Ali Dastgheib

Sand bypassing and shoreline evolution near coastal structure, comparing analytical solution and XBeach numerical modelling

ABSTRACT Ab Razak, M.S., Dastgheib, A., Roelvink, D. 2013. Sand bypassing and shoreline evolution near coastal structure comparing analytical solution and XBeach numerical modelling The present study is aimed at comparing the numerical and analytical estimation of the shoreline near an idealized groyne structure. Moreover, the impact of sand bypassing on the accretion at the updrift coast calculated by analytical Pelnard solution is compared against the XBeach numerical model. The application of the XBeach model shows some promising results. Prior to bypassing, the resulting shoreline pattern from numerical (XBeach) model resembled the Pelnard model with slight differences. The circulation of wave driven-currents due to diffraction is responsible for the formation of a sand wedge at the downdrift side which cause the coastline to prograde. Despite the fact that the bypassing volume simulated by XBeach is smaller than the analytical solution, the shoreline pattern seems to reasonably follow the Pelnard model. Nevertheless, the use of process based numerical model like XBeach, has been shown to be useful in this type of research. This moreover proves the capability of XBeach model of predicting shoreline evolution and clarifying the mechanism of the natural bypassing process which cannot be achieved by analytical models.

Analysis of Possible Actions to Manage the Longitudinal Changes of Water Salinity in a Tidal River

In previous studies we have ascertained that inflows and seawater intrusion in the Shatt al-Arab River (SAR) are two key physical factors behind fluctuating and sharply escalating salinities observed in recent years. Such levels require a series of countermeasures and investigative studies to translate physical factors into a salinity dynamics model to understand the problem and its impact as these factors vary in location, time and quantity. A one-dimensional hydrodynamic and salt intrusion numerical model was applied to simulate the complex salinity regime in the SAR based on hourly time-series data for the year 2014. The model was used to analyse the impact of different management scenarios on salinity under different conditions. The results show a high correlation between seawater intrusion and river discharge. Increased use of water upstream and local water withdrawals along the SAR will increase seawater intrusion and salinity concentrations. Improving the quantity and quality of the upstream freshwater sources could reduce salinity levels. Discharging the drainage water into the river could be used to counteract the salt intrusion, considering that its location affects both the salinity distribution and extent. A scenario analysis based on a numerical model constructed for the longitudinal salinity variation associated with different sources in a tidal regime, can efficiently screen alternative water management strategies.