Aspects of Summertime and Wintertime Hydrodynamics of Lake Champlain

Manley, T. O., Hunkins, K. L., Saylor, J. H., Miller, G. S. & Manley, P. L. (1999) Aspects of Summertime and Wintertime Hydrodynamics of Lake Champlain, in Lake Champlain in Transition: From Research Toward Restoration (eds T. O. Manley and P. L. Manley), American Geophysical Union, Washington, D. C.

Two and a half years of temperature and current observations obtained from longterm moorings within the central region of Lake Champlain were analyzed for wintertime and summertime circulation patterns. During wintertime periods, currents were consistently weaker than summertime observations. Water columns at individual sites were nearly isothermal with coldest temperatures approaching 0.5° C, however horizontal gradients were apparent. From early Spring to late Fall, the hydrodynamics of the Main Lake were dominated by the presence of a uninodal internal seiche. Spectral analysis showed the dominance of atmospherically controlled oscillations (7.1 and 10.7 days) and basin dominated modes (4.3, 2.7 and 1.8 days). A shifting of dominant periods inter- as well as intra-annually can be accounted for by varying conditions of the metalimnion as well as atmospheric forcing. The internal seiche also possessed a rotary component. Bottom currents tend to be preferentially aligned with bottom topography. Nonlinear aspects of the internal seiche in the form of internal surges and bores (gravity currents) were observed. Wave heights exceeding 10 m showed pronounced asymmetry of wave shape. Highly nonlinear events exceeding 60 m have been observed. Sudden increases in hypolimnetic temperature appear to be tied to these events. Whether these deep temperature shifts were a direct result of surface outcropping of the hypolimnion and/or significant internal mixing at the shoaling ends of the lake has yet to be determined. Near-bottom velocities of 30–50 cm/s have direct consequences for toxic sediment resuspension and dispersal.