Mean Water Level Research Articles

Long term water level and surface temperature changes in the lagoons of the southern and eastern Baltic

The paper studies variations in the water level and surface temperature of coastal lagoons along the southern and south-eastern shores of the Baltic Sea: the Curonian Lagoon, Vistula Lagoon, and Darss-Zingst Bodden Chain. Linear regressions for annual mean water level variations showed a positive trend in water level, but at different rates. The highest rate during the period between 1961–2008 was recorded for the Curonian and Vistula lagoons (~ 4mm year−1), the lowest for the DarssZingst Bodden Chain (approximately ~ 1mm year−1). The warming trend of the mean surface water temperature in the lagoons was 0.03°C year−1 in the period 1961–2008. Moreover, the variability in annual water temperature and sea level as well as their extreme values have increased most dramatically since the 1980s.

Nearshore circulation in a tropical fringing reef system

[1] The role of waves, tide, and wind on the circulation of a fringing reef system was investigated using data collected during a 6 week field experiment in a section of Ningaloo Reef off Western Australia. The high correlation observed between current velocities and wave height throughout the system revealed the dominant role wave breaking plays in driving the overall reef-lagoon circulation, whereas the modulation of the currents at tidal frequencies suggested that the wave-driven currents responded to tidal variations in the mean water level over the reef. The influence of the various forcing mechanisms on the current field was investigated for both high- and low-frequency bands. Wave breaking was found to be the dominant forcing mechanism for the low-frequency (subtidal) currents, with the subtidal flow pattern consisting of a cross-reef flow over the reef, alongshore flow in the lagoon, and water exiting back to the ocean through the main channel. The tides controlled the high-frequency current variability via two mechanisms: one associated with the ebb-flood cycle of the tides and the second associated with tidal modulations of the wave-driven currents. Wind-forcing and buoyancy effects were both found to be negligible in driving the circulation and flushing of the system during the observation period. Flushing time scale estimates varied from as low as 2 h to more than a day for the wide range of observed incident wave heights. The results suggest that the circulation of Ningaloo Reef will be strongly influenced by even a small mean sea level rise.

SEASONAL PATTERNS OF RIVER CONNECTIVITY AND SALTWATER INTRUSION IN TIDAL FRESHWATER FORESTED WETLANDS

ABSTRACTHydrology can be difficult to interpret in tidal freshwater forested wetlands because of several influencing factors including river discharge, tidal stage, local precipitation, evapotranspiration, groundwater and prevailing winds. River discharge and tidal stage are considered the primary factors affecting these wetlands and both vary on a seasonal basis and have potential implications for wetland saltwater intrusion. We examined the hydrologic patterns of tidal freshwater swamps along the lower reach (20 km) of the Apalachicola River system in northwest Florida, USA. Water level recorders were installed in five wetlands along this reach and recorded ground and surface water levels at 15‐min intervals from December 2006 to April 2009 (non‐continuously). Seasonal trends related to flooding frequency and duration were compared to long term (2000–2008) records of creek and river salinities measured in the tidal freshwater forested zone. Tidal freshwater swamps tended to maintain a narrow water level range (often ±20 cm of the ground surface) except during high river flows (>680 cms or 24 000 cfs) when levels increased 1 to 2 m above ground and dampened tidal effects. All tidal forested wetlands had the highest mean water levels and most days tidally pulsed during the Jul–Oct season which coincided with peak river/creek salinities and low river‐flows associated with drought conditions. We explored the implications for the timing of salt water intrusion in these swamps and potential changes related to sea level rise and water management in the Apalachicola River drainage basin. Copyright © 2011 John Wiley & Sons, Ltd.

APPLICATION OF A SIMPLE HYDRODYNAMIC MODEL TO ESTUARY ENTRANCE

Tidal inlets which link a tidal basin to the sea via a constricted entrance are common on the south-east Australian coast. Closure, or even significant constriction, raises water levels but restricts tidal range within the basin, while open entrances provide regular and significant tidal exchange with the ocean. A rapid assessment procedure with minimal data requirements has been shown to be informative for monitoring and a useful component of any Decision Support System set up as part of a management structure. Such a system is presented in this paper. It is based on one permanent water level gauge inside the inlet plus the use of a simple, first-order hydrodynamic model to relate the tide range, mean water level and river flow to the inlet cross sectional area. The method is tested against data from the
 Snowy River Estuary in south-eastern Australia but would be suitable over a range of estuaries. In addition, the framework presented can also provide a mechanism to explore conditions over the range of expected data, thus allowing better selection of model schematization and runs in estuarine systems where the use of 2 or 3D modeling can be justified.

MODELING OF THE REYNOLDS STRESS IN THE BURSTING LAYER AFFECTED BY TYPHOON

When large and intensive water surface displacements are caused by developed wind waves due to a typhoon, it is impossible in the Eulerian coordinate system to measure water particle velocities continuously in a domain between the wave trough level and the mean water level. Consequently, the domain between the wave trough level and the mean water level becomes a void zone where the Reynolds stress cannot be described. By treating the sea surface boundary layer including the void zone as a bursting layer, we modeled the Reynolds stress in the bursting layer. Validity of that modeling was verified by performing comparisons with experimentally obtained results.

LABORATORY EXPERIMENT ON CROSS-SHORE BARRIER SPIT EVOLUTION BY STORM DYNAMICS

Every year there are many severe storms occurring around the world, in general, and in Japan, in particular. The occurrence of storms is expected to increase because of the global warming effects. An increasing wave height together with a rising mean water level during a storm create a high possibility for waves to overtop the beach crest causing a lot of sediment to be eroded to offshore areas or deposited in the inland direction. The study of the barrier island response to storms has therefore become very important in terms of sediment transport and beach morphology change, as well as damage to nearshore structures due to runup overwash and inundation overwash. However, changes in the beach profile and prevailing sediment transport mechanisms during a real event are difficult to obtain. Thus, laboratory studies are necessary to conduct. This study presents a laboratory experiment on the impact of storms on a sandy barrier islands. The main aim is to investigate the entire barrier island (or sand spit) response due to storm conditions considering the increase in water level due to storm surge. Also, further development of an analytical model for barrier profile change caused by runup overwash is presented and obtained results overall captured order-of-magnitude barrier face retreat and volume changes after the storm.

The influence of tidal forcing on groundwater flow and nutrient exchange in a salt marsh-dominated estuary

Data from salt marshes in the U.S. Southeast show that long-term variations in mean water level (MWL) correlate strongly with salt marsh productivity and porewater salinity. Here we used numerical models of tidally-driven groundwater flow to assess the effect of variations in tidal amplitude and MWL on porewater exchange between salt marshes and tidal creeks. We modeled homogeneous and layered stratigraphy and compared flat and sloped topography for the marsh surface. Results are consistent with field observations and showed that increases in tidal amplitude increased groundwater flushing, particularly when increasing the tidal amplitude caused the marsh platform to be inundated at high tide. Increases in MWL caused groundwater flushing to increase if that rise caused greater areas of the marsh to be inundated at high tide. Once the marsh was fully inundated at high tide, further increases in MWL caused groundwater flushing to decrease. Results suggest that small increases in MWL associated with sea level rise could increase nutrient export significantly in marshes with elevations that are equilibrated near mean high water, but rising sea level could decrease the export of nutrients to, and thus fertility in, estuaries adjacent to marshes that are equilibrated lower in the tidal frame. Likewise, macrotidal estuaries are predicted to be subject to much larger groundwater and nutrient exchange than similar microtidal estuaries. We speculate that the early stages of rising relative sea level may significantly impact water quality in estuaries that are not river-dominated by raising the discharge of nutrients from coastal wetlands.

IMPROVEMENT OF BOTTOM BOUNDARY LAYERS MODELING UNDER INTERACTIONS OF WAVE AND WAVE-INDUCED CURRENT

The bottom boundary layer characteristics beneath waves transforming on a natural beach are specifically affected both by wave and wave-induced current. This study presents an improved approach for coastal bottom boundary layers modeling under interactions of wave and wave-induced current. The improvement is achieved by formulating the mean horizontal pressure gradient term in the boundary layer equation with wave parameters and mean water level. This formulation represents the balance between the wave excess momentum flux gradient and the hydrostatic pressure gradient in a spatially transforming wave field, accounting for the effect of the wave-induced cross-shore current. Model is validated with experimental data for normally incident shoaling wave over a sloping bed. Calculated results agree well with data for instantaneous velocity profiles, wave oscillating amplitudes and mean velocity profiles. In particular, model reasonably reproduces the observed local onshore mean flow near the bottom beneath shoaling wave. It is revealed that the proposed formulation of the mean horizontal pressure gradient plays an important role in bottom boundary layer modeling under wave transforming over an variable near-shore bathymetry, and that the present model can be conveniently and reliably coupled with a sediment transport model to study coastal processes in engineering applications.

Study on Wave Height and Mean Water Level around Rip Current

Mean water level around the rip channel in Uradome Beach in Tottori was measured by the stereo image analysis of the two video images. It is found that the mean sea level along the rip current was slightly higher than those in the region along each side of the rip current. A series of numerical simulations of wave-induced currents and mean sea levels were also carried out on the bottom profile measured at Uradome Beach. The numerical results show that rip current come up through the place where the wave height is low that just corresponds to the place where the mean water level is higher than the surrounding region.

Tidal rhythmites in a mixed-energy, macrotidal estuarine channel, Gomso Bay, west coast of Korea

Well-developed tidal rhythmites are documented from the intertidal point bar of sinuous tidal channel in Gomso Bay, west coast of Korea. Associated with inclined heterolithic stratification, rhythmites constitute the upper part of fining-upward succession formed by the lateral migration of a point bar. Occurring between mean sea-level and mean high water level, rhythmites commonly overlie rhythmic climbing-ripple cross-laminations. Various rhythmicities are registered in laminae thicknesses, which reflect hierarchical tidal cycles ranging from semidiurnal to monthly tidal cycles. Inferred neap–spring tidal cycle (half-synodic) thins upwardly with a proportionately reduced number of preserved laminae in the cycle. Such vertical organization of rhythmites seems to reflect decreased accommodation space through deposition. Tidal rhythmites exhibit longitudinal variation within fluvial–tidal transition with best developed ones formed in a highly meandering tidal channel, where the influence of offshore waves is minimal due to confined channel morphology that is characterized by low energy level in association with high water turbidity. Comparison of spectral peaks between modern and simulated rhythmites further substantiates that tidal rhythmites can serve as a reliable indicator of paleotide, paleoelevation and paleogeography of mixed energy, tide-dominated estuaries.

A New Lagrangian Asymptotic Solution for Gravity–Capillary Waves in Water of Finite Depth

A third-order Lagrangian asymptotic solution is derived for gravity–capillary waves in water of finite depth. The explicit parametric solution gives the trajectory of a water particle and the wave kinematics for Lagrangian points above the mean water level, and in a water column. The water particle orbits and mass transport velocity as functions of the surface tension are obtained. Some remarkable trajectories may contain one or multiple sub-loops for steep waves and large surface tension. Overall, an increase in surface tension tends to increase the motions of surface particles including the relative horizontal distance travelled by a particle as well as the time-averaged drift velocity

Long-Term Evolution of Columbia River Tides

A 170 km tidal channel connects the lower Columbia River ports of Portland and Vancouver to the Pacific Ocean. An increasing incidence of low water levels during summer and fall sometimes limits the draft of ships using the channel and can delay transits. Reduced spring freshet water levels have also decreased shallow-water habitat for juvenile salmon. Records from Tongue Point (km-30, 1925-date), and Vancouver (km-175, 1902-date) were used to analyze historic changes. Mean water levels (MWL) at Vancouver have dropped ∼0.3–1.5 m since 1902, depending on flow. Lower low water (LLW) at the lowest river flows has decreased ∼0.4–0.5 m since 1940. Vancouver LLW has dropped more than MWL and higher high water (HHW), increasing tidal range. Tides in the Columbia and many other river ports are evolving because of a combination of changing ocean tides and local alterations, including both harbor development and river-flow modification. Assessments of climate change impacts on harbors need to consider both factors.

Laboratory experiment on rip current circulations over a moveable bed: Drifter measurements

This study describes a laboratory experiment on rip current circulations over a moveable bed. Rip current characteristics over eight contrasting nature‐like beach morphologies are investigated. The seabed varied from reasonably alongshore uniform to strongly alongshore nonuniform with crescentic patterns and bar‐rip morphologies, representative of a full morphological down‐state sequence. The same offshore shore‐normal waves were generated by the wavemaker for the eight situations with the same mean water level to study the sensitivity of rip current characteristics as a function of the beach morphology only. In each case, a 30 to 60 min video run was used to track a large number of drifters released within the surf zone. Results show the presence of classic rip current patterns with counterrotating cells and a relatively narrow offshore‐directed jet varying from shore‐normal to strongly skewed. Wave‐driven circulations were strongly unstable. Computed standard deviations of flow intensity and direction provide high‐resolution information on the spatial variability of rip current instabilities. Highly pulsating and weakly directionally variable offshore‐directed flow is observed in the rip neck for well‐developed bar‐rip morphologies that turns into a weakly pulsating and highly directional variable rip current flow with decreasing beach alongshore nonuniformity. Proposing a definition of rip current intensity based on the rip current circulation geometry, rip current intensity was found to linearly increase with increasing measure of beach alongshore nonuniformity within both the low‐energy and moderate‐energy rip current regimes. To date, our laboratory experiment provides the first extensive quantitative rip current information during a full down‐state sequence for a given wave condition.

Modeling wave–current bottom boundary layers beneath shoaling and breaking waves

The boundary layer characteristics beneath waves transforming on a natural beach are affected by both waves and wave-induced currents, and their predictability is more difficult and challenging than for those observed over a seabed of uniform depth. In this research, a first-order boundary layer model is developed to investigate the characteristics of bottom boundary layers in a wave–current coexisting environment beneath shoaling and breaking waves. The main difference between the present modeling approach and previous methods is in the mathematical formulation for the mean horizontal pressure gradient term in the governing equations for the cross-shore wave-induced currents. This term is obtained from the wave-averaged momentum equation, and its magnitude depends on the balance between the wave excess momentum flux gradient and the hydrostatic pressure gradient due to spatial variations in the wave field of propagating waves and mean water level fluctuations. A turbulence closure scheme is used with a modified low Reynolds number k-e model. The model was validated with two published experimental datasets for normally incident shoaling and breaking waves over a sloping seabed. For shoaling waves, model results agree well with data for the instantaneous velocity profiles, oscillatory wave amplitudes, and mean velocity profiles. For breaking waves, a good agreement is obtained between model and data for the vertical distribution of mean shear stress. In particular, the model reproduced the local onshore mean flow near the bottom beneath shoaling waves, and the vertically decreasing pattern of mean shear stress beneath breaking waves. These successful demonstrations for wave–current bottom boundary layers are attributed to a novel formulation of the mean pressure gradient incorporated in the present model. The proposed new formulation plays an important role in modeling the boundary layer characteristics beneath shoaling and breaking waves, and ensuring that the present model is applicable to nearshore sediment transport and morphology evolution.

On the role of natural water level fluctuation in structuring littoral benthic macroinvertebrate community composition in lakes

We used traditional hydrologic endpoints and extracted novel water‐level fluctuation (WLF) characteristics through principal components analysis (PCA), to determine the relationship between WLF and rocky littoral benthic macroinvertebrate (BMI) richness in 16 boreal lakes. Yearly WLF amplitude (maximum minus minimum water levels) ranged from 35.9 cm to 157.5 cm. Using PCA we derived a new variable D80‐D210 (31 March minus 01 August) as a surrogate for change in mean water level and potential habitat squeeze (loss). Analyses of BMI richness with several physicochemical variables, including water quality (8), habitat variability (4), lake and basin morphology (6), land classification (28), water temperature (8), hydrology (9), and PCA axes (10) resulted in only three significant relationships. We found a classic species‐area relationship, as BMI richness increases with increasing lake area (r2 = 0.38linear, r2 = 0.69unimodal). Similarly, as littoral slope increases macroinvertebrate richness decreases (r2 = 0.32linear). Most importantly, lower water levels, quantified using D80‐D210, have higher macroinvertebrate richness (r2 = 0.38linear). Together these results suggest that a habitat squeeze in littoral areas is the direct result of lower mean water levels and that relatively small changes in natural WLF can be associated with changes in BMI communities.

Currents induced by waves in the surf zone and the pollutant transport analysis

As a long-term hydrodynamic phenomenon induced by waves, the currents dominate the pollutant transport in the shoaling and surf zones. The present study was focused on the analysis of the cross-shore currents induced by waves and the pollutant transport. The wave parameters were obtained by solving one phase-averaged wave model including wave shoaling and breaking in the surf zone. The effect of the breaking wave rollers in the surf zone was considered by specifying an additional boundary condition on the mean water level (MWL). We introduced a formula for the vertical varied wave radiation stress into the hydrodynamic model. Furtherly, we simulated and analyzed the pollutant transport in the domain for different pollutant release position.

Statistical characteristics of long waves nearshore

The random long wave runup on a beach of constant slope is studied in the framework of the rigorous solutions of the nonlinear shallow water theory. These solutions are used for calculation of the statistical characteristics of the vertical displacement of the moving shoreline and its horizontal velocity. It is shown that probability characteristics of the runup heights and extreme values of the shoreline velocity coincide in the linear and nonlinear theory. If the incident wave is represented by a narrow-band Gaussian process, the runup height is described by a Rayleigh distribution. The significant runup height can also be found within the linear theory of long wave shoaling and runup. Wave nonlinearity nearshore does not affect the Gaussian probability distribution of the velocity of the moving shoreline. However the vertical displacement of the moving shoreline becomes non-Gaussian due to the wave nonlinearity. Its statistical moments are calculated analytically. It is shown that the mean water level increases (setup), the skewness is always positive and kurtosis is positive for weak amplitude waves and negative for strongly nonlinear waves. The probability of the wave breaking is also calculated and conditions of validity of the analytical theory are discussed. The spectral and statistical characteristics of the moving shoreline are studied in detail. It is shown that the probability of coastal floods grows with an increase in the nonlinearity. Randomness of the wave field nearshore leads to an increase in the wave spectrum width.

Dynamics of the Mackenzie River plume on the inner Beaufort shelf during an open water period in summer

The oceanographic conditions of the Mackenzie River plume in the Arctic Ocean were examined during a 12-day period in August 2007. Field observations in the river channel and the delta region (2–6 m depth), ship-based observations on the shelf and satellite observations of sea surface temperatures indicate that movements of plume density fronts cause changes in water temperatures of over 10 C over a few days. We used a 1D model to compare the strength of stratification versus surface wind stress, and a 3D numerical model to simulate the plume motions under forcing from the river flows, local wind and water level variations from tides and wind-driven surge. The results indicate that the coastal region is stratified with a ∼2 m thick surface plume even in water depths of 3–4 m, resulting in strong vertical variation of horizontal currents. Moderate easterly winds of 5–10 m/s are sufficient to induce offshore transport of the surface plume and onshore transport of the deeper shelf water, leading to large fluctuations in temperature and salinity in the coastal region. This study examined a period of offshore transport and mean water level set-down, and indicates the rapid response of the plume to wind over the shallow delta.

Lagrangian experiment and solution for irrotational finite-amplitude progressive gravity waves at uniform depth

This study investigates the theory for predicting Lagrangian properties including particle orbit, Lagrangian mean level, Lagrangian wave frequency, mass transport velocity, wave profile, velocity distribution and wave pressure in progressive gravity water waves at uniform depth. A series of laboratory experiments are performed to measure the trajectories of particles and the wave pressure. Asymptotic solutions up to fifth order that describe irrotational finite amplitude progressive gravity water waves are derived in completely Lagrangian coordinates. The analytical Lagrangian solution that is uniformly valid satisfies the irrotational condition, the dynamic boundary condition and the zero pressure at the free surface. The explicit fifth-order parametric solution highlights the trajectory of a water particle and the wave kinematics above the mean water level and within a vertical water column, which were calculated previously by an approximation method using an Eulerian approach. Mass transport up to fourth order associated with a particle displacement can now be obtained directly in Lagrangian form. In particular, the Lagrangian wave frequency and the Lagrangian mean level of particle motion can also be obtained, which are different from those in an Eulerian description. By comparing the present fifth-order asymptotic solution with data from laboratory experiments, it is found that theoretical results show good agreement with experimental data.

A numerical model of wave overtopping on seadikes

This paper describes the development of a numerical model for wave overtopping on seadikes. The model is based on the flux-conservative form of the nonlinear shallow water equations (NLSW) solved with a high order total variation diminishing (TVD), Roe-type scheme. The goal is to reliably predict the hydrodynamics of wave overtopping on the dike crest and along the inner slope, necessary for the breach modelling of seadikes. Besides the mean overtopping rate, the capability of simulating individual overtopping events is also required. It is shown theoretically that the effect of wave breaking through the drastic motion of surface rollers in the surfzone is not sufficiently described by the conventional nonlinear shallow water equations, neglecting wave setup from the mean water level and thus markedly reducing the model predictive capacity for wave overtopping. This is significantly improved by including an additional source term associated with the roller energy dissipation in the depth-averaged momentum equation. The developed model has been validated against four existing laboratory datasets of wave overtopping on dikes. The first two sets are to validate the roller term performance in improving the model prediction of wave overtopping of breaking waves. The last two sets are to test the model performance under more complex but realistic hydraulic and slope geometric conditions. The results confirm the merit of the supplemented roller term and also demonstrate that the model is robust and reliable for the prediction of wave overtopping on seadikes.