Decreasing Water Depth Research Articles

浅水状態の桟粗度乱流場における水面変動のパターン変化に関する画像計測による検討

In shallow water conditions, open-channel flows are subject to the influence of channel bottom roughness because the boundary layer or vortices generated at the bottom interact with water surface. Such an influence become more pronounced when the bottom is composed of discrete roughness such as a strip roughness. In the present study, water surface variations were investigated experimentally by varying the water depth relative to the roughness height. Although the water surface is kept almost horizontal for a relatively large depth of water, it tends to show significant differences with decrease of water depth. As an example, the water surface exhibits three dimensional topographical features with various arrangement of lumps depending on hydraulic conditions. Moreover, water surface begins to oscillate quite periodically with a hydraulic jump under specific hydraulic conditions. A new image analysis technique was developed to capture such surface flow features.

洪水時のADCPデータに基づく更正係数の分布特性と流量推定の高度化に関する研究

In estimating river flow discharges from water surface velocity distributions measured by non-contact methods such as radio wave velocity meters or image-based techniques, it is important to use an appropriate value of surface velocity coefficient that yields a depth-averaged velocity from a surface velocity. Conventionally, a value of 0.85 has been widely used in practical purposes but its distribution feature under various conditions has not been clarified yet. In order to investigate a fundamental aspect of the coefficient, measurement data by a tethered ADCP, a remote-controlled ADCP and surface velocities obtained by space-time image velocimetry(STIV) as well as a three-dimensional numerical simulation data were compared for the floods of the Uono River and the Niyodo River. It was made clear from measured and numerical data that the variance of the coefficient distribution tends to increase with decrease of the relative water depth and vice versa.

Estimating Irrigation Requirement for Rice Cropping under Flooding Condition using BUDGET Model

This study explored the effect of rainfall pattern and soil characteristics on water management in rice paddy fields, using a soil water balance model, BUDGET. In two sites with different soil textural group, coarse loamy soil (Gangseo series) and fine soil (Hwadong series), respectively, we have monitored daily decrease of water depth, percolation rate, and groundwater table. The observed evapotranspiration (ET) was obtained from differences between water depth decrease and percolation rate. The root mean square difference values between observed and BUDGET-estimated ET ranged between 10% and 20% of the average observed ET. This is comparable to the measurement uncertainty, suggesting that the BUDGET model can provide reliable ET estimation for rice fields. In BUDGET model of this study, irrigation requirement was determined as minimum water need for maintaining water-saturated soil surface, assuming 100 mm of bund height and no lateral loss of water. The model results showed different water balance and irrigation requirement with the different soil profile and indicated that minimum percolation rate by plow pan could determine the irrigation requirement of rice paddy field. For the condition of different rainfall distribution, the results presented different irrigation period and amounts, representing the importance of securing water for irrigation against different rainfall pattern.

A numerical investigation of second-order difference-frequency forces and motions of a moored ship in shallow water

A 3D time-domain Rankine source method is developed to study the hydrodynamic loads and motions of a moored ship in shallow water waves in head sea conditions. Both the wave steepness and ship motions relative to the ship’s draft are assumed small and the exact free-surface and body-boundary conditions are expanded about the mean surface by a Taylor series. A formulation correctly to second order in the wave steepness is adopted. A fourth-order Runge–Kutta method is used to time integrate the boundary conditions and the six degree of freedom motion equations. It is found that the water depth has significant effects on the hydrodynamic coefficients, especially on the vertical modes of motions. The linear horizontal motions of a moored ship have distinct increment in shallower water depth in the low-frequency domain. Further, the horizontal slow-drift excitation forces increase significantly with decreasing water depth and the second-order velocity potential gives dominant contribution in a frequency range of importance for moored ships in shallow water. Lastly, the slowly varying motions of an LNGC is simulated and the satisfactory agreements with experiments demonstrate that the present method can predict the slowly varying motions of a moored ship in finite-amplitude shallow water waves with acceptable results.

Assessment of HICO data for Coastal Studies

Abstract. Coastal waters, in particular, are the regions of high productivity and biodiversity. Detailed investigations of the variability within them can aid in understanding many biogeochemical processes. With the advent of hyperspectral remote sensing having large number of closely spaced channels and highly improved signal-to-noise ratio (SNR), the coastal applications are expected to increase and improve. In India, very less work is done in the field of coastal studies, let alone using hyperspectral remote sensing. HICO, onboard ISS, is the most recent addition to this family of instruments. So, a pilot study was conducted to assess HICO data for coastal studies especially in deriving the shallow water bathymetry estimates. The methodology for deriving bathymetry estimates is based on the different responses of shallow-water reflectance on depth and substrate type because with decreasing water depth in case 2 waters, the spectral contributions arriving from pure water reduce while from other OCAs increase. This variability is typically higher in the wavelength range 480 to 610 nm. Using this wavelength range, bathymetric estimates were made at pixel level. Bathymetry estimates were found to vary from 1 m to >12 m. Spectral variability is clearly observed in the continuum removed spectral plots from waters of different depths and is reported in this paper.

Lithofacies, diagenesis and reservoir quality of Upper Shu’aiba reservoirs in northwestern Oman

ABSTRACTCore and log data from Lower Cretaceous limestones of the Upper Shu’aiba Member were used to characterize the distribution of lithofacies, clay and porosity within two low-angle clinoforms that form the reservoirs for an oilfield of northwestern Oman. Data from 15 vertical wells, including four with core, and four horizontal well cores were projected into a dip-oriented cross-section derived from a static reservoir model as a basis for visualizing the above variations. Each clinoform consists of a basal “argillaceous zone” and a thicker “reservoir zone” of clean limestone, together reflecting fourth-order cycles of progradation along the margin of the Bab intra-shelf basin. Lithofacies vary in a proximal direction from mudstone and wackestone (mid-ramp) to mud-dominated packstone (slope) to mud-rich floatstone, rudstone and boundstone (ramp crest) and are arranged in a pattern of decreasing water depth and increasing energy both upwards and landward within each clinoform. In contrast, the reservoir zone of a younger clinoform from a nearby oilfield consists of well-sorted grainstone and grain-dominated packstone, illustrating the wide range of depositional conditions that occurred in the ramp-crest facies belt of different units.Except within the proximal extent of the younger clinoform, where values are transitional toward reservoir zone values, the argillaceous zones have total porosity mostly < 10% and baseline-normalized gamma-ray (GR) activity > 23 API units, reflecting clay contents of around 10–18%. In contrast, most parts of the reservoir zones have GR of 15–23 API units and porosity of 10–35%. Higher clay content is suggested to be linked with lower porosity through facilitation of both mechanical and chemical compaction, the latter providing a local supply of calcite cement. XRD analyses show that the clays are kaolin, illite/smectite and illite, similar to the clays in the overlying Nahr Umr shale. Most former macropores have been filled by blocky calcite cement in the main oilfield studied, but all lithofacies have similar wide ranges of total porosity of 8% to > 30%.The cores were also studied for evidence of diagenesis related to the contact with the overlying Nahr Umr Formation, but profiles of stable-isotope ratios, bulk-rock strontium, petrography and porosity-permeability data show no trends indicative of upward-increasing meteoric diagenesis below this sequence boundary. Meteoric leaching could nevertheless be pervasive throughout the Upper Shu’aiba reservoirs, at least partially accounting for extensive aragonite dissolution and low Sr and δ18O values. Two of the cores show trends of upwards-increasing bulk-rock uranium, manganese and iron, possibly indicative of sea-floor authigenesis. In addition, saddle dolomite near the tops of these cores may reflect late influx of magnesium derived from clay in the Nahr Umr Formation.

Unsteady turbulence in expansion waves in rivers and estuaries: an experimental study

A sudden decrease in water depth, called a negative surge or expansion wave, is characterised by a gentle change in free-surface elevation. Some geophysical applications include the ebb tide flow in macro-tidal estuaries, the rundown of swash waters and the retreating waters after maximum tsunami runup in a river channel. The upstream propagation of expansion waves against an initially steady flow was investigated in laboratory under controlled flow conditions including detailed free-surface velocity and Reynolds stress measurements. Both non-intrusive free-surface measurements and intrusive velocity measurements were conducted for relatively large Reynolds numbers with two types of bed roughness. The data showed that the propagation of expansion waves appeared to be a relatively smooth lowering to the water surface. The wave leading edge celerity data showed a characteristic trend, with a rapid acceleration immediately following the surge generation, followed by a deceleration of the leading edge surge towards an asymptotical value: $$(\mathrm{U}+\mathrm{V}_\mathrm{o})/(\mathrm{g}\times \mathrm{d}_\mathrm{o})^{1/2}=1$$ for both smooth and rough bed experiments. The results indicated that the bed roughness had little to no effect, within the experimental flow conditions. Relatively large fluctuations in free-surface elevation, velocity and turbulent shear stress were recorded beneath the leading edge of the negative surge for all flow conditions. The instantaneous turbulent shear stress levels were significantly larger than the critical shear stress for sediment erosion. The present results implied a substantial bed erosion during an expansion wave motion.

Laboratory study of the nonlinear transformation of irregular waves over a mild slope

This paper considers the nonlinear transformation of irregular waves propagating over a mild slope (1:40). Two cases of irregular waves, which are mechanically generated based on JONSWAP spectra, are used for this purpose. The results indicate that the wave heights obey the Rayleigh distribution at the offshore location; however, in the shoaling region, the heights of the largest waves are underestimated by the theoretical distributions. In the surf zone, the wave heights can be approximated by the composite Weibull distribution. In addition, the nonlinear phase coupling within the irregular waves is investigated by the wavelet-based bicoherence. The bicoherence spectra reflect that the number of frequency modes participating in the phase coupling increases with the decreasing water depth, as does the degree of phase coupling. After the incipient breaking, even though the degree of phase coupling decreases, a great number of higher harmonic wave modes are also involved in nonlinear interactions. Moreover, the summed bicoherence indicates that the frequency mode related to the strongest local nonlinear interactions shifts to higher harmonics with the decreasing water depth.

Groundwater flow due to a nonlinear wave set-up on a permeable beach

Water flow through the beach body plays an important role in the biological status of the organisms inhabiting the beach sand. For tideless seas, the groundwater flow in shallow water is governed entirely by the surface wave dynamics on the beach. As waves propagate towards the shore, they become steeper owing to the decreasing water depth and at some depth, the waves lose their stability and start to break. When waves break, their energy is dissipated and the spatial changes of the radiation stress give rise to changes in the mean sea level, known as the set-up. The mean shore pressure gradient due to the wave set-up drives the groundwater circulation within the beach zone. This paper discusses the circulation of groundwater resulting from a nonlinear set-up. The circulation of flow is compared with the classic Longuet-Higgins (1983) solution and the time series of the set-up is considered for a 24h storm. Water infiltrates into the coastal aquifer on the upper part of the beach near the maximum run-up and exfiltration occurs on the lower part of the beach face near the breaking point.

The impact of flow regulation by hydropower dams on the periphyton community in the Soča River, Slovenia

The effects of hydropower dams and, in particular, the impacts of reduced river flows on the periphyton community were assessed in the Soča River, Slovenia. Sampling sites were selected upstream and downstream of the Podsela and Ajba dams. Sampling was carried out in 1998 during a period of low flows. Reaches downstream from the dams experienced prolonged periods of reduced flows, and a corresponding decrease in flow velocity and water depth. The chain of hydropower dams has stopped sediment inflow from the upstream reach. Below the dams, the oscillations of water temperature, dissolved oxygen and oxygen saturation are much larger than at unregulated sites upstream. The impact of prolonged periods of reduced flows, a lack of sediment supply from upstream and changes in physicochemical variables has caused high periphyton biomass, proliferation of green algae and increases in the number of periphytic algae species below the dams. This has significant implications for the design of environmental flow strategies that provide a sediment supply to maintain a healthy periphyton community.Editor Z.W. Kundzewicz; Associate editor M. AcremanCitation Smolar-Žvanut, N. and Mikoš, M., 2014. The impact of flow regulation by hydropower dams on the periphyton community in the Soča River, Slovenia. Hydrological Sciences Journal, 59 (5), 1032–1045.

Leatherback Turtle Movements, Dive Behavior, and Habitat Characteristics in Ecoregions of the Northwest Atlantic Ocean

Leatherback sea turtles, Dermochelys coriacea, are highly migratory predators that feed exclusively on gelatinous zooplankton, thus playing a unique role in coastal and pelagic food webs. From 2007 to 2010, we used satellite telemetry to monitor the movements and dive behavior of nine adult and eleven subadult leatherbacks captured on the Northeast USA shelf and tracked throughout the Northwest Atlantic. Leatherback movements and environmental associations varied by oceanographic region, with slow, sinuous, area-restricted search behavior and shorter, shallower dives occurring in cool (median sea surface temperature: 18.4°C), productive (median chlorophyll a: 0.80 mg m−3), shallow (median bathymetry: 57 m) shelf habitat with strong sea surface temperature gradients (median SST gradient: 0.23°C km−1) at temperate latitudes. Leatherbacks were highly aggregated in temperate shelf and slope waters during summer, early fall, and late spring and more widely dispersed in subtropical and tropical oceanic and neritic habitat during late fall, winter and early spring. We investigated the relationship of ecoregion, satellite-derived surface chlorophyll, satellite-derived sea surface temperature, SST gradient, chlorophyll gradient and bathymetry with leatherback search behavior using generalized linear mixed-effects models. The most well supported model showed that differences in leatherback search behavior were best explained by ecoregion and regional differences in bathymetry and SST. Within the Northwest Atlantic Shelves region, leatherbacks increased path sinuosity (i.e., looping movements) with increasing SST, but this relationship reversed within the Gulf Stream region. Leatherbacks increased path sinuosity with decreasing water depth in temperate and tropical shelf habitats. This relationship is consistent with increasing epipelagic gelatinous zooplankton biomass with decreasing water depth, and bathymetry may be a key feature in identifying leatherback foraging habitat in neritic regions. High-use habitat for leatherbacks in our study occurred in coastal waters of the North American eastern seaboard and eastern Caribbean, putting turtles at heightened risk from land- and ocean-based human activity.

Facies Architecture and Stratigraphic Evolution of A River-Dominated Delta Front, Turonian Ferron Sandstone, Utah, U.S.A

Abstract Facies architectural analysis of a river-dominated deltaic parasequence in the Turonian Ferron Sandstone Member, near Factory Butte, Utah, was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta. Five architectural elements were identified using 21 measured sections, paleocurrent measurements, and bedding diagrams. They are: (1) prodelta (PF), (2) frontal splay (FS), (3) detached distal bars (DBs), (4) distributary mouth bars (DMBs), and (5) terminal distributary channels (TDCs). Lower in the parasequence, detached bars consist of proximally located cross-bedded and quasi-parallel laminated subaqueous bars that onlap the delta-front slope and grade distally into finer-grained distal delta front splays. These bars translate downstream in a progradational–aggradational–degradational trajectory and are overlapped by adjacent bars, forming a bar assemblage. These bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet. Deposition of these bars occurs at the delta-front to prodelta chokepoint, presumably due to flow deceleration. The distal bar assemblage is capped by an extensive but discontinuous shale drape, suggesting local abandonment. Upper facies assemblages show a distinct switch to predominantly cross-bedded distributary mouth bars, corresponding to a decrease in water depth, an increase in friction, and a likely transition into planar versus axial jets. This is indicated by aggrading cross-bedded distributary mouth bars that overlie the distal bars. Laterally, the mouth-bar deposits are interstratified with terminal distributary-channel deposits with prominent scour surfaces at the base. Separate distributary channels and their bars coalesce, ultimately to build the entire delta lobe. The detached distal bars prograde locally west to northwest and lack fair-weather wave-formed sedimentary structures, suggesting a local embayment along the regionally northeast prograding shoreline. Low levels of ichnofaunal diversity indicate a stressed, river-dominated setting. At the base of the section, frontal splays and detached bars, dominated by storm-driven river-flood deposits, are deposited over muddy prodelta facies. Detached bars are likely initiated about 500 meters distal of the distributary channel, in water depths of ∼ 10–30 meters, based on the thickness of the parasequence. Once this subaqueous platform is constructed by the distal bar assemblage, more proximal distributary mouth bars fill the remaining shallow-water accommodation. As the system continues to shallow, distributary channels override and scour the bars, reflecting reduced accommodation.

Secular Trends in Tidal Parameters along the Coast of Japan

The secular trends for local tidal datums, tide ranges, and tidal harmonic constituents at 13 tidal gauge stations located along the coast of Japan were analyzed in this study. The general trends for mean higher high water (MHHW), mean high water (MHW), diurnal tide range (DTR), mean tide range (MTR), and relative mean sea level (RMSL) were positive, and for mean lower low water (MLLW) and mean low water (MLW) the trends were negative. The variation patterns were largest at Kushiro and Ofunato stations, both located in the open waters of the North Pacific Ocean. The tidal datums and tide ranges remained fairly stable at the Hakodate station, and an opposite trend was observed at the Maisaka station. The analysis of tidal harmonic constituents revealed a less pronounced pattern. The most distinct trend was observed for the M2 amplitude, which appears to be negative at a majority of the stations. The largest decrease in the M2 amplitude was observed at Kushimoto and Mera stations, also located in the open waters of the North Pacific Ocean. The negative trend is attributed to decreasing water depths at these stations, owing to small-scale local processes.

Factors affecting basin type solar still productivity: A detailed review

Abstract Reasonable amounts of fresh water can be produced via inexpensive and sturdy solar stills in places that are exposed to solar radiation and have a brackish water. This work intends to analyze the many studies on factors that affect the performance of solar stills. The results showed that the distillation productivity of solar stills are significantly influenced by ambient conditions (e.g., ambient temperature, insolation, wind velocity, dust and cloud cover), operating conditions (e.g., depth of water, various dyes, salt concentration and inlet temperature of water), and design conditions (e.g., different passive/active designs of solar stills, slope of the cover, materials selection, storing materials, reflectors, insulation, gap distance and sun tracking system). It was also determined that the performance of solar stills was improved through the increase in solar radiation, ambient air temperature, wind speed, and water absorptivity. This also rings through with the decrease in water depth, thickness of cover, gap distance between water surface and condensing cover. It was also determined that both internal and external reflectors are capable of increasing the amount of absorbed solar radiation on the basin liner. The potential output of a basin type still can potentially increase to almost 70–100%. On top of this, the utilization of a sun tracking system was determined to be way more effective in improving the performance of solar still. This translate to the fact that solar stills being able to produce potable water at a very economical cost. Due to the existence of different methods of cost estimation, it is not possible to determine a universal, comparable price per technology; the cost per liter of distilled water obtained from the basin type solar still is ranged from 0.035 to 0.074$/liter. This study proved the fact that distillation productivity of solar still is heavily influenced by climatic, operational, and design parameters. Its output can be further improved via operational and design conditions, as climatic conditions are beyond our control.

2船並走時の舵と船体の流体力学的干渉に及ぼす浅水影響

Ship is under way side by side in close proximity to the other ship in the case of meeting/overtaking in a narrow waterway or ship to ship transfer operation. Since it is required to understand the hydrodynamic force characteristics for safe navigation, a lot of studies on them have been done so far. However there have been few studies on the hull to rudder interactions between two ships alongside except for the previous study by authors. This study is a continuous work and the shallow water effect on them is discussed. Captive model tests were conducted in shallow water, i.e. the depth/draft ratio 1.2 and 1.5, with variations in the lateral clearance between hulls, hull drift angle and rudder angle. The authors found, for example, when a ship steered, the lift interaction force acted not only on the self-ship but also on the other ship moving side by side in close proximity. It turned in the opposite direction and its acting point was also shifted with decrease of water depth. The experimental results were compared with the numerical analysis based on a nonlinear lifting body theory and it was able to capture the tendency of the shallow water effect on those hydrodynamic force characteristics.

Habitat segregation by female humpback whales in Hawaiian waters: avoidance of males?

Humpback whales congregate annually in low-latitude winter breeding and calving grounds. While on these grounds, females with a dependent calf (‘maternal females’) are sometimes closely attended by one or more male escorts. Using data collected from a shore-based observation platform in the Hawaiian Islands, we tested the hypothesis that the spatial distribution of maternal females is driven primarily by avoidance of males. As predicted, we found that (1) pods containing a calf occurred in significantly shallower water than pods that did not contain a calf, (2) unescorted maternal females occurred in significantly shallower water than escorted maternal females, (3) the number of males escorting a female decreased significantly with decreasing water depth, and (4) the swimming speed of maternal females increased as a function of male presence, with escorted females travelling significantly more rapidly than unescorted females and a significant positive correlation between swimming speed and number of escorts. We suggest that maternal females incur increased energetic costs when escorted by males and consequently position themselves in shallow waters to reduce the likelihood of unwanted male attention.

Flow routing in mangrove forests: A field study in Trang province, Thailand

Flow routing in mangrove forests has great implications for the transport and distribution of sediments and nutrients and hence for mangroves' development and persistence. Whereas previous studies were limited to the creeks, supposedly feeding the surrounding mangroves, this study demonstrates the contribution of biogeophysical impacts on flow routing through estuarine mangroves. We present the results of a field campaign covering three pristine mangrove sites in two estuaries in Trang province, Thailand. The sites range from a mangrove forest elevated above mean sea level with steep cliffs and incised by tidal creeks, to smoothly inclining mangroves fronted by extensive mudflats and showing a clear vegetation zonation starting below mean sea level. It is shown how flow routing through estuarine mangroves is impacted by biogeophysical factors; elevation, exposure and vegetation. Within the higher elevated mangroves, creek flow prevails when water levels remain below a dense vegetation layer at the mangrove fringe bordering the estuary. Sheet flow prevails when this threshold is exceeded and direct water exchange takes place. The low-lying sites do not feature creeks and tidal flows are typically sheet flows, being susceptible to forcing by river discharges. With decreasing water depths and/or increasing vegetation densities, the effects of this forcing are reduced and flow velocities follow the vegetation induced cross-shore water level gradients. Flow velocities within the creeks are up to an order of magnitude greater than those within the vegetation, where velocities decrease progressively with increasing vegetation densities. Particular vegetation and elevation characteristics cause irregular velocity variations along the vertical, within the vegetation as well as in the creeks. Tentative tidal flux calculations demonstrate the significant contribution of creek flow to the total tidal prism in higher elevated mangroves. By explicitly quantifying and mapping flow routing through mangrove forests, this study provides observational evidence for flow routing phenomena that have been postulated in previous studies.

Water Wave Radiation Problem by a Submerged Cylinder

AbstractBased on the methods of variable separation and matching eigenfunction expansions for velocity potential, analytical solutions are developed for a water wave radiation problem by a submerged vertical cylinder in finite water depth. They are validated by comparison with results from the higher order boundary element method and convergent examinations on the number of expansion models. Numerical analysis is carried out to investigate the influence submerged depth, cylinder length, and water depth on added mass and radiation damping. When the submerged depth is large, the added mass approaches a stable value, and radiation damping tends to zero. At high frequency range, the heave and pitch of the added mass of the submerged cylinder is about twice that of the floating cylinder. The influence of cylinder length for hydrodynamic coefficients is quite complex and shows the various properties at different frequency ranges. Added mass can be increased with the decrease of water depth, whereas the effect o...

Factors Influencing Premetamorphic Body Mass of Two Polymorphic Spadefoot Species in Cropland and Grassland Playas

Spadefoot Toads, Spea bombifrons and Spea multiplicata, are often the most abundant amphibian species in playa wetlands in the semi-arid Southern Great Plains. Tadpoles of these species are morphologically indistinguishable, but both can develop omnivore and carnivore morphotypes. We tested the influence of species and morphotype on body mass of premetamorphic Spea tadpoles and the influence of land use (cropland vs. native grassland) and desiccation stress (water depth and daily rate of water-depth loss) on body mass of S. bombifrons carnivores and omnivores and on body mass of S. multiplicata and S. bombifrons omnivores. Spea bombifrons carnivores were larger than omnivores only in relatively deep playas. A decrease in water depth resulted in less body mass for carnivores, but omnivore body mass did not change. Spea bombifrons omnivores had larger body mass than did S. multiplicata omnivores at low and average playa depth. Spea bombifrons omnivores did not alter body size, whereas S. multiplicata omnivores were smaller when depth decreased. Generally, in average and deep playas, tadpoles were larger in cropland than grassland playas, but in shallow waters, cropland and grassland tadpoles had similar, smaller body mass. Also, cropland tadpoles had reduced body size, whereas grassland tadpoles had similar body mass when depth decreased. Our study documents body size divergence within the same morph in the two sympatric Spea species and species divergence within the omnivore morph depending on desiccation stress. Future studies should investigate whether these species may be mediating competition through both morph development and body size.

Finite depth effects on the wave energy resource and the energy captured by a point absorber

Most of the wave energy converters under development are planned for operation in shallow to intermediate water depths, typically 30m to 70m. However, the limited water depth reduces the wave energy resource as compared to offshore deep water. This paper presents an analysis of the water depth effects on the wave energy resource and on the energy absorbed by a floating device. The analysis is based on a procedure to modify the wave spectrum as the water depth reduces, namely the TMA method Bouws et al., 1985. J. Geophys. Res. 90 (C1), 975–986. The method is based on the hypothesis that the similarity principle for the saturation range of shallow-water spectrum is not restricted to the equilibrium range, but is valid across the entire spectrum. A point absorber-type wave energy converter is modelled and the wave climatology of Figueira da Foz (Portugal) is used as a case study. Significant reduction has been identified for both the wave energy resource and wave energy converted as the water depth decreases. The presented methodology can be used for preliminary cost benefit analysis and decision making regarding the best water depth for installation of specific wave energy converters.