The effectiveness of check dams on the morphology of ephemeral channels and their impact on sediment deposition was investigated in a semiarid catchment. According to results, dams located in downstream were more effective in deposition of fine sediment than upstream dams. The results showed that dams influenced the width/depth ratios. The stream channel became wider and flatter in downstream, resulting in an increase of the volume of sediment and present of fine sediments from upstream to downstream.

Introduction: This study was performed to determine the effect of two kinds of post dam (one created in laboratory and the other in clinic) in increasing the retention of upper complete denture and comparing it with a non-post dam condition.Materials and Methods: 10 patients were selected with good general health condition, a good and undercut- free tuberosity and without palatal tori and surgical scars. For each patient three bases were made: 1- Base without a post-dam.2- Base with a laboratory- post dam.3- Base with a clinical post dam.The face necessary for breaking the posterior sel for each group was measured. statistical analysis of the results revealed that:Results: 1- Group 2 and 3 were more retentive than group 1 2- Group 2 was slightly more retentive than group3, aConclusion: Although group 2 was more retentive than 3, a clinic- made post dam can be more advisable because of its anatomical more favorable relationship with patients' oral soft tissues.

Today, construction of dams to collect and store river water for different consumption purposes including drinking, agriculture, and industry is inevitable. Nevertheless, dams are colossal structures that pose potential dangers to their downstream community and their failure can be catastrophic. Dynamic analysis of concrete dams is more complex than that of conventional structures due to the presence of a reservoir. This complexity mainly results from the dam-reservoir interactions in seismic conditions. In this study, the seismic response of concrete gravity dams was investigated using Abaqus finite element software in different conditions of full, half-full, and empty reservoir. To this end, Koyna concrete gravity dam with specific geometric and physical characteristics was analyzed by applying Kobe earthquake records. The results from finite element analysis showed that the values of the main stresses in different modes of analysis were considerably significant. Most of these stresses occurred at the site of the downstream slope change (level of 66. 5 m), thus causing stress concentration in this area. Furthermore, according to the results, upon increasing the reservoir level, the amount and intensity of displacement fluctuations would increase, mainly due to the dam-reservoir interactions and effect of fluctuations in the hydrodynamic pressure of the reservoir in the time curve of the displacement in the crown of dam. In general, in case the reservoir is full, the levels of stress and displacement would be higher than those in other modes.

Mathematical simulations on dam break or failure using Boss Dambrk hydrodynamic flood routing dam break model were carried out to determine the extent of flooding downstream, flood travel times, flood water velocities, and impacts on downstream affected residences, properties and environmental sensitive areas due to floodwaters released by failure of the dam structure. Computer simulations for one of the worse-case scenarios on dam failure using BOSS DAMBRK software accounted for dam failure, storage effects, floodplains, over bank flow and flood wave attenuation. The simulated results reviewed a maximum flow velocity of 2.40 m/s with a discharge (Q) of approximately 242 m³/s occurred at 1.00 km downstream. The maximum discharge increased from 244 m3/s (flow velocity = 1.74 m/s occurred at 8th km) to 263 m3/s (flow velocity = 1.37 m/s occurred at 12th km); about a 39% drop in flow velocity over a distance of 4.00 km downstream. If the entire dam gives way instantly, some spots stretching from 0.00 km (at dam site) to approximately 3.40 km downstream of the dam may be categorized as “danger zone”, while downstream hazard and economic loss beyond 3.40 km downstream can be classified as “low” or “minimal” zones.

In spite of the fact that the effect of earthquake on earth dams has been widely studied during the past decades, the complicated behavior of such earth structures against different seismological characteristics is still unknown. Such ambiguities necessitate more accurate studies using more comprehensive computation tools to achieve new results describing the behavior of such structures subjected to earthquake loading. In the present study, the simple soil model of elastic, perfectly plastic (based on the Mohr-Coulomb criterion), and Rayleigh damping criterion have been adopted for the soil. First, the numerical model employed was verified by dynamic analysis of real cases such as “Long Valley” and “Santa Felecia” earth dams. The computational results were then compared with real recorded data or with those reported by other researchers. In addition to evaluating seismic stability of earth dams, their seismic stability was verified using pseudo-static analyses. Therefore, the “Carsington” dam was analyzed to verify the results of pseudo-static analyses and to check the results of FLAC software in calculating the pseudo-static factor of safety. The values of calculated factors of safety in the present study are in good agreement with the published results in the literature. Furthermore, the failure behavior revealed in the analysis shows the ability of FLAC software in defining the failure surface. In the main part of the analyses, a parametric study was conducted for different selected conditions and specially the effect of dam height and the optimum size of crest width were investigated. The results are presented in relevant diagrams.

In dam construction industry, the safety of dam is one of the most important challenges that should be considered in design, construction and operation phase. Recently, use of quantitative risk analysis, as a useful tool in dam safety risk management, is rapidly increasing. In this paper, first, risk assessment methods in dam safety are investigated and ANCOLD guideline for dam safety risk assessment is detailed. Then, as a case study, safety of Goleastan dam, in northeast of Iran, is assessed considering risk analysis approach for upstream flood hazard. For calculating the probability of failure of dam, the various methods were assessed and finally Event Tree Analysis (ETA), as most commonly method in dam safety risk analysis, was used. The number of life losses due to flooding of Golestan dam break is estimated based on USBR methodology, known as DSO-99-06. Finally, according to calculated risk and comparing with different criteria for acceptable risk, it is obvious that the risk of Golestan dam break due to upstream flood is unacceptable and immediate risk reduction measures are necessary.

Studying the responses of dams to explosion-induced loads and evaluating their overall safety under such loads is highly significant regarding the strategic importance of dams. The present study investigates TNT-induced wave effects on the Karun-4 Dam in Iran. For this purpose, dynamic analyses were carried out on the dam reservoir and foundation system via the finite element method (FEM) in ABAQUS. The CONWEP theory allows the imposition of pressure loading caused by an explosion in the air. The reservoir was considered empty, and then three different heights of 225, 115, and 5 m were analyzed. The failure explosive weights of the three heights were calculated by trial and error. Analyses were performed with 1000, 1200, and 1300 kg of TNT for the height of 225 m, 1900, 1950, and 2000 kg of TNT for the height of 115, and 1800, 1900, and 2000 kg of TNT for the height of 5 m. It was observed that the dam failed at loads of 1300, 2000, and 2000 kg of TNT when the explosion occurred at 225, 115, and 5 m, respectively. The analyses were performed based on these loads. The results indicated that the reservoir water level had a negligible effect on the arch dam's failure blast load. Moreover, analysis results of the dam-reservoir-foundation system in filled-up and empty reservoir cases suggest that the failure explosive loads of filled-up and empty reservoir dams do not significantly differ, and the failure explosive load of the filled-up case is slightly lower than that of the empty case. For example, at an explosion height of 225 m, the failure load of the filled-up reservoir case was derived to be 1500 kg of TNT, while that of the empty reservoir case was obtained to be 1300 kg of TNT.

Due to the immense damage caused by dam failure, especially dams constructed near large cities, it is necessary to consider the breaking phenomena as well as studying and designing different parts of the dam. For this purpose, the hydrograph of the outflow due to dam failure must be identified according to size of the fracture and then flood routing, and flood zone must be determined based on the downstream topography and morphology. The integration of hydraulic models and geographic information system is used to achieve this objective. In this research the effect of breaking Taleghan storage dam due to the slip of a pile of reservoir abutment and the creation of current wave toward the dam body as well as the vulnerability analysis due to the breaking of the dam on downstream lands was studied. At first, Taleghan dam failure for five different scenarios was modeled using the FLOW-3D numerical software and then the geometric data of the river was extracted using the ArcGIS software and modeling the flood due to dam failure was conducted in Hec-GeoRas model. Then, the risk analysis was performed for each break scenario of Taleghan dam. The results indicated that the maximum amount of inundation would occur in Razmian city at an approximate distance of 45 kilometers from Taleghan dam site.

In the history, Earthquakes have been a major source of many damages and human losses and there has always been a lot of concern about the destruction of large structures such as dams due to significant financial losses and casualties caused by it as well as the uncontrolled release of water in the towns and villages located downstream. Seismic risk analysis, one of the most important methods to deal with earthquake hazards. In this study a type of seismic risk analysis in dams is discussed and used and seismic hazard analysis is conducted for the Chah Nimeh Zabol dam. Semi-quantitative risk analysis for Chah Nimeh Zabol dam by seismic hazard analysis for the location of the dam was conducted which placed it in the medium risk category and there is no requirement to redesign or reinforce the dam body. The results can be used as a guide for seismic risk of the dams.

The dynamic interaction of fluid-solid systems has long been a subject of interest in many engineering fields. One of the most important problems of this nature, encountered in civil engineering, is the dynamic interaction of a dam and the reservoir under seismic loading. Recent research indicates the importance of this interaction and the resulting hydrodynamic forces, including the compressibility effects of water on the seismic response of concrete dams.In this thesis a combination of 2D finite-element and a closed form method based on a Eulerian approach is developed to study the dam-reservoir interaction effect. The mentioned procedure is used to investigate the interaction effect on stresses and displacements of the Kowsar Dam-reservoir system. To establish the accuracy of the method, the seismic response of the Pine Flat Dam is studied and the results are compared with other exact solutions.