Water Depth Ratio Research Articles

Effects of an Upstream Sluice Gate and Holes in Pooled Step Cascade Weirs on Energy Dissipation

Pooled step cascade weirs are hydraulic structures that are preferred over ordinary weirs due to their application on steep slopes and to their effectiveness in obtaining water aeration. However, these structures are subject to failure due to scour being initiated downstream, or to breakdown due to the high energy of impinging water. In this paper, an experiment was presented to study the effect of the number and ratio of holes in weirs to improve energy dissipation. To improve energy dissipation, cascade weirs with different configurations of openings were proposed. Furthermore, a sluice gate at the upstream of a cascade weir was proposed as a new technique to increase energy dissipation and reduce scour at downstream. Ten models of pooled step cascade weirs (nine models with different hole configurations and one with a sluice gate upstream), in addition to the ordinary weir, were constructed to investigate the effect of the sluice gate and holes on energy dissipation; the range of each type of flow (nappe, transition, and skimming); the relevant Froude number; and the ratio of water depth to critical depth over pooled step cascade weirs. To implement this, the ratio of holes to the area of the weir were between 0 and 21.22% and the number of holes used were one hole, two holes, and three holes. The results concluded that the best method to obtain maximum energy dissipation was putting a sluice gate at the upstream of a solid pooled step cascade up to a discharge of 2.0 l/s. The most effective ratio of holes to weir area was 7.15% at the minimum Froude number when the discharge exceeded 2.0 l/s. Moreover, the ratio of upstream water depth to critical depth decreased with increasing discharge. The nappe, transition, and skimming flow types were increased more on a pooled stepped cascade weir of 7 mm opening diameter with three holes (ratio of 7.15%) than the other models. The Froude number decreased as the hole numbers increased at high discharges for the pooled stepped cascade weir, especially with the hole diameter of 12 mm. Some empirical equations were established to represent the relation between the upstream head and discharge for each case.

Experimental investigation on the effects of bed slope and tailwater on dam-break flows

Understanding of the characteristics of dam-break flows moving along a sloping wet bed can help to timely issue flood warning and risk mitigation. In this study, laboratory experiments are carried out in a large flume for a wide range of upstream water depth, bed slopes and tailwater depth. The water level is recorded and processed to calculate the mean velocity and wave celerity. Results show that the increase of the bed slope will significantly accelerate the wave-front celerity for the downstream dry bed, while the negative wave celerity will decrease. When water depth ratio α ≥ 0.3 (defined as the ratio of initial downstream water depth over the upstream water depth of dam), there are extra negative waves propagating towards the reservoir area after the flow has developed for a period of time. When α ≥ 0.6, there are the Favre waves propagating downstream. The water level and the mean velocity fluctuate due to the influence of the extra negative waves and the Favre waves. Such fluctuant frequency increases with the increase of the water depth ratio. The empirical formulas are obtained for the celerity of the first extra negative wave and the first downstream wave. The variation of wave-front height is very similar under three bed slopes investigated in this study, while the maximum wave-front height occurs when α = 0.2. The present study broadens the understanding of the effects of the bed slope and the tailwater level on the movement of the dam-break flows. Furthermore, experimental results are also compared with some analytical solutions. The validity of the assumptions made during the development of these analytical solutions and their limitations are discussed by comparing with the experimental measurements.

Groundwater–Surface Water Interaction—Analytical Approach

Modelling of water flow in the hyporheic zone and calculations of water exchange between groundwater and surface waters are important issues in modern environmental research. The article presents the Analytical Hyporheic Flux approach (AHF) permitting calculation of the amount of water exchange in the hyporheic zone, including vertical water seepage through the streambed and horizontal seepage through river banks. The outcome of the model, namely water fluxes, is compared with the corresponding results from the numerical model SEEP2D and simple Darcy-type model. The errors of the AHF model, in a range of 11–16%, depend on the aspect ratio of water depth to river width, and the direction of the river–aquifer water exchange, i.e., drainage or infiltration. The AHF model errors are significantly lower compared to the often-used model based on vertical water seepage through the streambed described by Darcy’s law.

Similarities in the free-surface elevations and horizontal velocities of undular bores propagating over a horizontal bed

This paper presents experimental results regarding the existence of similarities and/or Froude number similitudes in the time series of the free-surface elevation (FSE) and horizontal velocity of undular bores (UBs) propagating over a horizontal bed. Two wave gauges and high-speed particle image velocimetry are employed to measure the FSEs and velocity fields. A complete evolution of the FSE (or horizontal velocity) of UBs is divided into four temporal stages, named stages I–IV. The surge-wave amplitudes, constant characteristic horizontal velocities, and specified time differences are then identified as the characteristic length scale, velocity scale, and timescale of UBs. Data for the dimensionless FSE and free-stream velocity vs the dimensionless shifted time are found to collapse onto two unique similarity trends. This demonstrates the existence of Froude number similitudes for the entire evolution of UBs with geometric similarity. Under the same water-depth ratio and length ratio, but distinct values of the relative basin and travel length for different UBs, larger values of the relative basin length produce greater end times for the final occurrence of the constant FSE and characteristic horizontal velocity. This demonstrates that the end time is not influenced by the relative travel length. Under identical values of the water-depth ratio and relative basin length, a smaller relative travel length results in a greater rate of decrease in the unit discharge during stage IV. Correspondingly, this results in earlier bifurcation of the time series of FSE (or free-stream velocity), which has a smaller (or larger) rate of decrease, from their counterparts with larger relative travel lengths.

Control of Hydraulic Load on Bacterioplankton Diversity in Cascade Hydropower Reservoirs, Southwest China.

Hydroelectric reservoirs are highly regulated ecosystems, where the understanding on bacterioplankton has been very limited so far. In view of significant changes in river hydrological conditions by dam construction, hydraulic load (i.e., the ratio of mean water depth to water retention time) was assumed to control bacterioplankton diversity in cascading hydropower reservoirs. To evaluate this hypothesis, we investigated bacterioplankton composition and diversity using high-throughput sequencing and related environmental variables in eleven reservoirs on the Wujiang River, Southwest China. Our results showed a decrease of bacterioplankton diversity index with an increase of reservoir hydraulic load. This is because hydraulic load governs dissolved oxygen variation in the water column, which is a key factor shaping bacterioplankton composition in these hydroelectric reservoirs. In contrast, bacterioplankton abundance was mainly affected by nutrient-related environmental factors. Therefore, from a hydrological perspective, hydraulic load is a decisive factor for the bacterioplankton diversity in the hydroelectric reservoirs. This study can improve the understanding of reservoir bacterial ecology, and the empirical relationship between hydraulic load and bacterioplankton diversity index will help to quantitatively evaluate ecological effects of river damming.

Laboratory Study on Solute Transport Affected by Rigid Vegetation

Lou, S.; Liu, H.Z.; Chen, M.; Liu, S.G., and Zhong, G.H., 2020. Laboratory study on solute transport affected by rigid vegetation. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 77-82. Coconut Creek (Florida), ISSN 0749-0208.Aquatic vegetation is ubiquitous in riverine and estuary environment. With the presence of vegetation, velocity and solute transport can be greatly impacted. In this paper, laboratory experiments were carried out to analyze the influence of rigid vegetation on flow velocity and solute transport. Results have shown that the mean velocity is significantly reduced by vegetation and the maximum values of solute concentration decrease more rapidly with lower relative water depth (ratio of vegetation height to water depth). The longitudinal diffusion coefficients are found to be related with Reynolds number positively and vegetation density negatively. A modified function is proposed in this paper to effectively estimate the longitudinal diffusion coefficients, which can be used under both emergent and submerged vegetation conditions.

Effects of floating breakwater on hydrodynamic load of low-lying bridge deck under impact of cnoidal wave

Extreme ocean surface waves generated during hurricanes or tsunamis can cause severe damage to coastal communities and infrastructures, especially coastal bridges. In this paper, installation of floating breakwater is proposed to protect coastal bridge decks against strong ocean surface waves. As an environmental-friendly wave-reduction device, floating breakwaters can be easily installed and removed before and after a storm, avoiding impacts on navigation and other coastal operations. To numerically investigate effects of a floating breakwater on the applied hydrodynamic load of a bridge deck under the impact of cnoidal waves, a high-resolution numerical wave tank (NWT) is established using the open-source flow solver REEF3D, which solves the governing equations of the incompressible two-phase flow on a staggered mesh and captures the interface between air and water using a high-resolution level-set method. Effects of prominent parameters, i.e. wave height, water depth, submersion depth, spacing distance and aspect ratio of breakwaters, on the performance of floating breakwater and reducing the hydrodynamic load on a coastal bridge deck are systematically analyzed. It is found that hydrodynamic loads of coastal bridge deck can be greatly reduced through the use of floating breakwaters. Results of this paper can further enhance our understanding on the damage mechanism of coastal bridges under extreme surge waves, and should be instructive for future bridge design.

Experimental and numerical investigations of similarity for dam-break flows on wet bed

The similarity brings great convenience to the description of the dam-break flows. The previous works mainly focus on the similarity of dam-break flows under the condition of dry bed downstream. In view of the fact that there is often a certain tail water depth in a river, this paper deals with both the gravity similarity and self-similarity of dam-break flows in a horizontal and smooth channel with a wet-bed downstream condition by using both physical and numerical models. In the laboratory tests, the digital image processing technique is adopted for flow measurement, providing water surface profiles, stage hydrographs and cross-sectional mean velocity. Three different upstream depths and ten water depth ratios α (i.e., the ratio of initial downstream water depth against the upstream water depth, ranging from 0.05 to 0.9) are considered. The numerical simulations on the vertical two-dimensional experiments are carried out using a computational fluid dynamics solver, providing velocity profiles in addition to the hydraulic parameters obtained in experiments. The following observations are made: (1) the water surface profiles, stage hydrographs, mean velocity distribution and horizontal velocity profiles are shown to satisfy the gravity similarity well; (2) the gravity similarity characteristic of the vertical velocity profiles in the reservoir performs better than that in the flooded area; (3) the water surface profiles, mean velocity distribution and horizontal velocity profiles approximately satisfy the self-similarity after a period of time for α < 0.3; (4) the undulations both in the rarefaction wave and the shock front destroy the self-similarity of dam-break flow for α ≥ 0.3, except that the self-similarity is valid in two non-undulation areas (located upstream the extra negative wave and in the neighborhood of dam site) after a period of time; (5) the gravity similarity could be applied in the small-scaled physical model of dam-break flow and the water depth ratio must be considered when applying the self-similarity; (6) the measurements and numerical simulations with the large eddy simulation (LES) model show satisfactory agreement, implying that the LES modeling is a viable approach for accurately predicting the dam-break flows with a wet bed downstream condition.

Complete Evaluation of Cell Mixing and Hydrodynamic Performance of Thin-Layer Cascade Reactor

Microalgae are a great source of food and supplements as well as a potential source for the production of biofuels. However, the operational cost must be reduced to allow viable productions of bulk chemicals such as biofuels from microalgae. One approach to minimize the cost is to increase the efficiency of the photobioreactor. Photobioreactor efficiency is correlated to hydrodynamic mixing, which promotes single cell exposure to sunlight, keeps algae cells in suspension, and homogenizes the distribution of nutrients. Thus, a possible route to enhance the efficiency of the photobioreactor can be identified through an improved understanding of the mixing phenomenon. Therefore, for the current thin-layer cascade reactor, two aspects of its performance—namely, cell mixing and hydrodynamic characteristics—are evaluated under varying mass flow rates, slope angles, water depths, and aspect ratios of the channel by using computational fluid dynamics. The resulting model is validated with experimental data. Results reveal that limited cell mixing is achieved in the thin-layer cascade reactor with increased water depth and large aspect ratios. However, cell mixing is significantly increased at high mass flow rates. The increase in the mass flow rate and slope angle results in increased flow velocity and power consumption.

On the mass source internal wave making method for ALE based numerical wave tank

In this study, we perform simulations for free surface wave tracking inside a numerical tank. A Navier–Stokes solver, combined with the arbitrary Lagrangian–Eulerian method, is introduced. To generate free surface waves, a mass source internal wave-maker, proposed by Lin and Liu (J Waterw Port Coast Ocean Eng 125(4):207–215, 1999), is employed and implemented in OpenFOAM. A line mass source distribution throughout the water depth is used to mimic a real-world wave-maker. Specifically, two types of line source wave-makers for shallow water, namely the piston and flap types, are established, together with the block mass source model used by Lin and Liu (J Waterw Port Coast Ocean Eng 125(4):207–215, 1999) . Numerical results of free surface profiles and horizontal velocity profiles are validated by experimental data (Umeyama in J Waterw Port Coast Ocean Eng 137(2):85–94, 2010) . It is concluded that in the case of shallow-water wave propagation, the line source model is better than the block source model at maintaining the wave form. The internal wave-making method has its ceiling (wave height and water depth ratio $$H/h = 0.1$$ ) for applications in numerical wave-making. Flow contamination induced by the wave-maker itself must be considered in complex flow situations such as wave-current interactions.

The improvement and application of the calculation formula of flow division ratio at anabranching channels within the Shashi Reach of the Jingjiang River

分汊河段冲淤调整会引起汊道分流比的复杂变化.建立准确的分流比计算公式是研究分流比在不同水沙、地形边界条件下变化的基础.以长江上荆江分汊河段——沙市段为例，利用三峡水库蓄水后的实测资料对现有分流比计算式的适用性进行比较，通过引入综合反映两汊糙率、比降差异的因子，建立了较高精度的分流比计算式，在此基础上，分析了沙市分汊段分流比的变化特点.结果表明：（1）当无法准确反映两汊糙率、比降的差异时，枯水分流比计算误差较大，最大计算偏差达15%；（2）两汊平均水深之比与糙率、比降综合影响系数比高度相关，引入两汊平均水深之比，建立了最大计算偏差小于5%的分流比计算式；（3）三峡水库蓄水后沙市段汊道冲淤变化对枯水分流比的影响大于洪水分流比，对微弯分汊段分流比的影响大于顺直分汊段.;Complex changes in flow division ratio can be aroused by channel morphological adjustments in anabranching reaches. Establishing a precise calculation formula of flow division ratio lays a foundation for investigating the changes in flow division ratio under different flow-sediment and channel boundary conditions. Taking the typical anabranching reach, namely the Shashi anabranching reach in the upper Jingjiang River as the case study, this paper compares the applicability in natural reaches of different flow division calculation formulas based on data observed after impoundment of the Three Gorges Reservoir (TGR) in 2003, and proposes an improved flow division formula with higher accuracy by introducing a comprehensive factor which can reflect the differences in roughness and water surface gradient between the primary and secondary branching channel. Based on this formula, the variation characteristics of flow division ratio at the study reach are further analyzed. The results reveal the following points:(1) Without accurately reflecting the differences in roughness and water surface gradient between the primary and secondary branching channels, the calculation error in low flow division ratio result is large and the maximum absolute difference (MAD) can reach 15%. (2) The average water depth ratio of the primary to secondary branching channel is highly related to their roughness-gradient comprehensive influence coefficient ratio and by introducing the average water depth ratio, a flow division calculation formula with a significantly improved accuracy of less than 5% MAD is established. (3) After impoundment of the TGR, the channel scouring and silting adjustments exert greater impacts on the low flow than high flow division ratio and led to a more significant variation of flow division ratio in the slightly curved branching reach than that in the straight branching reach.

Analytical solutions of tsunamis generated by underwater earthquakes

Tsunamis induced by underwater earthquakes are theoretically analyzed by applying the linear potential theory. Special attention is placed on the initial state of tsunami. For instantaneous seabed deformations, analytical wave solutions induced by three fundamental seabed deformations at initial stage are derived rather than integral expressions in past studies. These analytical solutions constitute a fundamental base for analyzing waves generated by arbitrary seabed displacement with the help of Fourier analysis. Tsunamis induced by non-instantaneous seabed deformation are analyzed as well. For the sake of examining the contributions of all wave components involved in the tsunami waveform, the amplitude density is proposed to examine the effects of deformation width, water depth, harmonic mode and rising time on waveforms. Results show that a larger ratio of water depth to deformation width results in a greater difference between initial waveform and seabed deformation, and the effect of the rising time is significant in deeper-water configuration. For cosine and sine seabed liftings, the effects of higher harmonic modes might be ignored.

Parameter Optimization and Control Characteristics Analysis of TLMD System Based on Phase Deviation

Combined with the advantages and disadvantages of tuned liquid damper (TLD) and tuned mass damper (TMD), a double tuned liquid mass damper (TLMD) is proposed by replacing the rigid connection of TLD with the spring structure. The motion equation of a single-degree-of-freedom structure with a TLMD attached at its top is found under harmonic excitation. Comparing the energy consumption and amplitude of primary structure with equal mass ratio TMD, it is found that the energy dissipation performance of TLMD is better in the effective phase region. The interaction process between TLMD and structure is analyzed, and the formula of phase deviation between the relative velocity of tank and the displacement of primary structure is deduced. By analyzing the influence of mass ratio, frequency ratio, damping ratio and water depth ratio on the damping effect, the results show that the frequency ratio and liquid depth ratio have great influence on the size and location of deep resonance peak, and the mass ratio and damping ratio have great influence on the width of the effective frequency band. The formula of equivalent damping ratio is proposed based on the principle of energy and it is found that the equivalent damping ratio is related to the phase deviation and change with the frequency ratio of the external excitation.

Control of the Hydraulic Load on Nitrous Oxide Emissions from Cascade Reservoirs.

Nitrous oxide (N2O) emissions show large variability among dam reservoirs, which makes it difficult to estimate N2O contributions to global greenhouse gases (GHGs). Because river damming alters hydraulic residence time and water depth, the hydraulic load (i.e., the ratio of the mean water depth to the residence time) was hypothesized to control N2O emissions from dam reservoirs. To test this hypothesis, we investigated N2O fluxes and related parameters in the cascade reservoirs along the Wujiang River in Southwest China. The N2O fluxes showed obvious temporal and spatial variations, ranging from -7.86 to 337.22 μmol m-2 d-1, with an average of 12.76 μmol m-2 d-1. Nitrification was the main pathway of N2O production in these reservoirs, and seasonal dissolved oxygen (DO) stratification played an important role in regulating the N2O production. The reservoir N2O flux had a significant negative logarithmic relationship with the hydraulic load, suggesting its control of the N2O emission. This was because the hydraulic load was a prerequisite for regulating the nitrification-denitrification and the DO stratification in the dam reservoirs. This empirical relationship will help to estimate the contribution of reservoir N2O emissions to global GHGs.

Maneuvering hydrodynamic derivatives and course stability of a ship close to a bank

Captive model tests are conducted for a pure car carrier in the proximity of a sloped bank with variations in water depth, distance between ship hull and bank, hull drift angle and heel angle. Using the hydrodynamic derivatives obtained, the check helm and hull drift angle required at equilibrium conditions are estimated. Course stability of the ship sailing in the proximity of the bank is also studied based on a simplified analysis method. In h∕d=1.2 where h∕d means ratio of water depth h to ship draft d, the check helm of the ship reaches 35° near η0∕L=0.27 where η0 is the distance between the ship center line and the bank. Although this ship is course unstable in case of no rudder control, the ship becomes course stable in any water depths by employing the autopilot with appropriate control gains. The present analysis method is useful for conventionally assessing the course stability of a ship in the proximity of a bank.

Hydrodynamic Features of an Undular Bore Traveling on a 1:20 Sloping Beach

The hydrodynamic characteristics, including local and convective accelerations as well as pressure gradient in the horizontal direction, of the external stream of an undular bore propagating on a 1:20 sloping beach are experimentally studied. A bore with the water depth ratio of 1.70 was generated downstream of a suddenly lifted gate. A high-speed particle image velocimetry was employed to measure the velocity fields during the run-up and run-down motions. The time series of free surface elevation and velocity field/profile of the generated bore, comprising a pure bore accompanied by a series of dispersive leading waves, are first demonstrated. Based on the fast Fourier transform (FFT) and inverse FFT (IFFT) techniques, the free surface elevation of leading waves and the counterpart of pure bore are acquired separately at a specified measuring section (SMS), together with the uniform horizontal velocity of the pure bore. The effect of leading-wave-induced velocity shift on the velocity profiles of the generated bore are then evaluated at the SMS. To understand the calculation procedure of accelerations and pressure gradient, three tabulated forms are provided as illustrative examples. Accordingly, the relationships among the partially depth-averaged values of the non-dimensional local acceleration, convective acceleration, total acceleration and pressure gradient of the generated/pure bore acquired at the SMS versus the non-dimensional time are elucidated. The trends in the non-dimensional accelerations and pressure gradient of the external stream of generated bore are compared with those of the pure bore. During the run-up motion from the instant of arrival of the bore front to the moment of the peak level at the SMS, continuous decrease in the onshore uniform horizontal velocity, and successive deceleration of the pure bore in the onshore direction are evidenced, exhibiting the pure bore under the adverse pressure gradient with decreasing magnitude. However, the pure bore once ridden by the leading waves is decelerated/accelerated spatially and accelerated/decelerated temporally in the onshore direction during the rising/descending free surface of each leading wave. This fact highlights the effect of pre-passing/post-passing of the leading wave crest on the velocity distribution of generated bore. It is also found that, although the leading waves have minor contribution on the power spectrum of the free surface elevation as compared with that of the pure bore, the leading waves do play an important role on the magnitudes of both accelerations and pressure gradient. The largest magnitude of the acceleration contributed by the leading waves is around 26 times the counterpart contributed by the pure bore. Further, during the run-down motion right after the moment for the peak level of the bore, a linear increase in the magnitude of the offshore uniform horizontal velocity and a constant local acceleration with increasing time are both identified. The partially depth-averaged value of the non-dimensional pressure gradient is equal to a small negative constant (−0.0115) in the offshore direction, indicating that the bore is subject to a constant favorable pressure gradient.

The third-order asymptotic solutions in the Lagrangian description for interfacial internal waves in a three layer fluid system

In this paper, we discuss the interfacial internal waves with a rigid boundary in a three-layer fluid system, where the density of the upper layer fluid is smaller than that of the lower layer. With the Lagrangian matching conditions at the interfaces, the first-order solutions, the second-order solutions and the third-order asymptotic solutions for the interfacial internal waves are obtained in the Lagrangian description using the perturbation method, and the mass transport velocity, the wave frequency, the mean level and the particle trajectory are also given. The results show that the discontinuities across the interfaces appear for the mass transport velocity, wave frequency and mean level, but we find that these discontinuities may disappear if the water depth ratio and the density ratio of the three layer fluids satisfy certain conditions.

Comparison of measured dam-break flood waves in triangular and rectangular channels

Dam-break flows in both triangular and rectangular channels are investigated experimentally in the present study. Laboratory measurements are carried out in a prismatic and smooth flume with a horizontal and wet bed for two different reservoir heads and four tailwater levels. During the experiments, digital image processing is applied as a flow measurement technique. Both water surface profiles and stage hydrographs are obtained effectively by means of video images with eight adjacent cameras. The dam-break flows in triangular and rectangular channels show common features: jet formation in the downstream of the dam during the initial dam-break stage; similarity of the water surface profiles behind the dam for different depth ratios at a specific time; insignificant effects of the depth ratio on the negative wave front; and strong dependence of the shock wave front on the depth ratio. In a triangular channel, the negative wave front moves slower than that in a rectangular channel; and extra negative waves propagating towards upstream direction does not form for all depth ratios considered in this study while they have been observed in a rectangular channel for large values of α representing the ratio of initial tailwater depth and reservoir depth (i.e., α = 0.3 and 0.4). Meantime, these extra negative waves result in an undulation of the water surface profile in the reservoir and an apparent increase of water depth at the dam. The water depth at the dam section for different depth ratios is 60–70% of the initial reservoir head; and the shock wave front propagates slower as the depth ratio increases for the triangular channel. For water depth ratios α = 0.1 and 0.2, the shock wave front moves faster than that in a rectangular channel, and the contrary is true for α = 0.4. For α = 0.3, the propagation speed of the shock wave front approximates that in a rectangular channel. Present study contributes to the understanding of the effect of wet downstream conditions on dam-break flows in triangular channels and provides detailed experimental data for validating both the analytical and the numerical solutions.

Frequency domain prediction of peak nonlinear wave heights of structure-TLD systems

Prediction of peak wave heights early in the TLD design process is critical to ensure proper tank freeboard is allocated. If insufficient freeboard is allocated, the performance of the TLD may be adversely affected by the waves impacting with the tank ceiling. A frequency domain model is developed to predict the spectral response of the first two TLD sloshing modes. A probability density function of the wave height envelop for the first two sloshing modes is derived and employed to predict the peak wave height expected during a specified duration of time.Scale-model structure-TLD tests and nonlinear simulations are employed to evaluate the proposed frequency domain model. The model predicts the RMS response of the second order sloshing mode within a relative error of 15% when compared to simulations. The error increases when the water depth ratio is small. The predicted peak structural responses are in excellent agreement with those that are simulated or measured. The predicted peak TLD wave heights show a maximum error of 20% for all the cases considered. The peak factor relating the peak wave height to the RMS response of the fundamental sloshing mode increases with a decreasing liquid depth and increasing RMS response amplitude. The proposed model enables a rapid estimation of the peak wave response without resorting to computationally expensive nonlinear time domain simulations.

Organic matter and nutrients removal in hybrid constructed wetlands: Influence of saturation

Three hybrid wetland systems were studied for organics and nutrients removal from synthetic wastewater recipe. Each system included a vertical flow (VF) followed by a horizontal flow (HF) wetland. The wetlands were filled with common and unconventional media (gravel, biochar and sand) with different saturation and water depth ratio. Input N, P and COD loadings ranged between 48–145, 1–7 and 56–191 g/m2 d, respectively across first stage VF wetlands. Recalcitrant compounds of synthetic recipe reduced organics removals in VF wetlands. NH4-N adsorption and carbon leaching properties of biochar triggered N removals (19–102 g/m2 d) in partially saturated VF wetlands. Carbon unavailability influenced N removals in gravel based unsaturated VF wetland. Input N load increment reduced nitrification and NH4-N adsorption in VF wetlands. However, such increment improved N removal percentages in shallow water depth second stage HF wetlands, primarily due to removals in previous stages and atmospheric oxygen transfer via unsaturated zone; HF wetland with deep water depth showed opposite removal trend. P removal in experimental wetlands was achieved via media based adsorption; decrease of P concentration in synthetic recipe enhanced removals. N and P contents percentage (with respect to total removal) in plants ranged between 1 and 7% (VF), 5–17% (HF) and 2–36% (VF), 23–35% (HF), respectively, indicating dominance of microbial transformation and media based adsorption on observed removals. Partially saturated-shallow water depth hybrid wetland systems achieved ≥90% BOD, ≥97% N and 100% P removals. This study signifies potential application of partially saturated-shallow water depth hybrid wetland systems packed with unconventional media for wastewater treatment.