Surface Seiches Research Articles

Surface Seiche and Wind Set-up on Lake Okeechobee (Florida, USA) During Hurricanes Frances and Jeanne

Hurricanes Frances and Jeanne (HF and HJ) passed over Lake Okeechobee, Fla., in September 2004. Strong winds produced a large surface seiche during both storms. The slope of the water surface reversed itself within 4 hrs as wind direction changed during HF, but shifted in only 2 hrs during HJ. The greatest water level difference was along the lake's north-south (N-S) axis during both storms (2.6 and 3.5 m, respectively). Differences between maximum wind set-up (storm surge) and set-down on the opposite shore indicated that the slope of the water surface was not symmetrical at the height of either storm. Using simple steady-state models, maximum wind set-up was forecast for opposing stations along the lake's N-S axis and compared to observed data and storm surge predictions by the SLOSH model. Steady-state model accuracy was not improved by using averaging periods >15 min in length or by lagging weather and water temperature data behind lake stage. Steady-state models calibrated to the data performed better than uncalibrated models. Prediction errors for maximum wind set-up during HF and HJ by SLOSH were comparable to errors in the steady-state models. While not a substitute for sophisticated hydrodynamic models like SLOSH and LOHM, properly calibrated steady-state models can provide lake managers with reasonable estimates of wind set-up. Future use of simple wind set-up models on Lake Okeechobee will require validation against data from other hurricanes.

Influence of stratification on decaying surface seiche modes

A traditional understanding of external (surface) seiche modes in lakes, bays and coastal seas is that their period depends exclusively on the basin geometry (size, depth) and planetary constants (gravity, Coriolis parameter) and is therefore independent of the water stratification. We show here that this is not the case. In enclosed water bodies such as lakes, in which external seiches are standing waves, their period is weakly dependent on the stratification (on the order of Δρ/ρ), lending support to the traditional understanding. But, in semi-enclosed systems such as bays and coastal seas, from which surface gravity waves can radiate into the open ocean, the external seiche period is a more sensitive function of stratification (on the order of Δρ/ρ). Those seiches also decay over time, as wave radiation gradually takes their energy away.

Surface seiches in lakes of complex geometry

In lakes of small to medium size, the characteristic frequencies of free oscillations of the water surface (seiches) depend only on the basin geometry. In irregularly shaped basins, such as dendritic reservoirs and multibasin lakes, these characteristic frequencies are not easily determined with simple formulas. Clear Lake, a multibasin lake in Northern California, is presented here as a case in point. The signature of the seiches in Clear Lake were only revealed after solving the eigenvalue problem governing the structure and frequency of seiches derived from the linear and frictionless depth‐averaged shallow water equations in a nonrotating frame.

Verification of seiching processes in a large and deep lake (Trichonis, Greece)

A computational analysis of the periods and structure of surface seiches of Lake Trichonis in Greece and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Myrtia, Panetolio and Trichonio is given. The first five theoretical modes are calculated with a finite difference code of tidal equations, which yield the eigenperiodes, co-range and co-tidal lines that are graphically displayed and discussed in detail.Experimental verifications are from recordings taken during spring. Visual observations of the record permit identification of the five lowest order modes, including inter station phase shift. Power spectral analysis of two time series and interstation phase difference and coherence spectra allow the identification of the same five modes. Agreement between the theoretically predicted and the experimentally determined periods was excellent for most of the calculated modes.

Surface Seiches and Internal Kelvin Waves Observed Off Zadar (East Adriatic)

Abstract Two campaigns, comprising the measurements of temperature, salinity, currents and sea level, were performed in the Zadar and Pasman Channels during summer 1994. Basic dynamics, including tidal, wind-driven and residual circulation, are briefly considered here, but the paper concentrates on the surface seiche and internal Kelvin wave analyses and modelling. Surface seiches are found to be excited by strong meteorological disturbances in the late summer of 1994, with a period of approximately 2·2 h and a sea-level and current amplitude of approximately 10 cm and 9 cm s−1, respectively. Internal Kelvin waves, having a period of approximately 4 days and maximum surface currents of approximately 8 cm s−1, appeared during July 1994. The energy loss at the head of the basin, occurring due to the basin bathymetry, is analytically modelled by imposing the radiation condition there, both for the surface seiches and internal Kelvin waves, while the nodal line is enforced at the basin mouth. The modelled periods of surface seiches and internal Kelvin waves are 2·1 h and 94 h, respectively. The currents and sea levels agree fairly well with the observed values. Furthermore, the Defant numerical procedure, which allows for a variable basin bathymetry, gives slightly lower periods (1·9 h for the surface seiches and 91 h for the internal Kelvin waves) and moves the maximum current amplitudes towards the head of the basin in agreement with the observations.

A numerical model for the winter circulation in Lake Trichonis, Greece

Abstract Progress in the understanding and eventual management of lakes depends upon iterative interactions between model-guided measurements and measurement-tested model development. A research example of this progress can be demonstrated by the measurement campaigns that were mounted in Lake Trichonis, in central Greece. Numerical simulations and analytical theories have been tested against currents, surface seiche and temperatures. Simultaneous water gauges, current meters, anemometric stations, thermometers, sediment and water samplers were used for the verification of the model. The agreement between the theoretically predicted and experimentally determined data was satisfactory for most of the verifications. The most significant error was due to atmospheric pressure. The computed surface seiche showed excellent agreement with the observations, even in spectral analysis. The computed currents showed circulation patterns very similar to those measured in the field. The computed temperature distributions throughout the lake were not in good agreement because of incoming water from the bottom.

Internal Surge in Lake Biwa Induced by Strong Winds of a Typhoon

The detailed structure and evolution of current and hydrography after a wind storm, typhoon T9313, is described from an intensive field study. The study was done using current meters deployed at 8 stations, as well as 15 thermistor chains, in the southern part of the North Basin of Lake Biwa in summer of 1993. In the morning of 4 September, strong southerly winds with the maximum speed of more than 20 m ⋅see-1 blew over the lake. After the wind speed peaked, the cold water in the thermocline of the North Basin intruded into the South Basin. This intrusion of cold water was induced by the surface seiche which was generated by the winds of the typhoon. Then a large amplitude internal surge (a steepfronted depression wave on the thermocline) traveled from north to south along the west coast of the North Basin as an internal Kelvin wave. The internal surge shoaled over the southern slope of the North Basin and finally collided against the slope. When the surge shoaled over the slope, a strong jet of over 60 cm⋅s-1 was generated in the lower benthic layer (benthic jet). Assuming the internal surge as a moving internal jump, we explain the mechanism which induced the benthic jet. When the surge collided against the slope, a homogeneous mixed water mass was generated in the thermocline. After the collision, the internal surge was reflected to travel north along the east coast of the North Basin.

Observation and computation of surface seiche in Lake Biwa, Japan

利用水动力学方程对日本琵琶湖表面定振波进行了计算和分析,结果表明其主要周期约为69.5min。另外,利用实测水位资料,采用最大熵谱法进行分析,得到的主要周期约为68min,两者吻合很好。;The periods of seiche oscillation in Lake Biwa, Japan were computed according to the hydrodynamics equations with the main period being about 69.5 minutes. In addition, the real water level data at the Great Bridge Station were analysed by using the maximum entropy method. The periods acquired was about 68 minute. These results coincided with each other.

High-frequency oscillations observed in the Krka Estuary

Abstract Current and temperature data, taken during 1986 and 1987 in the Krka Estuary (east Adriatic coast), are analysed for evidence of high-frequency oscillations. The spectra computed from the data show peaks at 0.006 and 0.022 min−1 (corresponding to periods of 2.8 h and 45 min, respectively). Detailed analysis of the 45-min oscillations in both time and frequency domains reveals that these oscillations occur intermittently. They probably represent internal waves travelling down the estuary. The waves appear to be generated by the interaction of the second-order surface seiches with topography. The system of coupled surface seiches and internal waves may be either of local meteorological origin or externally forced at the mouth of the estuary.

Natural Periods of Seiche in Lake Suwa and Lake Nojiri and its Numerical Model

Natural periods of surface and internal seiche in Lake Suwa and Lake Nojiri are determined using a numerical model and from the field observation data of water temperature and free water level. The finite element technique is applied to the surface seiche and is also extended to the internal seiche.The natural periods computed from the numerical model and those obtained from observation data are almost equal. The natural periods of first mode of the surface seiche in Lake Suwa and Lake Nojiri are about 1350s and 490s respectively, and those of the internal seiche in Lake Nojiri vary from 220 to 270 minutes.

On the generation of lateral internal waves by a surface seiche in a partially mixed estuary

Abstract Dyer (1982) observed internal oscillations in Southampton Water of predominantly 8 and 4 min periods. These were thought to be lateral standing waves generated by the interaction of the first- and second-order surface seiches, respectively, with estuarine topography. The present paper extends the work of Rattray (1960) to model the cross-sectional topography of Southampton Water, and shows that internal waves of the observed periods, wavelengths and amplitudes could indeed have been generated in the manner envisaged, but only near the times of certain internal resonant conditions. In general, about two or three such resonances occur per half tidal cycle, and this is in qualitative agreement with Dyer's observations.

87:6094 On the generation of lateral internal waves by a surface seiche in a partially mixed estuary: New, A.L. and K.R. Dyer, 1987. Estuar. coast. Shelf Sci., 24(4):557–566

87:6094 On the generation of lateral internal waves by a surface seiche in a partially mixed estuary: New, A.L. and K.R. Dyer, 1987. Estuar. coast. Shelf Sci., 24(4):557–566

Surface manifestations of internal oscillations in a highly saline lake (the Dead Sea)1

The manifestation of internal oscillations at the surface of the Dead Sea during summer 1981 is described. During that time the Dead Sea was highly stratified, with a density difference of 1.7 × 10−2 g liter−1 between its two layers. Measurements of lake level (limnograms) show oscillations with periods of internal seiches as confirmed by thermistor‐chain measurements as well as by a numerical model of internal oscillations. Wind measurements exhibit predominantly diurnal and semidiurnal periods. During autumn 1984 the Dead Sea turned over and its layered structure thereby destroyed. In contrast to the measurements of summer 1981 the limnograms for this timespan show only oscillations associated with periods corresponding to surface seiches, but no sign of internal oscillations.

Tests of an extension to internal seiches of Defant's procedure for determination of surface seiche characteristics in real lakes1

The success of A. Defant's method of calculating surface seiche periods and structures in real lakes is well known. To test whether it can be adapted and applied with similar success in studies of internal seiches in stratified lakes, in which density structure is simulated by two homogeneous layers, we compare the predictions of a computerized version of Mortimer's modified Defant procedure against observations of internal seiche motion in eight lake basins and (in three examples) against the results of more elaborate models. The acceptably close agreement inspires confidence that the modified method is useful for practical predictions which, although approximate, described the principal characteristics of the often large water mass displacements and oscillations. Through their influence on mixing and dispersal, those motions profoundly affect the chemical and biological economies of many lakes. To aid in microcomputer and even pocket calculator applications, we set out steps in the calculation in tabular flow‐chart form. A comparable table for surface seiche calculation is added.The procedure is not applicable to large lakes in which effects of the earth's rotation are dominant; but for the two largest basins tested here (Léman and Ness) a modification is introduced to take approximate account of rotation.

Wind‐induced internal seiches in Lake Zurich observed and modeled1

During August and September 1978, 31 current meters and 120 temperature sensors were deployed to record every 10 or 20 min at various depths at 12 moorings (with wind speed and direction at three moorings) in Lake Zurich. We explore here the baroclinic (internal seiche) response to wind impulses, observed as fluctuations in isotherm depth and current speeds. Those fluctuations and their energy spectra are compared with the predictions of two models fitted to basin topography and to the observed average thermal structure: a two‐layered variable‐depth (TVD) model developed by D. J. Schwab, fitted to basin topography and incorporating a two‐dimensional horizontal grid, and C. H. Mortimer’s two‐layered modification of a simpler procedure originally developed for surface seiche calculations by A. Defant.The dominant responses to wind impulses were internal seiches of the first longitudinal mode (average period 44 h). Weaker signals from the second (24 h) and third (17 h) modes were also seen in spectra of temperature and current fluctuations. The models displayed patterns of thermocline displacement and current which, in periodicity and structure, were closely similar to those observed. Predictions of the Defant model were less precise, particularly for current.Founded on linear theory and neglecting the effects of rotation, the models were unable to reproduce two features occasionally seen in the lake motions: clockwise or anticlockwise rotation of current direction; and internal surges arising when storms induced large‐amplitude downstrokes of the thermocline at one basin end or the other. The lake’s internal response was principally dependent on the timing, strength, and duration of the wind impulse, relative to and interacting with internal seiche motions already in progress.

INTERFACIAL SEICHE IN COMPOSITE CLOSED WATER MASS

The thermocline oscillation observed in the stratified water mass, such as, deep lakes, reservoirs and land-locked bays, are sometimes generated by the resurging effects after the stop of the wind set-up motion. The oscillation characteristics of the density interface become much complex in the case of complicated geometry, e. g. reservoirs with several branches, bays composed of many inlets, etc. The authors developed the theory for the, interfacial seiche motion in the two-layered and multi-composed water mass by applying the theory of the surface seiche. Additionally, a laboratory experiment was performed by using the model tank composed of four channel elements with rectangular cross sections. Satisfactory agreements between the theory and experiment were obtained.

Horizontal diffusivity in a small, ice‐covered lake1

A horizontal eddy diffusivity (Kx) value of 0.47 cm2 · s‒1 was calculated from tracer cloud expansion data from a previous experiment in which a 24Na solution was introduced as a point source under ice cover in Tub Lake, Wisconsin. This Kx value, the first from a lake where surface wind stress was not a factor, is lower than any lake Kx previously reported. The constancy of Kx found for the 48‐h period of monitoring implied mixing eddy lengths <1.6 m, the diffusion cloud size found at first monitoring. Surface seiches or convective flows appeared to be probable sources of mixing energy.

Strömungsdynamische Untersuchungen im Zürich- und im Luganersee Ein Vergleich von Feldmessungen mit Resultaten theoretischer Modelle

Density distribution and temperature and current data which were measured in Lake of Zurich and Lake of Lugano in two summer field programs are scrutinized and interpreted by means of hydrodynamic models. Barotropic surface seiches and baroclinic internal seiches are studied using a one-and two-layer model and measured data permit identification of the respective resonant periods. Wind induced barotropic and baroclinic circulation dynamics is also studied by means of three-dimensional finite difference models of the hydrodynamic viscous equations on the rotating earth. In general the predictions of these models agree favorably with observed data.

Mixing caused by lateral internal seiching within a partially mixed estuary

Abstract The salinity fluctuations at an STD near the halocline in Southampton Water have been spectrally analysed. Mixing is shown to commence at a layer Richardson number of about 20. The predominant energy inputs have periods of 7–9 and 3·5–4·5 min. These motions arise from lateral internal seiching and it is considered that they are produced by interaction of the surface seiche with the shallow side of the estuary. The wavelengths of the standing wave are calculated to be about 120 and 60 m respectively, and these compare well with echo-sounding surveys of the elevation of the halocline.

The surface seiches of Lake of Lugano

A computational analysis of the periods and structure of surface seiches of the southern basin of Lake of Lugano and its experimental verification from three simultaneous water gauge recordings, mounted along the shores in Agno, Morcote and Riva S. Vitale, is given. The first five theoretical modes are calculated with a finite element code of the tidal equations; it yields the eigenperiods and co-range and co-tidal lines, which are graphically displayed and discussed in detail.