Flash floods are an increasing hazard to human infrastructure and life. Effective disaster management and mitigation require accurate and fast predictions for decision-making. The Flood Inundation Parallel Computation (FIP) software presented in this paper shows how to fully exploit the tremendous computational capabilities of graphics processing units (GPUs) to accelerate shallow water solvers beyond the current state-of-the-art. The time efficient explicit shallow water scheme for structured grids RMG, is introduced and implemented in FIP. The optimized GPU implementation of FIP achieves balanced memory- and instruction throughputs of up to 80%. Validation and performance tests using laboratory and historical flood cases are presented that demonstrate the accuracy and effectiveness of FIP in predicting flood inundation. Our implementation achieves a fourfold speedup in comparison to state-of-the-art approaches. It enables faster-than real-time simulations of areas of over 600 km2 at 1 m resolution on consumer-grade GPUs.

Over the last 20 years, flooding has been the most common natural disaster, accounting for 44.7% of all disasters, affecting about 1.65 billion people worldwide and causing roughly 105 thousand deaths†. In contrast to other natural disasters, the impact of floods is preventable through affordable structures such as dams, dykes and drainage systems. To be most effective, however, these structures have to be planned and evaluated using the highest precision data of the underlying terrain and current weather conditions. Modern laser scanning techniques provide very detailed and reliable terrain information that may be used for flood inundation modelling in planning and hazard warning systems. These warning systems become more important since flood hazards increase in recent years due to ongoing climate change. In contrast to simulations in planning, simulations in hazard warning systems are time critical due to potentially fast changing weather conditions and limited accuracy in forecasts. In this paper we present a highly optimized CUDA implementation of a numerical solver for the hydraulic equations. Our implementation maximizes the GPU’s memory throughput, achieving up to 80% utilization. A speedup of a factor of three is observed in comparison to previous work. Furthermore, we present a low-overhead, in-situ visualization of the simulated data running entirely on the GPU. With this, an area of 15 km2 with a resolution of 1 m can be visualized hundreds of times faster than real time on consumer grade hardware. Furthermore, the flow settings can be changed interactively during computation. CCS Concepts • Human-centered computing → Scientific visualization; Geographic visualization; • Computing methodologies → Realtime simulation; Massively parallel and high-performance simulations; Massively parallel algorithms;

The effect of vegetation in hydraulic computations can be significant. This effect is important for flood computations. Today, the necessary terrain information for flood computations is obtained by airborne laser scanning techniques. The quality and density of the airborne laser scanning information allows for more extensive use of these data in flow computations. In this paper, known methods are improved and combined into a new simple and objective procedure to estimate the hydraulic resistance of vegetation on the flow in the field. State-of-the-art airborne laser scanner information is explored to estimate the vegetation density. The laser scanning information provides the base for the calculation of the vegetation density parameter ωp using the Beer–Lambert law. In a second step, the vegetation density is employed in a flow model to appropriately account for vegetation resistance. The use of this vegetation parameter is superior to the common method of accounting for the vegetation resistance in the bed resistance parameter for bed roughness. The proposed procedure utilizes newly available information and is demonstrated in an example. The obtained values fit very well with the values obtained in the literature. Moreover, the obtained information is very detailed. In the results, the effect of vegetation is estimated objectively without the assignment of typical values. Moreover, a more structured flow field is computed with the flood around denser vegetation, such as groups of bushes. A further thorough study based on observed flow resistance is needed.

The author would like to make the following corrections to the published paper [...]

At many locations turning pools have to be integrated into fish passes, for example due to restricted space available. To date the knowledge of the hydraulics and ecological performance of these special basins is limited. The flow patterns and vortices in the pools of fish passes can be simulated with 3D hydrodynamic models already during the design phase. The advantages and limitations of 3D hydrodynamic models were demonstrated in the context of a study of three turning pools of a planned fishway. In addition, a new turning pool shape was developed that best met the established passage criteria.

Two-dimensional modeling of the near-shore morphodynamics is an emerging field of coastal engineering. Today highly simplified one-dimensional models are widely used in practice for this task. Two-dimensional models bear the potential of computing the cross- and long-shore transport at the same time and in their direct interaction. In this paper a two-dimensional morphodynamic model named "Strand" is described, that is a process based simulation tool for the near-shore. An example application is given for the depth development a 5 km long part of the Baltic Sea coast.

With morphodynamic-numerical models the development of estuarine systems can be simulated for a period of several years. In areas exposed to high waves the effects from waves on the sediment dynamics can not be neglected. Especially if there are also currents acting on the sediments. In order to simulate these effects the hydrodynamic-morphodynamic-numerical-model TIMOR3 (TidalMorphodynamics) was coupled to the spectral wave model WWM (WindWaveModel). This coupling procedure enables calculations in both models on the same unstructured grid, which allows extremely efficient simulations.The coupled model is used in an estuarine system in southern Brazil. The outer navigation channel which leads to the port of Paranagua requires frequent maintenance dredging to guarantee safe navigational depths. The long shore tidal and wave induced currents in the area in conjunction with near shore high wave energy conditions cause turbulences that lead to a sediment transport along the beach and to permanent sedimentations in the navigation channel This complex system is simulated with the coupled model. The results as water levels, flow velocities and grain size distribution match well with measured values, nevertheless additional adjustments can be done to achieve even better results.With the coupled model it is possible to optimize the dredging and dumping process and to investigate the efficiency of building measures in the area.

Morphological evolutions in coastal and in fluvial areas are based on the same fundamental physical processes. In case of a sloping bed, sediment particles are additionally forced to move down the bed slope due to gravity. To know the quantity of particles moving downwards is crucial for morphological investigations. On a transversely sloped bed the transverse component of sediment transport leads to a levelling of the bed. This is fundamental in all processes with moving sediments. Knowing the bed levelling slope effect induced by gravity and developing useful mathematical expressions is very important for testing, improving and applying morphodynamic-numeric models.Several researchers give equations for down slope transport. These equations take into account the equilibrium of forces on a single particle. Hence they present some modifications of critical shear stress values from trigonometric relations and additionally a modified resultant transport rate equations. Using separation in a longitudinal and a lateral component gives a transverse transport approach.In this paper the development of a simplified formulation of the sediment transport direction is given. New experimental results are shown and approaches to interpret the results are given. In the experiments the decay of the initial bed slope under different hydraulic and sedimentologic conditions was determined. Different functional relations of the down slope transport depending on the bed forms and as a function of hydraulic and sedimentologic parameters are given.

F. Cioffi, F. Gallerano And E. Napoli, Journal of Hydraulic Research 2005, 43(3), 290–301

An experimental investigation on the sediment transport process on transverse sloped beds is presented. Experiments were conducted in a 60 m long laboratory tilting flume which is 1 m wide and 0.5 m deep. During the experiments bed levels have been measured at several positions of the cross section with a non-touch method. Longitudinal bed profiles were continuously measured from the chosen positions of the cross section to observe the bed levelling process. Based on the experimental data an accurate characterization of the bed morphology and the prevailing bed forms is given. With respect to the prevailing bed forms the experiments were conducted under different hydraulic and sedimentologic conditions to develop ripples and dunes. The presented work illustrates some new experimental results for the description of the transverse transport process. The transverse transport is an important process in morphologic evolutions. The knowledge of this component of the general, total sediment transport and the development of a useful approach are essential for testing as well as improving and applying numerical models.

Wave attack from the North Sea results in strong sediment transport at the North Sea coast of Germany. The use of nearshore wave models can deliver all the parameters needed for the design of the dikes. For the verification of the wave energy model SWAN data from several buoys near the island Amrum is used. Wave breaking and the flow field play a major role in this verification. In the shallow water double peak spectra are observed. To investigate the influence of the depth distribution north of the island Amrum on the wave attack at the Island Foehr calculations for different depth distributions are carried out. For all cases a severe storm situation was calculated and the wave height distribution plotted. A change of 13 % in wave height for the most extreme case is calculated that leads to a change of 7 % in the wave runup when using the standard formulas. The model provides valuable basic information for the design of the dikes.

The sediment transport in transverse direction to the main flow is a very important factor in morphodynamic-numeric computations. The transport direction differs from the direction of the main flow affected by an inclined bed. Following the gravity force the sediment particles move downwards the bed slope. The quantitative knowledge of this effect is important for morphological simulations with numerical models. The morphological evolution in coastal and in fluvial areas depends on the same physical processes. So the transverse transport process, a phenomenon which has to be investigated further on, is fundamental in all processes with moving sediments. The knowledge of the downslope transport, the gravity driven transverse component of the general, total sediment transport, and the development of a useful mathematical formulation are very important for testing, improving and applying morphodynamic-numeric models. With respect to the relevance of this process there is a need for more detailed information supported by experimental data. The presented work shows some new experimental results for the description of the transverse transport process. Investigations in sediment transport on a transversely sloped bed were conducted for different flow conditions. The studies took place in the laboratory of the Institute of Hydraulic and Water Resources Engineering at Darmstadt University of Technology. Measurements were carried out in a 60m long and 1m wide tilting flume under different hydraulic and sedimentologic conditions to succeed the state of ripples and dunes. The time dependant decay of the prepared cosine-shaped bed was determined by measuring multiple longitudinal bed profiles. Changing sedimentologic parameters led to different downslope transport approaches.

A process-based morphodynamic coastal area model (TIMOR3) is applied to simulate the virtual breaching of Hiddensee Island at the southwestern coast of the Baltic Sea during a storm flood. Furthermore the medium-term (3 years) development of the initial breach and of an adjacent inlet is simulated using a new approach of model input filtering for a nontidal site. The input filtering of forcing- and boundary conditions is based on typical weather patterns and on wind statistics. The modeled island breach is similar to a historic breach measured in 1866. The adjacent inlet adapts its morphology to the new hydraulic situation due to the island breach mainly within one year. A comparison study with and without a breaching of Hiddensee Island reveals that sedimentation in the adjacent inlet is less in the case of breaching.