Coastal areas in many parts of the world are vulnerable to tsunami waves. Large tsunamis are strong enough to bring about a substantial amount of sediment mobilization. Several post-tsunami field investigations performed in recent years have documented destruction induced by scouring process. For example, the 1993 Nicaraguan earthquake centred 100km off the Nicaraguan coast caused devastating tsunami-induced scour around structures and bridges (Satake et al., 1993). Differences in the scour depths were related to soil properties, shapes of structures, and tsunami hydrodynamics (Jayaratne et al., 2016). Furthermore, depending on the soil permeability, the flow and pressure propagate at different speeds within the soil, which affects water table fluctuations and the soil strength (e.g., Tonkin et al., 2003; Yeh and Li 2008). The primary objective of this research was to study the effect of different inland-propagating dam-break bore heights on pore pressure variations and scour evolution in saturated beds with two different bed slopes (i.e., zero and +5% slope) by performing comprehensive laboratory studies at a 1:40 scale. To achieve the objective, tsunami-like dam-break bores generated by rapidly opening a swing gate and propagated towards and over a sediment section and hit a structure centred within a sediment bed. The secondary objective of this experimental investigation was finding a relation between scour depths and pore pressure values as a function of still-to-impoundment water depth ratio. The results of this experimental investigation showed that effective pore pressures were consistently greater in the front face of a model than in the side face. Besides that, the highest effective pore pressures took place near the saturated bed surface. Such that, due to the propagation of supercritical bores the maximum effective pore pressure in the bottom of the front corner was 50% larger than the exact same location in the side face. While, this difference decreased to 10% in the case of subcritical bores. For the same hydrodynamic bore conditions, the maximum difference between effective pore pressure in the two faces of the model reduced by 70% in the inclined bed test than the horizontal bed tests and this difference was only 15%. However, the peak effective pore pressure around the model doubled in the inclined bed tests compared to the horizontal ones. The 5% upsloping decreased the maximum scour depths by two times as a result of the same hydrodynamic loading conditions.

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Cases of dam failure occur around the world almost each year. Dam failures can result in the formation and propagation of fast-moving unsteady flows that can cause loss of life as well as significant environmental and economic consequences in downstream flooded areas. The initial stages of a dam break are important due to wave-breaking front and the associated turbulence. Furthermore, characteristics of the river bed downstream of the dam (topography and bathymetry) as well as the presence of obstacles in the dam break wave path such as man-made or natural obstacles like bridges, trees, and local sills affect flow dynamics, which can lead to the formation of hydraulic jumps and the reflection of the flood wave. Accordingly, the precise prediction of flood parameters such as arrival times, free surface profiles, and flow velocity profiles is essential in order to mitigate flood hazards. This study aimed to assess the performance of various turbulence models in predicting and estimating dam-break flows and related positive and negative flood wave characteristics over different downstream bed conditions. Three-dimensional (3-D) Computational Fluid Dynamics (CFD) models were created to solve the unsteady Reynolds equations in order to determine the initial stages of the free surface profiles over dry and wet beds and to investigate the generation and propagation of dam-break flows and reflected flood waves in the presence of a bed obstacle. The performance of different Reynolds-averaged Navier-Stokes (RANS) turbulence models has been investigated, and the standard k-ε, RNG k-ε, realizable k-ε, k-ω SST, and v^2-f turbulence models have been studied using OpenFOAM software. Dam-breaks were modelled using the Volume of Fluid (VOF) method employing the Finite Volume Method (FVM). Both qualitative and quantitative comparisons of numerical simulations with laboratory experiments were completed in order to assess the suitability of different turbulence models. The results of the first study showed that the RNG k-ε model exhibited better performance in capturing the flood wave free surface profiles over both dry- and wet-bed downstream conditions, while from the second study, it was concluded that the k-ω SST model was able to accurately predict the formation and propagation of reflected waves against a bottom obstacle in terms of free surface profiles and negative bore propagation speeds.

Dam safety is a perpetual issue everywhere, when communities are located downstream of dams. This paper reflects experiences of the related practice and considerations in Germany. The probability of dam failure will be considered from a theoretical as well as from an empirical point of view. Information necessary in drawing up special hazard and risk maps are described and evaluated. For small dams further considerations to simplify the analysis procedure will be presented.

The old water system in Sala, formerly belonging to thesilver mine, is analysed with regard to dam safety focusing onthe hydrological aspects. The hydrological safety of the riskclass I dams in the area, built in the 16th century, is notconsidered adequate according to the Swedish guidelines fordesign flood determination. A review is made of internationalprinciples for design flood determination. The overview showsthat there is no common principle used internationally whendealing with design flood for dams. In some countries there isan ambition to implement risk assessment for evaluation ofhydrological safety. However, at present Australia is the onlycountry that has fully integrated risk assessment in theirdesign flood guidelines. A risk assessment of the water systemin Sala shows that neither increasing the spillway capacity norimplementing flood mitigation measures in the watershed haveany significant effect on dam safety in the area. Nothingindicates that watersheds with a high presence of mires, likein the Sala case, should be particularly well suited forimplementing flood mitigation in the watershed as a dam safetymeasure. In order to safely handle the design flood in Sala andavoid dam failure due to overtopping the flood needs to bediverted from the water system. <b>Key words:</b>dam safety; design flood; flood mitigation;hydrological; risk assessment

China’s government invests in hydropower and explicitly in larger dams. An increasing share of such large dams is globally represented by the type Concrete Face Rockfill Dam (CFRD) due to its safe behaviour at a relatively low construction cost. China is however building them higher than has earlier been done and the lack of worldwide experience requires thorough studies on their behaviour. This report presents a study of the Cihaxia dam that is to be built in the river basin of Huang He, regarding the optimisation of an increased rockfill compaction and its final effects on the settlements of the concrete face. The settlements of a typical cross section of the Cihaxia dam are modelled with a Finite Element Method (FEM) program with varying values for a number of structural properties. The effect of each variation indicates what properties that will have the largest effect on the behaviour of the finished structure and points out where focus shall be laid when optimising the design of a high CFRD. The outcome of the FEM analysis shows the static comportment of the rockfill body and its concrete face at two stages, at the end of construction and after reservoir impoundment. The difference between the two provides data on what effects the water load would cause, which constitute the main displacements of the concrete slabs. It is evident from the obtained results that the most important of the studied parameters alongside with the level of compaction is the geometrical extension downwards and inwards of the zone subject to increased compaction. A higher degree of compaction will always produce a beneficial decrease of settlements but might not always be economically legitimate as costs rapidly increase with higher levels of compaction. An adequate level of a CFRD’s compaction increase can with advantage be determined by comparing different designs regarding the volumetric percentage to compact against the calculated decrease in slab deflection.

Post-dam removal geomorphologic adjustment of a stream channel has been documented in the scientific literature at watershed, hillslope, and laboratory scales. Hillslope-scale studies in channel cross sections are most common and add significant value in the dam-removal literature. This study examines geomorphic stream channel adjustment following dam removal at the hillslope scale under natural climatic conditions. A sedimentfilled silt fence dam (1 m tall, 12.65 m wide) was removed in three stages, and the width and depth of the upstream developing channel was monitored at six transects for 15 months. Headcut retreat and changes in channel sinuosity were also recorded. After the silt fence dam was removed, channel development was initiated by headcut formation, which migrated upstream at a rate of 4 cm/d for about 10 months and then gradually reached attenuation. The channel progressed through four distinct stages: Stage 1 (Initial conditions); Stage 2 (Downcutting)-wide, shallow, meandering channel incised to a maximum depth of 0.52 m, and sinuosity decreased; Stage 3 (Floodplain development)-upon reaching base level, surface runoff began to meander within the channel, widening it through bank slumps and erosion; and Stage 4 (Quasi-equilibrium)-channel development reached dynamic (quasi-) equilibrium with only minor widening at downstream transects (maximum width of the incised channel reached 0.46 m), accompanied by sediment aggradation. The stages of upstream channel development and headcut retreat pattern in this study are consistent with the findings of other studies at the laboratory and watershed scales, indicating that channel development after dam removal is scale independent.

Two areas along the Blacksmith Fork River, in the Bear River Range southeast of Logan, Utah, were studied as sites for a storage dam and reservoir. An earth dam, 150-200 feet high, and a reservoir of 15,000-20,000 acre-feet are contemplated by the Bureau of Reclamation, U.S. Department of Interior. The lower area, located about 7 miles east of the mountain front, involves two possible dam sites on limestone. Thick overburden is present in the canyon bottom and on the right abutments. The upper area, located about 2 miles south of the headquarters of the Hardware Ranch, includes two possible dam sites on quartzite. The quartzite at the upstream site was found, by drilling and testing, to be extensively fractured; the downstream site has not been drilled. Acceptable topographic settings are present at both of these sites. Geological factors, as well as a difficult road relocation necessitated by the reservoir, exclude the lower area. It is recommended that the downstream site of the upper area be explored by means of a drilling program. A systematic evaluation of constructio materials near this site, based on appropriate excavations, is also required. (58 pages)

The aim of this diploma thesis is to determine the extent of territory endangered by dam break flood wave under Plumlov dam, using 2D mathematic modelling of water flow under the dam and in the inundation nearby. Output results of the model are maps of the extent territory with highlighted flood area.