Showing papers on "Waves and shallow water published in 2000"

Global Weak Solutions for a Shallow Water Equation

Abstract: We show the existence and uniqueness of global weak solutions for an equation describing the motion of waves at the free surface of shallow water under the influence of gravity.

Large-Scale Dynamical Fields Associated with Convectively Coupled Equatorial Waves

Abstract: Convectively coupled equatorial waves, as previously detected in studies of wavenumber-frequency spectra of tropical clouds, are studied in more detail. Composite dynamical structures of the waves are obtained using linear regression between selectively filtered satellite-observed outgoing longwave radiation (OLR) data, and various fields from a global reanalysis dataset. The selective filtering of the OLR was designed to isolate the convective variations contributing to spectral peaks that lie along the equatorial wave dispersion curves for equivalent depths in the range of 12–50 m. The waves studied are the Kelvin, n = 1 equatorial Rossby (ER), mixed Rossby–gravity, n = 0 eastward inertio–gravity, n = 1 westward inertio–gravity (WIG), and n = 2 WIG waves. The horizontal structures of the dynamical fields associated with the waves are all generally consistent with those calculated from inviscid equatorial β-plane shallow water theory. In the vertical, there are statistically significant structur...

Do Shallow-water Habitats Function as Refugia for Juvenile Fishes?☆

Abstract: The role of shallow salt marsh creeks as refuges for juvenile fish is unclear and recent investigations have produced conflicting results. Using gill nets, this study examined the distribution of large piscivorous fish in a range of shallow and deep water environments in a temperate southern African estuary. Results indicated that intertidal creeks, along with adjacent shallow water habitats, were not utilized by a number of piscivorous fish species which were common in the deeper estuarine channel environment. This study provides support for the hypothesis that shallow estuarine areas may provide refugia for fishes vulnerable to predation.

Tsunami features of solid block underwater landslides

Abstract: Near-field and far-field wave features generated by solid block underwater landslides are described qualitatively and quantitatively. The characteristic time of landslide motion and maximum near-field wave amplitude suffice to scale many of these water wave features. Criteria are provided to determine if water waves generated by underwater landslides propagate as deepwater or shallow water waves. Estimates of the dominant far-field wavelength are provided for both cases. A precise location is given for the beginning of far-field wave propagation for deepwater waves. Weakly nonlinear and dispersive effects of shallow water wave propagation are examined. Around 5% of solid block maximum kinetic energy is converted into wave energy.

Fish Assemblage Structure of the Shallow Ocean Surf-Zone on the Eastern Shore of Virginia Barrier Islands

Abstract: This study provides an in-depth description of the fishes in the shallow surf-zone (<0·4 m), a little-studied micro-habitat of the ocean surf. Fish assemblages were examined with respect to three temporal cycles (seasonal, diel and tidal) and at both large and small spatial scales. Sampling was conducted at the Virginia barrier islands using an 8 m bag seine dragged parallel to the beach in water with an average depth of 0·2 m. The fish assemblage was relatively species poor, in fact, there were only two year-round residents, Membras martinica (rough silverside) and Mugil curema (white mullet). Three species, M. martinica, Trachinotus carolinus (Florida pompano) and Menticirrhus littoralis (gulf kingfish), comprised 94% of all species captured. Both fish species richness and total abundance peaked in the late summer and were lowest in the winter. Multidimensional scaling analysis failed to identify a distinct nighttime fish assemblage. However, univariate analyses found there was a significant increase in species richness at night, due to an influx of predatory adult fishes. Further, significantly more species were collected at high than low tide. Higher species richness and total fish abundance occurred in the shallow water (<0·4 m) of runnels, low wave energy habitats on the backside of small sand bars. The increased richness and abundance suggests a small-scale movement of fishes parallel to the beach face as fishes seek sheltered runnel habitats. This study quantifies the observation that many fishes do utilize the shallow surf-zone, perhaps to minimize predator encounters and/or take advantage of an under-utilized intertidal food source.

Functional significance of bone ballastin in the evolution of buoyancy control strategies by aquatic tetrapods

Abstract: The primary function of pachyostosis, pachyosteo‐sclerosis, and osteosclerosis may be to act as ballast, not so much (as previously suggested) to neutralise the buoyancy of existing lungs, but to allow enlargement of the lungs. Enlarged lungs cause an animal to lose buoyancy more rapidly with depth. They also provide a larger oxygen store. These features are useful for slow swimmers and shallow divers, such as feeders on benthic plants and invertebrates. Examples are sirenians, primitive sauropterygians ("not‐hosaurs"), placodonts, and the sea otter Enhydra. These last two show convergent evolution of adaptations to feeding on hard‐shelled invertebrate prey in shallow water. Mesosaurids are problematical. Bone ballast uses body mass and volume less efficiently than other buoyancy control strategies. Theoretical analysis predicts that bone ballast should not occur in semiaquatic forms, fast swimmers or deep divers. It does not usually occur in such organisms. Marine iguanas of the Galapagos, desmostylians,...

Spatial resolution of time-reversal arrays in shallow water

Abstract: A series of time-reversal experiments was performed in shallow water including a range-dependent slope environment. Time-reversal arrays implemented with center frequencies of 445 and 3500 Hz achieved sharp focal regions up to ranges of 30 and 13 km, respectively in 110–130-m shallow water. In this paper, resolution expressions are derived using an image method to describe the focal sizes achieved with time-reversal arrays in various ocean environments. Analysis for the measured data indicates that the focal size approaches the diffraction limit of an array for given waveguide conditions, i.e., waveguide geometry and attenuation. The measured focal size has implications for the maximum achievable resolution of linear matched-field processing which is a computational implementation of the time-reversal process.

The distribution of Fe in the Australian sector of the Southern Ocean

Abstract: The vertical profiles of labile Fe in seawater in the Australian sector of the Southern Ocean (50–65°S along 140°E) were obtained in the austral spring 1994/1995 by concentration with 8-hydroxyquinoline immobilized fluoride containing metal alkoxide glass (MAF-8HQ) followed by determination with chemiluminescence on board. While the concentrations of Fe were low in the surface water column (0.14±0.12 nM, n=97 for 0–100 m) and increased in deep water at all stations, the profiles varied depending on the latitude. The Fe concentrations in intermediate and deep water were 0.30±0.12 (n=36 for 500–2000 m) between the Antarctic Front (AF) and Antarctic Divergence (AD), and steeply increased south of the AD. The high Fe region (<1.5 nM) extended northwards along the continental slope and coincided with the Antarctic Bottom Water. Another Fe maximum in deep water (∼1.2 nM) was located on the north side of the Pacific Antarctic Ridge. The Fe concentrations showed a minimum (∼0.3 nM) at 3000 m depth at 62°S, which was almost coincident with the maximum of SiO2 (∼125 μM) in the Lower Circumpolar Deep Water. There were some patchy Fe maximums in shallow water between the AF and AD, which did not coincide with the maximums of PO4 and NO3 in the Upper Circumpolar Deep Water. These results indicate that the distribution of Fe is nutrient-like but strongly influenced by local sources and water circulation. The Fe : PO4 ratios in the surface water column (<3×10−4) were lower than the critical value for a phytoplankton bloom (1×10−3) proposed by de Baar et al. (1990, Marine Ecology Progress Series 65, 105–122). Although the concentrations of Fe did not correlate with those of chlorophyll a, they positively correlated with the indices of primary productivity (growth rate, productivity by simulated in situ method and monthly integrated net community production). It seems that phytoplankton suffered Fe stress and that Fe was a limiting factor of the primary production. However, it is likely that there were some co-limiting factors, such as grazing at the ice edge and depletion of SiO2 and critical-depth/mixed-depth relationship in the Permanently Open Ocean Zone and Polar Front Zone.

Energy of Water Waves Induced by Submarine Landslides

Abstract: —Water waves generated by submarine landslides may constitute a serious hazard for coastal population and environment. These masses may be giant, as documented by several examples in recent history and by numerous geological traces of paleo-events. A theoretical investigation on wave generation and wave energy is performed here by using a model that is based on some simplifying assumptions. The landslide is treated as a rigid body moving underwater according to a prescribed velocity function. Water waves are governed by the shallow-water wave equations, where water velocity is constant through the water layer and vertical velocity is negligibly small. Geometrically simple basins are considered with either constant depth or constant slope, since attention is focused on the fundamental characteristics of the generation process. Analytical 1-D solutions as well as 1-D and 2-D numerical results obtained by means of a finite-element model are used to gain understanding of the energy transfer from a moving body to the water. From the 1-D examples, it is found that if slide duration is sufficiently long, water usually gains energy in the form of waves until a saturation point is reached, when body motion is no longer capable of producing a net transfer of energy from the rigid body to water. Finite-duration motions of a body moving at constant speed along a flat ocean floor can be used as canonical examples, since bottom slopes cannot significantly change the generated wave pattern. Typically, two trough-crest systems are developed that travel in opposite directions, with the leading crest in the direction of the slide and the leading trough toward the other direction. The amplitude of the former is generally higher, with amplitude controlled by the Froude number (ratio of body velocity to long waves phase celerity) and wavelength dictated by landslide length. Generation and propagation of 2-D cases show a more complicated pattern, since lateral radiation plays an important role. Some of the features present in the 1-D models are observed in 2-D wavefields, however substantial differences arise. The most significant difference is that no energy saturation takes place in 2-D, since the body transfers energy to the water as long as it moves.

A Method for Measuring Vertical Accretion, Elevation, and Compaction of Soft, Shallow-Water Sediments

Abstract: High-resolution measures of vertical accretion, elevation, and compaction of shallow-water sediments are fundamental to understanding the processes that control elevation change and the mechanisms of progradation (e.g., development of mudflats and intertidal wetlands) in coastal systems. Yet, measurements of elevation by traditional survey methods often are of low accuracy because of the compressible nature of the substrates. Nor do they provide measures of vertical accretion or sediment compaction. This paper evaluates the use in shallow-water systems of an approach designed to measure these variables in vegetated wetlands. The approach employs simultaneous measures of elevation from temporary benchmarks using a sedimentation-erosion table (SET) and vertical accretion from marker horizons with sediment cores collected with a cryogenic coring apparatus. The measures are made with a level of resolution sufficient to distinguish between the influence of surface and subsurface processes on elevation, thus providing quantitative estimates of shallow subsidence. The SET-marker horizon approach was evaluated on a developing splay created by an artificial crevasse of a distributary in the Mississippi River delta. The approach provided high-resolution measures of vertical accretion (48.3 ± 2.0 cm) and elevation (36.7 ± 1.6 cm) over a 4-year period, with the difference between the two indicating the amount of shallow subsidence. In addition, by laying new marker horizons in later years, the approach provided rates not only of shallow subsidence (3.9 ± 0.5 cm y-1) but also compaction of newly deposited sediments (2.1 ± 0.6 cm y-1) and compaction of underlying sediments (1.8 ± 0.20 cm y-1) over a two-year period. Hence, the SET-marker horizon approach has widespread applicability in both emergent wetland and shallow water environments for providing high resolution measures of the processes controlling elevation change.

Waves and breakers in shoaling water

Abstract: Wiegel and Johnson (1950) summarized useable wave theories for deep and shallow water. Mason (1950) discussed waves in shoaling water and compared theoretical predictions with measurements. The theories are shown to apply, within practical limits, to periodic systems of deep water waves, and to periodic waves progressing over a shoaling bottom to wave positions near the breaking point. Near and at the breaking position the wave features are not predicted from theory with desired accuracies and measured characteristics are used to describe breakers. The available measurements are limited and do not show the effects of variables such as the beach slope. Recent work at the University of California has resulted in information on the limits of applicability of the linearized wave theories as applied to wave transformation in shoaling water, and on breaker shapes and motion; including the effect of beach slope.

Measurement technique for bottom scattering in shallow water

Abstract: Sonar performance predictions of reverberation in shallow water rely upon good estimates of the bottom-scattering strength. However, little is understood about bottom scattering in shallow water in the frequency range 400–4000 Hz, particularly its dependency upon frequency and its relationship to the physical properties of the seafloor. In order to address these issues, a new measurement technique has been developed to probe the frequency and angular dependency of bottom-scattering strength. The experimental technique is described which employs either coherent or incoherent sources (lightbulbs). In addition, measurement and modeling results for two diverse shallow water sites are presented. At one site, the scattering appears to arise at or near the water–sediment interface. At the other site, scattering from a 23-m sub-bottom horizon is clearly apparent in the data at and below 1800 Hz. The fact that our measurement technique can directly reveal the presence of sub-bottom scattering is a significant advance in the development of methods to explore the physical mechanisms that control bottom scattering.

Shallow-water marine molluscs of the Azores : biogeographical relationchips.

Abstract: Shallow-water marine molluscs of thc Azores wcre surveyed t'rom supralittoral to a depth of 45 m which yielded an up-to-datc database. The resulting list of 23 1 coni'irmed taxa of the Azores was then compared with similar lists from Scandinavia, Belgium, British Isles. Gulf of Biscay to Galiza. Portugal, Western Mediterranean. Morocco and Mauritania, Madeira, Porto Santo, Dcsertas and Selvagcns, Canary Islands. Cape Verde, Ascension Island? Saint Helcna, and the Caribbean. A total of 18 species and 1 subspecies (Tricolin p~l1lu.s nzoricn) are considered to be endcmic to the Azores. There arc 20 new rccords to the Azores: Metnxin crbrrr]~tcl (Watson, 1 880), Motzopllonls erytlil-osot?~ci (Bouchet & Guillcmot, 1978), Melnrlellri sp., Latilellnriu lnteris ( 0 . F. Miiller, 1776), Ranella olenl-in (Linnacus, 1758), Ocbiebritln erlwarclsi (Payraudeau, 1826), F~;.~itzlrs sp., Nrr.rsorius c o r ~ ~ i n l l ~ i s (Olivi, 1792), Crr isso l~ lc~~rn it1cr~rs.mtn (Dujardin, 1837). Helinclls c~r.cl~itne ( 0 . G. Costa, 1867), Cirnn cf. trlblitnn (Jeffreys, 1858). Oclostotnicl cotioiclea (Brocchi. 1814), 012clitlrr r l i n l ~ l ~ a ~ ~ n (Jeffrcys, 1848), Chrotnorloris klzrol~i (Verany, 1846), Clllnniy~s flexrlosa Poli. 1795, Loripes lncteus (Linnaeus, 1758). Bornin sp.. Ptrrviccrrrli~1r~i exiguutil (Gmelin, 1791), Gnsrrrrtrn Jrngilis (Linnaeus. 1758) and Pr~pl,llia cull-ea (Gmclin, 179 I ). It was possible to infer thc life history of only 72 species out of thc 231. Of thesc, 38 have a frec-swimming stage and 34 have a non-planktotrophic type of development (cither lccithotrophic or dircct development). Thirteen endemic specics were found with a nonplanktotrophic typc of development, all belonging to the Rissoidae. The Meditcrranean, Madeira archipelago and Portugal mainland, are the regions which sharc a highcr numbcr of specics with the Azores. whereas Saint IJclena and Asccnsion Island share only a small numbcr of spccies with the Azores. Somc comments are made rcgarding the intluencc of the Gulf Current on the composition of the marine rnalacofauna of the Azores, as wcll on thc possible routes ol colonization of the Azorean islands by rnarinc molluscs.

Influence of Bottom Friction on Sea Surface Roughness and Its Impact on Shallow Water Wind Wave Modeling

Abstract: Using a selected subset of the measured data obtained in shallow waters near Vindeby, Denmark, during RASEX (Riso Air–Sea Experiment), the role of bottom friction dissipation in predicting wind waves (not swell) is assessed with a third-generation numerical wind wave model. The RASEX measurement site is located in relatively shallow waters (depths of about 3 to 4 m) in an area where the waves are predominantly fetch limited (i.e., maximum fetch of about 20 km). The bottom friction dissipation source term is modeled using the linearized bottom friction formulation. This formulation contains a dissipation coefficient, Cf, which depends on wave and sediment properties. In the numerical investigations, we considered three cases: (i) a constant value for Cf as obtained in the JONSWAP Experiment, (ii) a constant geometric roughness kN, and (iii) a constant median sediment size, d50. In the latter case, the bed is treated as a mobile bed and the geometric roughness is related to the dimensions of wave-f...

Bottom Currents and Sediment Transport in Long Island Sound: A Modeling Study

Abstract: A high resolution (300-400 m grid spacing), process oriented modeling study was undertaken to elucidate the physical processes affecting the characteristics and distribution of sea-floor sedimentary environments in Long Island Sound. Simulations using idealized forcing and high-resolution bathymetry were performed using a three-dimensional circulation model ECOM (BLUMBERG and MELLOR, 1987) and a stationary shallow water wave model HISWA (HOLTHUIJSEN et al., 1989). The relative contributions of tide-, density-, wind- and wave-driven bottom currents are assessed and related to observed characteristics of the sea-floor environments, and simple bedload sediment transport simulations are performed. The fine grid spacing allows features with scales of several kilometers to be resolved. The simulations clearly show physical processes that affect the observed sea-floor characteristics at both regional and local scales. Simulations of near-bottom tidal currents reveal a strong gradient in the funnel-shaped eastern part of the Sound, which parallels an observed gradient in sedimentary environments from erosion or nondeposition, through bedload transport and sediment sorting, to fine-grained deposition. A simulation of estuarine flow driven by the along-axis gradient in salinity shows generally westward bottom currents of 2-4 cm/s that are locally enhanced to 6-8 cm/s along the axial depression of the Sound. Bottom wind-driven currents flow downwind along the shallow margins of the basin, but flow against the wind in the deeper regions. These bottom flows (in opposition to the wind) are strongest in the axial depression and add to the estuarine flow when winds are from the west. The combination of enhanced bottom currents due to both estuarine circulation and the prevailing westerly winds provide an explanation for the relatively coarse sediments found along parts of the axial depression. Climatological simulations of wave-driven bottom currents show that frequent high-energy events occur along the shallow margins of the Sound, explaining the occurrence of relatively coarse sediments in these regions. Bedload sediment transport calculations show that the estuarine circulation coupled with the oscillatory tidal currents result in a net westward transport of sand in much of the eastern Sound. Local departures from this regional westward trend occur around topographic and shoreline irregularities, and there is strong predicted convergence of bedload transport over most of the large, linear sand ridges in the eastern Sound, providing a mechanism which prevents their decay. The strong correlation between the near-bottom current intensity based on the model results and the sediment response, as indicated by the distribution of sedimentary environments, provides a framework for predicting the long-term effects of anthropogenic activities.

Cruoriella rhodoliths from shallow-water back reef environments in La Parguera, Puerto Rico (Caribbean Sea)

Abstract: The occurrence of shallow-water (0.9 to 1.3 m) rhodoliths in back reef environments in southwest Puerto Rico is reported. The rhodoliths were generally cylindrical, discoidal or irregular in shape with an average longest dimension of 7.2 cm. They occurred at a maximum density of 524 m−2. The rhodoliths were composed of mostly coral nuclei with concentric laminations of aragonite-producing Cruoriella armorica (Peyssonneliaceae, Rhodophyta). Maximum Cruoriella accretion around coral nuclei was 30 mm although accretions of 1 to 20 mm were more common. Based on measurements of Cruoriella accretion, these shallow water rhodoliths are estimated to have minimum ages of 12 to 24 years. It is further estimated that approximately 2% of the rhodoliths are turned over daily.

An Accurate Model of Wave Refraction Over Shallow Water.

Abstract: A computer model of wave refraction is desirable, in the context of landscape modeling, to generate the familiar wave patterns seen near coastlines. In this article, we present a new method for the calculation of shallow water wave refraction. The method is more accurate than previously existing methods and provides realistic wave refraction effects. We resort to Fermat’s principle of the shortest path and compute the propagation of wavefronts over an arbitrary inhomogeneous medium. The propagation of wavefronts produces a phase map for each terrain. This phase map is then coupled with a geometric model of waves to generate a heightfield representation of the sea surface.

Bottom classification in very shallow water

Abstract: Bottom classification based on echo features and multivariate statistics is now a well established procedure for habitat studies and other purposes, over a depth range from about 5 m to over 1 km. Shallower depths are challenging for several reasons. To classify in depths of less than a metre, a system has been built that acquires echoes at up to 5 MHz and decimates according to the acoustic situation. The multirate signal processing accurately maintains the echo spectrum, preventing aliasing of noise onto the signal and preserving its convolution spectral characteristics. Trials have been done over sediments characterized visually and by grab samples. The major applications are expected to be in lake, river, and near-shore marine environments where the water is opaque or the information sought is not just surficial.

Interplay of orbital forcing and tectonic pulses in the Cambrian Iberian platform, NE Spain

Abstract: The stratigraphy of carbonate/shale couplets, cycles and cycle-stacking patterns in a Cambrian shallow water platform (Iberian Chains, NE Spain) are related to sea-level changes driven by orbital forcing and by tectonic pulses. The interplay of both effects can be discriminated in the Iberian fault-controlled platform, in which the tectonic activity can be analysed by accurate and detailed biostratigraphic correlations based on trilobite zonation. The stratigraphic hierarchy of rhythmically interbedded limestones and shales, in two coeval but structurally separated geodynamic settings, yields cycle ratios of 1.44 :1. This ratio is supported by time thickness and spectral analysis, which is based on a graphic method of analysis: the Map of Grey Lines. The cycle ratio seems to be evidence for orbital forcing by obliquity and precession cycles predicted for early Paleozoic time. Carbonate/shale couplets, the smallest rhythmic units recognisable in the field, represent short-term, periodic fluctuations in supply of terrigenous sediments and carbonate productivity of uncertain origin, which could be associated with one of several harmonics of the former orbital cycles. The pulsating tectonic activity was approximated by using a quantitative analysis of tectonically induced subsidence (Shaw method). Recurrence frequencies of tectonic pulses were estimated and dated by biostratigraphy. As a result, tectonic disturbances in the Cambrian Iberian platform show an episodic periodicity comparable to that of orbital eccentricity cycles, which could mask their recognition.

Conservation of energy for schemes applied to the propagation of shallow‐water inertia‐gravity waves in regions with varying depth

Abstract: The linear equations governing the propagation of inertia-gravity waves in geophysical fluid flows are discretized on the Arakawa C-grid using centered differences in space. In contrast to the constant depth case it is demonstrated that varying depth may give rise to increasing energy (and loss of stability) using the natural approximations for the Coriolis terms found in many well known codes. This is true no matter which numerical method is used to propagate the equations. By a simple trick based on a modified weighting that ensures that the propagation matrices for the spatially discretized equations become similar to skew-symmetric matrices, this problem is removed and the energy is conserved in regions with varying depth too. We give a number of examples both of model problems and large scale problems in order to illustrate this behavior.

Sediment-Driven Downslope Flow in Submarine Canyons and Channels: Three-Dimensional Numerical Experiments

Abstract: The role of submarine canyons and channels in sediment-driven downslope flow (sediment plumes) is examined, using a three-dimensional, rotational numerical model that couples the hydrodynamics and sediment transport. The model domain consists of a bottom ocean layer of constant height coupled with an essentially inert upper ocean. The model equations are cast in a rotated, bottom-following coordinate system in which vertical grid spacing is independent of the ocean depth and bathymetry can be resolved accurately. This allows for tracing bottom-attached sediment plumes (∼decameters in height) from shallow water into great depths of the ocean. The calculations reproduce morphologic features related to the occurrance of sediment plumes, such as the formations of 1) localized deposition areas of sediment off the mouth of submarine canyons and 2) levees at both sides of submarine channels. Furthermore, it is demonstrated that sediment plumes are not only important for the transport of littoral sedimen...

Inference of tidal elevation in shallow water using a vessel‐towed acoustic Doppler current profiler

Abstract: Vessel-towed acoustic Doppler current profilers (ADCPs) have been widely used to measure velocity profiles. Since the instrument is usually mounted on a catamaran floating on the surface, previous studies have used the water surface as the reference level from which the vertical coordinate for the velocity profile is defined. However, because of the tidal oscillation, the vertical coordinate thus defined is time-dependent in an Earth-coordinate system, which introduces an error to the estimated harmonic constants for the velocity. As a result, the total transport will also be in error. This is particularly a problem in shallow waters where the tidal elevation is relatively large. Therefore tidal elevation needs to be resolved to make a correct harmonic analysis for the velocity. The present study is aimed at resolving the tidal elevation change in shallow water using a vessel-towed ADCP. Semidiurnal and diurnal tidal elevations across the lower Chesapeake Bay have been determined using a vessel-towed ADCP. Data from four cruises ranging from 25 to 92 hours in 1996 and 1997 are used. Water depth averaged every 30 s by the ADCP is studied by harmonic and statistical analysis. By selecting only the data within a narrow band (∼320 m) over the planned transect, we are able to improve the reliability of the data. We then grid the depth data along the 16 km transect into 200 equal segments and use harmonic analysis to resolve the semidiurnal and diurnal tidal variations within each segment. We find that (1) the depth data from the ADCP contain both semidiurnal and diurnal signals that can be resolved, from which the surface elevation can be inferred, (2) the major error appears to come from spatial variation of the depth, (3) the semidiurnal and diurnal tidal variations of elevation inferred over flat bottom topography account for almost 100% of the total variability, while those measurements over large bottom slopes account for a much lower percentage of the total variability, (4) at least 70% of the variability of depth can be explained by semidiurnal and diurnal tides if the bottom slope is smaller than 0.006, and (5) the spatial variation of both amplitude and phase of the elevation along the transect appears to be small with a slightly lower tidal amplitude at the south of the Chesapeake Bay entrance, consistent with the Coriolis effect. The inferred elevations from the ADCP readings are consistent with sea level measurements at a tide station 10 km inside the estuary.