Dynamic Water Quality Model Research Articles

Modeling the Effects of Macrophytes on Hydrodynamics

A computer model was created as a scientific and management tool for understanding the effects of macrophytes on hydrodynamics and water quality. A model was required that could simulate macrophytes in a complex water body and could be coupled to a multicompartment water quality model of phytoplankton, dissolved oxygen, nutrients, pH, and organic matter. This would permit the investigation of water resource issues where macrophyte growth, phytoplankton growth, nutrient loadings, and flood control were all contributing factors. The model was added as a compartment to the U.S. Army Corps of Engineers two-dimensional, laterally averaged, dynamic water quality model, CE-QUAL-W2 (Corps of Engineers, water quality, width averaged, two dimensional) and applied to the Columbia Slough, Ore. Features of the macrophyte model include the capability to simulate multiple submerged macrophyte species; transport of nutrient fluxes between plant biomass and the water column and/or sediments; growth limitation due to nutri...

Modeling the effect of agricultural best management practices on water quality under various climatic scenarios

The South Nation (SN) watershed in Eastern Ontario was studied for improvements in surface water quality due to best management practices (BMPs). Contributions of non-point sources (NPS) to nutrient loadings are both significant and poorly defined in the region. The study used the dynamic Annualized Agricultural NPS (AnnAGNPS) model to run continuous annual simulations, coupled with a dynamic water-quality model for simulation of riverine water chemistry. The simulation case matrix focused on the potential of BMPs within the context of climate change. Results of the work were then analyzed to determine ecological intensity (severity), duration, and frequency (IDF) of violations to species survivability within the stream network. Best management practices were found to reduce water quality impacts but stream standards were not reached. Adjustment of fertilizer application rates (FAR) and vegetative filter strips (VFS) outperformed alternative BMPs in the model. Results suggest that agricultural activity within the watershed must be diminished to reach standards.

Monitoring, assessment and modelling using water quality data in the Saale River Basin, Germany

The European Water Framework Directive (WFD) is the overall driver for this environmental study and currently requires the identification of patterns and sources of pollution (monitoring) to support objective ecological sound decision making and specific measures to enhance river water quality (modelling). The purpose of this paper is to demonstrate in a case study the interrelationship between (1) hydrologic and water quality monitoring data for river basin characterization and (2) modelling applications to assess resources management alternatives. The study deals with monitoring assessment and modelling of river water quality data of the main stem Saale River and its principal tributaries. For a period of 6 years the data, which was sampled by Environmental Agencies of the German states of Thuringia, Saxony and Saxony-Anhalt, was investigated to assess sources and indicators of pollution. In addition to the assessment a modelling exercise of the routing of different pollutants was carried out in the lower part of the test basin. The modelling is a tool to facilitate the evaluation of alternative measures to reduce contaminant loadings and improve ecological status of a water body as required by WFD. The transport of suspended solids, salts and heavy metals was modelled along a selected Saale reach under strong anthropogenic influence in terms of contaminants and river morphology between the city of Halle and the confluence with the Elbe River. The simulations were carried out with the model WASP5 which is a dynamic flood-routing and water quality model package developed by the US Environmental Protection Agency.

Effect of reservoir flushing on downstream river water quality

The effect of short-term reservoir flushing on downstream water quality in the Geum River, Korea was studied using field experiments and computer simulations. The reservoir release was increased from 30 to 200 m 3/s within 6 h for the purpose of this experiment. The flushing discharge decreased the concentrations of soluble nitrogen and phosphorus species considerably, but the experimental results revealed a negative impact on organic forms of nutrients and biochemical oxygen demand (BOD). A dynamic river water quality model was applied to simulate the river hydraulics and water quality variations during the event. The model showed very good performance in predicting the travel time of flushing flow and the variations of dissolved forms of nitrogen and phosphorus constituents. However, it revealed a limited capability in simulating organic forms of nutrients and BOD because it does not consider the re-suspension mechanism of these constituents from sediment during the wave front passage.

A random search methodology for examining parametric uncertainty in water quality models

The advent of the modern high-speed digital computer has tremendously enhanced the utility of Monte Carlo methods for evaluating complex environmental simulation models. In particular, random searching is becoming popular, as thousands of model runs can now be executed quickly and with minimal effort. Indeed, the issues of computational burden and inefficiency, hitherto the bane of random searching, are now receding. This paper presents one such method, uniform covering by probabilistic rejection (UCPR), which combines a pure random search with a probabilistic rejection algorithm that significantly enhances its efficiency. Using nearest-neighbor distances, an ensemble of points in a predefined parameter sampling domain migrates to locate and define a final distribution of optimal parameter vectors, thus providing a realistic depiction of parameter uncertainty. In a prototypical case study of the Oconee River (Georgia, USA), UCPR and regionalized sensitivity analysis, are employed for identifying the parameters of sediment-transport-associated nutrient dynamics, a dynamic river water quality model. Results indicate the existence of a complex interactive parameter structure, evidenced by multiple sets of optimal points widely dispersed over a broad domain of feasible parameter values.

A combined suspended particle and phosphorus water quality model: Application to Lake Vänern

A dynamic model describing the flow of phosphorus and suspended particulate matter for large fresh water lakes is proposed and validated against data from Lake Vänern in Sweden. The model was modified to handle two separate sub-basins, but increasing the horizontal resolution further by splitting the basins into coastal area and pelagial failed, as the model fit to experimental data deteriorated. Besides, the scant reference data available for the coastal areas makes this a dubious exercise. Parameters for the nutrient dynamics in the water column required less tuning (up to 60%) than the sedimentation and sediments (up to a factor 70). The fit to experimental data is good for the periods between 1900 and 1940 and that after 1980, but is less satisfactory for the more polluted conditions in the middle of the century. The model is applied to two scenarios: increased emissions from a pulp and paper mill by the lake, and decreased phosphorus emissions achieved by a combination of effects on farmland, woodland, and rural households. These two scenarios demonstrate the usefulness of a dynamic quantitative lake water quality model.

A water-quality model for the Lagoon of Venice, Italy

A water-quality model for the Lagoon of Venice is proposed. The model is based on the results of an existing, deterministic, hydraulic-dispersive model of the Lagoon to provide the distribution of salinity and residence time in the Lagoon of Venice. This model has been implemented by Magistrato alle Acque di Venezia and Consorzio Venezia Nuova to evaluate the environmental impact of the MOSE Project, that has the aim to defend the city of Venice from extraordinary high tides [CVN, 1997. Allegato allo studio di impatto ambientale del progetto di massima delle opere mobili per la difesa dei centri abitati lagunari dagli allagamenti, vol. 2., CVN, 2002. Studio di nuove configurazioni dei canali di bocca e del relativo adeguamento progettuale delle opere mobili alle bocche di porto]. The water-quality is simulated by statistic analysis on water-quality data, monthly collected in 30 stations. The data-set covers a period of 2 years, and has been collected in the framework of MELa1, the institutional water-quality monitoring program (Magistrato alle Acque di Venezia, Consorzio Venezia Nuova). The Spearman correlation index of salinity and residence time versus the water-quality variables (nitrogen, phosphorus, chlorophyll-a and the trophic index TRIX) has been studied on a yearly average basis and for the spring–summer periods. The spatial distribution of the water-quality variables, based on the yearly average of nutrients, is mostly driven by the dispersive processes and is well correlated to salinity [Bianchi, F., Acri, F., Alberghi, M., Bastianini, M., Boldrin, A., Cavalloni, B., Cioce, F., Comaschi, A., Rabitti, S., Socal, G., Turchetto M.M., 1999. Biologocal variability in the Venice Lagoon. In: Lasserre, P., Marzollo, A. (Eds.), The Venice Lagoon Ecosystem. Input Interaction between Land and Sea, UNESCO, Man and Biosphere Series, vol. 25, pp. 97–125]. The model has been applied to simulate the variation of nutrients and trophic index distribution in the Lagoon as a consequence of an increase of hydraulic dissipation at the Lagoon outlets. The work presented in this paper shows that, coupling a deterministic, distributed-parameters, dynamic, hydraulic-dispersive model to a statistic one that accounts for the correlation between hydraulic related forcing functions (salinity, residence time) and water-quality data is a promising and simple way to evaluate the water-quality of the Lagoon of Venice. Of course, this methodology is applicable because a very large data-set is now available. The usual limitations of the statistical model methodology are present in this application too. E.g., it cannot precisely estimate the values of the water-quality variables, but it can indicate how they react when the system hydrological features change. Besides, the outcomes depend strongly on site characteristics and on the actual ecosystem state. The model has not been validated yet, due to the short data time lag, but the aim of this work is to suggest a simple simulation tool whose reliability is at least the same of that obtained by complex, deterministic, dynamic water-quality models. These models, accounting for several processes and hence including a lot of parameters, require for calibration a much more detailed data-set not yet available. The increase of dissipation is altering nutrient concentrations in the Lagoon of an average +3.2%, while the average variation for TRIX is +0.4%, and for chlorophyll-a is +3.0%. These variations are small enough to confirm a posteriori the validity of the adopted statistical approach.

Dynamic in-stream fate modeling of xenobiotic organic compounds: a case study of linear alkylbenzene sulfonates in the Lambro River, Italy.

Using a conceptual hydraulic model, a one-dimensional dynamic river water quality model has been developed to assess the short-term fate of linear alkylbenzene sulfonates (LAS) in the river compartments water and benthic sediment. The model assumes local equilibrium sorption and that both dissolved and sorbed chemical are available for biodegradation. To investigate the interaction of nutrient dynamics and organic contaminant fate, the model is coupled with a basic water quality model. On the basis of the Lambro River (Italy) as a case study, the result shows that the model predictions agree well with the measured data set. The model output sensitivity to model parameters has been tested, and the results depict that the model is highly sensitive to the biodegrading parameters. Also, a comparison of a steady state with a dynamic simulation and the effect of nutrient dynamics on the LAS fate in the Lambro River as a scenario analysis are presented. The results indicate the usefulness of the proposed model for the short-term simulation of organic contaminant fate in unsteady environmental conditions.

Reply to “Comments on ‘STAND, a dynamic model for sediment transport and water quality’ by W. Zeng and M.B. Beck, 2003. Journal of Hydrology 277, 125–133”

Reply to “Comments on ‘STAND, a dynamic model for sediment transport and water quality’ by W. Zeng and M.B. Beck, 2003. Journal of Hydrology 277, 125–133”

Comment on “STAND, a dynamic model for sediment transport and water quality” by W. Zeng and M. Beck, 2003. Journal of Hydrology 277, 125–133

Comment on “STAND, a dynamic model for sediment transport and water quality” by W. Zeng and M. Beck, 2003. Journal of Hydrology 277, 125–133

DETERMINING CRITICAL WATER QUALITY CONDITIONS FOR INORGANIC NITROGEN IN DRY, SEMI‐URBANIZED WATERSHEDS1

ABSTRACT: Traditional approaches to establishing critical water quality conditions, based on statistical analysis of low flow conditions and expressed as a recurrence interval for low flow conditions (e.g., 7Q10), may be inappropriate for drier watersheds. The use of 7Q10 as a standard design flow assumes year‐round flow, but in these watersheds, 7Q10 is zero or very small. In addition, the increasing use of multiple year dynamic water quality models at daily time steps can supercede the use of steady state approaches. Many of these watersheds are also under increasing urbanization pressure, which accentuates the flashiness of runoff and the episodic nature of critical water quality conditions. To illustrate, the conditions in the Santa Clara River, California, are considered. A statistical analysis indicates that higher inorganic nitrogen concentrations correlate strongly with low flow. However, peaks in concentrations can occur during the first storms, particularly where nonpoint source contribution is significant. Critical conditions can thus occur at different flow regimes depending on the relative magnitude of flow and pollutant contributions from various sources. The use of steady state models for these dry semi‐urbanized watersheds based on 7Q10 flows is thus unlikely to accurately simulate the potential for exceeding water quality objectives. Dynamic simulation of water quality is necessary, and as the recent intense storm event sampling data indicate, the models should be formulated to consider even smaller time steps. This places increasing demand on computational resources and datasets to accurately calibrate the models at this temporal resolution.

Simplifying Dynamic River Water Quality Modelling: A Case Study of Inorganic Nitrogen Dynamics in the Crocodile River (South Africa)

The ultimate goal of this study is to develop a simple dynamic river water quality model that can be applicable in a data limited situation and is compatible with typical activated sludge models, so that the model can be used in integrated modelling of wastewater and river water quality in the future. A simplified river water quality model was formulated based on a conceptual hydraulic sub-model and simplification of an existing river water quality model. The simplified water quality was derived from the River Water Quality Model No. 1, which is one of the most comprehensive basic river water quality models available in literature. The applicability of the simplified model in data limited situations was investigated using a case study of inorganic nitrogen (nitrate and ammonia) in the Crocodile River (South Africa). The model was calibrated and validated on the basis of independent data collected for four years (1987–1990). The results show that the model can adequately describe the seasonal dynamics of inorganic nitrogen in the Crocodile River. The sensitivity of the model output to the model inputs was also analysed, and the results indicate that the model is most sensitive to the microbial biomass (nitrifier) followed by hydraulic parameters. The relation of river flow versus concentration of inorganic nitrogen in the downstream section of the river was also examined in order to identify the main source and critical time for nitrate pollution.

Building 3D frameworks of accessory aquatic systems

We consider a mathematical framework for spatially describing accessory aquatic systems that belong to a major hydric complex like a large reservoir created by damming a river. The central purpose is to provide a precise and complete mathematical covering of short-scale or localized water bodies, with typical lengths between 1 to 10 km, that are laterally attached to the main river. Such bodies may deserve a more detailed mathematical representation due, for instance, to their tendency to develop stagnant like hydric behaviors. The proposed framework may work as an infrastructure for developing and/or installing dynamic water quality models. It can generate tetrahedrizations of the aquatic system in question by working according to a procedure which builds, successively, reliable candidates for the following entities: (a) Free Surface Triangular Mesh; (b) Submerged Terrain Triangular Mesh; (c) Three Dimensional Partition of the Domain; (d) Basic Tetrahedrization of 3D Partitions; and (e) Refinement of the Basic Tetrahedrization through a Multi-Layer Tetrahedrization Algorithm. The required input for this procedure is only composed by terrain contour data and 3D located points. We present example applications including a real scenario belonging to a recent flooded system in Brazil.

STAND, a dynamic model for sediment transport and water quality

We introduce a new model–STAND (Sediment-Transport-Associated Nutrient Dynamics)–for simulating stream flow, sediment transport, and the interactions of sediment with other attributes of water quality. In contrast to other models, STAND employs a fully dynamic basis for quantifying sediment transport, thus distinguishing it from the well-known HEC-6 model. This latter, in particular, computes a steady-state form of sediment transport based on an approximation of transient flow regimes by a sequence of steady-state hydraulic conditions. STAND has a three-level structure. The first level accounts for the hydraulics of open-channel flow, using the conventional St Venant equations. The second level computes sediment transport potential and actual transport rates based on the information provided by the first level. In the third level (not discussed herein), changes of nutrient concentrations along the studied river can be computed as a function of nutrient transport, adsorption/desorption of nutrients to suspended sediment, and releases from bed-sediment pore water. Having introduced STAND and compared and contrasted its structure with HEC-6, STAND's performance is evaluated against a comprehensive data set obtained from a section of the Weihe River, a major tributary of the Yellow River, in China, and compared to results from HEC-6. From both visual evaluation and the statistics of the residual time series, it can be concluded that STAND provides the better simulation, notably under conditions of strongly transient stream behavior.

Control options for river water quality improvement: a case study of TDS and inorganic nitrogen in the Crocodile River (South Africa)

Using a simple conceptual dynamic river water quality model, the effects of different basin-wide water quality management options on downstream water quality improvements in a semi-arid river, the Crocodile River (South Africa) were investigated. When a river is impacted by high rates of freshwater withdrawal (in its upstream reaches), and receives polluted side-stream inflows and wastewater effluent discharges (in the middle reaches), river water quality can deteriorate seriously over time. This study focused on two water quality problems: Progressive increases in the concentrations of total dissolved solids (TDS) as a measure of salinity, and the concentrations of nitrate-plus-nitrite and ammonia (as inorganic nitrogen) as a measure of eutrophication. Based on a lowflow analysis for the period prior to construction of the Kwena Dam (1960 to 1979), the 7d low flows that could be expected to occur every 10 years (7Q10) are generally very low (< 0.5 m3·s-1), both in the upstream (Montrose Weir) and the downstream (Kruger National Park) sections of the Crocodile River. During such critical periods of low river flow, very low effluent standard limits would be required to prevent adverse river water quality. However, these options are not economically feasible. Furthermore, inflows from the highly polluted tributary stream, the Kaap River, which drains an area where considerable gold mining takes place, govern water quality in the Crocodile River downstream of the Crocodile-Kaap confluence. Subsequently, two additional water quality control options (setting limits for maximum water withdrawal and low-flow augmentation) were analysed. The results show that a decrease in maximum water withdrawal could reduce the TDS concentration. Furthermore, controlling water release patterns from a dam at the Montrose Weir can have a remarkably positive effect on the downstream river water quality. On the basis of the 1989/90 monitoring data, a minimum flow of 5 m3·s-1 at the Montrose Weir can reduce concentrations of TDS and ammonia nitrogen by about 20% and 60%, respectively, in the Kruger National Park (at the downstream point of the considered river). However, this management option does not reduce nitrate nitrogen concentrations. The proposed model used in this study is relatively simple and can be used as a tool for the evaluation of short-term (monthly) basin-wide water quality management options. Keywords: Dynamic model, Flow regulation, Water quality management, Tank in series model (WaterSA: 2003 29(2): 209-218)

Mass balance of a wastewater loaded canal system: case study of Bangkok

A dynamic water quality model was applied in order to investigate self-purification processes in highly loaded canals in the centre of Bangkok, capital city of Thailand. Oxygen production by aquatic plants induces a significant diurnal variation of the dissolved oxygen concentration. The corresponding profiles of heterotrophic growth and BOD5 concentration demonstrate the limiting impact of oxygen shortage during night time. Both self-purification mechanisms--biological degradation and settling--are considered and water-sediment interactions are calculated. Simulation results and measurement data are summarized by mass balance schemes which offer a telling characterization of the complex system.

Sensitivity analysis and auto-calibration of an integral dynamic model for river water quality

ESWAT--Extended Soil and Water Assessment Tool--was developed to allow for an integral modelling of the water quantity and quality processes in river basins. ESWAT is a physically based, semi-distributed model, with a moderate-to-large number of parameters and input and output variables (depending on the desegregation scheme). An auto-calibration procedure was implemented for the optimisation of the process parameters. The procedure is based on a new approach for multi-objective calibration and incorporates the algorithms of the Shuffled Complex Evolution Method. The optimisation uses a global optimisation criterion, whereby several output variables can be taken into account simultaneously. A statistical method enables the aggregation of the objective functions for individual variables, hereby avoiding the weighting problem. To select the important parameters for the optimisation, a sensitivity analysis precedes the calibration. The latter analysis is based on the One-factor-At-a-Time (OAT) design approach. The sensitivity analysis and the calibration procedure are applied to the river Dender in Belgium. The river is characterised by high pollution loads and long residence times in summer periods.

SIMPLE: Assessment of non-point phosphorus pollution from agricultural land to surface waters by means of a new methodology

In the past, environmental Phosphorus (P) parameters like soil P indices have been used to catogorize the potential risk of P losses from agricultural land. In order to assess the actual risk of P pollution of groundwater and surface waters, dynamic process oriented soil and water quality models have been frequently used. Recently, an approximating model for phosphorus, called SIMPLE, has been developed. This model approximates the output from a complex dynamic water quality model. The approximating model is called a metamodel. This simple P-model proves to be a powerful tool for quick assessment of the risk of P pollution from agricultural land to surface waters.

A three-dimensional water quality-macrophyte interaction model for shallow lakes

A dynamic three-dimensional water quality model for macrophyte-dominated shallow lakes was proposed and tested. The proposed model is capable of simulating macrophytes and its interactions with water quality constituents such as dissolved oxygen (DO), organic nitrogen, ammonia, nitrate, organic phosphorus, orthophosphate, biochemical oxygen demand, phytoplankton and the sediment layer in shallow lakes. An existing two-dimensional hydrodynamic model has been utilized in conjunction with the water quality model to simulate water levels, velocities and flow rates. The modelled macrophyte processes are photosynthesis, respiration, mortality and excretion. Hourly simulation of photosynthesis process has been realized. The hourly simulations need special attention to predict diurnal variations of DO in macrophyte dominated lakes. The proposed water quality simulation model was subjected to calibration, verification and prediction processes using the data collected from Mogan Lake, Turkey. Mogan Lake exhibits wide variations of macrophyte biomass seasonally. The lake also exhibits highly variable DO levels both seasonally and diurnally. Statistical error quantification methods have been utilized to test the goodness of fit between the water quality model predictions and field measurements. Good agreement has been achieved between model predictions and measurements. Moreover, uncertainty analysis has been carried out for macrophyte and DO constituents. The analysis showed that the magnitude of the saturated growth rate of macrophyte is the most sensitive model parameter both for macrophyte and DO. The proposed water quality simulation model gave some promising initial results as a management tool to predict the expected reductions for the undesired consequences of eutrophication problem.

Dynamic modelling of roadside gully pots during wet weather

Roadside gully pots form a common and important part of many surface water drainage networks. Their primary function is to retain larger solids from road runoff in order to minimise the problems associated with sediment deposition in downstream drainage structures and receiving waters. Typical processes occurring in pots during wet weather are dilution, dispersion, sedimentation, sediment bed build-up and erosion, washout of suspended and dissolved pollutants from the pot liquor and reaeration of the pot liquor. A dynamic water quality model has been developed to simulate these processes. To study the pollutant washout patterns and sludge bed erosion, simulated wet weather tests were carried out on pots draining six different types of roads. Results corroborated earlier findings and were used to successfully calibrate and verify the model.