Hydrodynamics and mass transport are fundamental to the study of water quality in all waterbodies. Besides the complex chemistry, physics and biology of the water quality constituent under consideration, the transport as a result of the carrier fluid is an integral part of temperature and water quality analyses. The distribution of temperature and water quality constituents within a water body can be modeled only to the detail with which the time varying flow field is known. In modern studies of water quality, it is increasingly common to include the application of hydrodynamic models as an integral component of the model application. The hydrodynamic models are then used to "drive" models of water quality, providing information used to predict the movement of water quality constituents through the constituent transport equation.The hydrodynamic equations are based upon conservation of water mass and momentum. The water quality transport equations are based upon conservation of constituent mass and heat. An additional equation of state is used to relate the water density to salinity, temperature, and suspended solids that can affect momentum transfer. Typical assumptions of the flow field are related to the dimensionality of the system in space (one, two or three-dimensions), whether the flow field is dynamic or steady-state, and the 4-1 Energy Production and Reservoir Water Quality Downloaded from ascelibrary.org by New York University on 02/03/15.