ABSTRACT
This chapter focuses on distinguishing when longitudinal mixing in reservoirs and lakes might influence the choice of modeling approaches. It covers important mixed layer and eddy-diffusivity approaches. The chapter also covers two-dimensional laterally averaged models of typical reservoirs that follow one-dimensional models. One mass balance equation is solved for each water quality constituent of interest. Outflow measurements, like inflows, are often quite accurate, particularly measurements at flood control outlets or through hydropower generators. Evaporation is primarily controlled by meteorological conditions, but the nature of the water surface affects evaporation to a limited degree. A variety of groundwater hydraulics models could be used to estimate seepage or infiltration. There are several methods available for solving the continuity equation and accomplishing reservoir routing, including the mass-curve method and the storage-indication method. Laterally averaged two-dimensional models of lakes and reservoirs simulate water quality changes in the longitudinal and vertical directions.
