Inundation Process Research Articles

Numerical Investigation on Coastal Inundation of Storm Surges in Estuarine Wetland Waters

Zhang, H.; Zhang, M.; Shen, Y., and Xu, T., 2020. Numerical investigation on coastal inundation of storm surges in estuarine wetland waters. In: Malvarez, G. and Navas, F. (eds.), Proceedings from the International Coastal Symposium (ICS) 2020 (Seville, Spain). Journal of Coastal Research, Special Issue No. 95, pp. 1383-1388. Coconut Creek (Florida), ISSN 0749-0208.Coastal flooding caused by storm surges poses serious threats to coastal areas, communities and ecosystems. Plants that widely distributed in tidal flats play an important role in protecting the coastline from erosion, and mitigating extreme nature hazards. In this paper, based on the finite volume method (FVM), an explicit depth-averaged 2D model is established to investigate the interaction between salt marsh plants and storm surges in estuarine wetland waters. The Roe approximate Riemann solver, coupled with a drying-wetting boundary technique, is proposed in order to evaluate the effectiveness of interface fluxes for tracking the moving coastline and calculating storm surge land intrusions. The drag force induced by vegetation is added to momentum equations as an internal source to express the vegetation resistance to storm surges. The Jelesnianski 65 typhoon model is adopted to simulate the wind and pressure fields of the storm surges, and the background wind field is included in the total wind field. The proposed model is applied to investigate tidal levels, storm surges and flow currents during Typhoon Winnie and Typhoon Matsa in the Bohai Sea. Moreover, the model is used to explore the land intrusion and storm surge attenuation in Liao River Estuary (LRE) wetlands during Typhoon Winnie. Numerical predictions are found to match perfectly with those given by the measured data. The storm surge model can accurately reproduce the storm surge inundation process in wetland waters. The simulated results also indicate that salt marsh plants can reduce the flow current in vegetated regions, thus effectively attenuating the potential threats of storm surges.

Tsunami Squares simulation of megathrust-generated waves: Application to the 2011 Tohoku Tsunami

Large subduction zone earthquakes often cause tsunamis, but observational data for hazard analysis is limited. Synthetic catalogs of seismically-generated tsunami scenarios can be created by pairing earthquake and wave simulations. Tsunami Squares is one such wave simulator, explicitly tracking water mass and momentum, allowing simulation of dry land and the inundation process. We demonstrate a C++ port of Tsunami Squares paired with the Virtual Quake simulator by replicating the 2011 Great East Japan Earthquake and Tsunami. Comparisons of coastal run-up and wave heights with observations finds good agreement, with future improvements coming from tsunami source time dependence.

Development of water and energy Budget-based Rainfall-Runoff-Inundation model (WEB-RRI) and its verification in the Kalu and Mundeni River Basins, Sri Lanka

Distributed Hydrological Models (DHMs) with the capability of simulating catchment-scale water and energy budgets as well as rainfall-runoff-inundation processes are essential tools for Integrated Water Resource Management (IWRM) as well as Water-related Disaster Risk Reduction (WDRR) under changing climate. This research developed a new DHM, the Water and Energy Budget-based Rainfall-Runoff-Inundation (WEB-RRI) model, by integrating the RRI model’s diffusive wave flow equations into a land surface model (hydro-SiB2) to incorporate water and energy budget processes, land-vegetation-atmosphere interactions, soil moisture dynamics, and 2-D lateral water flows to improve interception, evapotranspiration (ET), soil moisture, runoff, and inundation processes. The performance of the new model was assessed using river discharge data, MODIS and GLEAM ET data, and ground as well as satellite inundation extents in the Kalu (wet) and Mundeni (dry) River basins in Sri Lanka. The model was well calibrated and validated (Nash > 0.9) and confirmed to be highly capable of reproducing the long-term (~20 years) observed river discharges (Nash > 0.89) and hydrological flow regime properties for both basins. Particularly, the simulated low flow just before the flood and the peak discharges during the flood, as well as their timings, coincided well with the observed discharges in both basins, which indicates that the model is capable of reproducing soil and vegetation water storages reasonably well, and therefore it can be used for real-time and forecasting applications with the re-starting capability. The model-simulated basin averaged ET fluxes and their trends agreed better with GLEAM (RMSE: ~0.7–0.95 mm/day, correlation: ~0.35–0.39) than with MODIS (RMSE: ~0.96–1.04 mm/day, correlation: ~0.14–0.25). The simulated inundation extents were also consistent with the ground- and MODIS-driven inundation extents. The future focus of this research will be on expanding the model applicability for basin-wide IWRM and WDRR, including flood- and drought-related risk assessments, by employing the model to operational applications (e.g., flood forecasting and seasonal flow prediction) and long-term applications (e.g., catchment responses to past and future climatology, water cycle variability, hydrological extremes, and land-use changes).

Simulating Tsunami Inundation and Soil Response in a Large Centrifuge

Tsunamis are rare, extreme events and cause significant damage to coastal infrastructure, which is often exacerbated by soil instability surrounding the structures. Simulating tsunamis in a laboratory setting is important to further understand soil instability induced by tsunami inundation processes. Laboratory simulations are difficult because the scale of such processes is very large, hence dynamic similitude cannot be achieved for small-scale models in traditional water-wave-tank facilities. The ability to control the body force in a centrifuge environment considerably reduces the mismatch in dynamic similitude. We review dynamic similitudes under a centrifuge condition for a fluid domain and a soil domain. A novel centrifuge apparatus specifically designed for exploring the physics of a tsunami-like flow on a soil bed is used to perform experiments. The present 1:40 model represents the equivalent geometric scale of a prototype soil field of 9.6 m deep, 21 m long, and 14.6 m wide. A laboratory facility capable of creating such conditions under the normal gravitational condition does not exist. With the use of a centrifuge, we are now able to simulate and measure tsunami-like loading with sufficiently high water pressure and flow velocities. The pressures and flow velocities in the model are identical to those of the prototype yielding realistic conditions of flow-soil interaction.

Visualization and Spatio-temporal Analysis of Tsunami Inundation: A Case of the Great East Japan Earthquake

Abstract. This study visualized the spatio-temporal changes in the tsunami inundation area and analyzed its expansion mechanism. The most characteristic of the Great East Japan Earthquake is the damage caused by the tsunami. And 90% of the dead was caused by it. One of the factors is that the preparation of countermeasures corresponding to the huge tsunami was not fully prepared. Therefore, after the Great East Japan Earthquake, the Japanese government has emphasized the importance of the advance preparation of the hugest tsunami expected. According to the past experience the occurring of huge tsunami is very rare. Earthquake researchers have observed same scale tsunami in every 1000 years in Japan. According prediction, next huge tsunami may be happened around the 2030. Therefore, analyzing the tsunami inundation mechanism of the Great East Japan Great Eastern is important for the future tsunami countermeasure. The arrival time and spatial distribution of tsunami inundation can be considered as a main important component of evacuation planning. In addition, a wide range of inundation area caused by huge tsunami is suitable for analyzing the inundation mechanism compared with a small-scale tsunami inundation. In this study I would like to examine the tsunami inundation process caused by the Great East Japan Earthquake in 2011.The method is as follows. First, movies shooting the tsunami inundation are collected from DVDs and TV hosting services. And they are examined as analysis materials. As a result, movies that taken from the ground were impossible to shoot the dynamic process of tsunami flooding. So that movies that taken from the helicopter or airplane was selected in this research. Next, the movies are converted into images at regular intervals of time. And adding position information to images (geo-reference), images are imported on the geographic information system (GIS). After that, Inundation limit lines are digitized. In this study, inundation limit lines are created at intervals of around 5 seconds. However, when the image is disturbed by dust etc., images of around 5 seconds are used. Basic information on the tsunami inundation handled in this study is shown in Table 1 and Figure 1.As the result, tsunami inundation process was strongly affected by the location of buildings (Figure 2). On the other hand, the inundation distance declined even where the fields spread. The spatio-temporal variation of the inundation process was quantitatively clarified. Regression analysis was performed with variables of inundation time and inundation distance. As a result, changes in correlation were observed in a certain section. In order to analyze the factors, two regression analyses were conducted. First is the inundation time and elevation as variables. Second is the inundation time and distance from buildings as variables. The building data had acquired the image before the earthquake (April 4, 2010) from Google Earth, and created the building shape data. As a result of each analysis, it became clear that sections where the elevation suddenly changes and the short distance from buildings, overlapped sections where the inundation distance does not extend (Figure 3). These results suggest that it is possible to predict inundation time and distance in other areas if parameters can be acquired.

Coping with Extreme Events: Effect of Different Reservoir Operation Strategies on Flood Inundation Maps

The need of addressing “residual flood risk” associated with structural protection measures, such as levee systems and flood-control reservoirs, has fostered actions aimed at increasing flood risk awareness. Structural measures have lowered risk perception by inducing a false sense of safety. As a result, these structures contribute to an underestimation of the “residual risk”. We analyze the effect of different reservoir operations, such as coping with drought versus coping with flood events, on flood inundation patterns. First, a hydrological model simulates different scenarios, which represent the dam regulation strategies. Each regulation strategy is the combination of an opening of the outlet gate and of the initial water level in the reservoir. Second, the corresponding outputs of the dam in terms of maximum discharge values are estimated. Then, in turn, each output of the dam is used as an upstream boundary condition of a hydraulic model used to simulate the flood propagation and the inundation processes in the river reach. The hydraulic model is thus used to determine the effect, in terms of inundated areas, of each dam regulation scenario. Finally, the ensemble of all flood inundation maps is built to define the areas more prone to be flooded. The test site is the Casanuova dam (Umbria, central Italy) which aims at: (i) mitigating floods occurring at the Chiascio River, one of the main tributaries of Tiber River, while (ii) providing water supply for irrigation. Because of these two competitive interests, the understanding of different scenarios generated by the dam operations offers an unique support to flood mitigation strategies. Results can lead to draw interesting remarks for a wide number of case studies.

Physical Modeling and Numerical Analysis of Tsunami Inundation in a Coastal City

This study conducted a physical model experiment to investigate inundation processes in a complex coastal city model using the Hybrid Tsunami Open Flume in Ujigawa Open Laboratory (HyTOFU). The physical model was constructed at a 1:250 scale as an idealization of the coastal town of Onagawa. Two tsunami waveforms were used, hydraulic bore and solitary wave, which were produced by a pump-type wave generator and a mechanical piston-type wave generator, respectively, at HyTOFU. Tsunami wave generation similar to the 2011 Tohoku earthquake tsunami in Onagawa was successfully reproduced, and the spatial distribution of the tsunami wave propagation and inundation processes on land was clearly observed. A comparison of experimental and numerical models was performed using two-dimensional (2D) and quasi-three-dimensional (Q3D) models. The 2D and Q3D results agreed well with the experimental results in terms of maximum water surface elevations and arrival times for hydraulic bore conditions. For solitary wave trials, the maximum water surface elevations of the 2D results were underestimated, and the arrival times in the numerical models were slower than those in the experimental results. In this study, as a benchmark for the 2011 Tohoku earthquake tsunami, the dataset of tsunami inundation is provided, which will be useful to validate other numerical tsunami models.

Increasing flood risk due to river runoff in the estuarine area during a storm landfall

Unlike inundation from a tsunami, inundation originating from a tropical cyclone is rather complex since it is usually accompanied by torrential rain. Runoff in the vicinity of an estuarine outlet may thus incur additional inundation damage. In this study, a modeling system is proposed that considers the river discharge effect in addition to tides and surges to enhance the modeling accuracy of storm-induced inundation in coastal areas. The hydrodynamic model (Delft3D) and hydrological model (HEC-HMS) were coupled to account for all the flooding drivers, such as tides, storm surges, river discharges, and their interactions. In the coupled model, Delft3D was responsible for tidal and storm-induced surging motions, while HEC-HMS was used to calculate the river discharge at the downstream outlet of basins. Typhoon Maemi, which caused severe inundation damage to the Korean peninsula in 2003, was simulated by the model with a focus on the localized inundation process. The increase in inundation risk caused by river discharge was of particular interest and was assessed through a comparison of two different cases: Case ST (Storm-Tide) and Case STR (Storm-Tide-Riverine flow). The results clearly show that the case considering the rainfall-runoff process in the storm surge simulation outperforms that in which storm surge is not considered. A further detailed investigation of the inundation depth and coverage of both cases revealed several findings. The proposed model is expected to be of great aid in producing the flood hazard mapping with enhanced accuracy.

PROBABILISTIC TSUNAMI HAZARD ASSESSMENT (PTHA) AND PTHA-BASED TSUNAMI SCENARIO AT A PACIFIC COAST OF TOHOKU

When planning tsunami disaster mitigation and designing important infrastructure from the viewpoint of tsunami resistance in coastal areas, the scale and frequency of tsunamis that will arrive at coastal areas in future are important information. On the other hand, there are large uncertainties in predicting future tsunamis, and thus it is difficult to predict a future tsunami correctly. The technology of probabilistic tsunami hazard assessment (PTHA) has been proposed to evaluate the relationship between the height and frequency of tsunamis that will arrive at coastal areas in future. To consider the uncertainties of the prediction in the PTHA, the logic-tree approach is often adopted. In this approach, both epistemic and aleatory uncertainties are considered systematically. The epistemic uncertainties are caused by lack of knowledge and the aleatory uncertainties are variabilities due to natural randomness. In the logic-tree approach, the epistemic uncertainties are expressed by tree branches and the aleatory uncertainties are expressed by the probabilistic density functions of predicted tsunami heights. By carrying out PTHA, we can obtain a hazard curve, which expresses the relationship between the tsunami height and annual frequency of exceedance. Recently, methodologies by which PTHA-based-tsunami-scenarios are determined have been proposed. By using tsunami scenarios, detailed inundation processes and patterns can be evaluated. In this study, we apply the technologies of PTHA to the pacific coast of Tohoku, Japan. Then, we determine PTHA-based tsunami scenarios, that overflow a seawall constructed at the target coast and can be used for the evaluation of inundation processes.

Modelling of flood risks to people and property in a flood diversion zone

Extreme floods often occur in the middle Yangtze River. The Jingjiang flood diversion zone needs to be operated during these events to protect the safety of the levees along the Jingjiang Reach. Therefore, it is important to be able to predict the potential flood risks to people and property in such an area for the purpose of flood management. In this study, an integrated numerical model for estimating the flood risks in a flood diversion zone is proposed, including a module for predicting the 2D hydrodynamic processes of flood inundation in a study area with complex topography, and a special module for estimating the flood risks to people (children and adults) and property (vehicles, buildings, and crops) using newly developed safety criteria. The proposed model was used to predict the flood inundation process and variation in hazard degrees of people and property, based on a hypothetical discharge hydrograph during the operation of the Jingjiang flood diversion zone. The model predictions show high flood loss rates for various flooded objects such as people, vehicles, buildings, and crops, with a mean loss rate for these subjects of 75% after 140 h. This suggests that the operation of a flood diversion zone should be cautiously considered, as it would likely result in a huge loss of people and property. Furthermore, an investigation was conducted into the effects of different roughness coefficients and people stability criteria on the model predictions. The results show that variable Manning’s roughness coefficients need to be used in the hydrodynamic module according to different underlying surface conditions, and a mechanics-based criterion for the stability of people in floodwaters should be adopted to assess the potential hazard degrees.

Disaster emergency response technology based on digitization of reservoir dam

With the help of GIS, Terra Vista and MultiGen Creator platform, this paper achieves the digitalization of high precision dam, reservoir area and flood. Using DEM technology to simulate flood evolution, it analyzes flood inundation process and possible disaster area, and combines material reserve, traffic situation, and possible refuge path, and uses GIS geographic information to seek the best withdrawal. The path provides a scientific analysis way for the scientific decision of dam disaster response.

Impacts of Inundation on Bird Assemblages in Forests in and around a Hydrodam in Terengganu, Malaysia

Despite the increasing numbers of hydrodam worldwide, only a handful of studies evaluated their impacts on biodiversity. Compared to terrestrial animals, birds were thought to be less affected by inundation process, following impoundment. At the Hulu Terengganu Hydroelectric Dam in Peninsular Malaysia, our study compared species assemblages and diversity of birds within the dam area (i.e. the dam reservoir and catchment area) after recent logging and inundation in relation to a nearby forest logged 30 years ago. Using point count and mist-netting techniques, we recorded a total of 64 species (Shannon Index (H’) = 3.827) in the dam area and 91 species (H’=3.99) in historically-logged forests. Insectivore species richness was significantly higher in the historically-logged forests (Mann-Whitney: Z=4.339, N=205, p<0.005). These results indicated that richness and diversity of bird species assemblages appear to decline following recent inundation phase. Nevertheless, the forests in the dam area still harbour charismatic species such as eagles (Family: Accipitridae) and hornbills (Family: Bucerotidae) which suggests that this habitat is relatively important for birds.

Sediment transport modeling of multiple grain sizes for the 2011 Tohoku tsunami on a steep coastal valley of Numanohama, northeast Japan

The grain size distribution of a tsunami deposit may have a correlation with the tsunami inundation process, and further with the tsunami source characteristics. We test this hypothesis using thickness and grain size distribution data of the 2011 Tohoku tsunami deposit in Numanohama coast, Iwate Prefecture, Japan. Here, we build and validate a tsunami sediment transport model that can simulate deposit thickness and grain size distribution. Our numerical model has three layers: parent (bed), deposit (bed), and suspended load layers. The two bed-layers contain information about the grain size distribution. This numerical model can handle a wide range of grain sizes from 0.063 (4ϕ) to 5.657 mm (−2.5ϕ). The grain size distributions at 12 sample points along a 900 m transect from the beach, through a marsh, and up to the inundation limit, are used to validate the tsunami sediment transport model. We adopt a reference tsunami source model that can well reproduce the observed tsunami run-up heights ranging from 16 to 35 m along the steep valley during the 2011 tsunami. The simulated sand thickness distribution along the transect is consistent with the observed thickness ranging from 3 to 23 cm. The computed net erosion and deposition suggest that most of the sand deposit was originated from the near shore. The shapes of the simulated grain size distributions represented by their sorting, skewness, kurtosis, and mean at most of the sample sites are similar to the observations. The differences between the observed and simulated peak of grain size distributions are less than 1ϕ. To evaluate the sensitivity to the tsunami source model, we test five tsunami scenarios which are modified from the reference source model. While the tsunami scenario with 120% of the reference amplitude can also reproduce the thickness and grain size distribution, the scenarios with amplitudes smaller than 80% of the reference or with wave periods shorter than 50% of the reference source model underestimate the thickness and cannot reproduce the grain size distributions. Our simulation results suggest that it is possible to estimate tsunami wave amplitude and wave period from sediment deposit thickness and grain size distribution data.

Tsunami run-up estimation based on a hybrid numerical flume and a parameterization of real topobathymetric profiles

Abstract. Tsunami run-up is a key value to determine when calculating and assessing the tsunami hazard in a tsunami-prone area. Run-up can be accurately calculated by means of numerical models, but these models require high-resolution topobathymetric data, which are not always available, and long computational times. These drawbacks restrict the application of these models to the assessment of small areas. As an alternative method, to address large areas empirical formulae are commonly applied to estimate run-up. These formulae are based on numerical or physical experiments on idealized geometries. In this paper, a new methodology is presented to calculate tsunami hazard at large scales. This methodology determines the tsunami flooding by using a coupled model that combines a nonlinear shallow water model (2D-H) and a volume-of-fluid model (RANS 2D-V) and applies the optimal numerical models in each phase of the tsunami generation–propagation–inundation process. The hybrid model has been widely applied to build a tsunami run-up database (TRD). The aim of this database is to form an interpolation domain with which to estimate the tsunami run-up of new scenarios without running a numerical simulation. The TRD was generated by simulating the propagation of parameterized tsunami waves on real non-scaled profiles. A database and hybrid numerical model were validated using real and synthetic scenarios. The new methodology provides feasible estimations of the tsunami run-up; engineers and scientists can use this methodology to address tsunami hazard at large scales.

THE IMPACT OF RAINFALL VARIATIONS ON FLASH FLOODING IN HAOR AREAS IN BANGLADESH

The north-eastern part of Bangladesh is famous for rice production and fishing. A lot of bawl shaped depressed areas are located in this region which is locally called as haor area. Among seven haor districts Sunamganj has the maximum extent of haors and net cultivable area. The flash flood which is recurrent during April and May is the number one ranked hazard that affects agriculture in Sunamganj severely. Flash flood in 2017 was the most devastated in the recent past. Different researchers predicted that the rainfall during April/May will increase here due to the impact of climate change in future. The objective of present study is to evaluate the impact of rainfalls on inundations owing to flash floods using rainfall runoff inundation model (RRI-model) proposed. Ten rainfall events are prepared for computations of inundation, using reference rainfall in April in 2017, and their sizes normalized by the reference event range from 0.6 to 2.0, respectively. The size level of a flash flood is determined by means of RRI-model by water surface elevation at Sunamganj station in the Surma river and it is translated into return period. The inundation proc ess were computed for each of the specified rainfall events, together with inundation depths in Tahirpur upazilla (sub-district) in Sunamganj district in order to investigate the relation between the sizes of rainfall event, flash flood event and extents of inundation. The computed results suggest that the return periods of the computed flash floods are determined as 3.7,10, —,142.86 years corresponding to the normalized rainfall sizes such as 0.6, 0.9, —, 2.0 and suggest that inundated areas increase with the size of normalized rainfall and increase sharply in the range of rainfall size larger than about 1.1-1.2. Such results are useful to identify and quantify the associated inundated areas due to temporal variation of rainfall which is necessary for disaster preparedness and management.

ASSESSMENT OF FLOODING IN THE DOWNSTREAM AREA OF KIEN GIANG RIVER BASIN, QUANG BINH PROVINCE BASED ON USING THE MATHEMATICAL MODEL AND REMOTE SENSING TECHNIQUE

Floods frequently occur in the central region in general and in Quang Binh province in particular, including the Kien Giang river basin. In recent years, due to the effects of global climate change and socio-economic development, natural disasters and floods are increasing and threatening the lives of people. This affects the socio-economic development of Quang Binh province. This paper presents the results of a study on the flooding and flooding levels of some typical floods in the downstream area of ​​Kien Giang river, Quang Binh province based on the combination of using MIKEFLOOD model with remote sensing. This is one of the modern research methods that are quite useful in simulating, calculating and forecasting natural disasters occurring in coastal estuaries including floods. Combined use of these two methods yielded, quite accurate and similar results in calculating the flood level and inundation in the Kien Giang river basin. The authors have applied the MIKEFLOOD model to simulate the continuous evolution of inundation processes combined with remote sensing technology to compare and verify the calculation results of the model at the occurrence time of typical floods from 1999 up to now in the study area. The results of this article are the basis for warning and suggesting some measures to prevent flooding before the occurrence of heavy rains in Kien Giang river basin.

Tsunami deposits in a super-large wave flume

Understanding the process of sediment transport under tsunami inundation is essential to providing credible information about potential tsunamis from tsunami deposits. In this study, a super-large wave flume 205m long and 3.4m wide was used to investigate the hydraulic process of tsunami inundation and sedimentary features of the resulting tsunami deposit. A uniformly sloping topography (1/50) with a sand dune 0.2m high was built in the flume and the topography change induced by a solitary wave was measured. The maximum wave height at the shoreline was 0.6m and the horizontal velocity reached up to 3.5m/s, resulting in a sediment concentration of up to 5% by volume. The inundation and return flow completely eroded the dune and caused deposition, which showed landward and seaward thinning and fining. The vertical distribution of grain size and density in the inundation flow indicated upward fining and an upward decrease in density, and the deposits showed inverse grading at the base in addition to normal grading. Therefore, the inverse grading was attributed to the depositional process instead of the vertical distribution of grain size in the flow, such as via a traction carpet. The inundation flow was classified into two phases. The first phase flow, which appeared at the front of the inundation flow, was governed by the wave speed at the shoreline. The second phase flow, which occurred near the dune, was controlled by the difference in wave levels in front of and behind the dune. The deposits caused by the first phase flow (near the inundation limit) were constant regardless of the presence of the dune, indicating that the effect of the dune on the deposits was limited in the nearshore region. The deposits near the inundation limit, showing rapid fining and different chemical compositions, were carried by muddy foam floating on the water surface. The sediment supply from offshore to onshore over the dune was small and the erosion of the sand dune accounted for 36% of the onshore deposits. The offshore deposits were mainly caused by wave motion and the contribution of the onshore sediment brought by the return flow was small (24%). However, the return flow had a large effect on the sedimentary structure of the offshore deposits, such as seaward fining. Our results will help to examine the physical processes resulting in the empirically established common sedimentary characteristics of tsunami deposits and will provide a detailed data set to validate sediment transport models used in numerical simulations.

A numerical study of tsunami wave impact and run-up on coastal cliffs using a CIP-based model

Abstract. There is a general lack of understanding of tsunami wave interaction with complex geographies, especially the process of inundation. Numerical simulations are performed to understand the effects of several factors on tsunami wave impact and run-up in the presence of gentle submarine slopes and coastal cliffs, using an in-house code, a constrained interpolation profile (CIP)-based model. The model employs a high-order finite difference method, the CIP method, as the flow solver; utilizes a VOF-type method, the tangent of hyperbola for interface capturing/slope weighting (THINC/SW) scheme, to capture the free surface; and treats the solid boundary by an immersed boundary method. A series of incident waves are arranged to interact with varying coastal geographies. Numerical results are compared with experimental data and good agreement is obtained. The influences of gentle submarine slope, coastal cliff and incident wave height are discussed. It is found that the tsunami amplification factor varying with incident wave is affected by gradient of cliff slope, and the critical value is about 45°. The run-up on a toe-erosion cliff is smaller than that on a normal cliff. The run-up is also related to the length of a gentle submarine slope with a critical value of about 2.292 m in the present model for most cases. The impact pressure on the cliff is extremely large and concentrated, and the backflow effect is non-negligible. Results of our work are highly precise and helpful in inverting tsunami source and forecasting disaster.

Modeling anisotropy in free-surface overland and shallow inundation flows

Regular patterns, which are found in both natural and man-modified environments, are strongly interwoven with free-surface flows. Examples are ridge and slough landscapes, cultivated terrains with ditches and furrows, and urban areas, with many of them characterized by a marked anisotropy. Simulation of overland and shallow inundation flows in these contexts is complex and demanding, especially if very different spatial scales are involved. Anisotropic effects are introduced to cope with two-dimensional shallow water models and, particularly, with the subgrid modeling technique. Application to schematic test cases shows the key role played by anisotropy in shallow flows, and second, that anisotropy can be effectively captured by the subgrid model with low computational effort and preserving mesh-independentness. High-resolution model results are accurately reproduced on coarser meshes using one fiftieth of the original computational elements, with a speed-up of more than 20. The subgrid approach could serve in view of physically based, large-scale modeling of floodplain inundation processes, in irrigation science, and in high-resolution hydrodynamic-hydrological simulations at the basin scale.

An implicit wetting and drying approach for non-hydrostatic baroclinic flows in high aspect ratio domains

A new approach to modelling free surface flows is developed that enables, for the first time, 3D consistent non-hydrostatic baroclinic physics that wets and dries in the large aspect ratio spatial domains that characterise geophysical systems. This is key in the integration of physical models to permit seamless simulation in a single consistent arbitrarily unstructured multiscale and multi-physics dynamical model. A high order continuum representation is achieved through a general Galerkin finite element formulation that guarantees local and global mass conservation, and consistent tracer advection. A flexible spatial discretisation permits conforming domain bounds and a variable spatial resolution, whilst atypical use of fully implicit time integration ensures computational efficiency. Notably this brings the natural inclusion of non-hydrostatic baroclinic physics and a consideration of vertical inertia to flood modelling in the full 3D domain. This has application in improving modelling of inundation processes in geophysical domains, where dynamics proceeds over a large range of horizontal extents relative to vertical resolution, such as in the evolution of a tsunami, or in urban environments containing complex geometric structures at a range of scales.