Flow Wetland Research Articles

Effects of bulk degradation and boundary absorption on dispersion of contaminant in wetland flow

The paper presents transport phenomena of solute in a shallow wetland channel considering the effects of the bulk degradation and boundary absorption at both the channel banks. A piece-wise uniform mesh on the finite difference implicit scheme is adopted to investigate the present problem. The current solution has achieved an excellent agreement with the existing experimental and numerical results. It is seen that the transport of contaminant in the width dominated wetland stream is influenced by various parameters such as boundary absorption, bulk degradation, vegetation parameter, tortuosity and dispersion time. The significant effects of the bulk degradation and boundary reactions are observed on the contaminant emission. The work measures the dispersion of contaminant in both longitudinal and transverse directions. Also, the transversal and longitudinal mean concentration distributions are shown in the shallow wetland flow. The results of this study may be used to control the water degradation, flood mitigation and coastal protection.

Spatiotemporal Variations in Water Flow and Quality in the Sanyang Wetland, China: Implications for Environmental Restoration

Spatiotemporal modeling of wetland environments’ hydrodynamics and water quality characteristics is key to understanding and managing these ecologically important areas’ physical and environmental properties. We developed a two-dimensional numerical model based on the MIKE 21 module to analyze flow and pollution dynamics in the island-dominated Sanyang wetland of eastern China. Three simulation periods representing annual precipitation cycles were used to model freshwater discharge and water quality in the wetland. The results showed that the flow velocity in the study area had hydrodynamic characteristics typical of such a setting, with an average monthly flow velocity ranging from 0.01 to 0.04 m/s, contributing to an increased risk of serious eutrophication. The water quality problems (represented by ammonia nitrogen, NH3-N, and total phosphorus, TP, levels) peaked during the early summer peak rain season, followed by a gradual decline during a later flood period and the lowest values during the fall/winter dry period. Moreover, the spatial distribution of NH3-N and TP levels decreased from northwest to east, reflecting the influence of a highly polluted source. Our results provide a useful context for restoration efforts in the Sanyang wetland and other similar areas.

A comparison of radon, heat tracer and head gradient methods to quantify surface water - groundwater exchange in a tidal wetland (Kooragang Island, Newcastle, Australia)

Subsurface flow plays an important role in the functioning of wetlands and in the maintenance of their ecosystem services. Specifically, the transport and exchange of dissolved matter between sediments and surface waters is regulated by subsurface flow, which can strongly affect ecological zonation and productivity. Having a quantitative understanding of this subsurface flow is therefore important. Field techniques based on Darcy’s equation or natural tracers are often used separately to assess flows. Here, radon and heat (both natural groundwater tracers) and Darcy’s equation are used simultaneously to quantify the subsurface flow in a tidal wetland (Kooragang Island, Newcastle, Australia) and the results of the independent methods are compared. A steady-state radon mass balance model indicated an overall net subsurface exfiltration of 10.2 ± 4.2 cm/d while a 1D, vertical fluid heat transport model indicated a net exfiltration of 4.3 ± 2.9 cm/d. Flow estimated from analysis of hydraulic heads indicated an exfiltration rate of 3.2 ± 1.8 cm/d. The difference in flow rates is likely due to the localised measurement of the heat and head methods relative to radon, and therefore, these methods are less likely to capture zones of preferential subsurface flow. The main advantage of radon is that it provides the total subsurface flow regardless of the driving force. While head gradient or heat tracer method have the advantage of temporally quantify infiltration and exfiltration, we highlight that these methods may underestimate subsurface flows in highly dynamic coastal systems, such as tidal wetlands where a large portion of the subsurface flow is recirculated seawater. This could potentially lead to errors in solute flux estimates. This study highlights the importance of employing a multi-tracer approach and has implications towards quantifying the hydrological export of dissolved constituents (e.g., carbon and nitrogen) in coastal wetlands.

Revisiting Surface-Subsurface Exchange at Intertidal Zone with a Coupled 2D Hydrodynamic and 3D Variably-Saturated Groundwater Model

A new high-performance numerical model (Frehg) is developed to simulate water flow in shallow coastal wetlands. Frehg solves the 2D depth-integrated, hydrostatic, Navier–Stokes equations (i.e., shallow-water equations) in the surface domain and the 3D variably-saturated Richards equation in the subsurface domain. The two domains are asynchronously coupled to model surface-subsurface exchange. The Frehg model is applied to evaluate model sensitivity to a variety of simplifications that are commonly adopted for shallow wetland models, especially the use of the diffusive wave approximation in place of the traditional Saint-Venant equations for surface flow. The results suggest that a dynamic model for momentum is preferred over diffusive wave model for shallow coastal wetlands and marshes because the latter fails to capture flow unsteadiness. Under the combined effects of evaporation and wetting/drying, using diffusive wave model leads to discrepancies in modeled surface-subsurface exchange flux in the intertidal zone where strong exchange processes occur. It indicates shallow wetland models should be built with (i) dynamic surface flow equations that capture the timing of inundation, (ii) complex topographic features that render accurate spatial extent of inundation, and (iii) variably-saturated subsurface flow solver that is capable of modeling moisture change in the subsurface due to evaporation and infiltration.

Neuronal Brownian dynamics for salinity of river basins’ water management

Salinization of streams, rivers and other water sources threaten the civilizations, ecologies enduring constituent species that results in rendering the precious water unusable for human chores. Increase in salinity across the flow in streams and wet-lands have been mostly to raise a concern towards salt tolerance to various limits. Hence, it becomes important to monitor the acidity/alkalinity causing water parameters that can be referred to as salinity. The prime measure scale of salinity is the quality of potential-of-hydrogen (pH) present in river waters at two sample locations. Two locations that have been identified by CPCB as per the highly reported pollutants’ level found, have been analysed through artificial-intelligence (AI) conjucted with Multivariate Adaptive Regression Spline (MARS). The hybrid of wavelet neuro-fuzzy inferences with that of MARS (WNF-MARS) predicted with more accuracy. Simulation of performance measures: root meant square error (RMSE); mean absolute error (MAE); goodness-of-fit (R2) together with their execution time for the three prototypes provided remarkable results. RMSE outcomes diminish on the whole on applying the training and validating data division in Wavelet conjucted MARS and WNF-MARS as compared to studying the data through MARS. Goodness-of-fit statistic analysed the concentration levels of salinity in the river at the identified sites. Thus, it is observed from this study that the pH levels provide future estimation of inapt quality of water at the source, so that it prohibits the further-decay of water consumed in the ecosystem. Thus, these predictors would be helpful towards formulation of strategies for protection of vegetation and other required purposes.

Numerical study on dispersion of fine settling particles in a depth dominated wetland flow

Wetlands were long considered a nuisance because they were not suitable for growth of many agriculture products. Nowadays, owing to it’s importance in agriculture engineering, wetlands are invaluable to the mankind. Wetlands due to their commanding influences on ecosystem, benefited people and the environment in terms of water supply, climate regulation, biodiversity conservation and contaminant erosion are very useful in water resources. This investigation presents a numerical approach to detect the environmental dispersion of the fine particles with settling velocity in a wetland flow. A finite difference implicit scheme with layer-adapted mesh is employed to find the solution of the problem. The consequences of the various relevant parameters on the flow and concentration profiles are illustrated graphically. The computed concentration profiles agreed well with the existing experimental data as well as with the numerical solution. The vertical concentration profiles of fine settling particles are presented in different downstream stations with various settling velocities. It is found that the mixing of tracers into the wetland stream significantly influenced by settling velocity, dispersion time, damping factor, porosity, tortuosity, and mass dispersivity. This study finds great importance in understanding and organizing the elementary methods of wastewater treatment and flood damage control in natural and manufactured wetland flows.

Blue, green and in-between: objectives and approaches for evaluating wetland flow regimes based on vegetation outcomes

Evaluating wetland vegetation responses to flow regimes is challenging because of the inherently complex, variable and dynamic nature of wetland vegetation in space and time. We propose four principles to guide the development of management objectives and evaluation approaches to support adaptive management of wetland vegetation in flow-managed systems. First, we assert a need for more explicit, direct and defensible alignment of management objectives, targets and indicators to reflect broader ecological, sociocultural and economic values, and the underlying ecosystem functions that support them. Second, we propose a framework for indicator selection across multiple spatiotemporal scales and levels of ecological organisation, from individuals to landscape mosaics (vegscapes). Third, we emphasise the need to evaluate vegetation condition and responses to environmental flows in relation to a more nuanced understanding of temporal flow dynamics. Finally, we discuss the importance of considering the effects of non-flow variables that can modify vegetation responses to environmental flows. We highlight key knowledge needs required to support the implementation of these principles, particularly the urgency of improving our understanding of ecological, sociocultural and economic values of wetland vegetation and the attributes and functions that support these values.

Transport model of active particles in a tidal wetland flow

A concentration transport model has been formulated to characterize the transport of a mass of self-propelling active particles in an unsteady wetland flow at the phase-averaged scale. The vertical distribution and motion of mass center are rigorously derived for an active-particle cloud in the tidal wetland flow by use of the concentration moment method, while the longitudinal dispersivity is calculated by means of finite difference method. It is found that the distribution of total quantity of active particles in each streamline in the tidal wetland flow is identical to that in the fully developed wetland flow. The velocity and longitudinal dispersivity of mass center of the active-particle cloud eventually reach a stable oscillatory status for the case of tidal wetland flow rather than an asymptotic constant velocity which occurs in the steady wetland flow. The effects of dimensionless parameters on the amplitude, phase and period of the velocity of mass center and longitudinal dispersivity are discussed in detail for the active-particle cloud in the tidal wetland flow.

Lateral concentration distribution of contaminant transport in tidal wetland flows

Tidal flows, in addition to the vegetation, introduce considerable complexity into the transport of contaminants in wetland flows. Under the hypothesis that wetlands can be treated as porous media, we apply the phase averaging technique to obtain the apparently continuous concentration distribution at the macro phase-average scale in tidal wetland flows, rather than the extremely complex concentration distribution at the micro plant scale. To meet the requirements of precise concentration in terms of peak concentration position and value for strict environmental and health risk assessments, this work studied the lateral concentration distribution rather than the generally studied approximate longitudinally distributed mean concentration. The lateral concentration functions for tidal wetland flows are concretely derived to support the first-order series expansion of the generalized dispersion model. We show that the lateral concentration nonuniformity can be qualitatively altered as the contaminant cloud is carried back upstream by tidal flows. The peak concentration position periodically appears at the center line or at the wall depending on the tidal flows, and the peak concentration value can even be increased in the transport process. Due to its analytical features, this work provides a model with low computational cost for effective environmental management.

Gate operation for habitat-oriented water management at Budai Salt Pan Wetland in Taiwan

Commercial salt pans around the world act as important habitats for waterbirds due to their unique trophic and physical attributes. Today, most commercial salt pans in Taiwan have been decommissioned and many have been designated as protected wetland habitats. Due to the dike and water gate systems controlling water flow in the salt pan wetlands, water management plans are important for habitat maintenance. Despite this, creation and implementation of habitat-oriented water management plans in protected salt pan wetlands is not common practice, especially in areas where flooding is a concern. In order to understand the potential for implementing water management plans for habitat creation in salt pan wetlands located in flood prone regions, this study designed and conducted three water management experiments for Budai Salt Pan Wetland, a wetland of national importance along the southwestern coast of Taiwan. The three experiments were designed to better understand the impacts of allowing water into the wetland during both the end and the beginning of the dry season in Taiwan. The design of each water gate operation was unique, based on the initial hydrologic conditions, and needs of the experiment in order to inform the design of future water management plans for the wetland. The consequent influence of gate operations on water depth, salinity, and immediate bird use of the wetland were analyzed. The experiments show that the water management techniques adopted in the study can allow for the creation of habitat types with varying water depths and salinity while not increasing flood risk to surrounding communities. Because the gate operation experiments were short term, a complete understanding of bird responses was limited. Even so, the responses of waterbird communities to these depth manipulations did indicate the potential of water management to increase foraging opportunities. The methods and findings of this research can inform wetland management and policy throughout Taiwan and the rest of the world.

Impact of Dynamic Storage Management of Wetlands and Shallow Ponds on Watershed-scale Flood Control

This paper presents a case study on the impact of dynamic management of wetland storage on downstream flood control at the Cypress Creek Watershed in Houston, Texas. Dynamic storage management is performed by optimizing the schedule of flow releases from managed wetlands for minimizing downstream inundation. The novelty of this study is to increase the available storage capacity of wetlands on a watershed scale and thus improve their performance on flood mitigation. The main objective of this study is to compare the extent of downstream flood inundation with and without dynamic management of wetland storage. This study used HEC-HMS for the overland flows and the level pool routing in the wetlands and HEC-RAS for simulating river inundation. Wetlands were implemented in the midstream region of the watershed. The schedule of optimal wetland flow releases were determined using the MATLAB Genetic Algorithm toolbox. The optimization results indicate that, when wetland size exceeds a fairly low threshold, dynamic storage management of wetlands can significantly reduce flood area, flood depth and flood duration at the downstream region of the watershed compared with the case without dynamic storage management.

Open channel flow within and above a layered vegetation: Experiments and first-order closure modeling

Flow within vegetation characterized by non-uniform roughness density is drawing significant research attention given its relevance to a plethora of applications in eco-hydraulics including river restoration, and flow in wetland and marshes. The focus here is on flume experiments and modeling of the mean longitudinal velocity profile in a two layered cylindrical vegetation system. Layer 1 represents the region close to the channel bottom where the flow experiences maximum drag due to the densely placed vegetation, while layer 2 represents the flow region above the short vegetation characterized by a smaller vegetation density. Considering the aforementioned arrangements, a new analytical model based on Reynolds-averaged closure principles is proposed to describe the vertical distribution of mean streamwise velocity in an open channel with two different vegetation densities. In the proposed model, the one-dimensional steady and planar-homogeneous momentum equation is used where the turbulent eddy viscosity is assumed to be linearly related to the local mean velocity. The proposed analytical model has been calibrated using experiments reported here in which vegetation is represented by using circular plastic cylinders of two different heights. The proposed model is further tested against published experiments with similar arrangements. In total, 22 different experimental conditions with distinct densities, rigidity, and flow depths have been analyzed. The Root Mean Square Error (RMSE) of the velocity comparisons is found to be less than 0.0342 m/s, which is acceptable.

Transient Solute Dispersion in Wetland Flows With Submerged Vegetation: An Analytical Study in Terms of Time‐Dependent Properties

AbstractPredicting the concentration distribution of solute transport in vegetated flows is significant for associated environmental applications in water resources. While a semianalytical study has been made for the steady dispersion with a continuous release (Rubol et al., 2016, https://doi.org/10.1002/2016WR018907), an in‐depth analytical investigation has yet to be performed for the more complicated case of transient dispersion due to an instantaneous release. In regard to the pioneering benchmark observation (Murphy et al., 2007, https://doi.org/10.1029/2006WR005229) of transient solute dispersion in a submerged vegetated flow for an instantaneous source release at the top of the canopy, an extensive analytical effort is paid in this work to derive the time‐dependent basic properties and to investigate the temporal evolution of concentration distribution. Obtained large‐time asymptotic dispersivities agree well with available experimental results (Murphy et al., 2007, https://doi.org/10.1029/2006WR005229), with higher significance ( , ) for correlation between analytical results and experimental data. Analytical solutions covering effects of dispersivity, skewness, and kurtosis of detailed concentration distribution are compared satisfactorily with numerical results obtained by the random displacement method. The findings illuminate the applicability of this analytical approach in environmental risk assessment and water quality management.

Estimating Late 19th Century Hydrology in the Greater Everglades Ecosystem: An Integration of Paleoecologic Data and Models

Restoration of the Greater Everglades Ecosystem requires an understanding of the hydrology of the natural system prior to significant alterations due to water management and land use. Large scale models such as the Natural Systems Model (NSM 4.6.2) have been used by the South Florida Water Management District and other agencies responsible for restoration to estimate past hydrologic conditions; however, these models typically portray a drier natural system for the beginning of the 20th century than what is indicated by paleoecologic analyses and historical data. The purpose of this study is to estimate pre-20th century water levels, hydroperiods and flow in the freshwater wetlands of the Everglades by using pollen assemblage data in three sediment cores to adjust the Natural Systems Model. This study is designed to further test estimates of flow through the Everglades derived from analysis of sediment cores collected in Florida Bay. The results demonstrate that the NSM 4.6.2 underestimates water levels and hydroperiods in the Everglades compared to the paleo-adjusted NSM 4.6.2 model outputs. Flow models that use the paleo-adjusted water levels as input indicate flow through Shark River Slough in the late 19th century was approximately two times observed levels, and flow through Taylor Slough was approximately three times observed levels. The flow estimates derived from this study agree with the estimates derived from earlier studies using estuarine cores.

Analyzing solute transport in modeled wetland flows under surface wind and bed absorption conditions

Both surface wind and bed absorption can greatly impact the pollutant dispersion processes, however, the two factors are not jointly considered in existing models due to the intricacy of analyzing the simultaneous influence of surface wind shear and bottom bed absorption. In this work, a multi-scale approach is employed to formulate the environmental dispersion process with both factors considered jointly within wetland flows. By adopting this method, the effect of wind and bed absorption on vertical concentration distribution and longitudinal concentration distribution are discussed. To visualize the results, the flow velocity contours under different wind conditions (i.e. upstream wind and downstream wind), the pollution concentration distributions versus time and spatial position, and the spatial contaminant cloud contours are presented. Moreover, numerical experiments of the interested scenarios are presented to verify the accuracy of the analytical method. The comparison shows that the results of the proposed multi-scale method agrees well with the dataset generated numerically. Finally, the multi-scale method in this work is compared to the Aris? concentration moment method in the literature by setting the bed absorption rate to zero. The comparison shows that the present model can reduce the substantial integration processes and derive accurate spatial concentration profiles.

Contaminant transport in wetland flows: Different fate between the upper and bottom layers

Abstract The mechanism of contaminant transport in wetland flows plays a central role in various applications. A two-zone model is applied to study the transport process. The significantly different fate of concentrations between the upper and bottom layers is characterized. This model provides a practicable and useful tool to quickly capture the evolution of contaminant concentration, being of particular importance in engineering science. The results agree well with the numerical solutions, which reveal that the concentrations in the fast-moving zone in the upper layer and in the slow-moving zone in the bottom layer perform quite different in the transient dispersion stage. The two concentrations respectively form a leading right-skewed Gaussian curve and a tailing left-skewed Gaussian one. Under the effect of vertical diffusion at the interface of two zones, the two concentrations gradually approach the depth-averaged mean, and all evolve to asymptotically Gaussian distribution finally. The concentration variation rate between the two zones reaches about 50 % as the process falls into the asymptotic Taylor dispersion stage at dimensionless time 1.0. And it remains about 10 % even at one order larger dimensionless time 10.0. The findings of the different fate of two concentrations will offer meaningful information to study the benthon and plankton in related areas.

Solute dispersion in wetland flows with bed absorption

Bed absorption and vegetation in natural wetlands exert considerable influence on contaminant transport. A three-scale perturbation method is extended in this work to present an exact analytical solution for the spatial concentration distributions affected by vegetation distribution and bed absorption. Compared with concentration moments-based analytical methods that were adopted previously to solve vertical concentration distribution in wetland flows, the multi-scale method used in this study is more concise without complicate integrated operations. The analytical solution is explicit and applicable without complicated integral form. Moreover, by comparing with the analytical solution obtained by the moments method, the analytical solution given in this work is accurate particularly after the initial stage. This study focuses on a large time scale in investigating spatial concentration distribution. Results show that concentration distribution is not uniform in the vertical direction. Hence, this study recommends the accurate two-dimensional spatial distribution rather than the cross-section averaged concentration distribution to achieve accurate concentration predictions.

Effect of bed absorption on contaminant transport in wetland channel with rectangular cross-section

Predicting the evolution of concentration distribution for contaminant transport in wetland flows has a wide range of ecological applications. To account for the ecological effect such as substrate absorption, the influence of bed absorption on the dispersion process of contaminant transport in a wetland channel with rectangular cross-section is analytically investigated in this study by the technique of long-time asymptotic expansion. The combined effects of bed absorption, free-water-surface-effect and the bank-sidewall-effect are demonstrated, by parameter analysis in terms of the bed absorption coefficient and the aspect ratio of the channel section. The studied cases illustrate that bed absorption decreases the total mass of the contaminant cloud retained in the flow and causes the contaminant cloud to concentrate more in the upper layer. The mean advection velocity of the contaminant cloud increases as the intensity of bed absorption amplifies. Environmental dispersivity is augmented with bed absorption in a deep wetland channel, which is inverse in a shallow channel. The effect of bed absorption weakens the positive skewness of the cross-sectional mean concentration distribution when the wetland channel approaches square, while strengthens the negative skewness of the cross-sectional mean concentration distribution when the channel is relatively shallow. Moreover, the cross-sectional mean concentration decays faster under the effect of bed absorption. For applications, the critical length and duration of the influenced region are presented with bed absorption.

On the bicomponent contaminant transport in wetland flow with reactions

Contaminant transport in the wetland flow is subject to various reactions. Most researches on this topic have limited to the single component contaminant, relatively little has concerned the effect of competitive reaction on the transport of coupled bicomponent contaminant. This work analytically studies the bicomponent contaminant transport in the free surface wetland flow under the combined conditions of reversible competitive transfer, irreversible degradation and bed absorption, by solving the constant-coefficient second-order linear system of parabolic type and the method of concentration moments. Up to the fourth order concentration moment in the previous work (Wang and Chen, 2017a) is applied to support the fourth order expansion of Hermite polynomials to rigorously derive the solutions with high accuracy. The results demonstrate that the masses of binary components decay at different rate, and the vertical concentration distributions of binary components are tremendously non-uniform in the asymptotic dispersion stage. Three types of reactions in addition to the hydraulic dispersion exert separate control on the concentration distributions. It suggests that the peak concentration rather than the mean should be based for strict environmental implements.

Theoretical and numerical analysis of vertical distribution of active particles in a free-surface wetland flow

Presented in this paper is a theoretical and numerical analysis for active particles in a fully developed steady wetland flow dominated by the free-surface effect. An ecological risk assessment model for the concentration distribution of active particles is devised as an extension of the general form of concentration transport equation for passive particles in wetland flows. The vorticity in the free-surface wetland flow is found to depend on the dimensionless parameter α, which reflects the combined action of vertical momentum dispersion, microscopic curvature of flow passages, friction of vegetation and water depth. The large α results in the decrease of vorticity at the free surface and the increase at the bed bottom. The analytical solution of stable concentration distribution is rigorously derived for the active particles in both weak and strong vortical flows, under the combined action of the effective mass dispersion by the ambient flow, as well as the translational diffusion and vertical swimming by the active particles. It is found that the strong vorticity weakens the concentration of active particles in the free-surface wetland flow, while the strong diffusion, by the wetland flow and active particles, enhances the concentration. The large α results in the increase of concentration near the free surface and the decrease of concentration near the bed bottom. The time scale for active particles to reach the stable concentration distribution is mainly dependent on the dimensionless parameter, Pe, which reflects the relative strength of the vertical swimming and the total diffusion due to the wetland flow and the active particles.