External gravity oscillations in Lake Onega

Abstract

Abstract. Lake Onega is located in the southern part of Karelia, in the north-west of Russia. We report data taken by various limnigraphs and current meters and isolate, by spectral analysis, the most conspicuous barotropic periods of these signals. The analysis that follows is based on the linearized shallow-water equations, that are solved for the free oscillations and thus identify the eigenperiods and corresponding mode structures for this lake. Computational results are presented for a finite difference representation for these surface-seiche equations applied to the entire Lake Onega including its bays. The grid consists of quadratic elements of 1000 m side length corresponding to 9344 active cells. The emerging matrix eigenvalue problem exceeds the storage and compuational capacity of standard PCs or workstations and thus requires use of the approximate Lanczos procedure to isolate the first ten eigenperiods and corresponding mode structures of the barotropic seiches, lying between 12.1 and 2.2 h. Comparison of computational results and inferences from the water level and current-meter records, disclose satisfactory agreement between theory and observation.

Seiche modes in multi‐armed lakes

“…particular arms or reaches of the lake (e.g., Rudnev et al 1995;Carter and Lane 1996;Kirillin et al 2014). As seen in the present study, in some cases this could be a consequence of a decoupled mode; however, Fig.…”

“…Surface (barotropic) seiches do not contribute significantly to mass transport, but are studied for their role in re-suspension of bottom sediments (Chung et al 2009), shoreline erosion (Kirillin et al 2014), coastal structure safety (Barberopoulou 2008), and estimation of lake level (e.g., to backcalculate lake inflows; Carter and Lane 1996). Despite the broad analytical work on the subjects of both barotropic and baroclinic seiching for lakes of simple geometry (e.g., Chrystal 1905;Longuet-Higgins 1952;Defant 1960), the study of more complex geometries has required both numerical techniques and detailed field studies (e.g., Rudnev et al 1995;Kirillin et al 2014).…”

“…Studies of multi‐armed lakes show considerable spatial variation in the amplitudes of the deflection mode‐shapes throughout the domain of the lake (e.g., Lake Te Anau (Carter and Lane ), and Nechako Reservoir (Imam ; Imam et al, unpubl.)) which, in some cases, appears as mode‐shapes that have deflections localized to individual arms or bays of a lake (e.g., Lake Onega, Rudnev et al ), or a response in which some arms are seemingly decoupled for some modes (e.g., Lake Como, Guyennon et al ). Numerical equation solvers and hydrodynamic models can make accurate representations of mode‐shapes and periods in multi‐armed lakes; nonetheless, a estimation of modal periods may be desired to explain some observed behavior in a lake without having to go through with the procedure of applying a numerical model (e.g., Laval et al ).…”

“…Numerical equation solvers and hydrodynamic models can make accurate representations of mode‐shapes and periods in multi‐armed lakes; nonetheless, a estimation of modal periods may be desired to explain some observed behavior in a lake without having to go through with the procedure of applying a numerical model (e.g., Laval et al ). In this case, researchers may opt to ignore the role of secondary arms, and consider only the longest continuous extent of a lake so that the theories developed for simple basins may be applied (Caloi and Spadea ; Malinina and Solntseva , as cited in Rudnev et al ; Laval et al ; Imam et al ). It is, however, unclear whether such an assumption is valid, particularly for higher modes (Rudnev et al ).…”

Surface seiches in Flathead Lake

“…(1) (Rueda and Schladow, 2002;Hutter et al, 1982), may strongly increase amplitudes of nearshore water level oscillations (Hollan et al, 1980;Rudnev et al, 1995), or give rise to local rotating modes (Rao and Schwab, 1976). These seiche effects are especially important in large lakes, gulfs, and seas, where a local increase in seiche amplitudes can threaten populated areas with flooding (Hollan et al, 1980;Kulikov and Medvedev, 2013).…”