Major flood events occurred in the Arda River region in the last decades with great economic, social and environmental effects. A specific software package has been developed for the simulation of the flood runoff and routing process of the transboundary Arda River basin. The software package is taking into account the existence of the three cascade Bulgarian reservoirs aiming to flood protection and power optimization. Inflow estimations for duration of five days ahead and initial water levels at the three reservoirs are imported at the beginning of the simulation. The management tool includes all the alternative operation modes of hydropower plants, water released from spillways, and river and reservoir flow characteristics in order to optimize the total system (power generation and flooding costs) during the flood event. The developed software is also an efficient tool for the establishment of a flood warning system.
11This study investigates the long-term capacity of the North Aegean coastal systems to transport and store 12 conservative pollutants that originate from the Black Sea. Emphasis is placed on modeling the dispersion and
Abstract:Flooding is a natural disaster that damages infrastructure, properties, and may even cause loss of life. Major floods occur in the Arda river basin, which is shared between Greece and Bulgaria in Southeastern Europe. A flood warning system can sufficiently minimize adverse effects by helping to create a more successful and well-organized response plan. This paper presents an extensive numerical simulation of flood hydrograph routing between levees of the downstream section of the Arda river for floods with return periods from 2 to 10,000 years, using the one-dimensional software HEC-RAS. The main objective is to calculate the inundation areas, travel times of flood waves, water depths, water levels, flow velocities, and overflow volumes by simulating the hydraulic behavior of the Arda river outside its mountain watershed, where it flows through agricultural plane land with very mild slope. The great importance of the water level at the confluence of the Arda and Evros rivers (downstream boundary condition) has been pointed out for the regions near the confluence because the flow is the subcritical type. A significant finding of this work is the determination of the upper limit of the peak discharge hydrograph entering from the Arda to the Evros river to prevent the flooding of the Evros river. This finding is very important for the management of the flood flows of the Evros river, which is a major river with a complicated river system.
Gravity or density currents constitute a wide class of flows that are generated and maintained due to the density difference between two or even more fluids. The density difference between two fluids, usually arises from corresponding differences in temperature or salinity. However, this density difference can also arise by the presence of suspended sediment particles. Such particle-laden flows, in the case of sediment-laden water that enters a water basin, are classified into three major categories according to their density difference with the ambient fluid: (a) hypopycnal currents, when the density of the sediment-laden water is lower than that of the receiving water basin, (b) homopycnal currents, when the density of the sediment-laden water is almost equal to the density of the receiving water basin and (c) hyperpycnal currents, when the density of the sediment-laden water is greater than that of the receiving water basin. The most common example of such particulate currents, is a type of currents that are usually formed at river outflows into the sea, lakes or reservoirs. During floods, the suspended sediment concentration of river waters rises to a great extent. Therefore, when the sediment-laden river discharges into the water of a receiving basin, it plunges underneath the free surface forming a hyperpycnal plume that continuous to flow along the bottom of the basin. This hyperpycnal plume is also known as turbidity current. Turbidity currents can travel remarkable distances along the bottom of the sea, lakes or reservoirs, transferring, eroding and depositing large amounts of suspended sediment particles. Therefore, the study and understanding of such complex and rare phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into the ocean or into lakes and reservoirs. Turbidity currents are very difficult to be observed and studied in the field, due to their rare and unexpected occurrence nature as they are usually formed during flood river discharges. Therefore, field investigations are usually limited to the study of the deposits originating from turbidity currents, aiming to identify various depositional and erosional elements such as lobes, levees and subaqueous channels. Scaled laboratory experiments constitute a widely used alternative method for simulating and studying the dynamics as well as the erosional and depositional characteristics of turbidity currents, providing valuable and detailed results. However, laboratory experiments are usually limited in the study of small-scale turbidity currents. Moreover, the installation, maintenance and operation of the required experimental set-ups, demands a lot of time and money. On the other hand, mathematical and numerical models when properly designed and tested against field or laboratory data, can constitute a quite promising tool for understanding and predicting the hydrodynamics of three-dimensional turbidity currents as well as their erosional and depositional characteristics. T...
During floods, the density of river water usually increases due to the increase in the concentration of the suspended sediment that the river carries, causing the river to plunge underneath the free surface of a receiving water basin and form a turbidity current that continues to flow along the bottom. The study and understanding of such complex and rare phenomena is of great importance, as they constitute one of the major mechanisms for suspended sediment transport from rivers into the ocean, lakes or reservoirs. In the present paper a previously tested and verified numerical model [1] is applied in laboratory scale numerical experiments of continuous, high density turbidity currents. The turbidity currents are produced by the steady discharge of fresh water -suspended sediment mixtures, into an inclined channel which is connected at its downstream end to a wide horizontal tank. Both, channel and tank are initially filled with fresh water. This configuration serves as a simplified experimental analog of natural, hyperpycnal turbidity currents that are formed at river outflows in the sea, lakes or reservoirs and usually travel within subaqueous canyon-fan complexes. The main aim is to investigate the exact qualitative and quantitative effect of fundamental, flow controlling parameters in the hydrodynamic and depositional characteristics of continuous, high density turbidity currents.According to the authors' best knowledge, the present paper constitutes the first attempt in the literature, where the isolated effects of each individual controlling parameter as well as their relative importance on the hydrodynamic characteristics of continuous, high-density turbidity currents are quantitatively evaluated in detail. The numerical model used, is based on a multiphase modification of the Reynolds Averaged Navier-Stokes equations (RANS). For turbulence closure the Renormalizationgroup (RNG) k-ε model is applied, which is an enhanced version of the widely used standard k-ε model.
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