Sediment retention in river deltas and feedbacks with delta morphology

2021 ◽  
Author(s):  
Jaap Nienhuis ◽  
Juan Paniagua-Arroyave ◽  
Frances Dunn ◽  
Sagy Cohen ◽  
Torbjorn Tornqvist
Keyword(s):  
River Mouth ◽  
Sediment Traps ◽  
Sediment Supply ◽  
Sediment Retention ◽  
Sediment Delivery ◽  
Cross Sectional ◽  
Fluvial Sediment ◽  
River Deltas ◽  
Sediment Loads ◽  
The Mean

<p>Fluvial sediments have collectively formed about 900,000 km<sup>2</sup> of deltaic land since Holocene sea-level rise slowed down. The rate at which deltas have retained fluvial sediment to build deltaic land, however, has varied greatly between different deltas. Here we quantify sediment retention in the delta topset and foreset for 3,556 deltas globally. We estimate retention from data on delta morphology and cross-sectional area, combined with WBMSed data on fluvial suspended sediment supply. Deltas, on average, retain 25±2% (standard error of the mean) of the fluvial sediment in their topset and 31±2% in their foreset. Because topset sediment retention reduces the sediment delivery to the river mouth, it sets up a feedback with processes that build delta morphology. Waves reduce topset sediment retention whereas tides increase it. Tide dominated deltas retain 61±24% on their topset, on average, compared to 21±3% and 24±2% for river- and wave-dominated deltas, respectively. Larger deltas trap more sediment, but not in comparison to their larger sediment loads, making them relatively inefficient sediment traps.</p>

scholarly journals Design optimization of permeable sediment traps for fluvial bed load transport

2018 ◽  
Vol 40 ◽  
pp. 03009 ◽  
Author(s):  
Anita Roth ◽  
Mona Jafarnejad ◽  
Sebastian Schwindt ◽  
Anton Schleiss
Keyword(s):  
Sediment Trap ◽  
Sediment Traps ◽  
Sediment Supply ◽  
Bed Load ◽  
Hydraulic Control ◽  
Check Dam ◽  
Sediment Retention ◽  
Existing Structures ◽  
Load Transport ◽  
Set Up

Sediment traps are crucial elements for flood protection in mountain rivers with high sediment transport capacity. Existing structures often interrupt the channel connectivity. Ideally, a sediment trap should be permeable for bed load during non-hazardous floods and ensure sediment retention during hazardous discharges. A new sediment trap concept, fulfilling these requirements was recently developed and tested in a laboratory flume. A guiding channel trough the deposition area is combined with a slot check dam having an upstream bar screen with bottom clearance. This study aims to validate the proposed concept with a finer sediment mixture on an experimental set-up. Furthermore, we provide improved recommendations for bar screen design regarding minimal bar spacing and the range of applicable clearance heights. Optimal bar spacing and clearance heights of the bar screen are determined through individual tests of the bar screen with steady discharges and varying sediment supply intensity. The best performing bar screen configuration is subsequently tested in combination with a slot check dam using a flood hydrograph to simulate the influence of quasi-unsteady discharge. The proposed concept corresponds to a combined mechanical-hydraulic control and works well for a large range of grain sizes, if the bar screen is correctly adapted.

scholarly journals PROJEVY ZDROJOVÝCH OBLASTÍ SEDIMENTŮ V ZRNITOSTNÍM SLOŽENÍ KORYTOVÝCH AKUMULACÍ VODNÍCH TOKŮ V RELIÉFU BUDOVANÉM FLYŠOVÝMI HORNINAMI

2014 ◽  
Vol 21 (1-2) ◽  
Author(s):  
Václav Škarpich ◽  
Tomáš Galia
Keyword(s):  
Particle Size ◽  
Mean Value ◽  
Sediment Supply ◽  
Material Transport ◽  
Sediment Delivery ◽  
Size Index ◽  
The Mean ◽  
Continuum Systems ◽  
Channel Segment

The character of bed sediments reflects fluvial processes and the dynamics of material transport in fluvial (dis)continuum systems. The approach in this study was based on the measurement of the five largest boulders located within a channel, and on the observation of changes in their size in the longitudinal profi le of headwater streams Kobylská and Pulčínský potok. All three axes (dimensions) of the five largest boulders were measured at 10 ± 1m intervals of the longitudinal profile. The resulting trends in a particle-size index reflect the character of sediment delivery into the channel segment. The largest boulders were observed in channel sections with a strong interaction of slope processes. But local lithological conditions affect changes of the mean value of the particle-size index of the largest boulders. The role of slope processes can be accentuated by the presence of uniform sandstone lithology of the studied bed particles. In the lithology built by claystone layers the role of slope processes has problematic identification. The main reason is erodible character of claystone layers which affects sediment supply of finer particles from adjacent slopes into the channel segment.

scholarly journals Suspended-Sediment Distribution Patterns in Tide-Dominated Estuaries on the Eastern Amazon Coast: Geomorphic Controls of Turbidity-Maxima Formation

Water ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1568
Author(s):  
Vando J. C. Gomes ◽  
Nils E. Asp ◽  
Eduardo Siegle ◽  
José Diego Gomes ◽  
Ariane M. M. Silva ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
Regional Climate ◽  
Strong Dependence ◽  
River Sediments ◽  
River Mouth ◽  
Sediment Supply ◽  
Amazon River ◽  
Sediment Delivery ◽  
Sediment Distribution ◽  
The World

In tide-dominated estuaries, maximum-turbidity zones (MTZs) are common and prominent features, characterized by a peak in suspended-sediment concentration (SSC) associated with estuarine processes. The Brazilian Amazon coast includes many estuaries, experiencing macrotidal conditions. MTZs are expected to occur and are crucial for sediment delivery to the longest continuous mangrove belt of the world. The area is under influence of the Amazon River plume (ARP), the main SSC source, as local rivers do not deliver substantial sediment supply. To assess the processes that allow the ARP to supply sediment to the estuaries and mangrove belt along the Amazon coast, the results from previous individual studies within five Amazon estuaries (Mocajuba, Taperaçu, Caeté, Urumajó and Gurupi) were compared with regards to SSC, salinity, morphology and tidal propagation. This comparison reinforces that these estuaries are subject to similar regional climate and tidal variations, but that their dynamics differ in terms of distance from the Amazon River mouth, importance of the local river sediment source, and morphology of the estuarine setting. The Urumajó, Caeté and Gurupi are hypersynchronous estuaries where perennial, classic MTZs are observed with SSC > 1 g·L−1. This type of estuary results in transport convergence and MTZ formation, which are suggested to be the main processes promoting mud accumulation in the Amazonian estuaries and therefore the main means of mud entrapment in the mangrove belt. The Mocajuba and the Taperaçu estuaries showed synchronous and hyposynchronous processes, respectively, and do not present classic MTZs. In these cases, the proximity to the ARP for the Mocajuba and highly connected tidal channels for the Taperaçu estuary, assure substantial mud supply into these estuaries. This study shows the strong dependence of the estuaries and mangrove belt on sediment supply from the ARP, helping to understand the fate of Amazon River sediments and providing insights into the mechanisms providing sediment to estuaries and mangroves around the world, especially under the influence of big rivers.

Relationship of Sense of Coherence to Other Psychosocial Indices

2004 ◽  
Vol 20 (4) ◽  
pp. 227-236 ◽  
Author(s):  
Sara Holmberg ◽  
Anders Thelin ◽  
Eva-Lena Stiernström
Keyword(s):  
Social Support ◽  
Psychosocial Factors ◽  
Sense Of Coherence ◽  
Living Conditions ◽  
Strong Negative Correlation ◽  
Cross Sectional ◽  
Positive Correlation ◽  
Work Related ◽  
Job Demand ◽  
The Mean

Summary: The concept of “sense of coherence” (SOC) has been widely recognized since it was first introduced by Antonovsky. The originality and usefulness of the SOC scale and its relation to other psychosocial measures has been the subject of lively debate. The aim of this paper was to test for associations between SOC and work-related psychosocial factors (mainly the Job Demand-Control model), general living conditions, education, and social network factors. Cross-sectional data from a population-based sample of 1782 rural males from nine counties in Sweden were analyzed with a multiple regression technique. The subjects were occupationally active at inclusion and the mean age was 50 years (range 40-60). SOC was assessed with the original 29-item questionnaire. Psychosocial variables and lifestyle factors were assessed using questionnaires and structured interviews. The mean SOC among the subjects was 152.3 (standard deviation, 19.4). A strong negative correlation was found between SOC and job demand, whereas a positive correlation with job control was demonstrated. A positive correlation with general living conditions and with social support was also found. However, there was no correlation to education and occupation. Thus, SOC was shown to be strongly correlated to work-related psychosocial factors and social support, but independent of sociodemographic factors.

Age related volume of cadaver-prostates in Bangladesh

1970 ◽  
Vol 4 (2) ◽  
pp. 74-77
Author(s):  
Rukshana Ahmed ◽  
Shamim Ara
Keyword(s):  
Prostate Gland ◽  
Age Groups ◽  
Clinical Settings ◽  
Cross Sectional ◽  
Medical College ◽  
Age Related ◽  
Group A ◽  
Key Words Prostate ◽  
The Mean ◽  
Group B

Pathological changes in the prostate gland occur commonly with advancing age including inflammation, atrophy, hyperplasia and carcinoma and a change in volume is also evident. Estimation of volume of prostate may be useful in a variety of clinical settings. A cross-sectional descriptive study was designed to see the changes in volume of the prostate with advancing age and done in the Department of Anatomy, Dhaka Medical College, Dhaka from August 2006 to June 2007. The study was performed on 70 post-mortem human prostates collected from the unclaimed dead bodies that were under examination in the Department of Forensic Medicine, Dhaka Medical College, Dhaka. The samples were divided into three age groups; group A (10-20 years), group B (21-40 years) and group C (41-70 years). Volume of the sample was measured by using the ellipsoid formula. The mean ± SD volume of prostate was 7.68 ± 3.64 cm3 in group A, 10.61 ± 3.99 cm3 in group B and 15.40 ± 6.31 cm3 in group C. Mean difference in volume between group A and group C, group B and group C were statistically significant (p<0.001). Statistically significant positive correlation was found between age and volume of prostate (r = + 0.579, p < 0.001). Key Words: Prostate; volume; Bangladeshi. DOI: 10.3329/imcj.v4i2.6501Ibrahim Med. Coll. J. 2010; 4(2): 74-77

Brief Overview and Experience of Visual Evoked Potential of First 67 cases at Referral Neuroscience Hospital in Bangladesh

2020 ◽  
Vol 6 (2) ◽  
pp. 74-77
Author(s):  
Mohammad Enayet Hussain ◽  
Bithi Debnath ◽  
AFM Al Masum Khan ◽  
Md Ferdous Mian ◽  
Md Nahidul Islam ◽  
...  
Keyword(s):  
Multiple Sclerosis ◽  
Optic Neuritis ◽  
Clinical Diagnosis ◽  
Optic Neuropathy ◽  
Cross Sectional Study ◽  
P Value ◽  
Pattern Reversal ◽  
Cross Sectional ◽  
The Mean ◽  
Visual Evoked

Background: The visual evoked potentials (VEP) is a valuable tool to document occult lesions of the central visual channels especially within the optic nerve. Objectives: The purpose of the present study was to observe the findings of first few cases of VEP done in the neurophysiology department of the National Institute of Neurosciences (NINS), Dhaka, Bangladesh. Methodology: This cross-sectional study was conducted in the Department of Neurophysiology at the National Institute of Neurosciences and Hospital, Dhaka, Bangladesh from September 2017 to March 2020. All patients referred to the Neurophysiology Department of NINS for VEP were included. Pattern reversal VEPs were done using standard protocol set by International Federation of Clinical Neurophysiology (IFCN). Results: The mean age of the study population was 30.70 (±12.11) years (6-68 years) with 31 (46.3%) male and 36 (53.7%) female patients. The mean duration of illness was 8.71 (±1.78) months (3 days- 120 months). Most common presenting symptom was blurring of vision (37.3%) and dimness of vision (32.8%). Patterned VEP revealed mixed type (both demyelinating and axonal) of abnormality in most cases [29(43.35)]. The most common clinical diagnosis was multiple sclerosis (29.85%) and optic neuropathy (26.87%). In the clinically suspected cases of multiple sclerosis, optic neuropathy and optic neuritis most of the cases of VEP were abnormal and the p value is 0.04 in optic neuropathy and optic neuritis. Conclusion: The commonest presentation of the patients in this series were blurring of vision and dimness of vision. The most common clinical diagnosis for which VEP was asked for, was optic neuritis and multiple sclerosis. Most abnormalities were of mixed pattern (demyelinating and axonal). Journal of National Institute of Neurosciences Bangladesh, 2020;6(2): 74-77

Sonographic Assessment of Amniotic Fluid Volume using Single Deepest Pocket (SDP) among Igbo Women with Uncomplicated Singleton Pregnancies.

2019 ◽  
Vol 2 (1) ◽  
pp. 1-18
Author(s):  
Chijioke Okeudo ◽  
B.U. Ezem
Keyword(s):  
Amniotic Fluid ◽  
Gestational Age ◽  
Cross Sectional Study ◽  
Fluid Volume ◽  
Singleton Pregnancy ◽  
Cross Sectional ◽  
South Eastern ◽  
Amniotic Fluid Volume ◽  
The Mean ◽  
Singleton Pregnancies

Background: The amniotic fluid is fundamental for proper fetal development and growth. Ultrasound visualization of the amniotic fluid permits both subjective and objective estimates of the amniotic fluid. Objective: The objective of this study was to determine the reference values of normal single deepest pocket (SDP) – upper and lower limits, mean SDP and variation of the SDP with gestational age among Igbo women of South-Eastern Nigeria extraction carrying uncomplicated singleton pregnancy. Methodology: This was a prospective cross sectional study involving 400 women carrying uncomplicated singleton pregnancies and who were sure of the date of the first day of their last menstrual period. The single deepest pocket / maximum vertical pool were determined once at presentation at the hospital.. The study was conducted from January 1st to December 31st 2015. The second author carried out all the scanning. The SDP was obtained. Results: The womens’ mean and median ages were the same at 28 years. The gestational age range of the pregnancies was 14-41 weeks. The mean SDP was 5.8cm, while the 5th and 95th percentiles were 3.3cm and 8.5cm respectively. There was no difference in the mean SDP in both term and preterm. There was irregular but continuous rise of mean SDP to a peak of 6.8cm at gestational age of 39 weeks. In conclusion, the participants had a mean SDP of 5.8cm. There was also a positive correlation between SDP and Gestational age. We therefore recommend a longitudinal study to assess perinatal outcome and abnormal amniotic fluid volume among Igbo women of South-Eastern Nigeria. Key words: Single Deepest Pocket, Uncomplicated Singleton Pregnancy, Igbo Women.

Advantages and limitations of the endoscopic tympanoscopy a prospective study

2020 ◽  
Vol 1 (1) ◽  
pp. 012-017
Author(s):  
Najib Zouhair ◽  
Anass Chaouki ◽  
Amine M’khatri ◽  
Youssef Oukessou ◽  
Sami Rouadi ◽  
...  
Keyword(s):  
Middle Ear ◽  
Operating Time ◽  
Cross Sectional Study ◽  
Cross Sectional ◽  
Invasive Approach ◽  
Intraoperative Bleeding ◽  
Advantages And Disadvantages ◽  
Early Return ◽  
The Mean ◽  
Endoscopic Tympanoplasty

Tympanoplasty is one of the most performed procedures in ENT. The aggressiveness of its microscopic approach has led otologists to adopt the endoscopic approach as a less invasive alternative. The purpose of this work is to appreciate the advantages and disadvantages of this surgical technique. We conducted a prospective descriptive cross-sectional study on 20 interventions within the ENT department of August the 20th 1953 Hospital of Casablanca from April 2019 to June 2019. The average age of operated patients was 36.3 years. Perforations were unilateral in (71%) of the cases with a predominance of the anterior (29%) and subtotal (36%) locations. The tympanoplasties were performed by 3 different senior otologic surgeons, and were left in (57%). The mean operating time was (59.5 min) and the mean anesthesia duration was 75.1 min. Intraoperative vision allowed us to fully visualize the margins of all perforations (100%) and anatomical structures of the middle ear in almost all interventions. The first procedures carried out were filled with difficulties whose management of intraoperative bleeding was the main one in (42.8%) of the cases. (57%) procedures were described as easy. No complication was detected intraoperatively or immediately postoperatively. Endoscopic tympanoplasty has several advantages, including: Minimally invasive approach to the middle ear; panoramic perioperative vision; Gain of operating time; decrease in the duration of anesthesia; Valuable educational tool; postoperative comfort; Decrease in hospital stay and early return to daily activities; Better aesthetic rendering; cost and transportability. However, we also note a number of disadvantages of endoscopic tympanoplasty, particularly: performing the procedure with one hand; difficulty passing through the EAC; 2D vision that alters the perception of depth; management of intraoperative bleeding; fogging; learning curve.

Comparison of Heffner Criteria and Light Criteria in Differentiating Exudative and Transudative Pleural Effusion

2020 ◽  
Vol 22 (3) ◽  
pp. 141-145
Author(s):  
Krishna Chandra Devkota ◽  
S Hamal ◽  
PP Panta
Keyword(s):  
Pleural Effusion ◽  
Cross Sectional Study ◽  
Pleural Space ◽  
Sectional Study ◽  
Inclusion Criteria ◽  
Cross Sectional ◽  
Medical College ◽  
The Common ◽  
The Mean ◽  
Exudative Pleural Effusion

Pleural effusion is present when there is >15ml of fluid is accumulated in the pleural space. It can be divided into two types; exudative and transudative pleural effusion. Tuberculosis and parapneumonic effusion are the common cause of exudative pleural effusion whereas heart failure accounts for most of the cases of transudative pleural effusion. This study was a hospital based cross sectional study performed at Nepal Medical College during the period of January 2016-December 2016. A total of 50 patients who fulfilled the inclusion criteria were enrolled. Pleural effusion was confirmed by clinical examination and radiology. After confirmation of pleural effusion, pleural fluid was aspirated and was analysed for protein, LDH, cholesterol. The Heffner criteria was compared with Light criteria to classify exudative or transudative pleural effusion. Among 50 patients, 30 were male and 20 were female. The mean age of patient was 45.4±21.85 years. The sensitivity and specificity of using Light criteria to detect the two type of pleural effusion was 100% and 90.9%, whereas using Heffner criteria was 94.87%, 100% respectively(P<0.01). There are variety of causes for development of pleural effusion and no one criteria is definite to differentiate between exudative or transudative effusion. In this study Light criteria was more sensitive whereas Heffner criteria was more specific to classify exudative pleural effusion. Hence a combination of criteria might be useful in case where there is difficulty to identify the cause of pleural effusion.

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