Simulation of storm surge associated with cyclones land falling Bangladesh coast

This paper describes the basic features of storm surge phenomena using Indian Institute of Technology (IIT) model (installed at Bangladesh Meteorological Department) for the Bay of Bengal. To capture the storm surge scenarios, after the entrance of the cyclone into the northern part of the Bay of Bengal, high resolution IIT model has been used. The analysis area is from 18° N to 23° N and 83.5° E to 94.5° E. Bathymetric data required for the model has been taken from Royal Admiralty Table and ETOPO2 dataset. In this paper, various scenarios of storm surges are developed and then investigated for varying input parameter values. This paper also examines the time-series of surges at the fixed landfall point by using the data of three severe cyclonic storms when the cyclone approaches the landfall point.

Temporal Characteristics of Debris Flow Surges

Debris flow is one of the most destructive geomorphological events in mountainous watersheds, which usually appears in the form of successive surge waves as observed all over the world. In particular, debris flows in the Jiangjia Gully in southwest China have displayed a great variety of surge phenomena; each debris flow event contains tens or hundreds of separate surges originating from different sources. Therefore, the surge sequence of an event must encode the information of debris flow developing. The unmanned aerial vehicle photos provide an overview of debris flow sources, showing the different potentials of the debris flow and surge sequences present various patterns responding to the rainfall events. Then the variety of rainfalls and material sources determine the diversity of surge sequence. Using time series analysis to the surge discharge sequences, we calculate the Hurst exponent, the autocorrelation function, and the power spectrum exponent and find that all the sequences commonly share the property of long-term memory and these parameters are correlated in an exponential form, with values depending on rainfall patterns. Moreover, all events show a gross trend of discharge decay, despite the local rainfall process, which implies the intrinsic nature of the surge sequence as a systematic behavior of watershed. It is expected that these findings are heuristic for establishing mechanisms of debris flow initiation and evolution in a watershed.

Numerical Study of the Process of Salt Water Inflow to the Don Mouth from the Taganrog Bay

Purpose. Numerical study based on the model example is aimed at examining the process of the salt water inflow to the Stary Don sleeve from the Taganrog Bay due to the wind water surge. Methods and Results. Complex mathematical model of the flow and salt distribution in the open riverbed is described. The section of the River Don, consisting of the Stary Don sleeve and a part of the main channel was considered. Salt is delivered through the host reservoir – the Taganrog Bay. The model is described by the system of Saint-Venant equations and the convection-diffusion equation. The problem is solved by the finite-difference methods. The results of the numerically studied influence of the sea surface level in the Taganrog Bay both on the flow nature in the Don Delta area and the degree of salt penetration upstream of the river are obtained. It was numerically established that the flow rate did not significantly affect salt concentration in the Don main channel. Conclusions. The computational experiments showed that the decisive factor in the process of the salt water inflow to the Don Delta from the Taganrog Bay consisted in the sea level significant increase resulting from extreme wind surges; and the preceding runoffs enhanced this effect even greater. The represented model gives an idea of the general trend in the process of the Don Delta possible salinization as a result of the surge phenomena.

Numerical Study of the Process of Salt Water Inflow to the Don Mouth from the Taganrog Bay

Purpose. Numerical study based on the model example is aimed at examining the process of the salt water inflow to the Stary Don sleeve from the Taganrog Bay due to the wind water surge. Methods and Results. Complex mathematical model of the flow and salt distribution in the open riverbed is described. The section of the River Don, consisting of the Stary Don sleeve and a part of the main channel was considered. Salt is delivered through the host reservoir – the Taganrog Bay. The model is described by the system of Saint-Venant equations and the convection-diffusion equation. The problem is solved by the finite-difference methods. The results of the numerically studied influence of the sea surface level in the Taganrog Bay both on the flow nature in the Don Delta area and the degree of salt penetration upstream of the river are obtained. It was numerically established that the flow rate did not significantly affect salt concentration in the Don main channel. Conclusions. The computational experiments showed that the decisive factor in the process of the salt water inflow to the Don Delta from the Taganrog Bay consisted in the sea level significant increase resulting from extreme wind surges; and the preceding runoffs enhanced this effect even greater. The represented model gives an idea of the general trend in the process of the Don Delta possible salinization as a result of the surge phenomena

Granular effect on debris flow rheology

<p>Debris flow is characterized by the multi-disperse grain composition and intergranular collision and friction, but the granular effects on rheology are often reduced to the volumetric concentration of solid (C<sub>v</sub>), almost ignoring the specific grain size distribution (GSD). In this study, small debris flows occurring in a tributary of Jiangjia Gully were taken as the material sources for rheology experiments. From the real flows we selected slurries with different C<sub>v</sub> and maximum grain sizes (D<sub>m</sub>) for rheological tests under shearing rate up to 40 (s<sup>-</sup><sup>1</sup>), which is usually the real rate for debris flows in natural conditions. The results indicate that the flows follow the Herschel-Bulkley (HB) rheology, with randomly changing consistency coefficient and relatively constant exponent of 0.45 on average. Only at high shear rate will the flow exhibit Bingham behavior. The HB rheology also reveals shear thinning behavior in surge phenomena observed in the field. Shear-thinning behavior is revealed by the viscosity-shear rate relationship: η<sub>a</sub>=pγ<sup>q</sup>, with the exponent (thinning index) dependent on shear rate. This greatly concerns the surge phenomena observed in field. Moreover, both the yield stress and the effective viscosity are found to be perfectly related to the scaling GSD parameters in power-law and exponential form, with nearly constant exponents independent of the shear rate(Figure 1). The rheology properties can be calculated from their relationships to GSD parameters (μ, D<sub>c</sub>), which in turn can be used to infer the HB rheology for the concerned flows and then build the dynamical equations(Figure 2). This implies the presence of some interlock between the fine and coarse grains. Finally the rheology model (general in HB form) can be completely determined by the GSD parameters. This study has for the first time proposed quantitative formulas for rheology incorporating GSD parameters, which is helpful for more accurate dynamic analysis of debris flow.</p>

Revealing the Surge Phenomena Contribution of the Heavy Metals Inflow to the River Don Delta

Purpose. The aim of the study is to evaluate the surge phenomena effect on the heavy metals inflow to the Don Delta based on the archival and expedition data analysis, as well as using mathematical modeling. Methods and Results. To achieve the purpose, the Hydrologic Engineering Center River Analysis System (HEC-RAS) mathematical hydrodynamic model and the original model of the heavy metal compounds’ transfer and transformation in the Don Delta, developed by S. V. Berdnikov were applied. The models included the irregular grid for the Don Delta region with the average resolution 100 × 100 m. The grid cells were grouped into the compartments according to the hydrological principle. Twelve scenarios of dynamics of the suspended solids, and the dissolved and suspended forms of Ni, Cu, Pb and Cd were calculated for the surges of various intensity under the conditions of variable water content and seasonal dynamics of near-water vegetation. In accordance with the scenarios, the graphs showing the changes in the suspended matter content and accumulation, and the maps of the deposited substance distribution resulted from the surges in the delta were constructed. During two days the calculations for which include the surges of varying repeatability and the variable water content, about 0.3–3 t of nickel compounds, 0.1–1.8 t of copper compounds, 0.2–1.8 t of lead compounds and 0.01–0.04 t of cadmium ones deposit in Don. The obtained results made it possible to reveal two regions where the increased accumulation of the precipitated suspended matter and the heightened concentrations of the heavy metal dissolved forms were observed: the interfluve of the Don shipping channel, and the systems of the Kalancha and Kuterma river branches. Conclusions. As for their influence upon formation of the flow of the heavy metal suspended forms, the surge phenomena surpass the river flow. The suspended matter concentration in the Taganrog Bay waters during the surges is the governing factor for the heavy metals inflow to the Don Delta. At the same time, the regions characterized by the highest suspended solids sedimentation and the increased concentrations of the heavy metal dissolved forms are the closest to the Taganrog Bay areas covered by reed vegetation.