Critical Discharge Research Articles

Evaluating the thresholds for predicting post-earthquake debris flows: Comparison of meteorological, hydro-meteorological and critical discharge approaches

Post-earthquake debris flows pose significant hazards in mountainous regions following large seismic events. Evaluating the thresholds for predicting the occurrence of these flows is crucial. However, the absenting of comparison for different predicting methods hampers progress in improving and updating predictions for debris flows. In this study, based on on-site measurements of post-earthquake debris flows in an active catchment during the first year following the 2022 Luding Ms6.8 earthquake, 30 debris-flow events were identified and observed. We established and compared three distinct methods—namely, the meteorological approach, the hydro-meteorological approach, and the critical discharge approach for predicting the occurrence of post-earthquake debris flows. Additionally, we introduced a factor called absolute energy to improve the accuracy of the traditional meteorological approach. Absolute energy is defined as the sum of squared values within a time series. Our findings indicate that the hydro-meteorological model outperforms others in predicting post-earthquake debris flows, whereas the meteorological approaches especially the intensity–duration (I–D) thresholds exhibit suboptimal performance. Furthermore, the updated meteorological model incorporating absolute energy demonstrates improved predictive capability compared to traditional meteorological approaches like intensity–duration (I–D) thresholds. We argue that this comparative analysis will aid in selecting the suitable method for predicting post-earthquake debris flows.

Coupling reservoir depletion and geomechanics to assess risks during post-blowout well capping: Case study on Macondo

Reservoir depletion can be consequential to wellbore integrity after a blowout, especially offshore. A prolonged post-blowout discharge extends reservoir depletion. “Underground blowouts” (tensile-fracture initiations) occurring after well capping, or shear-driven slow slippage of naturally-occurring pre-existing faults (PEFs) in the near-well vicinity, can compromise post-blowout wellbore integrity. Upward propagation of the initiated tensile fractures may trigger seafloor broaching by reservoir hydrocarbons.This study examines reservoir depletion analytically, evaluating associated geomechanical implications on the in-situ reservoir conditions and assessing the likelihood of tensile-fracture initiation (oriented longitudinally or transversely-to-the-wellbore) during post-blowout-well-capping operations, in addition to shear-driven slow slippage along PEFs in the near-well vicinity. A set of calculational procedures and thinking sequences are presented, necessary for encompassing the primary effects of post-blowout reservoir depletion on the in-situ stress state and the limits of tensile and shear failures that could aid in the appropriate blowout-contingency decision-making.Our novel, physics-based scheme (analytical-coupling approach) is applied to parameters from the MC 252–1 “Macondo Well” blowout from April 20, 2010 and the targeted M56 oil reservoir in deepwater Gulf of Mexico (GoM). The reservoir rock is modeled as a porous-permeable medium, considering fluid infiltration to-and-from the pressurized wellbore. The likelihood of an underground blowout correlates with the shut-in wellbore pressure buildup, after successful well capping.Elevated reservoir depletion via higher post-blowout-discharge flowrates and longer post-blowout-discharge periods (in terms of time duration) are shown to reduce the shut-in wellbore pressure buildup against time following well capping. The “critical discharge flowrate,” an established predictive indicator for underground blowouts following shut-in of an installed subsea-capping stack (SCS) is employed, using data from the post-blowout-discharge period, suggesting underground blowouts to be highly-unlikely for the set of parameters assessed. Finally, the Mohr-Coulomb criterion indicates that shear-driven slow slippage along PEFs in the near-well vicinity is also unlikely, considering the Macondo Well's bottomhole-wellbore-pressure history in the aftermath of the blowout.

Hydrology controls sulfuric acid-mediated weathering in an orogenic regime of southwestern Taiwan

Chemical weathering is a pivotal geochemical process that shapes the carbon cycling and climates in the critical zone. Among its critical drivers, river discharge holds a particular significance, especially in the orogenic landscapes. Here, we examined the impact of discharge on mineral weathering in southwestern (SW) Taiwan by analyzing river water chemistry across a wide discharge range. Current observations indicated that carbonate contributes significantly to total weathering (50–80 %), with sulfuric acid accounting for one-half to two-thirds of carbonate weathering. A statistically strong correlation between river discharge and sulfuric acid-mediated carbonate weathering was highlighted, while the silicate weathering remained constant. This relationship suggests an increased influx of fresh minerals, such as pyrite, into the weathering regime as water flow increases. Our model identifies a critical discharge threshold of 4.6 m3 s−1, determining whether mineral weathering acts as a net source or sink of CO2. Consequently, mineral weathering in SW Taiwan acts as a net CO2 sink during dry periods but turns into a net source during wet periods. Through analyzing a decade of daily discharge data, we found mineral weathering in SW Taiwan is a net CO2 source, with a 2.6-fold increase in annual mean discharge causing a 3.8-fold increase in net CO2 flux. This pattern is likely to be applicable to other similar minerals containing mountain-building regions, highlighting the significant role of hydrology in determining weathering sources and their potential impact on the carbon cycle balance.

Experimental study of deformation characteristics of ice-melting droplets at voltages less than and greater than the critical discharge voltage

Experimental study of deformation characteristics of ice-melting droplets at voltages less than and greater than the critical discharge voltage

Finite element model to investigate the dynamic instability of ring stiffened conical shells subjected to flowing fluid

In this study, the vibration stability (i.e., static divergence) and critical velocity of fluid-conveying, ring-stiffened, truncated conical shells are investigated under various boundary conditions. The shell is characterized using Sanders’ theory, while the fluid is modeled using a velocity potential approach with the impermeability condition at the fluid-shell interface. Using linear superposition, the natural frequencies corresponding to each flow velocity are determined by satisfying the dynamic characteristic equation and boundary conditions. Critical velocities are identified where the natural frequencies vanish, indicating static divergence. Parametric studies are conducted to investigate the effect of ring stiffeners on the critical velocities with respect to the semi-cone angle, number of rings, and boundary conditions. The proposed model is validated through comparison with published data. It is found that the rings significantly affect the stability of the cone under different boundary conditions. Instability in stiffened shells occurs at higher critical fluid velocities than in unstiffened shells across all boundary conditions. An increase in the vertex angle leads to a decrease in critical flow discharge.

524 Outcomes From Preoperative Risk Scoring for Emergency Laparotomy

Abstract Aim Risk scoring systems can be used to predict outcome, facilitate perioperative decision making and guide management in emergency laparotomy (EL). This study aims to evaluate the differences in outcome between EL patients who were prospectively risk assessed and those who were not. Method A retrospective study was conducted on all 782 patients aged over 18 years who underwent EL at four Australian hospitals between 1 January 2018 and 31 December 2019. Data recorded included demographics, preoperative risk assessment, case urgency, involvement of anaesthetic and intensive care consultants, critical care bed requirement, mortality, and discharge destination. NELA scores were retrospectively calculated for all patients. Results 209 patients had been preoperatively risk assessed, with a mean NELA score of 16.45%, compared to 8.72% for those who were not preoperatively risk assessed. They tended towards a higher ASA score, were booked as a higher urgency operation, and were more likely to receive consultant led care by anaesthetics and intensivists. Postoperatively these patients had increased critical care bed utilisation, 30-day mortality was 14.4% compared to 5.8%, and by 365 days mortality rose to 24.9% compared to 13.8%. Conclusions Use of preoperative risk prediction scores does not in itself reduce risk of mortality. In a health system that does not mandate formal preoperative risk assessment, it appears that clinicians use preoperative risk assessment tools when they perceive risk to be higher, rather than as a routine part of emergency laparotomy care.

Rainfall-runoff modelling using GIS based SCS-CN method in umiam catchment region, Meghalaya, India

Rainfall-runoff is a crucial parameter and is often applied in assessing water resources. It is a significant constituent for recharging groundwater and plays an important role in understanding the hydrological characteristics of a basin for watershed management practices. In the current work, the soil conservation service-curve number (SCS–CN), coupled with GIS and remote sensing techniques, has been utilized to estimate the runoff and discharge in the Umiam Catchment area of Meghalaya for the years 2011 and 2020. This area receives heavy rainfall throughout the year, which contributes to the degradation of topsoil and the initiation of landslides. The rainfall-runoff modelling incorporates various thematic layers prepared in the GIS platform to calculate the weighted CN value. The antecedent moisture condition (AMC) was applied for CN correction. Both annual and monthly runoff and discharge were calculated for a total of four sub-watersheds. The result showed that land alteration and an increase in rainfall have been the predominant reasons for an increase in runoff in 2020 compared to 2011. Comparing both years, agricultural land, built-up, and open scrub have increased followed by shrinking open and dense forests. Sub-watersheds 2 and 4 had critical discharge changes of 75.95 and 75.82 cubic meters per second (cumec) from year 2011–2020 respectively. This study emphasizes the efficacy of SCS-CN method for simulating and estimating the runoff of a basin for better watershed planning and sustainable management at the regional level. It may also help in recognizing and examining the characteristics and volume of water resources.

Reply to Comment by Poppema and Wüthrich on “Momentum and Energy Predict the Backwater Rise Generated by a Large Wood Jam”

AbstractFollett et al. (2020, https://doi.org/10.1029/2020gl089346) demonstrated that a large wood jam can be modeled as a porous obstruction with momentum loss proportional to the number, size, and packing density of the logs and jam length. Poppema and Wüthrich (2024, https://doi.org/10.1029/2023gl106348) incorporated uniform flow Froude number, broadening the scope of our work. Here, we demonstrate that Froude number can be directly introduced to equations in the main body of Follett et al. (2020, https://doi.org/10.1029/2020gl089346), without requiring uniform flow. Based on this, we show that a managed increase in upstream depth is possible for conditions below a critical discharge, in which equilibrium upstream depth over uniformly distributed jams can be adjusted with inter‐jam spacing. This design could retain water in low flow conditions, allowing jams to act independently above critical discharge. Finally, we suggest that log orientation can be included in our model by varying both drag coefficient and frontal area perpendicular to the flow.

Delirium and Its Associations with Critical Care Utilizations and Outcomes at the Time of Hospital Discharge in Patients with Acute Brain Injury.

Background and Objectives: We analyzed delirium testing, delirium prevalence, critical care associations outcomes at the time of hospital discharge in patients with acute brain injury (ABI) due to acute ischemic stroke (AIS), non-traumatic subarachnoid hemorrhage (SAH), non-traumatic intraparenchymal hemorrhage (IPH), and traumatic brain injury (TBI) admitted to an intensive care unit. Materials and Methods: We examined the frequency of assessment for delirium using the Confusion Assessment Method for the intensive care unit. We assessed delirium testing frequency, associated factors, positive test outcomes, and their correlations with clinical care, including nonpharmacological interventions and pain, agitation, and distress management. Results: Amongst 11,322 patients with ABI, delirium was tested in 8220 (726%). Compared to patients 18-44 years of age, patients 65-79 years (aOR 0.79 [0.69, 0.90]), and those 80 years and older (aOR 0.58 [0.50, 0.68]) were less likely to undergo delirium testing. Compared to English-speaking patients, non-English-speaking patients (aOR 0.73 [0.64, 0.84]) were less likely to undergo delirium testing. Amongst 8220, 2217 (27.2%) tested positive for delirium. For every day in the ICU, the odds of testing positive for delirium increased by 1.11 [0.10, 0.12]. Delirium was highest in those 80 years and older (aOR 3.18 [2.59, 3.90]). Delirium was associated with critical care resource utilization and with significant odds of mortality (aOR 7.26 [6.07, 8.70] at the time of hospital discharge. Conclusions: In conclusion, we find that seven out of ten patients in the neurocritical care unit are tested for delirium, and approximately two out of every five patients test positive for delirium. We demonstrate disparities in delirium testing by age and preferred language, identified high-risk subgroups, and the association between delirium, critical care resource use, complications, discharge GCS, and disposition. Prioritizing equitable testing and diagnosis, especially for elderly and non-English-speaking patients, is crucial for delivering quality care to this vulnerable group.

Bedload transport fluctuations, flow conditions, and disequilibrium ratio at the Swiss Erlenbach stream: results from 27 years of high-resolution temporal measurements

Abstract. Based on measurements with the Swiss plate geophone system with a 1 min temporal resolution, bedload transport fluctuations were analysed as a function of the flow and transport conditions in the Swiss Erlenbach stream. The study confirms a finding from an earlier event-based analysis of the same bedload transport data, which showed that the disequilibrium ratio of measured to calculated transport rate (disequilibrium condition) influences the sediment transport behaviour. To analyse the transport conditions, the following elements were examined to characterise bedload transport fluctuations: (i) the autocorrelation coefficient of bedload transport rates as a function of lag time (memory effect), (ii) the critical discharge at the start and end of a transport event, (iii) the variability in the bedload transport rates, and (iv) a hysteresis index as a measure of the strength of bedload transport during the rising and falling limb of the hydrograph. This study underlines that above-average disequilibrium conditions, which are associated with a larger sediment availability on the streambed, generally have a stronger effect on subsequent transport conditions than below-average disequilibrium conditions, which are associated with comparatively less sediment availability on the streambed. The findings highlight the important roles of the sediment availability on the streambed, the disequilibrium ratio, and the hydraulic forcing in view of a better understanding of the bedload transport fluctuations in a steep mountain stream.

QUALITATIVE AND QUANTITATIVE ANALYSIS OF WATER CONING AND BREAKTHROUGH TIME PREDICTION ON ZNC FIELD

Given the current public need for oil and gas as a primary energy, all oil and gas companies need to increase production to meet this demand. One of the things companies usually do to achieve this is to evaluate and analyze the productivity of each well. Of course, production decreases from time to time, so the company must try to increase its production. One of the reasons for the decline in oil production from the ZNC-1 well in the ZNC Field is the production of excessive water content. There are several factors that cause excessive water content in oil wells, and this is called water coning. The method used to determine the occurrence of the water cone problem requires qualitative and quantitative analysis. In using qualitative analysis, two analyzes were carried out, including an analysis of the production history of the well and an analysis of the Chan Diagnostic Plot showing bottom-water coning problems with late-time channeling. Meanwhile, based on the quantitative results, the critical flow rate of the ZNC-1 well calculated using the Bornazel and Jeanson method is 167 STB/D. With these results, the value of the critical flow discharge is greater than the actual discharge, which is 291.3 STB/D. Thus it can be ascertained that there has been water coning in the ZNC-1 well. After that, the breakthrough time obtained by the Bournazel and Jeanson method was 361.3 days.

Effect of spindle position on the performance and two-phase characteristics of controllable ejector for transcritical CO[formula omitted] refrigeration system

Spindle-controlled variable-geometry ejectors can adjust the system capacity to meet varying load requirements in transcritical-CO2 refrigeration systems. The present study numerically explores the effect of spindle position on the performance and flow characteristics of a controllable two-phase CO2 ejector. Spindle-controlled ejectors achieved entrainment ratios higher than that of fixed geometry ejector. Motive and suction flows exhibited high sensitivity to the spindle position near the critical operating range because of the transition between operating modes. The two-phase and shock characteristics associated with ejector flow and the variations observed for different spindle positions are discussed. Critical discharge pressures and entrainment ratios are estimated for various spindle positions. The critical compression and entrainment ratios correlate with the respective normalized spindle position in the ejector. The impact of the effective nozzle throat area on the flow entrainment range and achievable pressure lift is investigated. The results showed that the critical entrainment ratio bears a common linear relationship with the critical compression ratio for all positions of the spindle. The study relates the most significant performance and geometric parameters of the spindle-controlled two-phase CO2 ejector.

Characterization of salt wedge intrusion process in a geographically complex microtidal deltaic estuarine system

Deltas are strategic systems of high ecological and economic importance since they provide various environmental resources and fertile alluvial soils. Different types of hydrodynamic processes occur in deltas, including saline intrusion. We implemented a three-dimensional numerical modeling system using the EFDC + Explorer Modeling System to analyze the characteristics of saline intrusion in the Sinú River delta, Colombia. We configured the model with field data from two measurement campaigns in February and November 2021, dry and wet seasons, respectively, and with secondary information. Several climatic conditions to cover a wide range of variability in the main forcing factors were simulated, specifically river discharge and tides: (1) without the influence of the El Niño Southern Oscillation (ENSO) climatic phenomena; (2) under critically low conditions of flow discharge; and (3) with sea level rise forecasts. The model was calibrated using in-situ water velocity data and salinity profiles. We obtained Index of Agreement (d) values between 0.67 and 0.99 for salinity and higher than 0.9 for water velocity. The numerical simulation provides valuable information about this stratified salt wedge system's dynamic nature, mainly due to changes in river discharge. The simulation demonstrated that river discharges above 319 m3/s were sufficient to prevent salt wedge intrusion, which are typical values registered annually between May and November. The scenarios under critical low discharge conditions and sea level rise projections showed a maximum reach of the salt wedge intrusion of 7.40 km. The model proved efficient in evaluating the saline intrusion process in the Sinú River delta, obtaining practical results that describe the dynamics of this process. It was shown that by simulating physical processes, such as salinity stratification, numerical models provide useful information on how these estuarine systems respond to different environmental stress factors associated with current climate variability, such as long drought periods or El Niño South Oscilation (ENSO), since salinity gradients play an important role in deltas' aquatic life, since they influence the distribution of phytoplankton, which is a key player for primary productivity.

Microwave ignition of a combustible gas mixture with a critical streamer discharge in a high-speed flow

Ignition of combustible air/propane mixture in a high-speed flow with a microwave streamer discharge is considered. The experimental results of structure of streamer discharge and quantities at various pressures are presented. Pressure and temperature measurements in various sections of the streamer discharge in high-speed flow are analysed. The results obtained demonstrate the possibility of ignition of air/propane combustible mixture. The main physical mechanisms responsible for heating the discharge plasma to the ignition temperature of the combustible mixture and their characteristic time scales are discussed. The minimum time and minimum level of microwave radiation required to ignite a combustible mixture under various conditions are determined.

Critical Discourse Analysis Of Child Marriage Practices In The Yuni’s Movie

This research generally strives to see the discourse of the marriage practices of children who are raised in the movie Yuni with the method of researching the critical discourse discharge of the Norman Fairclough known as 3-dimensional analysis is text, scholary practice) (socialche practice) and social practice. According to him there is a kind of dialectic that occurs between social context (macro) and language (micro) itself. Thus, Fairclough tries to combine linguistic traditional and socio-linguistic. According to him, to know the meaning of the text as a whole, not enough if it only sees the linguistic aspects that it is necessary to connect it to the social context. That way, although the film is part of the literary study, this study will not lose its sociological aspect. This study will analyze each scene containing text or discourse of child marriage practices, analyze how the audience interprets the film through the application that has comments and analyzes the social context outside the media affecting the text raised in the movie Yuni. Data collection was done through the analysis which was then captured the screen in the scene containing child marriage text. Not only that, researchers also collect data through library studies and documentation which then the overall data was analyzed using 3-dimensional analysis of Norman Fairclough. From the results of the analysis conducted by the researcher, at least 9 scenes containing discourse of child marriage practices in Yuni's film including themselves that there is still an assumption that education for women is not important, some societies do not know the existence of the law Article 7 Number 16 of 2019, the marriage of children is not equipped with physical, psychic and mature knowledge, the environment plays an important role in directing teenagers, the income of the pigs that encourage the practice of marriage of children, and the school that has not functioning maximally.

A coarse graining CFD–DEM simulation on contact erosion of layered cohesionless soils

A coarse graining computational fluid dynamics–discrete element method (DEM) model is developed to analyze the contact erosion of cohesionless soils at the coarse/fine soil interface. Two benchmark cases are provided to verify the model implementation, including the collision of two groups of particles and collapse of a soil column in water. It is demonstrated the CG approach significantly reduces the computational cost with sufficiently good accuracy. Two typical CG approaches, i.e., the relative overlap scaling (ROS) and absolute overlap scaling approaches, are compared and show similar model performance. While the DEM time step of ROS approach is scaled up by the scaling factor, it is recommended in this study for the better computational performance. The verified model is used to simulate the laboratory contact erosion experiment under various flow conditions. The critical discharge rate calculated from the numerical model is 357 mL/s, which achieves a high consistency with the experimental value of 311 mL/s. Further study shows the scaling factor influences the critical discharge rate, as large parcels introduce boundary effects especially for coarse soils. It is also shown the packing state of coarse soils is a determinant in the erosion initiation, as the void fraction distribution is the key for particle and fluid transports, especially near the contact surface.

Flood dynamics and its spatial prediction using open-channel hydraulics and hydrodynamic model in the dam-controlled river of India

The spatial prediction of flood inundation, in the monsoon months (July–October), around the downstream southern part of the Damodar River Basin (Hooghly and Howrah districts of West Bengal) is very uncertain due to analytical lack of database, channel hydraulics and steady or unsteady flow anomaly. Using techniques of flood hydrology and HEC-RAS module of flood prediction, this study estimated the critical hydrological range of recurrent floods (1651–1822 m3 s−1 peak discharge) which are annually observed in the low-lying active floodplains of lower basin. The four days heavy rainfall (52.5 to 268 mm), yielded a runoff range of 10–207 mm which triggered maximum discharge of 7035 m3 s−1, causing havoc flood at downstream. There is possibility of channel shifting and embankmnet breaching during floods in the Mundeswari and Damodar/Amta channel, as Unit Stream Power can exceed 30 Wm−2 in tweleve cross-section stations. During 5-year and 10-year flood event (6676 m3 s−1) the floodplain inundation depth can reach 4–12 m in the Khanakul, and Udaynarayanpur region, having maximum chance of overbank flow. The most vulnerable site of embankment failure and overbank flow is stretch between Rajbalhat and Udaynarayanpur where the flood depth can cross 10 m limit for the critical discharge of 1811 m3 s−1. The flood risk is aggravated because within 42.5 km stretch of lower Damodar the channel can accommodate maximum flow of 1378 m3 s−1 (average flow area of 687 m2) at upstream cross-sections, but at downstream cross-sections the carrying capacity of channel is reduced to 1081 m3 s−1 (21.55 percent reduction) due to increasing siltation and decreasing average flow area (478 m2).

Driving Forces and Influences of Flood Diversion on Discharge Fraction and Peak Water Levels at an H-Shaped Compound River Node in the Pearl River Delta, South China

The SiXianJiao (SXJ) is the first-order exchange node of the West River and the North River and redistributes water (mass) to the downstream river network in the Pearl River Delta (PRD), South China. The lateral SXJ waterway plays a critical role in flow (mass) diversion between the West River and the North River, forming a unique H-shaped compound river node. Previous studies mainly focused on Y-shaped bifurcation and confluence nodes, and there is a lack of research on deltaic H-shaped river nodes. This study established the Delft3D model to investigate the driving forces and influences of flood diversion at the SXJ node. The results showed that the H-shaped SXJ river node was usually in hydraulic equilibrium but was often disturbed by large water level differences between the two rivers, due to unbalanced and asynchronous upstream flood waves. The large water level differences drove mutual flood diversion through the lateral SXJ waterway, which synchronized the downstream discharge and reduced the peak water levels (flood hazards), resulting in similar water levels or hydraulic equilibrium in the two rivers. There exists a critical flow fraction—about 75.9% (West River)—at which the incoming flow from both rivers presents similar water levels at the SXJ node, resulting in little flood diversion. Above the threshold, the flood water will divert from the West River to the North River with a maximum rate of −11,900 m3/s, accounting for 20% of the West River, reducing the peak water level up to 1.48 m at Makou. Below the threshold, the flood water will divert from the North River to the West River with a maximum rate of 11,990 m3/s, accounting for 55% of the North River, reducing the peak water level up to 6.63 m at Sanshui. Meanwhile, the discharge fraction at downstream Makou (Sanshui) maintained a near-constant value during individual floods and fluctuated around 76.6% (23.4%). This critical discharge fraction and the analytical approach are of significance in flood-risk management and hydraulic engineering design in the PRD. The concept model of the H-shaped compound river node clearly elucidates the flood diversion mechanism via the lateral SXJ waterway and may work for other similar river nodes as well.

Research on Seawater Intrusion Suppression Scheme of Minjiang River Estuary

Seawater intrusion in the Minjiang River estuary has gravely endangered the water security of the surrounding area in recent years. Previous studies mainly focused on exploring the mechanism of intrusion, but failed to provide a scheme for suppressing seawater intrusion. The three most relevant determinants to chlorine level, which represented the strength of seawater intrusion, were determined using Pearson correlation analysis as being the daily average discharge, daily maximum tidal range, and daily minimum tidal level. Considering the lower requirement of sample data and the ability to handle high-dimensional data, the random forest algorithm was used to construct a seawater intrusion suppression model and was combined with a genetic algorithm. The critical river discharge for suppressing estuary seawater intrusion determined using this model. The critical river discharge was found to gradually increase with the maximum tidal range, which in three different tide scenarios was 487 m3/s, 493 m3/s, and 531 m3/s. The practicable seawater intrusion suppression scheme was built up with three phases to make it easier to regulate upstream reservoirs. In the scheme, the initial reading of river discharge was 490 m3/s, and it rose to 650 m3/s over six days, from four days before the high tide's arrival to two days following it, and before falling down to 490 m3/s at the end. Verified with the 16 seawater intrusion events in the five dry years, this scheme could eliminate 75% of the seawater intrusion risk and effectively reduce the chlorine level for the remaining 25% of events.

Migrating bars influence the formation and dynamics of their peers in large sandy‐gravel bed rivers

AbstractThe present study investigates the morphodynamic interactions between migrating bars in a sandy gravel and nearly straight channel of the Loire River (France). From a large dataset collected from field campaigns performed between 2016 and 2020, we analysed the deflection power exerted by bars on flow and sediment transport that influences the dynamics of other bars present in the channel. We also investigated the role of low flows in bar formation. To this aim, the riverbed evolution has been documented using four years of bathymetrical and aDcp surveys. Flow deflection induced by the presence of bars in the channel differs for pre‐existing (first‐order) bars and bedload sediment accumulations identified as new developing bars (second‐order bars). The latter needs to reach an equilibrium size to influence flow direction. During low flows, first‐order bars emerge and create contraction/expansion zones in the channel, inducing a temporary local geometrical forcing that leads to sediment deposition at the outlet of these zones. Sediment deposited in these specific areas can constitute a nucleus for second‐order bar formation or contribute to first‐order bar aggradation. According to the linear free bar theory, the critical discharge that contributes to expressing an alternate bar pattern is exceeded during moderate flood, leading to the observation of a transitional bar pattern between alternate and central bar pattern.