Hydrodynamic Modelling of a complex marine system: Application for the Inland Sea Khor AlAdaid Qatar

Physical Oceanography is the study of the conditions and processes that govern the movement of ocean water, and its interaction with coastal, seafloor, and atmospheric boundaries. Understanding these processes helps to provide deeper insight into various ecological and physical phenomena that affect the earth's near-surface systems. Furthermore, consideration of physical oceanography is critical for sustainable development and effective urban planning, as most human settlements are along coastlines and thus they experience the combined effects of marine weather, waves, tides, and coastal currents. To help understand the response of marine systems to physical forcing, such as changes in temperature, wind, and humidity, computational eco-hydrological models are created. These models seek to mimic the real environment by using both general and site-specific data related to the hydrodynamics and ecological / physical phenomena, which are then combined with mathematical principles to describe a functional ecosystem. Most modeling software are designed to simulate flow in “normal marine” systems, i.e. relatively deep systems with near-normal seawater salinities. Khor Al-Adaid (including the Inland Sea), Qatar, however, presents a globally unique marine system, as it is aerially extensive, very shallow (mostly less than 5 m), and hyper-saline. It is surrounded by Eocene rock outcrops, sandy sabkhas, and large mobile dunes which migrate into the Inland Sea water. This marine embayment can be divided into three main areas including: (i) an inner lagoon less than 2 m in depth but 53.5 km2 in extent, with salinity reaching 90 ppt in the summer season, (ii) a 74 km2 outer lagoon up to 18 m in depth with typical salinities of 60 ppt in the summer season, and (iii) a linear channel that is about 10 km long, less saline (∼45 ppt), and it is connected to the Arabian Gulf. The varying range in average salinity, depth, and temperature between these three areas, makes the Inland Sea an intricate system, and thus the hydrodynamics of this system cannot be characterized using existing commercial modeling software, which typically handle more homogenous systems. This work presents a proposed workflow that will be developed through iteration and testing of existing software, which will account for the modeling challenges faced with a complex heterogeneous system like the Inland Sea. As a starting point, GEMSS (Generalized Environmental Modeling System for Surface waters) will be used, as it provides a set of hydrodynamic, sediment transport and water quality modules, and has been used and calibrated previously in various locations around the Qatari coast to date. Comprehensive field data will be collected and processed to help understand the flow dynamics of the system. Measurements will be made using current meters, ADCPs (Acoustic Doppler Current Profiler), tidal gauges as well as temperature and salinity meters deployed throughout the study area. The data will then be used to build and calibrate the model to assess whether the system can be handled as a whole using GEMSS, or if the areas should be subdivided and treated separately. The findings of this work will act as a stepping stone to help understand current flow dynamics in the system and how these flows shape the salinity profiles and physical structures. In turn, this will offer insight into the important habitat features currently observed in the system, and add better understanding as to how these may be altered naturally and potentially by anthropogenic means.