Flow Wetland Research Articles

Application of satellite altimetry in understanding river–wetland flow interactions of Kosi river

Flood-plain wetlands are the seasonal water bodies formed along a river. These wetlands become active during the monsoon season, which frequently grow in size with seasonal floods and eventually dry up during the non-monsoon season. The flow interaction between flood-plain wetlands and the river sometimes vary over a very short period in response to rapid rise in the river water level due to high precipitation in its upstream catchment. Understanding the complex flow interactions between the river and its associated flood-plain wetlands with field-based measurements of wetland hydrologic characteristics is always a challenging task. To overcome these challenges, an attempt has been made to utilise Topex/Poseidon satellite altimetry-derived water levels into a hydrodynamic model (HEC-RAS) to study river and wetland flow interactions in the lower reach of the Kosi river in India. The satellite altimetry-derived water levels and Landsat satellite images on the Kosi wetlands are used to develop volume-elevation relation. HEC-RAS is setup over the study area and calibrated for different values of manning’s roughness coefficient (n) for the river bank and the main channel of the river for the period of 1993–1996. Unsteady flow simulations are carried out for different monsoon seasons to simulate daily river flow interaction (inflow/outflow) between river and wetlands. Statistical analysis is performed between the altimetry-derived and the model-simulated water levels. It is found that simulated water levels are in good agreement ( $$R^{2}=0.87$$ , root mean square error of 0.84 m and Nash–Sutcliffe efficiency coefficient of 0.85) with altimetry-derived water levels. The analysis of simulations indicates that interactions between the wetland and the river are bidirectional with most of the flow coming out from the river during the month of August and leaving out from the wetlands during the month of September. The wetlands respond in three different ways, i.e., (i) gaining stage, (ii) wetland and river in equilibrium and (iii) loosing stage, which is reflected on water levels of the river and wetland. This study demonstrates complex interaction processes happening between the Kosi river and its surrounding wetlands.

Comparative study on different horizontal subsurface substrates in flow wetlands

A greenhouse experiment has been conducted to study the effect of using different wetland substrates that have been compiled on the basis of effluent treatment efficiency. Wetland beds have been prepared with locally available plants, in particular (Phragmites Australis). The effectiveness of the treatment was evaluated on parameters such as biological oxygen demand (BOD), chemical oxygen demand (COD), total Kjeldahl nitrogen (TKN), total suspended solids (TSS) and total phosphorus (TP). The results indicate that nutrient reduction corresponds to lower flow in wetland beds. At the lower flow rate of 2.34 m3/day, the system with plastic supports showed the highest removal efficiencies of BOD, COD, TKN, TSS and TP in percentages of 74.42, 74.9 %, 63.28, 87.49 and 71.29 %, correspondingly.

The new German standard on constructed wetland systems for treatment of domestic and municipal wastewater.

The German Association for Water, Wastewater and Waste e.V. (DWA) has published a new standard for the dimensioning, construction, and operation of constructed wetlands for treatment of domestic and municipal wastewater. The changes to the standard are based on a wide range of experience gained in recent years in Germany and Europe. For the first time ever, the standard has been officially translated and published in English. This paper summarizes the new standard for secondary treatment of domestic wastewater with classical one-stage unsaturated vertical flow (VF) wetlands, VF wetlands with lava sand for treatment of wastewater from combined sewer systems, and actively aerated VF and horizontal flow (HF) flow wetlands. Two-stage unsaturated VF wetlands treating raw wastewater (French VF wetlands), are also included in the new standard. HF wetlands are no longer described in the standard for secondary treatment of domestic wastewater. This does not exclude their application. Existing HF wetland systems in Germany may continue to be operated so long as effluent parameters are met and proper operations and maintenance is ensured. This paper gives an overview of the new design standard, including key information on wastewater type and loading, as well as primary attributes of each wetland design.

Indicators for contaminant transport in a periodical wind-driven wetland flow

Understanding indicators for contaminant transport in wetlands under wind is essential to agricultural pollution assessment associated with chemical fertilizers and pesticides. Presented in this paper is an analytical study of indicators for contaminant transport in a periodical wind-driven wetland flow. Analytical solutions of velocity profile, total quantity of contaminant in a streamline, position and moving velocity of mass center of contaminant cloud, and environmental dispersivity are rigorously derived and analyzed for a typical wetland flow under the combined action of periodical wind stress and superficial pressure gradient. It is found that the flow direction changes alternatively only for a large oscillatory wind stress. For instantaneous emission of multiple point sources, the total quantity of contaminant in each stream line parallel to the free surface is dependent on the initial distribution of contaminant only in the initial stage and eventually reaches a constant. For long time evolution of contaminant cloud, the mass center of contaminant cloud oscillates periodically around the origin of a coordinate system moving at a speed of the mean value of depth-averaged velocity during one period, and corresponding oscillatory amplitude enhances with the increasing oscillatory wind stress. The amplitude of environmental dispersivity increases with the increase of oscillatory wind stress, and negative environmental dispersivity appears for partial time in an oscillatory period for a large oscillatory wind stress.

Transient dispersion of an initial point pollutant concentration in wetland flows.

Initial point pollutant transport in wetland flows acts as a typical form in various applications. Accurate determination of the basic characteristics for dispersion fundamentally supports the predication of pollutant transport especially in the transient stage. This work analytically studies the transient dispersion of an initial point pollutant concentration in wetland flows through the phase average technique and the method of concentration moments. The characteristics including the vertical mass distribution, longitudinal displacement, dispersivity, skewness, and kurtosis corresponding to the zeroth- to fourth-order concentration moments are accurately illustrated in their full-time dependance for the first time. Present results show to be distinctive from those of initial uniform concentration in the transient dispersion process. The temporal evolutions of the five characteristics are all dependent of the initial point release position. The results further demonstrate that the timescale 3.0 as measured by the skewness, rather than 0.5 as measured by the dispersivity, should be characterized as the transient period for the dispersion of initial point concentration in comparison with that of initial uniform. Furthermore, the longitudinally distributed mean concentration is as well analyzed through the Hermite polynomials. The results imply that strict criteria for environmental and ecological implications should be established by further accounting for the five characteristics.

Indicators for evaluating uncertainties of solute concentration prediction in wetland flows

Abstract Solute transport in wetland flows is an important process to understand for agricultural practices, providing essential information to assist in decision making and regulation for both cases of agricultural water contamination and agricultural pollution. Recent study has suggested that in the application of the one-dimensional Taylor dispersion model for solute concentration distribution in wetlands, uncertainties can arise even when contaminants are initially released at the same streamwise location. In this paper, we present an analytical study of instantaneous point-source release of solute in a wetland flow dominated by bank wall effects. The movement of the solute centroid and the long-term asymptotic Taylor dispersion coefficient are determined by the Aris concentration moment method, which are required for quantifying the streamwise distribution of the mean concentration and the transverse concentration distribution profiles. It is shown that the additional longitudinal displacement serves as a key indicator revealing the uncertainties of concentration distribution caused by different lateral positions of the contaminant release. More indicators including the lateral concentration distribution and the relative difference of the concentration are analyzed in detail. With given physical parameters, simple applications are provided to illustrate the streamwise transport of the solute plume centroid and the evolution of the additional longitudinal displacement affected by the bank wall effects.

Environmental transport in wetland channel with rectangular cross-section: Analytical solution by Chatwin’s asymptotic expansion

Predicting the evolution of concentration distribution of environmental transport in wetland flows has a broad range of applications in ecological engineering practice. By extending a previous study, the spatial concentration distribution of solute transport due to an instantaneous environmental emission in a wetland channel with rectangular cross-section is presented in this work by means of Chatwin’s long-time asymptotic technique. To account for the effect of high order moment, skewness of the transverse mean concentration distribution is analyzed. Two important parameters, i.e., aspect ratio (depth to width) and damping factor, on the dispersion process are discussed. Four studied cases illustrated that the transverse concentration distribution is nonuniform even at large time and the aspect ratio can affect the transverse concentration distribution greatly. The cross-sectional mean concentration distribution is asymmetrical in the initial stage and shows an asymptotic Gaussian distribution at large time. The dispersion process in a thick (width equals depth) wetland channel is quicker than that in a thin wetland channel. The spatial concentration distribution is dominated by the lateral-sidewall-effect on a large time scale for environmental transport in a thin wetland channel.

Indicators for contaminant transport in a three-layer wetland with wind

Abstract The effect of global climate change is increasing and it can influence agriculture in many ways, especially in that it makes great threaten on agricultural water resources. Since agricultural water supply is a key issue for agricultural production, indicators for contaminant transport in wetlands should be considered in order to solve agricultural water pollution and promote water protection. In this paper, we analyze the environmental dispersion in a typical three-layer wetland flows with the effect of wind taken into account. The analytical solution for velocity distribution is rigorously derived and the dependence of characteristic parameters on averaged dimensionless velocity is recorded. The asymptotic analysis theory of Gill is employed to measure dispersivity for natural wetland flows with a commonly high Peclet number. Both velocity and environmental dispersion are significantly influenced by wind, in terms of its direction and the magnitude of force. The effects of hydraulics and ecological degradation are considered to obtain the analytical solution for the mean concentration and maximal critical length of the region influenced by the process of contaminant transport.

Environmental Benefit of Improving Wastewater Quality: A Shadow Prices Approach for Sensitive Areas

The use of effluents from wastewater treatment plants (WWTPs) as a non-conventional source of water for wetlands in arid and semi-arid regions is becoming the most-often sought solution for maintaining water flow in sensitive wetlands there. However, the managing effluent quality should be a requirement because excess nutrients (mainly nitrogen and phosphorus) can generate eutrophication problems in wetlands. In the Mediterranean area in general, wetlands are strongly vulnerable to eutrophication, which is why they are classified as sensitive areas. Our study uses a data set from 24 WWTPs, effluents of which are discharged to wetlands in the coast of Community of Valencia. We use the shadow prices methodology to quantify the environmental avoided costs and the environmental benefit (both in monetary units) of nitrogen and phosphorus removal in wastewater effluent. The results highlight the importance of reducing these pollutants in WWTP effluents for maintaining the suitable water quality in wetlands. Our study demonstrates the potential for using shadow prices methodology for monetary valuation of environmental externalities in wetlands that use treated wastewater as a non-conventional water source.

Analysis of environmental dispersion in a wetland flow under the effect of wind: Extended solution

The accurate analysis of the contaminant transport process in wetland flows is essential for environmental assessment. However, dispersivity assessment becomes complicated when the wind strength and direction are taken into consideration. Prior studies illustrating the wind effect on environmental dispersion in wetland flows simply focused on the mean longitudinal concentration distribution. Moreover, the results obtained by these analyses are not accurate when done on a smaller scale, namely, the initial stage of the contaminant transport process. By combining the concentration moments method (the Aris’ method) and Gill’s expansion theory, the previous researches on environmental dispersion in wetland flows with effect of wind have been extended. By adopting up to 4th-order moments, the wind effect—as illustrated by dimensionless parameters Er (wind force) and ω (wind direction)—on kurtosis and skewness is discussed, the up to 4th-order vertical concentration distribution is obtained, and the two-dimensional concentration distribution is illustrated. This work demonstrates that wind intensity and direction can significantly affect the contaminant dispersion. Moreover, the study presents a more accurate analytical solution of environmental dispersion in wetland flows under various wind conditions.

Evaluation of Existing and Modified Wetland Equations in the SWAT Model

AbstractThe ability to accurately simulate flow and nutrient removal in treatment wetlands within an agricultural, watershed‐scale model is needed to develop effective plans for meeting nutrient reduction goals associated with protection of drinking water supplies and reduction of the Gulf of Mexico hypoxic zone. The objectives of this study were to incorporate new equations for wetland hydrology and nutrient removal in Soil and Water Assessment Tool (SWAT), compare model performance using original and improved equations, and evaluate the ramifications of errors in watershed and tile drain simulation on prediction of NO3‐N dynamics in wetlands. The modified equations produced Nash‐Sutcliffe Efficiency values of 0.88 to 0.99 for daily NO3‐N load predictions, and percent bias values generally less than 6%. However, statistical improvement over the original equations was marginal and both old and new equations provided accurate simulations. The new equations reduce the model's dependence on detailed monitoring data and hydrologic calibration. Additionally, the modified equations increase SWAT's versatility by incorporating a weir equation and an irreducible nutrient concentration and temperature coefficient. Model improvements enhance the utility of SWAT for simulating flow and nutrients in wetlands and other impoundments, although performance is limited by the accuracy of inflow and NO3‐N predictions from the contributing watershed. Editor's note: This paper is part of the featured series on SWAT Applications for Emerging Hydrologic and Water Quality Challenges. See the February 2017 issue for the introduction and background to the series.

Contaminant transport in wetland flows with bulk degradation and bed absorption

Ecological degradation and absorption are ubiquitous and exert considerable influence on the contaminant transport in natural and constructed wetland flows. It creates an increased demand on models to accurately characterize the spatial concentration distribution of the transport process. This work extends a method of spatial concentration moments by considering the non-uniform longitudinal solute displacements along the vertical direction, and analytically determines the spatial concentration distribution in the very initial stage since source release with effects of bulk degradation and bed absorption. The present method is demonstrated to bear a more accurate prediction especially in the initial stage through convergence analysis of Hermite polynomials. Results reveal that contaminant cloud shows to be more contracted and reformed by bed absorption with increasing damping factor of wetland flows. Tremendous vertical concentration variation especially in the downstream of the contaminant cloud remains great even at asymptotic large times. Spatial concentration evolution by the extended method other than the mean by previous studies is potential for various implements associated with contaminant transport with strict environmental standards.

Doing ecohydrology backward: Inferring wetland flow and hydroperiod from landscape patterns

AbstractHuman alterations to hydrology have globally impacted wetland ecosystems. Preventing or reversing these impacts is a principal focus of restoration efforts. However, restoration effectiveness is often hampered by limited information on historical landscape properties and hydrologic regime. To help address this gap, we developed a novel statistical approach for inferring flows and inundation frequency (i.e., hydroperiod, HP) in wetlands where changes in spatial vegetation and geomorphic patterns have occurred due to hydrologic alteration. We developed an analytical expression for HP as a transformation of the landscape‐scale stage‐discharge relationship. We applied this model to the Everglades “ridge‐slough” (RS) landscape, a patterned, lotic peatland in southern Florida that has been drastically degraded by compartmentalization, drainage, and flow diversions. The new method reliably estimated flow and HP for a range of RS landscape patterns. Crucially, ridge‐patch anisotropy and elevation above sloughs were strong drivers of flow‐HP relationships. Increasing ridge heights markedly increased flow required to achieve sufficient HP to support peat accretion. Indeed, ridge heights inferred from historical accounts would require boundary flows 3–4 times greater than today, which agrees with restoration flow estimates from more complex, spatially distributed models. While observed loss of patch anisotropy allows HP targets to be met with lower flows, such landscapes likely fail to support other ecological functions. This work helps inform restoration flows required to restore stable ridge‐slough patterning and positive peat accretion in this degraded ecosystem, and, more broadly, provides tools for exploring interactions between landscape and hydrology in lotic wetlands and floodplains.

Concentration distribution of environmental dispersion in a wetland flow: Extended solution

Hydrological processes of contaminant transport in wetland flows are characterized by environmental dispersion. For concentration distribution of scalar dispersion, the preliminary estimate of vertical distribution (Wu et al., 2015) on small time scale is rigorously extended to account for high order effects as skewness and kurtosis. Based on a combination of Aris’ method of concentration moments and Gill’s generalized dispersion model, up to fourth order terms of vertical distribution functions and full-time two-dimensional concentration distribution are derived. The increments of damping factor, mainly representing the density of vegetation in wetlands, is shown to strengthen the mean distribution asymmetry and reduce the longitudinal dispersivity (with respect to skewness and kurtosis), and to increase the non-uniformity of vertical distribution. Therefore, dense vegetation corresponding to a large damping factor will postpone the time when Taylor’s dispersion model holds, and the first order approximation becomes rough on small time scale, demanding higher order modifications. The results provide more detailed and more accurate analytical solution for the typical environmental dispersion in wetland flows.

Indicators for environmental dispersion in a two-layer wetland flow with effect of wind

For typical two-layer wetland flows where wind occurs frequently, indicators for flow and contaminant dispersion with wind effect are considered in this paper. Based on the general formulation for porous media flows, the velocity distribution of a fully developed flow through a wetland is illustrated, with that for a single-layer wetland flow under wind recovered as a special case. And the contrary wind of high speed might result in the appearance of an inverse-flow layer. For the more complex case of a two-layer wetland flow under wind, the more simplified method of asymptotic analysis is adopted instead of Aris's method of concentration moments to determine the dispersivity in terms of the longitudinal evolution of the depth-averaged concentration. And it is illustrated with the effect of dimensionless parameters. The velocity profile and environmental dispersivity for the two-layer wetland flow in the absence of wind can be included as a limiting case. Both the direction and the strength of the wind can affect the environmental dispersivity considerably under long-term evolution. Analytical solutions for the mean concentration and the region influenced by the contaminant cloud are derived. And for the instantaneous emission of typical contaminant constituents, the related indicators for water quality assessment, such as the critical length and duration of the influenced region are illustrated. The results show that the critical length and duration of the concentration cloud can change considerably because of the wind and vegetation heterogeneity.

Opportunities for hydrologic research in the Congo Basin

We review the published results on the Congo Basin hydrology and summarize the historic and ongoing research. Annual rainfall is ~1900 mm/yr along an east-west trend across the basin, decreasing northward and southward to ~1100 mm/yr. Historic studies using lysimeters, pans, and models suggest that the annual potential evapotranspiration varies little across the basin at 1100 to 1200 mm/yr. Over the past century, river discharge data have been collected at hundreds of stream gauges with historic and recent data at 96 locations now publicly available. Congo River discharge at Kinshasa-Brazzaville experienced an increase of 21% during the 1960–1970 decade in comparison to most other decades. Satellite altimetry measurements of high and low flows show that water levels in the “Cuvette Centrale” wetland are 0.5 m to 3.0 m higher in elevation than the immediately adjacent Congo River levels. Wetland water depths are shallow at about a meter and there does not appear to be many sizable channels across the “Cuvette”; thus, wetland flows are diffusive. Cuvette waters alone are estimated to emit about 0.5 Pg CH4 and CO2 equivalents/yr, an amount that is significant compared to global carbon evasions. Using these results, we suggest seven hypotheses that focus on the source of the Cuvette waters and how these leave the wetland, on the river discharge generated by historic rainfall, on the connection between climate change and the rainfall-runoff generated by the migrating “tropical rainbelt,” on deforestation and hydroelectric power generation, and on the amount of carbon emitted from Congo waters.

Contaminant transport in a three-zone wetland: Dispersion and ecological degradation

To further understand the fate of contaminant transport in real waterways interacting with riparian buffers and adjacent aquatic vegetation, solute dispersion is analytically explored for three-zone wetland flows with usually high Peclet number in this paper. Ecological effects are also taken into account. Environmental dispersion is addressed independently via an exponential transformation of the basic formulation of mass transfer in the context of porous media flow. After rigorously generalizing Taylor’s classical analysis, asymptotic analysis was used instead of the method of concentration moment or multi-scale analysis to simplify the examination. The mean concentration expansion base in Gill’s method is adopted to model concentration deviations produced in the lateral-average operation. With a previously derived velocity profile, environmental dispersivity is obtained, effectively illustrating the effects of critical dimensionless parameters. Analytical expressions for evolution of the lateral mean concentration and critical length of the contaminant cloud are determined by combining the effects of both hydraulic dispersion and ecological degradation. An application example is provided to illustrate the evolution of contaminant cloud in terms of the critical length and duration with concentration greater than a given environmental standard level. Results show that for three-zone wetlands, the duration is clearly increased while the region affected by the contaminant cloud is slightly smaller than that for two-zone wetland flows.

Relative importance of Microcystis abundance and diversity in determining microcystin dynamics in Lake Erie coastal wetland and downstream beach water.

Microcystis population and microcystin (MC) dynamics were investigated in western Lake Erie coastal wetlands and downstream beach water. A three-dimensional (3-D) model was developed to quantify how Microcystis population size and structure affect MCs. Real-time PCR, denaturing gradient gel electrophoresis (DGGE) and enzyme-linked immunoabsorbent assay (ELISA) were used. A moderate-low level of Microcystis abundance and MCs were detected with a significant increase along the wetland flow and the spatiotemporal homogeneity of Microcystis populations. The proportion of toxigenic and nontoxgenic genotypes appeared to be more affected by the variation in two major Microcystis PC-IGS genotypes. MC dynamics was associated with the changing Microcystis population size and structure. The 3-D model showed that Microcystis population with greater Microcystis PC-IGS abundance (and simultaneously higher diversity) had more MCs. Microcystin variation was significantly affected by Microcystis population size and structure. The 3-D model also revealed the relative importance of Microcystis population size and structure in determining MCs in the Lake Erie costal wetland and downstream beach water. This study enriches our understanding of Microcystis population and microcystin ecology in a western Lake Erie coastal wetland and downstream beach water. Our illustrative model brings a new perspective for understanding the ecological relationship between Microcystis population size and structure and MCs.

Unrestricted dairy cattle grazing of a pastoral headwater wetland and its effect on water quality

Unrestricted cattle access to pastoral wetlands can result in increased pollutant loads from agricultural areas. We quantified the time a herd of dairy cattle spent grazing a pastoral headwater wetland and its associated impact on water quality. Over a two year period a herd of ∼220 dairy cattle rotationally grazed a paddock containing a permanently saturated pastoral wetland. Flow and turbidity were continuously monitored at a v-notch weir and baseflow and event samples were collected and analysed for TSS, Escherichia coli and various forms of N and P. Cattle were detected grazing the wetland paddock on 18 days by time-lapse cameras. Cattle only entered and grazed the saturated wetland area for 30–40% of the time and there were usually only a few animals in the wetland at one time. Cattle that did graze the wetland tended to remain near the edge. We attribute the low level of wetland grazing to the cattle recognizing the risk of entrapment in the deep (up to 2m), boggy wetland soil. A measurable increase in pollutants (attributable solely to cattle generated disturbance) occurred only once. This occurred when a cow became entrapped in close proximity to the water quality monitoring location on a day when wetland flow was elevated. Exclusion of cattle from our study wetland by fencing is therefore unlikely to substantially improve downstream water quality. Further research is required to determine whether this is the case for similar wetlands in different environments.

Numerical investigation of wave-induced flow in mound–channel wetland systems

Coastal wetlands are an important ecosystem in nearshore regions, but they are also significant in affecting the flow patterns within these areas. Wave-induced flow in wetlands has complex circulation characteristics because of the interaction between waves and plants, especially in discontinuous vegetation. Here, a numerical investigation is performed to analyze the wave-averaged flow in vegetated mound–channel systems. Different water levels, vegetated conditions, and mound configurations are studied with the COULWAVE (Cornell University Long and Intermediate Wave) Boussinesq model.Model simulations show rip currents in the mound–channel systems, whose strength varies with different mound separation distances. The relative influence of vegetation depends on both mound configuration and water level. Approximately a 15% change in significant wave height results as waves propagate over the vegetated mounds, while up to a 75% decrease in the mean shoreward flow speed through vegetation is observed. In addition, vegetation influences the spatial distribution of mean water level within the wetlands. Dimensional analysis shows that rip current strength and primary circulation size depend on mound spacing, water depth, wave height, and vegetation cover.