Bathymetry, stratification, and internal seiche structure

Internal seiches play a significant role in a broad range of physical, chem ical, and biological processes in lakes. A detailed assessment of the impac t of seiching requires an understanding of seiche structure, which is deter mined by bathymetry and stratification. In this study, internal seiche solu tions are evaluated for arbitrary bathymetry and continuous stratification using a two-dimensional numerical model. Formulated in terms of a stream fu nction, the model produces a finite set of linear internal wave eigenmodes and allows the computation of the complete velocity field (over a grid) ass ociated with each seiche mode. Several idealized configurations of continuo us stratification and variable bathymetry are used to explore the effect of nonuniform systems on internal wave structure. In particular, we focus on bed velocity distribution and the resulting potential impact on scalar flux es, sediment transport, and internal wave damping. Model results are also c ompared to thermistor chain data collected in the Upper Mystic Lake (UML, W inchester, Massachusetts). Using an idealized description of the UML bathym etry and density profiles which emulate the seasonal variation of stratific ation in the lake, the evolution of bed velocities during the autumnal brea kdown in stratification is assessed, providing insight into the fate of the contaminants entering the lake.