Aging Dams Research Articles

Increasing dam failure risk in the USA due to compound rainfall clusters as climate changes

A changing climate, with intensifying precipitation may contribute to increasing failures of dams by overtopping. We present the first analysis of rainfall sequences and events associated with recent hydrologic failures of 552 dams in the United States. We find that the maximum 1-day rainfall associated with failure was often not extreme compared to dam spillway design criteria, even when accounting for rainfall statistics changing with time at each site. However, the combination of the total rainfall 5 to 30 days prior and the maximum 1-day rainfall associated with dam failure is rare. Persistent atmospheric circulation patterns that lead to recurrent rainfall events, rather than just more moisture in the atmosphere is a possible reason. The probability of these compound precipitation risks has increased across much of the country. With over 90,000 aging dams still in service, the increasing likelihood of intense rainfall sequences raises concerns about future dam failures.

Fast Finance and the Political Economy of Catastrophic Dam Collapse in Lao PDR: The Case of Xe Pian-Xe Namnoy

In the dark of a July night in 2018, a 5-billion-cubic-metre torrent of muddy water crashed through rooftops and ripped through the downstream villages of southeast Lao People's Democratic Republic (Lao PDR). An auxiliary "saddle" dam had collapsed in the US$1.02 billion Xe Pian-Xe Namnoy (XPXN) Hydropower Project that was still under construction and had just reached financial contractual close five years prior, in 2013. In the aftermath of the collapse, official state narratives pointed to extreme weather conditions and "unforeseen" construction and engineering miscalculations, viewing soil conditions as the primary culprit. This paper examines the financial dimensions of dam failure and introduces the term "fast finance": financier-driven timelines that have drastically expedited and shortened the legal, social, and pre-construction processes involved in hydropower dam projects to the detriment of dam safety, due diligence, and local participatory input. Extreme weather and anthropogenic climate change are not sole explanatory factors in the XPXN dam disaster. This paper highlights the also significant role of financial and political interests as contributing factors in dam safety and failure alongside extreme weather. The paper challenges conventional "natural disaster" framing of dam collapse by bringing into focus ex-ante political decision-making, financial engineering, and construction planning prior to dam construction to highlight the ways in which the XPXN catastrophe also had anthropogenic and "unnatural" contributing factors. Fast finance encompasses the role of temporality and the responsibility of state-business actors in ex-ante financial and infrastructure decisions that conclude with catastrophic outcomes. The article examines the re-engineering of contemporary dam finance through a case study of Lao PDR and argues that issues of financial engineering should be examined alongside other forms of civil, mechanical, structural, and hydrological engineering in the analysis of dam disasters. The temporal logics of financial actors—particularly the financialized logic of fast finance—has displaced the public-good-producing logic of patient capital. Financial logics shape and condition other forms of engineering and construction and are central to considerations of dam safety and accountability. Naturalizing discourses around extreme weather and aging dams deflect from the financial decisions and policy action, or inaction, of state-business actors to prevent dam collapse.

Quantifying landscape change following catastrophic dam failures in Edenville and Sanford, Michigan, USA

AbstractDam failures due to changing hydroclimate and ageing infrastructure pose a significant threat to downstream river systems and communities. The detailed geomorphic effects of catastrophic dam failures are not well known because of a lack of high‐resolution topographic data before and after failures. On 19 May 2020, the 17‐m‐tall Edenville and 11‐m‐tall Sanford dams near Midland, Michigan, USA, failed as a result of significant rainfall over the preceding 2 days. We analysed the geomorphic impacts of these failures using a pre‐failure airborne lidar dataset and three uncrewed aerial vehicle (UAV)‐based lidar surveys collected 2 weeks, 3 months and 11 months after failure. Our survey following the dam failure revealed 47 100 ± 11 900 m3 of net floodplain erosion and 17 300 ± 4200 m3 of net deposition downstream of the Edenville and Sanford dam breaches, respectively. Over the year following failure, most geomorphic change was confined to new knickpoints migrating slowly through underlying glacial till substrate, with little change to riverbanks or surrounding floodplains. A lack of impounded reservoir sediment and antecedent downstream topography, including valley width and the location of the breaches relative to the river below the dams, contributed to relatively modest geomorphic changes despite the magnitude of water released. We provide insight into how landscapes are shaped by catastrophic floods, which are likely to become more common with ageing dams and a changing hydroclimate.

Liquefaction characteristics of aging earth dam body by dynamic centrifugal model test

Earth dams have been damaged or even collapsed owing to earthquake liquefaction. Although a liquefied foundation is a major factor affecting the safety of earth dams, the damage caused by the liquefaction of the dam body itself cannot be ignored, particularly for aged earth dams. However, in the presence of high water levels, liquefaction of the dam body cannot be considered solely in terms of the seismic load. Consequently, in this study we used dynamic centrifuge tests and numerical analysis to simulate the liquefaction process of an earth dam body under high water levels and analyzed the damage mechanism. The aging dam body, which can be easily liquefied, was simulated by controlling the density of the dam body, the low-density dam body exhibiting greater acceleration-amplification characteristics and displacement. Liquefaction was evident in the contact area between the slope and water level, with segmental settlement occurring. Through numerical analysis, it was evident that the core area accumulated considerable plastic deformation, and the sliding damage extended from the water contact surface to the dam toe. This study could compensate for the dearth of liquefaction model experiments of earth dams, providing a necessary reference for the seismic reinforcement of earth dams.

Effect of Breed and some Non-Genetic Factors on Productive Performance in Two Sheep Breeds

This study was conducted with the animal field of Al-Kafeel Company/Barakat Aba Al-Fadl (peace be upon him) station during the period from December 2021 to July 2022, the experiment included 200 lambs (100 lambs of Iranian Karakul breed, 100 lambs of local Hamdani) The number of male lambs was 88 while the female was 112, this study aims to compare the productive performance between the two breeds from birth to the age of 6 months, and to study the effect of non-genetic factors (dam’s weight, dam age, and sex of lambs) in productive traits, Birth and weaning weights were recorded at the age of six months, and body measurements for both breeds (body length, height at the wither and rump, chest and abdomen circumference) The results indicated a highly significant (P<0.01) superiority of the Karakul lambs over the local Hamdani breed in body weights, chest circumference at birth, body weight, chest and abdominal circumference at weaning, body weight and all body measurements at six months of age, Highly significant (P<0.01) for male lambs over females in body weights and body length, wither and rump height at weaning, body weight, all body measurements at six months of age, for both breeds. In addition to the presence of a highly significant difference (P<0.01) for the weight of lambs produced from dams with a high weight of more than 50 kg compared with lambs produced from dams with a weight of 30-49 kg at birth and weaning and at the age of six months, respectively, and most of the body measurements, While the non-significant effect of the age Dam on the weights of the lambs was on the weights of the lambs and most of the body measurements of both breeds. The results showed a positive and significant correlation (P < 0.01) between the weight of dams and lambs weight at birth and weaning and at six months of age, also to the correlation of the weights of the previous lambs with the subsequent weights of both breeds, Thus The possibility of using these factors of lambs in breeding programs for early selection of lambs and improving productive performance near marketing.

Assessing dam spillway discharge capacity in response to extreme floods in Perak river hydroelectric scheme: Simulation and proposed mitigation measures

The aged dams in Perak river Hydro-Electric Scheme (HES) have been constructed decades ago and a common concern raised during dam safety reviews is that they were not designed to safely reroute the Probable Maximum Flood (PMF) but rather the Inflow Design Flood (IDF) of 1,000 years’ design floods. Failure due to the insufficient spillway discharge capacity has been identified as one of the primary causes leading to overtopping. This applied research has thus been initiated to evaluate the spillway discharge capacity of dams in response to PMF extreme flooding. Besides, the safety of the dams has been evaluated by calculating the highest flood level achieved in response to the specified extreme floods. In order to simulate PMF hydrographs, various durations of Probable Maximum Precipitation (PMP) have been calculated using Hershfield statistical approach based on historical annual maximum rainfall statistics. Using a calibrated and validated hydrological model developed in HEC-HMS, PMF simulation was performed. It was discovered that the PMF generated at 120 hrs (5 days) resulted in the maximum flood level for all dams/reservoirs. The achieved highest PMF flood levels are still lower than the designated dam core and crest level in respective dams, indicating that the dams in Perak river HES are safe from overtopping failures during the occurrences of extreme events up to PMF level. While routing the worst-case scenario over 120 hr, the maximum spillway discharges predicted for Temengor and Bersia are beyond their design capacity, while Kenering and Chenderoh remain within design limits. Mitigation that will be implemented to minimize the possibility of risks to occur include improvement of emergency management system and dams monitoring data collection. It is anticipated that the outcomes of this applied research will be adopted for development of Risk Informed Decision Making (RIDM) frameworks for dams in Perak river HES in future.

A Watershed Moment for Western U.S. Dams

AbstractThe summer of 2023 is a notable time for water‐resource management in the western United States: Glen Canyon Dam, on the Colorado River, turns 60 years old while the largest dam‐removal project in history is beginning on the Klamath River. This commentary discusses these events in the context of a changing paradigm for dam and reservoir management in this region. Since the era of large dam building began to wane six decades ago, new challenges have arisen for dam and reservoir management owing to climate change, population increase, reservoir sedimentation, declining safety of aging dams, and more environmentally focused management objectives. Today we also better understand dams' benefits, costs, and environmental impacts, including some that were unforeseen and took decades to become apparent. Where dams have become unsafe, obsolete (e.g., due to excessive reservoir sedimentation), and uneconomical beyond saving, dam removal has become common. The science and practice of dam removal are accelerating rapidly, and some long‐term physical and biological response studies are now available. Removal of four hydroelectric dams on the Klamath River will be a larger and more complex project than any previous dam removal. The imminency of this project reflects a very different situation for dam and reservoir management than 60 years ago. Looking forward, dam and reservoir management in the western United States and worldwide will require continued collaboration and innovative thinking to meet a wide range of objectives and to manage water resources sustainably for future generations.

Maternal impacts of pre-conceptional glyphosate exposure

Maternal glyphosate (GLY) impacts remain unclear despite associations between urinary GLY and birth outcomes. Whether maternal pre-conceptional GLY exposure would have phenotypic and molecular impacts in the dam and offspring was tested. Female C57BL6 mice (6 wk) were exposed to saline (CT; n = 20) or GLY (2 mg/kg; n = 20) per os five d per week for 20 wk. Females were housed with males and on gestation day (GD) 14, divided into: CT non-pregnant (CNP), CT pregnant (CP), GLY non-pregnant (GNP), GLY pregnant (GP). Another cohort (CT; n = 10 or GLY; n = 10) completed three pregnancy rounds and pregnancy index (PI), number of pups per litter and pups surviving to postnatal day (PND) 5 calculated. The PI in GLY mice was higher in breeding rounds 1 and 2, but lower in round 3. Pregnancy increased (P ≤ 0.1) GD14 liver and ovary weight. Spleen weight was increased (P < 0.05) in GP relative to GNP mice. No offspring phenotypic impacts were observed. Approximately six months after cessation of exposure, secondary follicle number was reduced (P < 0.05) by pre-conceptional GLY exposure. The ovarian proteome analyzed by LC-MS/MS was altered (P < 0.05) by pregnancy (49 increased, 43 decreased) and GLY exposure (non-pregnant: 75 increased, 22 decreased, pregnant: 27 increased, 29 decreased; aged dams: 60 increased, 98 decreased) with several histone proteins being altered. These findings support ovarian transient and persistent impacts of GLY exposure and identify pathways as potential modes of action.

The effect of tauroursodeoxycholic Acid (TUDCA) treatment on placental endoplasmic reticulum (ER) stress in a rat model of advanced maternal age.

Advanced maternal age (≥35 years) is associated with an increased risk of pregnancy complications such as fetal growth restriction and preeclampsia. We previously demonstrated poor pregnancy outcomes (reduced fetal body weight), altered vascular function, and increased expression of endoplasmic reticulum (ER) stress markers (phospho-eIF2α and CHOP) in mesenteric arteries from a rat model of advanced maternal age. Further, treatment of aged dams during pregnancy with an ER stress inhibitor, tauroursodeoxycholic acid (TUDCA) increased fetal body weight (both male and female), tended to improve uterine artery function, and reduced expression of phospho-eIF2α and CHOP in systemic arteries. Placental ER stress has been linked to poor pregnancy outcomes in complicated pregnancies but whether placental ER stress is evident in advanced maternal age is not known. In addition, sex-specific changes in the placental labyrinth and junctional zones from male and female offspring in advanced maternal age have not been investigated. Therefore, the current study aimed to investigate the effect of TUDCA intervention on placental ER stress. We hypothesize that placental ER stress is increased in a rat model of advanced maternal age that is alleviated by TUDCA intervention for both sexes. Placental ER stress markers (GRP78, phospho-eIF2α, ATF-4, CHOP, ATF-6α, and sXBP-1) were quantified by Western blot in placentas from male and female offspring; the labyrinth and junction zones were analyzed separately. In the placental labyrinth zone from male offspring, only GRP78 (p = 0.007) was increased in aged dams compared to young dams; TUDCA treatment reduced the placental expression of GRP78 in aged dams (p = 0.003). In addition, TUDCA reduced the levels of phospho-eIF2α (p = 0.021), ATF-4 (p = 0.016), and CHOP (p = 0.012) in aged dams but no effect was observed in young TUDCA-treated dams. In the placental labyrinth zone from female offspring, an increased level of phospho-eIF2α (p = 0.005) was observed in aged dams compared to young dams, and TUDCA treatment had no effect in both young and aged groups. In the placental junctional zone from male and female offspring, no changes in the expression of GRP78, phospho-eIF2α, ATF-4, CHOP, and ATF-6α was observed with or without TUDCA treatment in both young and aged groups, however, a reduced expression of sXBP-1 protein was observed in from both male (p = 0.001) and female (p = 0.031) placentas from aged-TUDCA treated dams compared to aged control. In conclusion, our data highlight the complexity and sex-specificity of ER stress responses in advanced maternal age with TUDCA treatment maintaining ER stress proteins to basal levels and improving fetal growth in both male and female offspring.

Needs for Portfolio Risk Assessment of Aging Dams in the United States

Dam failure can cause extraordinary flooding. Water and wastewater treatment plants, electricity generation facilities, bridges, highways, population centers, and other dams often lie downstream of a dam. If poorly maintained, aging dams can be overtopped by extreme rainfall events, and long-term loss of critical infrastructure services for many communities and regions may result. Such events are now more likely as the climate changes. How should we prioritize dams that need immediate attention and retrofit or remove them? Losses from a dam failure could exceed the infrastructure’s replacement costs, through cascading effects in multiple sectors such as electricity, transportation, water supply, and environmental services. The existing dam hazard classification frameworks in the US and many other countries do not formally characterize “hazard hotspots” considering these impacts. Given that there are over 90,000 dams at different stages of repair, maintenance, and budgetary constraints, a systematic approach is needed to rank their potential failure hazard and allocate resources for risk mitigation. In this paper, we synthesize an approach for preliminary ranking of the priority areas of concern. The approach is scalable over many regions for rapid assessment of magnitude and exposure of a dam failure. The estimation of the consequences of a dam failure, including its financial losses, as well as affected critical infrastructures and population, is explored using publicly available dam break and consequence tools as well as national infrastructure data sets.

The drawdown phase of dam decommissioning is a hot moment of gaseous carbon emissions from a temperate reservoir

ABSTRACT Dam decommissioning (DD) is a viable management option for thousands of ageing dams. Reservoirs are large carbon sinks, and reservoir drawdown results in important carbon dioxide (CO2) and methane (CH4) emissions. We studied the effects of DD on CO2 and CH4 fluxes from impounded water, exposed sediment, and lotic water before, during, and 3–10 months after drawdown of the Enobieta Reservoir, north Iberian Peninsula. During the study period, impounded water covered 0–100%, exposed sediment 0–96%, and lotic water 0–4% of the total reservoir area (0.14 km2). Areal CO2 fluxes in exposed sediment (mean [SE]: 295.65 [74.90] mmol m−2 d−1) and lotic water (188.11 [86.09] mmol m−2 d−1) decreased over time but remained higher than in impounded water (−36.65 [83.40] mmol m−2 d−1). Areal CH4 fluxes did not change over time and were noteworthy only in impounded water (1.82 [1.11] mmol m−2 d−1). Total ecosystem carbon (CO2 + CH4) fluxes (kg CO2-eq d−1) were higher during and after than before reservoir drawdown because of higher CO2 fluxes from exposed sediment. The reservoir was a net sink of carbon before reservoir drawdown and became an important emitter of carbon during the first 10 months after reservoir drawdown. Future studies should examine mid- and long-term effects of DD on carbon fluxes, identify the drivers of areal CO2 fluxes from exposed sediment, and incorporate DD in the carbon footprint of reservoirs.

Short‐term effects of a large dam decommissioning on biofilm structure and functioning

Aging dams and the rising efforts to restore stream ecosystems are increasing the number of dam decommissioning programs. Although dam decommissioning aims at improving in‐stream habitat, biodiversity, and ecosystem functioning in the long term, it might also cause ecological impacts in the short term due to the mobilization of the sediment accumulated in the reservoir. Benthic biofilm in particular can be impaired by episodes of high turbidity and scouring. We conducted a multiple before‐after/control‐impact experiment to assess the effects of the drawdown of a large dam (42 m tall), a first step to its decommissioning, on biofilm structure (biomass and chlorophyll‐a) and functioning (metabolism, nutrient uptake, and organic matter breakdown). Our results show that the reservoir drawdown reduced the autotrophic biofilm biomass (chlorophyll‐a) downstream from the dam, which in turn lowered metabolism. However, nitrogen and phosphorus uptake by the biofilm was not affected. Organic matter breakdown was slower below the dam than in nearby undammed reaches before and during drawdown. All drawdown effects quickly disappeared and reaches downstream from the dam approached values found in nearby undammed reaches. Thus, our results indicate that the effects of reservoir drawdown on stream biofilms exist but may be small and disappear rapidly.

Advanced Maternal Age Impairs Uterine Artery Adaptations to Pregnancy in Rats.

Advanced maternal age (≥35 years) is associated with pregnancy complications. Aging impairs vascular reactivity and increases vascular stiffness. We hypothesized that uterine artery adaptations to pregnancy are impaired with advanced age. Uterine arteries of nonpregnant and pregnant (gestational day 20) young (4 months) and aged (9 months; ~35 years in humans) Sprague-Dawley rats were isolated. Functional (myogenic tone, n = 6–10/group) and mechanical (circumferential stress-strain, n = 10–24/group) properties were assessed using pressure myography and further assessment of elastin and collagen (histology, n = 4–6/group), and matrix metalloproteinase-2 (MMP-2, zymography, n = 6/group). Aged dams had worse pregnancy outcomes, including smaller litters and fetal weights (both p < 0.0001). Only in arteries of pregnant young dams did higher pressures (>100 mmHg) cause forced vasodilation. Across the whole pressure range (4–160 mmHg), myogenic behavior was enhanced in aged vs. young pregnant dams (p = 0.0010). Circumferential stress and strain increased with pregnancy in young and aged dams (p < 0.0001), but strain remained lower in aged vs. young dams (p < 0.05). Arteries from young nonpregnant rats had greater collagen:elastin ratios than the other groups (p < 0.05). In aged rats only, pregnancy increased MMP-2 active capacity. Altered functional and structural vascular adaptations to pregnancy may impair fetal growth and development with advanced maternal age.

The Effect of Tauroursodeoxycholic Acid (TUDCA) Treatment on Pregnancy Outcomes and Vascular Function in a Rat Model of Advanced Maternal Age.

Advanced maternal age (≥35 years) increases the risk of vascular complications in pregnancy that can result in fetal growth restriction and preeclampsia. Endoplasmic reticulum (ER) stress has been linked to adverse pregnancy outcomes in these complicated pregnancies. However, the role of ER stress in advanced maternal age is not known. We hypothesize that increased ER stress contributes to altered vascular function and poor pregnancy outcomes, and that treatment with the ER-stress inhibitor TUDCA will improve pregnancy outcomes. First, young and aged non-pregnant/pregnant rats were used to assess ER stress markers in mesenteric arteries; mesenteric artery phospho-eIF2α and CHOP expression were increased in aged dams compared to young dams. In a second study, young and aged control and TUDCA-treated dams were studied on gestational day (GD) 20 (term = 22 days). TUDCA treatment was provided via the drinking water throughout pregnancy (GD0-GD20; calculated dose of 150 mg/kg/day TUDCA). ER stress markers were quantified in mesenteric arteries, blood pressure was measured, pregnancy outcomes were recorded, mesenteric and main uterine arteries were isolated and vascular function was assessed by wire myography. Aged dams had increased phospho-eIF2α and CHOP expression, reduced fetal weight, reduced litter size, and impaired uterine artery relaxation. In the aged dams, TUDCA treatment reduced phospho-eIF2α and CHOP expression, reduced blood pressure, improved fetal body weight, and tended to improve uterine artery function compared to control-treated aged dams. In conclusion, our data illustrate the role of ER stress, as well as TUDCA as a potential therapeutic that may benefit pregnancy outcomes in advanced maternal age.

Dam Renovation to Prolong Reservoir Life and Mitigate Dam Impacts

Dams are essential to society, yet have tremendous environmental impacts, for which there is an increasing interest in mitigation. At the same time, sedimentation threatens the sustainability of reservoir storage and reservoir functions. We use the term dam renovation to encompass a wide range of measures, including dam rehabilitation, a term commonly used for structural retrofits, typically of the dam structure or spillway, fishway retrofits for migratory fish passage, reservoir reoperation, which involves modifying dam operations to improve flow regimes for ecological purposes, and sustainable sediment management, which includes measures to pass sediment through or around dams, as well as other mechanical measures to restore sediment connectivity. Compared to dam renovation, an inordinate amount of literature has been published on the topic of dam removal. While in some cases dam removal is a practical way to improve river condition and to resolve the safety problems of aging dams, the reality is that most dams in existence today will remain for the foreseeable future, provided they do not fill with sediment, or their structures deteriorate to the point of failure. Thus, it is imperative that we understand the options available to renovate dams with poor environmental performance or whose sustainability is threatened.

Rival Eco-Anxieties: Legacy of Soviet Water Management in the Syr Darya Basin

Abstract This article focuses on the security and human rights implications of the water infrastructure legacy bequeathed to the Syr Darya river basin in the border area of the Ferghana Valley, by the Soviet period. Taking an environmental history approach, I consider the complex legacy of the system of ageing dams, irrigation canals, and reservoirs which for the most part were set in place between the 1950s and 1980s. Correcting the prevailing narrative that post-Soviet water tensions are often caused by the Soviet habit of disregarding borders and republican-level interests in designing water infrastructure, I show how Soviet water policy in the region fanned and exacerbated inter-republican tensions even while the national territorial divisions were ongoing. Current tensions are therefore not a response to a sudden and unexpected hardening of borders, but the fruit of much longer processes.

Evaluation of Electrical and Electromagnetic Geophysical Techniques to Inspect Earthen Dam and Levee Structures in Arkansas

Within the State of Arkansas, there is an increasing number of aging dams and levees that have little to no documentation concerning their construction or composition. Surface geophysical surveys offer a non-intrusive method for investigating these structures to describe their lithologic makeup, evaluate the materials constructed upon, and identify potential flow paths through them. Techniques such as electrical resistivity tomography, seismic refraction, and electromagnetic induction have been used to image dams and levees. They require additional information from geologic outcrops, geotechnical borings, or drill cores to make informed geologic interpretations of the geophysical models. These geologic models then allow the owners of these structures to make more informed decisions about their operation and maintenance. Between 2011 and 2018, the U.S. Geological Survey conducted geophysical and geotechnical investigations of three earthen structures in Arkansas. Electrical and electromagnetic geophysical data were used to develop lithologic models of these structures and characterize the underlying geology. Self-potential surveys were utilized to detect the movement of water through these structures and identify any possible seepage pathways. Geotechnical methods such as electric and hydraulic direct-push well logs and cores acted as a control on the geophysical interpretations and a confirmation of anomalies. This integrated approach detected the lack of an impermeable core within a levee, imaged a change in lithology of the bedrock forming the seal beneath a gravity dam, and identified a potential seepage feature within the core of an earthen dam. These results further support that this method of extending known lithologic features via surface and borehole geophysics is a useful approach for characterizing earthen water-control structures.

Wind power as an alternative to sustain the energy needs in Garoua and Guider, North Region of Cameroon

The North Region of Cameroon is home to a 72 MW hydroelectric dam, which provides electricity beyond the region’s needs. However, aging dam and distribution network leading to frequent load shedding, are contributing factors to look for other environmentally friendly alternatives such as wind power to sustain the energy needs of the region. Wind energy can significantly contribute to the energy mix, mainly during the dry season (March, April and May) when energy demands highly rise and load shedding can last forever, mainly in rural or remotes locations. The main purpose this study to evaluate the wind energy production, using bihourly data collected at 10 m above ground level over a period of fifteen years from 2005 to 2019 for the localities, Garoua and Guider. The novelty of this study is 2D and 3D topographical maps of the wind resource of Garoua and Guider have been computed as well as the map of wind energy produced using the WAsP software, with an accurate determination of wind speed, wind power density and energy produced. Based on the results, wind power can be considered as a reliable alternative for renewable energy production, if optimal site selection is made.

Risk Assessment of Dam-Breach Flood Under Extreme Storm Events

In recent years, as a result of increasingly intensive rainfall events, the associated water erosion and corrosion have led to the increase in breach risk of aging dams in the United States. In this study, a hydrodynamic model was used to the inundation simulation under three hypothetical extreme precipitation-induced homogeneous concrete dam-breach scenarios. All hydraulic variables, including water depth, flow velocity, and flood arriving time over separated nine cross-sections in the Catawba River, were calculated. The hypothetical simulation results illustrate that the impact of Hurricane Florence’s rainfall is far more severe over the downstream of hydraulic facilities than that of the Once-in-a-century storm rainfall event. Although Hurricane Florence’s rainfall observed in Wilmington had not historically happened near the MI Dam site, the river basin has a higher probability to be attacked by such storm rainfall if more extreme weather events would be generated under future warming conditions. Besides, the time for floodwaters to reach cross-section 6 under the Hurricane Gustav scenario is shorter than that under the Once-in-a-century rainfall scenario, making the downstream be inundated in short minutes. Since the probability can be quantitatively evaluated, it is of great worth assessing the risk of dam-break floods in coastal cities where human lives are at a vulnerable stage.

Removal of 80-Year-Old Gravity Dam and Mechanical Properties of Aging Dam Concrete

Service life of concrete structures depends on the structure design, construction management, and the durability of concrete in aggressive exposure conditions. The old Fengman Dam is an 80-year-old gravity dam, and due to design and construction defects, it has worked with leakage and freeze-thawing problems for more than 70 years. In this study, the durability of the dam concrete is investigated, and a coring program is conducted. The static and dynamic mechanical properties of aging dam concrete (ADC) are tested and the micropores are also observed by scanning electron microscope. Young laboratory concrete (LC) with similar compression strength of the ADC is prepared for comparison. The experimental results show that despite the harsh working conditions, the ADC exhibits good mechanical characteristics in terms of static and dynamic strength and microporosity of interfacial transition zones. The dam concrete is proved to exhibit good durability, and the service life of old Fengman Dam was limited by the poor construction management.