. 10mm, 20mm, 30mm and 40mm) for uniform sediments.

Sand transport processes and bed level changes induced by two alternating laboratory swash events

Sand transport processes and net transport rates are studied in a large-scale laboratory swash zone. Bichromatic waves with a phase modulation were generated, producing two continuously alternating swash events that have similar offshore wave statistics but which differ in terms of wave-swash interactions. Measured sand suspension and sheet flow dynamics show strong temporal and spatial variability, related to variations in flow velocity and locations of wave capture and wave-backwash interactions. Suspended and sheet flow layer transport rates in the lower swash zone are generally of same magnitude, but sheet flow exceeds the suspended load transport by up to a factor four during the early uprush. The bed level near the inner surf zone is relatively steady during a swash cycle, but changes of O(cm/s) are measured near the mid swash zone where wave-swash interactions lead to strongly non-uniform flows. The two alternating swash events produce a dynamic equilibrium, with bed level changes up to a few mm induced by single swash events, but with net morphodynamic change over multiple events that is two orders of magnitude lower. Most of the intra-swash and the single-event-averaged bed level changes in the swash zone are caused by a redistribution of sediment within the swash. The transport of sediment across the surf-swash boundary is minor at intra-swash time scale, but becomes increasingly significant at swash-averaged time scales or longer (i.e., averaged over multiple swash events).

Effect of Type of Support on The Responce of Offshore Sructure Under Seismic Load

The seismic force has very important effects in the response of offshore structures and it is considered as applied dynamic forces. The seismic must be taken in consideration in designing stage due to their high effects on the safety of platform under earthquake. In this paper a comparison in response between offshore structures with fixed support at sea bed and with embedded piling support. AL-Basrah oil port (ABOP) is taken in consideration as a case study where two models are used, in the first model the pile –soil interaction (PSI) is neglected and the fixed support is used in the level of sea bed however in the second model, the effect of pile –soil interaction is considered. For two models the finite element analysis was performed in linear behavior for piles and deck while the soil is treated as nonlinear. The results are shown that the natural frequency for fixed support is more than for structure with piling support and the responses are more influenced by the near in frequency between structure and seismic action

Electrical resistivity tomography along the Himalayan Frontal Thrust in the northwestern Frontal Himalaya for active tectonics studies

Dependence of ground resistivity upon mineral content, porosity, degree of water saturation in the rock and fluid content makes it ideal for imaging and understanding the subsurface. Results of resistivity imaging, used for active tectonics studies at Kala Amb region in the northwestern Frontal Himalaya are discussed. Study area is selected across the exposed section of the Himalayan Frontal Thrust based on a previous trench excavation survey. An electrical resistivity tomography 2D profile survey is conducted along two lines in Kala Amb region. The lines are selected with the primary objective of extending the features identified in the trench section into the subsurface. The study found to be helpful in understanding the efficacy of this method for the recognition and geometrical characterisation of faults across morphotectonic scarps or fault traces in a region which experienced late Quaternary tectonic activity. The inverted resistivity model has lateral and vertical resistivity variations according to different depositional units in the area. The presence of a north dipping fault at 54-m distance from zero electrode position towards south clearly distinguishes two separate lithological units. The liquefaction feature identified on the trench wall section which is also inferred from the resistivity section appears to be originated from greater depth. Similarity of resistivity features and spatial distance of two profiles allow us to interpret the lateral continuity of subsurface features and to identify the thickness of Quaternary deposit over river bed level.

Impact of a rocky outcrop on hydrodynamics and geomorphology in a mesotidal channel

The purpose of the present work is to study the effect of an isolated depression and a related rocky outcrop on the flow field in a mesotidal channel of the Bahía Blanca Estuary, Argentina. To this end, measurements of current velocity (ADCP), swath bathymetry (multibeam), and seismostratigraphic surveys (3.5 kHz) were made in the study area. In general, the channel bed studied (Cabeza de Buey Channel) is flat and mainly composed of clayey silts. In the inner sector, there is a depression 6 m-deep and 50–60 m in diameter, and on either side (in a streamwise sense) there are two isolated rocky outcrops that extend up to 2 m in height relative to the prevailing bed level. The two features differ in that the up-estuary outcrop is longer and extends over the whole width of the hole, while the down-estuary outcrop is shorter and only extends over part of the diameter of the hole. Seismostratigraphic analysis, in correlation with bathymetric and lithological data, indicates that these high points correspond to the outcropping of relict deltaic materials that formed part of a regional Late Pleistocene drainage system. Fine-grained estuarine sediments deposited above the old deltaic materials show evidence of the present-day sedimentological conditions related to the hydrodynamics of the channel. The flow patterns within the depression observed over a complete tidal cycle demonstrate that the flow behaves differently depending on the stage of the tide. The depth-averaged flow shows higher velocities during the ebb tide, generating a net flow directed towards the sea. Results reveal the generation of return flows (turbulent eddies) at the bottom of the hole, which expand immediately towards the water surface. During the ebb tide, intense vertical currents develop inside the hole. The eddy formation is attributed to the unequal size of the outcrops. Hence, the larger upstream channel outcrop plays an important role in eddy generation, just as downwelling-upwelling interaction produces erosion and transport of sediments, which exerts a strong influence on the deepening of the hole.

Evaluation of Electrical Resistance Tomography imaging algorithms to monitor settling slurry pipe flow

Electrical Resistance Tomography (ERT) is used in process tomography to measure multi-phase fluid flow in pipes. ERT has the advantage of a non-invasive interface, but has challenges such as noise, a relatively low spatial resolution and the ill-posedness of the inverse problem. Many different image reconstruction algorithms have been developed in the medical imaging community, which offer promise to help improve ERT performance. However, no evaluation or methodology for comparison of different algorithms for industrial applications is available. To provide such an evaluation, we tested six ERT reconstruction algorithms for the identification in static and dynamic flow situations. Metrics were developed to evaluate the algorithms in terms of image quality and accuracy, different objects/shapes and coarse solids bed levels were tested statically in a spool piece, and bed levels dynamically in a pipe loop. An algorithm comparison methodology was developed and used to evaluate the different images based on the results obtained. Overall, results show significant variability between reconstruction algorithms, with some giving poor results at the pipe boundary and others poor results at the centre of the image. We identified two high performing algorithms and show that averages of individual algorithm images can achieve improved performance.