Numerical and Experimental Investigations of Dam and Levee Failure

Both numerical and experimental investigations are conducted to study the failure of earthen dams and levees. Boussinesq equations describing one-dimensional unsteady flow including non-hydrostatic pressure distribution are solved numerically along with Exner equation for the sediment mass conservation to include the effects of the streamline curvature on the failure of non-cohesive earthen embankments. In addition, the effects of the steep bottom slope on the flow variables during the failure are studied by solving the Saint- Venant equations modified for steep bed slope along with the Exner equation to simulate non-cohesive earthen embankment failure due to overtopping. The Boussinesq equations are solved by using the two-four finite-difference scheme which is second order accurate in time and fourth order accurate in space, while the modified Saint-Venant equations are solved by using the MacCormack finite-difference scheme which is second order accurate in time and space. The performance of three sediment transport formulae, namely Ashida and Michiue, Meyer-Peter and Müller, and Modified Meyer-Peter and Müller for steep slope is compared. The comparison of the numerical results with the experimental results shows that: (1) The improvement in the prediction of the breach evolution and the downstream hydrograph by including the Boussinesq terms is minimal; (2) The predicted results by using the modified Saint-Venant equations are slightly better than those calculated by using the classical Saint-Venant equations; (3) Ashida and Michiue transport equation overestimates the erosion rate which results in an overestimation of peak discharge but predicts the time to peak fairly well; (4) Meyer-Peter and Müller and Modified Meyer-Peter and Müller equations give almost the same results for the top elevation of the eroded dam and the water surface levels, and the peak value and time to peak of the downstream hydrograph. A number of non-dimensional equations are presented to relate different model variables to the peak discharge of the downstream hydrograph. A sensitivity analysis of different model parameters to determine the most dominant factor affecting the peak downstream discharge indicates that the most dominant factor affecting the peak discharge is the upstream reservoir volume, while the sediment grain size shows very little effect on the peak discharge. The lateral outflow through a levee breach may be computed as an outflow over a broad-crested side weir. The lateral outflow has been computed previously by assuming the flow in the main channel to be one-dimensional, and most of the equations for computing the outflow are based on the local flow variables near the breach. These are unknown and difficult to measure during a flood. In this study, a numerical model is developed to solve the two-dimensional, shallow water equations using MacCormack finite-difference scheme. The model is applied to a breach in a rectangular channel. A comparison of the numerical results with the experimental measurements shows satisfactory agreement. Different cases are simulated by varying the breach width, the bottom level of the breach, and the discharge in the main channel. Comparison between the breach outflows obtained using the numerical model with the results of a simple one-dimensional approach indicates that the breach outflows are overestimated by the latter. A new discharge correction factor is introduced for the lateral breach outflow predicted using the simple one-dimensional approach. The correction factor is a function of the submergence ratio of the breach, breach width, and inlet Froude number. An accurate prediction of the evolution of the breach resulting from overtopping of a non-cohesive earthen levee is important for flood mitigation studies. Laboratory experiments are conducted with various inlet discharges, and downstream water depths. The breach shape is recorded using a sliding rods technique. A sequence of discrete mass failure of the sides of the breach due to slope instability is observed during the failure process. A simple geostatic failure mechanism is suggested to calculate the lateral sediment load due to the mass failure. This mechanism is implemented in a two-dimensional numerical model which solves the shallow water equations along with the sediment mass conservation. In order to assess the effect of the lateral sediment load resulting from slope instability on the failure process, the predicted breach shape evolution and breach hydrograph with and without the slope failure mechanism are compared with the experimental results. The predicted breach shape is improved by adding the lateral sediment inflow due to slope instability especially in terms of the maximum depth of erosion. Also, the peak discharge of the breach hydrograph is captured more accurately by adding the slope failure mechanism

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

Performance evaluation of pilot-scale reverse osmosis spiral wound membrane for water desalination systems

The increasing scarcity of potable water increases the demand for non-conventional potable water resources such as desalination. Experiments are carried out using a pilot-scale device of the desalination process for three configurations of membrane allocation inside the pressure vessel. Configuration (A) is one pressure vessel containing one spiral wound membrane (SWM), (B) is four pressure vessels each containing one SWM connected in parallel, and (C) is one pressure vessel containing four membranes connected in parallel. The effect of applied pressure, temperature, and water salinity is studied. Moreover, a mathematical model using ANSYS Fluent was developed and verified using the experimental data. The mathematical model is applied to an idealized case of an actual desalination plant. The main findings are (1) configurations (B) and (C) accomplished higher permeate discharge comparing to (A) by an average percentage of 60 and 50, respectively, while (C) has the lowest output salinity by 30% from configuration (A). (2) The mathematical model is found to reduce the operating pressure of the plant by 8%. HIGHLIGHTS Evaluation of membrane allocation inside the pressure vessel.; A new approach is proposed by putting four elements inside one pressure vessel.; The new approach achieved higher water quality with almost the same flux.; Numerical model was used to find the optimum applied pressure at an existing RO desalination plant.; It succeeded to reduce the pressure by 8% compared to the operating one.

Estimation of the flood vulnerability index (FVI) for Alexandria city , Egypt: A case study

Climate change and urbanization are likely to increase the vulnerability of cities by increasing the intensity of flooding, which causes damage to the communities. The objective of this research is to estimate the Flood Vulnerability Index (FVI) for Alexandria City to assist decision-makers develop priority urban flood plans and identify methods for reducing flood risk. In this study, the FVI is generally estimated throw three components: social, physical, and environmental. Moreover, eleven major indicators are used to represent each of these three components, and they are classified according to the three flood factors: exposure, susceptibility, and resilience. Geographic information system (GIS), and remote sensing (RS) are applied to obtain the required data and develop maps for identifying the urban flood indictors. The study area has been divided to 16 zones regarding its administrative classification The 16 zones in Alexandria city's Vulnerability Index for the three components (social, physical , and environmental ) and the overall FVI have been estimated. Population, population density, population access to sanitation, and warning system are used as the four indicators for the social component, whereas the four indicators used for the physical components, are approximately of stream, elevation, rainfall amount , and slope. The environmental component, is evaluated by using three indicators , land use, urban growth, and flood recovery time. The index assigns a number among 0 and 1, indicating relatively low or high urban flood vulnerability. The findings demonstrate that FVI offers a way to assess flood vulnerability and obtain appropriate adaptation choices

Development of suitability map for managed aquifer recharge: Case study, West Delta, Egypt

Managed aquifer recharge (MAR) is considered an innovative method for storing water in the subsurface. In this work, multi-criteria decision analysis (MCDA) was used to delineate potential groundwater recharge areas for MAR implementation in Western Delta using reclaimed wastewater. By employing geographical information systems (GIS) and pairwise comparison matrix (PCM), a modified approach was utilized for the development of the suitability map by capturing the interlinkages between a specified MAR technique (spreading methods) and MAR suitability mapping processes. The developed approach was created with a range of constraining and factorial considerations. Based on the findings, MAR potential recharge zones included four main suitability classes. The presence of high-suitability areas was mainly delineated in the northeast part, particularly around the left side of the Nile River valley. Areas of low suitability were located around the west-north side where the hydrological criterion seems to hinder the implementation due to the low productivity of the hydrogeologic layer. The developed methodology reflected the importance of specific determining factors (i.e., slope and depth to the water table) that govern the successful implementation of infiltration basins and maximize the benefits from soil aquifer treatments effects when taken into account with other hydrogeological and socio-economic variables. HIGHLIGHTS An enhanced vision for the future management of groundwater in West Delta.; The use of multi-criteria decision analysis for improved groundwater management.; Assessing land suitability for future managed aquifer recharge (MAR) developments.; The use of suitability mapping for better-informed decision-making for MAR planning.