Water movement and mixing are driven by the effects of wind and tide on coastal lagoons. The basic hydrodynamics of coastal systems are well represented by physics-based simulation models of various kinds. A number of two- and three-dimensional (2D and 3D) models now exist (both research tools and commercially available products) which can adequately represent wind-induced wave patterns and currents, tidal exchanges and circulation, and changes in surface elevations due to tides and winds. (For an introduction to a variety of models, see www.estuary-guide.net/toolbox or www.smig.usgs.gov; models by Delft Hydraulics at www.wldelft.nl and DHI www.dhigroup.com/) Input data required are basic meteorological data: wind speed and direction, plus solar insolation, and a detailed knowledge of the morphometry and bathymetry of the lagoon in question. Based on the conservation of mass and momentum and various turbulence closure schemes, it is possible to adequately model and predict both velocity fields and turbulent diffusion in the water column. Calibration and validation data are obtained from in situ current meters and pressure sensors. Bottom stress, sediment resuspension, and wave-induced erosion can also be represented. It is thus possible to model the effects of various climate and engineering scenarios, everything from sea level rise to construction projects of various kinds. These models are widely used to develop environmental impact statements (EIS) for major projects and to manage major dredging projects around the world. Only some of these models are capable of long-term predictions of water balance and of water residence times. Such predictions require careful analysis of long-term meteorological records and good predictive models of inflows and evaporation. Nevertheless such models also exist.
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Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.