| 81. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety : Sediments and Debris Problems
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 27-63
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentation of reservoirs has its negative impacts on dams, first by reducing useful storage, altering the benefit/cost ratio originally calculated for the dam, and second by reducing the dams’ capacity for flood routing; increasing flooding hazards on the dam itself and for the downstream. More problems can be created by sediments and floating debris during floods on outlet structures by clogging them and thus creating dangerous situations, or damage trash screens leading to even more problems. If these debris and coarse sediments are allowed in, then they may damage dam structures such as gates, spillways intakes in addition to chutes, stilling basins and power penstocks by the mechanical abrasion impacts of such sediments on them. Frequent inspections, especially after floods must be made to ensure proper functioning of such structure and take actions for reducing the damage. In small reservoirs, dredging; although it adds to maintenance cost, may ease the problem, but in very large reservoirs, this may prove unpractical. Designers, therefore, have a duty to consider sedimentation problem seriously in the initial stages of design by: checking the anticipated accumulation of sediments, allowing enough storage free from siltation, foreseeing their negative impacts on intakes and outlet structures and taking design measures to reduce these impacts. At the same time, dam stability calculations shall have to provision for the anticipated new conditions of silting up at the face of the dam. Operators of dams, on the other hand, shall have to keep open eyes for all the negative issues created by sediments and floating debris, repairing damages caused by them and take measures to reduce their impacts in the future.
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| 82. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Dams Hazards
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 23-40
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Tidskriftsartikel (refereegranskat)abstract
- Dam safety hazards towards human communities have increased tremendously during the last decades. They have resulted from dam safety problems leading to failure and being exasperated by the large losses at downstream areas due to increasing populations and land use. In this work, an attempt is being made to review the procedures being followed to reduces these hazards by improving dams safety standards. Classification of dams by their potential hazards are explained as used today for prioritize remedial actions in various countries of the world. The guiding principles of these classification are indicated and they are based on height of such dams and their storage and linked to the potential damage and harm they can create. Normally such classification and follow up actions are supported by various legislations and regulations issued by the respective governments. Moreover, conventions signed by riparian countries promote cooperation on mitigating safety problems of dams on transboundary rivers. Examples of such legislations and conventions are mentioned. Looking for having safer dams is an objective continually which is being pursued as more dams are needed in the future while existing dams continue to serve their objectives. Therefore, using lessons learned from previous failures is recommended taking the question of loss of life as a main doctrine.
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| 83. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Earthquakes
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 79-132
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Tidskriftsartikel (refereegranskat)abstract
- Earthquakes may cause failure or profound damage for dams. Factors contributing to this are, magnitude on the Richter scale, peak horizontal and vertical accelerations, time duration, in addition to the epicentral distance, nature of foundation rock, criteria of the design, and finally, if appropriate type of dam and materials has been used. Extensive lists of dam failures and damaged once are presented with many case histories. Most failed dams were tailing dams or hydraulic fill dams or small earth fill dams, which reflect the weight of the design and construction factors. Embankment dams, normally, are less tolerant to ground shacking than concrete dams. While rockfill and RCC dams have shown good performance. The developments of design methods and criteria are traced here, from the early use of the pseudoptotic method to the more rational dynamic analysis, which is used nowadays making construction of very large safe dams in seismic regions possible. The method adopts peak ground accelerations from anticipated earthquakes as inputs to the analysis which produce a full spectrum of the factor of safety during any considered event. This has led to increased use of seismic instrumentation to produce seismographs of actual events in the free field, and on dams hit by earthquakes for comparison with outputs of this analysis and for future use for similar dams in similar circumstances, and to decide on rehabilitation measures. The safety levels to which any dam is to be designed are defined in terms of the Maximum Credible Earthquake, Safety Evaluation Earthquake, Maximum Design Earthquake and other similar terms. Dam repairs after sustaining earthquake damages are described in real cases and upgrading of older dams to withstand higher expected seismic events are also treated here and supported by case histories.
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| 84. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety and Οvertopping
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 41-78
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Tidskriftsartikel (refereegranskat)abstract
- Overtopping is one of the most serious modes of failures for all dams causing great numbers of human fatalities and material damages. Statistics show that overtopping failures are the highest, especially for embankment dams. The main reason for this is the erroneous prediction of the inflow design discharge, which has resulted from lack of realistic flow data and imperfect hydrological procedures. Failure in most cases occurs when the inflow exceeds the spillway design capacity, but to a lesser extent from the buildup of very high wave setup and runs up. This has led to active efforts in upgrading dams for such occurrences, by either upgrading spillways, adding auxiliary spillways, increasing freeboard by either heightening the dams or the parapet walls on the crest. Advancement in predicting the safe inflow discharges are also made by adopting such procedures as the calculation of the Probable maximum flood based on predicting the Maximum Probable Precipitation or using statistical methods by treating long records of available flow data. Recently, another challenge has come up facing dam owners and builders who are represented by the climate change impacts on the hydrological cycle; this has put a new responsibility to the governments to issue new regulations and plans to mitigate these impacts reducing failure possibilities and improve dam safety against overtopping.
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| 85. |
- Adamo, Nasrat, et al.
(författare)
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Dam Safety Problems Related to Seepage
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 191-239
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Tidskriftsartikel (refereegranskat)abstract
- Dangerous occurrences affecting dams take multiple forms, but seepage caused cases are the most numerous. Some of the cases are related to the geology of the foundation and the magnitude and type of discontinuities in the rock mass of the dam. Other are mainly due to of construction material in earth fill dams. Seepage occurs in all earth fill dams regardless of its materials, and seepage water can daylight at the downstream face causing erosion, piping and sloughing and instability; unless certain measures are taken. Instability can be controlled mainly by adding, filter material zones at the contacts with the clay core, chimney filter drain at the downstream part of the dam, filter zone or bench at the toe together with the drainage blanket under the downstream part of the dam. Seepage within the dam is enhanced by cracks which may result from uneven settlement of the dam due to different elastic behavior of the foundation materials, hydraulic fracturing, and differential settlement of parts of the dam or due to ground shaking in earthquakes. Preferential seepage paths can develop in such cracks, especially if the fill material is dispersive or suffusive. Similarly, such paths may develop along the contact surfaces of conduits installed under dams as outlet structures due to the low degree of compaction as a result of narrow trench dimensions. Using properly designed filter and drainages can reduce seepage quantities and the erosive force which causes internal erosion. In dam’s foundation grout curtains or other type of cutoffs can reduce the hydraulic head and hence uplift under the dam and hinder seepage. Drainage, however, remains as the most efficient method in controlling this uplift in artesian conditions under dams, especially under concrete gravity dams. Generally, such drainage may take the form of drainage blanket and use of filters material.
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| 86. |
- Adamo, Nasrat, et al.
(författare)
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Dams Safety : the Question of Removing Old Dams
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 323-348
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Tidskriftsartikel (refereegranskat)abstract
- Many old dams in the world today may not be safe enough and represent threats to the communities they serve. They have reached the end of their technical and economic lives making upgrading them questionable. This raises the question of decommissioning or removing them open for further discussion. In this paper the issues related to keeping old dams are discussed showing with one example that the soaring costs of upgrades make it impossible to perform for countries with limited resources without outside financial support. An explanation is also given to show how even in rich countries this is met by budgeting obstacles. Other objections to the presence of these dams, added to the safety question which support of dam’s removal are discussed. They include the accumulated damage they have caused to the ecosystems such as siltation and fish migration. An emphasis is put on the need for intensive studies required before removing any such dam in order to mitigate any negative impact subsequent to such removal; and many actual examples are given to illustrate this.
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| 87. |
- Adamo, Nasrat, et al.
(författare)
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Dams Safety : Inspections, Safety Reviews, and Legislations
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 109-143
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Tidskriftsartikel (refereegranskat)abstract
- When a dam is built, its safety becomes a constant concern for the owner, the public and for governments. Therefore, continuous observation through routine inspections and safety reviews become necessary. Acting as protectors of public safety, governments and professional organizations save no effort in the promulgation of legislations and laying out guidelines for such inspections and reviews. These issues are discussed here starting with the basic first step of visual inspections by the operators and the follow up of detailed safety reviews by specialists. Careful visual inspections assisted by instrumentation measurements may reveal an early negative issue such as, but not limited to, increased seepage, increased uplift pressure, signs of weakness like cracking in the body of the dam, or dams’ slope sloughing, and even damaged hydraulic control equipment. Documenting and reporting these observation helps in taking remedial measures in good time and may lead to more intensive safety reviews. Suggested check lists for the inspection engineers are given here, but these may be tailored for each dam according to its needs. These lists cover issues common to both embankment and concrete dams, and include other specific issues related to each type of them. Metal equipment take their share by listing such areas as corrosion, fatigue and cracking, tear, and wear and so on. Instrumentation measurements are also given their due consideration by giving brief mention of types of measurements needed and points to be observed in instrumentation control work. Finally, guidelines, rules, and legislations for Dam Safety Reviews are generally discussed giving examples from four countries in the world.
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| 88. |
- Adamo, Nasrat, et al.
(författare)
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Dams Safety : Review of Satellite Remote Sensing Applications to Dams and Reservoirs
- 2021
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 11:1, s. 347-438
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Tidskriftsartikel (refereegranskat)abstract
- Remote sensing is the collection and interpretation of information of an object, areaor phenomenon by a recording device that is not in physical or intimate contact with the object or phenomenon under study. It generally refers to the use of satellite borne or airborne sensors to capture the spectral and spatial relations of objects and materials on Earth from the space. This is done by sensing and recording reflected or emitted electromagnetic radiation from the objects. A brief history of satellite remote sensing is given in this review but the bulk of it is devoted to the scientific satellites launched into orbit and their sensors tracking, and presenting changes in water resources fields. The used technologies and satellite systems for monitoring movements and changes include American GNSS, GPS, the Russian GLONASS, Europe’s European Satellite Navigation System (GALILEO), China’s COMPASS/BeiDou, the Indian (IRNSS); Japan’s (QZSS) and many others. Details are presented on the present (LANDSAT), the Moderate Resolution Imaging Spectroradiometer (MODIS), as well as Synthetic Aperture Radar (SAR), and RADARSAT, JERS‐1, and ERS, which are developed by various countries, especially the USA. These sensors have the refined capability of providing estimates of variables, which depending on the purpose and design of the sensor, can follow critical issues related to water management problems. This review presents examples of actual studies carried out including; building databases of small dams and lakes on regional scale, derivation of volume vs. elevation and surface area vs. elevation of hundreds of reservoirs around the world, various bathymetric reservoir surveys, siltation of reservoirs and catchment areas erosion problems, monitoring of water quality changes, and above all monitoring dam deformation and stability problems of dams. The presented case studies cover the use of these different sensor together with the imagery used, their sources, methods of interpretation, validation and gives presentation of the end results. This review, which is only a very brief presentation of satellite remote sensing applications concludes that; in spite of the large volume of research done on this subject so far, which this review cites some of them , the expected future developments in satellite remote sensing technology coupled with advances in algorithms and models used in refining satellite imagery and validating the results will bring more accurate results and less laborious treatment work in addition to wider scope of applications.
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| 89. |
- Adamo, Nasrat, et al.
(författare)
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Dams Safety and Geology
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:6, s. 133-189
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Tidskriftsartikel (refereegranskat)abstract
- Geological hazards that can face dams are very important in deciding their safety and successful performance during their lifetime without excessive and costly repairs. Recognizing such hazards must be made at an early stage of the investigation works. Geological hazards which have caused dam failures or resulted in redundant reservoirs can vary between presence of karsts in the reservoir or in dam foundation, presence of soluble rocks, hidden faults, or the presence of hazardous materials. Learning from case histories of dam failures and incidents is important to avoid problems raised by these hazards. Many such cases are presented in the preceding paragraphs to show the variety of such problems and help understand their nature. These case histories, can help the designer in the selection of the most appropriate type of dam suited for a particular geological condition, avoiding dangerous situations such as but not limited to excessive or differential settlement. Understanding the real conditions of foundation decides also the efficiency, scope and type of foundation treatment. The Teton dam failure given in this paper illustrates one case when such understanding was missing. In any case, the active participation of geologists working with the designers in all stages of dam construction process is very important to eliminate or reduce to safe limits any geological hazard that can the future dam.
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| 90. |
- Adamo, Nasrat, et al.
(författare)
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Epilogue
- 2020
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Ingår i: Journal of Earth Sciences and Geotechnical Engineering. - UK : Scientific Press International Limited. - 1792-9040 .- 1792-9660. ; 10:3, s. 283-285
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Tidskriftsartikel (refereegranskat)abstract
- In more than six centuries which followed the fall of Baghdad to the hands of Hulagu and his Mongol troops in 1258 until the establishment of the modern state of Iraq in 1920. The timeline of the country cannot be described but only as a sequence of tragic events in which this once most prosperous land sank into unending bloodsheds, destruction, constant retrogression and deep poverty. Calamities such as flooding, epidemics, locusts and famines did not spare millions of its population, and to speak of Baghdad only, the 1,000,000 who used to live there in the golden days of the Abbasids dwindled to merely few thousands at the turn of the twentieth century. The early stage of this severe collapse was due to the interference of the Mongols with the irrigation systems on which the life of people had depended. Admitting that the damage that was sustained during the Buwayhids and Seljuks times left these systems in dilapidated and bad conditions, but the Mongols managed to add more destruction so that agriculture diminished to small plots of lands, which could not keep up the large population anymore and made any effort of reform nearly impossible. Borrowing from the words of Stephen Hemsley longrigg in his book “Four Centuries of Modern Iraq” he says:“Most ruinous of Holagu’s acts had been the studied destruction of the dykes and head works, whose ancient and perfect system had been the sole source of the wealth. Disordered times, and the very silting and scouring of the rivers once let loose, soon made the restoration of control the remote, perhaps hopeless problem today still unsolved”[1].
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