Hydrodynamic Modeling

Hydrodynamic models are tools for simulating water movement and material transport in ocean, riverine, and lacustrine environments as acted upon by forces. As water current moves, it can cary with it materials, sediments, pollutants, and dissolved substances. Hydrodynamic models describe how current moves in space at different monsoon seasons, weather conditions, and tidal fluctuations. In order to set-up a hydrodynamic model of an actual water body, the physical space/volume of water is discretized into grids which which will contain information on bathymetry, water levels, velocities, water quality and others. External forcing factors such as tides, wind, river discharges, solar radiation, and others, define the distribution of various hydrodynamic parameters (water levels, velocities, etc.) in time and space within the model domain. These models are technically mathematical representation of real-world systems and their accuracy is determined by the availability and reliability of input data, the stability and accuracy of the modeling platform used, and the suitability of modelling processes and parameters selected.

Hydrodynamic models are important in characterizing water movement in relation to climate, tide, freshwater flux and other forcing mechanisms. Information on hydrodynamics are essential for the design of coastal infrastructures, climate change and sea-level rise impact assessment, sediment transport, water quality modeling analysis, resource-use and conservation strategies (reclamation, dredging, waste management, etc.), and rehabilitation planning, among others. Hydrodynamic models also serve as effective decision-support tools for identifying resource-use and conservation strategies. What-if scenarios can be simulated to better understand how events like oil spills or solid waste would be dispersed and flushed out of a water body, how storm surges develop over coastal areas, or how wind waves can erode and transport materials from/to beaches.

Inputs of a model depend on the type of environment being modeled and the surrounding environments that affect the water body. For example, the set of information needed to set up lake hydrodynamics slightly differs from that of coastal hydrodynamics. Manila Bay’s hydrodynamics is affected mainly by forces of tides, wind, river discharges, and solar radiation. It is also hydraulically connected to Laguna Lake (which has its own catchment area) that it exchages both water quantity and quality with through the Pasig River. To capture the complete water balance of the integrated Manila Bay-Pasig-River-Laguna Lake modeling domain therefore, there is a need to account for the river discharges coming from the surrounding watersheds. This was accomplished using hydrologic modelling (see concepts here: http://bit.ly/HydrologicModelling). In hydrodynamic modeling, it is important to capture the morphology (shape) and morphometry (measurement of shape), meteorology (weather), and hydrology (discharge characteristics of surrounding rivers) of the modeled systems. Weather conditions affect the temperature and density of water and consequently influence its movement and mixing potential. Moreover, the moisture exchange between the water body and the atmosphere (evaporation and precipitation) should also be considered for a complete water balance representation.

The main objective of hydrodynamic modeling is to characterize the movement of water in a water body. For instance, water level maps can describe water level fluctuations as influenced by difference forcing factors (tides, discharges, winds, surge). On the other hand, current velocity maps describe the dirrection of current flow and can illustrate how near-bottom currents can be affected by tides and how surface water movements can be influenced by seasonal wind patterns. In a system like Manila Bay, that is hydraulically connected to Laguna Lake through the Pasig River, the exchanges of freshwater and saltwater between the two water bodies can be assessed using density and salinity maps. With such hydrodynamic result, the saltwater intrusion dynamics in the lake can be described in both time and space in more detail (see http://bit.ly/PMLDB1_PasigRiver). Moreover, hydrodynamic models can depict through scenario analysis how coastal development and reclamation can affect the overall flow of water and the fate and transport of materials within a water body. Indeed, hydrodynamic models serve as effective decision-support tools and their outputs provide a great deal of support in conservation planning, rehabilitation program development and implementation, and ultimately, in science-based policy-making where different stakeholders may participate and contribute.