Addressing Design Issues of an Orthogonal Unstructured Grid Using the Grid Generator JANET Demonstrated on the Delaware Estuary

Concentrated efforts over the past 50 years have dramatically improved the water quality of the Delaware Bay Estuary. From conditions that saw part of the estuary being "dead", the system has improved to a level where a significant amount of fauna and flora has reinstated itself; in fact, many water quality parameters reach state and federal standards. Yet, the diversity and sheer volume of discharges that enter the estuary continue to pose a challenge for regulators and dischargers alike to achieve the stipulated water quality objectives. Typically, numerical models assist in determining current conditions and assessing what-if-scenarios. The Delaware Bay has a very complex geometry that combines fjord-like areas with very narrow stream segments, resulting in vastly different flow regimes. In addition, it is used heavily by the dense agglomeration of population and industry, all of which result in very different and sometimes contradicting and competing water quality objectives. Consequently, the numerical models used for the Bay need to be able to respond to the imposed complexity of tasks by being able to map the governing physics and associated processes appropriately on the scales and directions required. The UnTRIM module (Unstructured TRIM), an enhancement of the models comprising the TRIM family, is capable solving the equations of motion in all three dimensions on an unstructured grid. As such, it is ideally suited to map out the highly irregular geometry of the bay including all of its tributaries, capturing all processes in the horizontal and vertical directions. Because of its efficiency and speed in solving the governing equations, the model can afford to use a very fine meshing pattern further enhancing the accuracy of the mapping. This paper focuses on the development of a high resolution unstructured orthogonal grid for the Delaware Bay estuary that is mostly driven by the requirements of the pollutant fate and transport scenarios (those are quite different if compared to the needs resulting from the computation of the hydrodynamics only ) using a program package called JANET.