Study on the Applicability of the Exterior Condition Assessment to Evaluate The Physical Vulnerability of Check Dams

Check dams are a typical structural approach used in watershed disaster management systems. Currently, approximately 12,000 check dams have been estimated to be constructed on mountain streams in Korea. More than 90% of these have been constructed in the last 20 years. This rapid increase over a short period of time has attracted attention to the necessity of maintenance strategies for check dams. The purpose of this study is to examine the applicability of the exterior condition assessment to evaluate the degree of deterioration in check dams. We classify the typical damage types of check dams and describe its key characteristics. Moreover, we apply a modified version of the condition assessment for large dams to meet the characteristics of check dams.

Optimizing efforts to restore aquatic ecosystem connectivity requires thinking beyond large dams

Infrastructure-induced fragmentation of riverine ecosystems has prompted the need for more effective aquatic restoration efforts globally. Fragmentation assessments have been extensively undertaken to inform connectivity restoration efforts for fish and other aquatic biota, but they have potentially underestimated the extent of fragmentation by fixating on large dams and overlooking the contribution of other barriers like road crossings and small irrigation structures. The current study addresses this limitation in Mekong region countries (MReCs) of Southeast Asia, by assessing the fragmentation impacts of road crossings and small irrigation structures together with large dams. Our analysis indicates that the basin-scale fragmentation impact of road crossings is similar to that of large dams in MReCs, while small irrigation structures have a far greater impact. These findings raise concerns about the real global extent of aquatic fragmentation, and highlight the need for decision-makers to think beyond dams when attempting to restore connectivity for aquatic biota.

Wind-Wave Interaction in Sengguruh Reservoir and The Effect to Riprap Material

The Sengguruh Dam is one of the large dams managed by Jasa Tirta I Public Company. This reservoir has been operating for more than 38 years (operating since 1982 and the latest data is for 2020). This research was conducted to determine the effect of wind and the interaction of wind on the water in the Sengguruh Dam. Most of the interaction of water and wind is mostly carried out on coastal structures but rarely investigated in the upstream area of the river basin. Investigations were carried out to obtain an overview and characteristics of the influence of the two variables of wind and water on the hydraulics of the reservoir storage, sedimentation in the water column, and side effects of the embankment material in the riprap dam. This study will provide an overview of the condition of the Sengguruh Dam which is full of sediment and shows the wind and water interaction that occurs in the reservoir as well as the potential hazards that are quite large for the management of water resources and disasters in the surrounding community if there is a high risk or threat that occurs if these conditions do not meet dam safety standards in Indonesia.

Assessing Structural Safety of an Arch Dam Using in Situ Vibration Tests

Safety of large dams has always been a major concern for engineers throughout the world but also for public opinion, mass-media and politicians. This is usually based on the fact that the collapse of a large dam could result in huge consequences such as fatalities, economic and/or environmental losses. Nowadays, it is well known that an important factor adversely influencing the safety of such a complex structure like a dam is represented by ageing as a process and ageing related phenomena. Since some 85% of all existing large dams are built in the last 50 years, safety influenced by different decay processes became an important issue to be analysed by dam engineers. In this regard, in situ ambient vibration measurements used to identify the dynamic response characteristics of a large dam seems to represent an appealing non-destructive technique to assess the structural and material characteristics changes and thus to monitor the safety status of the structure. The paper presents the use of the above mentioned procedure by a Romanian team of dam specialists who developed a method combining experimental and analytical techniques for the assessment of the health status of large concrete dams. The Global Elastic Modulus Method (GEMM) was initially used for analysing buttress dams, then it was extended to assess arch dams’ safety state. The most recent evaluation was made upon a 48 m height arch dam in Romania, Cincis dam, located in the central part of the country. The paper is structured into 3 main parts: Introduction, explaining the concept of the hybrid model (the mathematical model bounded to a certain in situ measurement program and calibrated using the recorded data) and of the global elastic modulus (GEM) associated with the dam structure; Experimental, presenting the used equipment, measuring scheme and the processing of the recorded data, ending with the results from spectral analyses; Analytical, presenting the mathematical model developed for the dam structure and its calibration aiming to identify the natural response frequencies and the corresponding mode shapes of the analysed structure. Final conclusions and recommendations are made.

Effects of Dams on Vertebrate Diversity: A Global Analysis

Dams are crucial for water supply in human populations and are becoming more common globally for hydroelectric power generation. Dams alter natural habitats and their biodiversity; however, studies are inconclusive about their effects on them. This study aimed to examine the effects of dams on vertebrates and the determinants of changes in global biodiversity and their relationship with critical areas for conservation. We evaluated the effects of dams on vertebrate richness and abundance. We performed a meta-analysis based on 120 case studies. We evaluated the overall effect on richness and abundance and examined these effects regarding taxa, disturbance type, latitudinal zone, zoogeographic zone, biodiversity hotspots, dam size and purpose, and species extinction risk. We conducted an overall analysis that included all species, and then we conducted separate analyses for terrestrial and aquatic species. Dams had a negative effect on vertebrate richness but not on vertebrate abundance. These effects were influenced by larger dams with fragmentation and were more pronounced within hotspots and in countries with a low species extinction risk. Such negative effects were explained by terrestrial vertebrates (particularly birds and mammals) because species richness and the abundance of aquatic vertebrates (fish) were not affected by dams in any case. Our results showed that habitat fragmentation created by large dams changes vertebrate communities, negatively affecting species richness in some areas of conservation concern. We propose implementing reservoirs in areas where they would have a lower impact on biodiversity and avoiding large dams in priority areas for conservation and where endangered species inhabit.

Seismic risk analysis for large dams in West Coast basin, southern Ghana

Dams are parts of the critical infrastructure of any nation, the failure of which would have a high-risk potential on the people and properties within the dam vicinity. Ghana is one of the most seismically active regions in West Africa and has at least 5 large dams across the region, constructed in strategic locations. The area is characterised by low-to-moderate seismicity, yet historical events suggest that major earthquakes that are potentially damaging have occurred in the study basin. This paper summarises the method used to analyse seismic risk and discusses the seismic hazards of three large dams across the study basin based on the seismicity at the dam sites and their risk due to structural properties and the location of each dam. The peak ground acceleration (PGA) values for the dam sites estimated are within the range of (0.31 g and 0.52 g) for 10,000 years return period. The study shows that one large dam has a high-risk class in the basin. This dam should be inspected and analysed for its seismic safety and people’s protection in the downstream paths.

The Role of Large Dams in a Transboundary Drought Management Co-Operation Framework—Case Study of the Kabul River Basin

Hydrologic drought is a frequent phenomenon in the transboundary Kabul River Basin (KRB), the vital resource shared between the two nations of Afghanistan and Pakistan. While the KRB has vast water resources, these resources are subject to extreme hydrologic events and, as a result, are not adequately managed to deal with the stress during drought conditions in the transboundary setting with no formal agreement or treaty. Rapid population growth and increases in agricultural land will require balanced water distribution to meet the array of needs. The Soil and Water Assessment Tool (SWAT) is used to evaluate distribution options for flow frequencies under existing and proposed large dams in the headwaters of the KRB. The calibrated SWAT streamflow results are employed for statistical analyses of the Standardized Streamflow Index (SSI) and Annual Cumulative Deficit Volume (ACDV) to investigate hydrologic drought time series and identify the role of proposed dams to be used for drought mitigation. Based on the SSI, proposed dams can provide additional storage that will partially address hydrologic droughts in the future. At the same time, restrictions on agricultural land expansion and water intakes are other measures to facilitate balanced water resource availability. This study discusses the intricacies of transboundary conflict and cooperation, water rights, and drought risk management; as well, recommendations for a KRB transboundary Drought Task Force (DTF) between Afghanistan and Pakistan are provided, to develop a science-based policy for using the stored waters in large dams for drought relief, fairly and transparency.

Analyzing the Impact of Large Dams on Seismicity Patterns around Their Locations

Dam construction is one of the most popular solutions for managing water resources. In recent years, changes in patterns of regional seismicity associated with large impoundment dams have raised concerns among environmentalists. In this study, five large dams located in Iran were studied from this perspective. The Gutenberg-Richter, linear regression and T-test were used to examine the seismic changes in the radius of 100 km of each of the dams during a twenty-five-year period before and after the construction of the dams. The results revealed that the seismicity level and relative density of large and small earthquakes in three of these dams have increased after dam construction. A significant difference between the magnitude of earthquakes, as well as the number of earthquakes before and after the construction of dams in the region, was recognized. However, the results of the T-test statistical analysis indicated that the mean depth of the earthquakes and their distance from the dams before and after construction have not changed significantly. Overall, these results indicated that the construction of large impoundment dams has been associated with some changes in patterns of regional seismicity. The findings would guide researchers to further investigate the type of impacts that dam construction may have on seismicity patterns.

The Mysteries of Lake Copais and the Island Fortress of Gla

The Bronze Age drainage of Lake Copais, Boeotia, is unique within Europe as the largest and most complex work of engineering of the period. Comprising large dams, polder dykes, canals, massive levees, cuttings and tunnels, it made at least 95km² of drained lake bed available for agricultural production. The first polders were established in the Middle Helladic period with great extensions in the Late Helladic. During the latter period the largest of all the Mycenaean citadels was constructed at Gla which had been a rocky island in the lake prior to the drainage. But exactly what type of settlement it was still remains something of a mystery. This paper draws together the history of research on the citadel of Gla.