Dynamic Water Quality Model Research Articles

Calibration and identifiability analysis of a water quality model to evaluate the contribution of different processes to the short-term dynamics of suspended sediment and dissolved nutrients in the surface water of a rural catchment

A method that combines calibration and identifiability analysis of a dynamic water quality model to evaluate the relative importance of various processes affecting the dynamic aspects of water composition is illustrated by a study of the response of suspended sediment and dissolved nutrients to a flood hydrograph in a rural catchment area in the Netherlands. Since the water quality model simulates the observed concentrations of suspended sediment and dissolved nutrients reasonably well, the most important processes during the observed flood hydrograph could be determined. These were erosion, exchange between dissolved phase and bed sediments and denitrification. It is concluded that the method is very useful for identifying the most significant model parameters and processes that are essential for water quality modelling. © 1998 John Wiley & Sons, Ltd.

Calibration and identifiability analysis of a water quality model to evaluate the contribution of different processes to the short‐term dynamics of suspended sediment and dissolved nutrients in the surface water of a rural catchment

A method that combines calibration and identifiability analysis of a dynamic water quality model to evaluate the relative importance of various processes affecting the dynamic aspects of water composition is illustrated by a study of the response of suspended sediment and dissolved nutrients to a flood hydrograph in a rural catchment area in the Netherlands. Since the water quality model simulates the observed concentrations of suspended sediment and dissolved nutrients reasonably well, the most important processes during the observed flood hydrograph could be determined. These were erosion, exchange between dissolved phase and bed sediments and denitrification. It is concluded that the method is very useful for identifying the most significant model parameters and processes that are essential for water quality modelling. © 1998 John Wiley & Sons, Ltd.

Validation of a fish habitat model for lakes

Water temperatures and dissolved oxygen concentrations in 27 classes of lakes have been hindcast by simulation models and related to presence of coldwater, coolwater, and warmwater fishes in 3002 Minnesota lakes. A one-dimensional, dynamic water quality model driven by 25 years of daily weather data was used to model water temperature and dissolved oxygen profiles of these lakes. Fish presence data were available for these lakes from the Minnesota Lake Fisheries Data Base. Water temperature and dissolved oxygen criteria derived from a very large United States Environmental Protection Agency fish-temperature database and dissolved oxygen observations were used to define and link simulated water temperatures and dissolved oxygen conditions to suitability of habitats for coldwater, coolwater, and warmwater fish assemblages. Good agreement was found between fish presence and numerical simulations of fish habitat defined by water temperatures and dissolved oxygen concentrations. Generally water temperature and DO are good indicators of suitable fish habitat.

Stratification dynamics in wastewater stabilization ponds

Measurements show that wastewater stabilization ponds although often only 1–2 m deep stratify and destratify intermittently depending primarily on weather. Stratification can be observed in vertical profiles of water temperature, dissolved oxygen, pH and other water quality parameters. In three stabilization ponds of a small Minnesota town, stratification develops primarily by differential heating of the pondwater through its surface and, in the absence of artificial aeration or mixing devices, by insufficient wind mixing. The resulting water temperature stratification affects other parameters in a variety of ways through chemical, microbial and planktonic kinetics and reduced vertical mixing. To gain a better understanding of stabilization pond water quality dynamics, temperature profiles were monitored at 20-min intervals, and a dynamic lake water quality model was modified and applied to simulate the temperature stratification. A 12-h timestep option was incorporated into the program in order to capture the diurnal variation in stratification. Measurements and simulations were made for three wastewater stabilization ponds at Harris, Minnesota. The level of agreement between field measurements and numerical simulations demonstrated that water temperatures and stratification dynamics in a shallow and small pond can be simulated on a diurnal timescale with a standard error from 1.0 to 1.5°C between simulation and measurements. The model includes wastewater inflow in the form of a vertical jet and water transfer between ponds in the form of non-surface inflow and outflow. Three types of stratification were identified and their respective durations were determined. Stratification occurred on about 55% of all days from 1 April to 30 November. Information on pond stratification presented can be used to guide field studies and reactor modeling of ponds which can lead to further improvements in design and operation.

Time‐averaging water quality assessment

A time‐averaging model is a fast, efficient way to continuously assess water quality in the distribution system.While reauthorization of the Safe Drinking Water Act is pending, many water utilities are preparing to monitor and regulate levels of distribution system constituents that affect water quality. Most f requently, utilities are concerned about average concentrations rather than about tracing a particular constituent's path. Mathematical and computer models, which provide a quick estimate of average concentrations, could play an important role in this effort. Most water quality models deal primarily with isolated events, such as tracing a particular constituent through adistribution system. This article proposes a simple, time‐averaging model that obtains average, maximum, and minimum constituent concentrations and ages throughout the network. It also computes percentage flow contribution and percentage constituent concentration. The model is illustrated using two water distribution systems, and results are compared with those obtained using a dynamic water quality model. Both models p redict average water quality parameters with no significant deviations; the time‐averaging approach is a simple and efficientalternative to the dynamic model.

Animation and Visualization of Water Quality in Distribution Systems

Water may undergo a number of changes in the distribution system, making the quality of the water at the customer's tap different from the quality of the water that leaves the treatment plant. Such changes in quality may be caused by chemical or biological variations or by a loss of system integrity. A computer‐visualization technique, coupled with a dynamic water quality model for analyzing spatial and temporal water quality variations, was studied at two systems.

Lake Aerator Effect on Temperature Stratification Analyzed by “MINLAKE” Model

ABSTRACT The paper deals with the prediction of the vertical temperature profiles in a stratified lake during the operation of an air bubble aeration system. The use of such systems is widespread and their effect on water quality very significant. They are installed for a variety of purposes and act as aerators (increasing dissolved oxygen), mixing devices, and often unintentionally as nutrient pumps and local destratification devices. It is not easy to predict the total impact of an air bubble system installed in lake. To gain a better appreciation of its effect, a model can be developed to simulate the flow induced by an air bubble system in a stratified lake. If such a model is incorporated into a dynamic water quality model, the cumulative synoptic interaction between the air bubble system and lake water quality can be simulated. Since lake destratification is not instantaneous, a dynamic model can simulate the interactions of continuous inputs of water, energy, and materials from the watershed and th...

Improved Microcosm Design for Performing Reservoir Water Quality Investigations

Microcosms suspended in lakes and reservoirs have been effective for performing in situ water quality studies; these systems have also been proposed for the determination of rate constants for dynamic water quality models. A number of different microcosm designs have been used. The most common design consists of a polyethylene cylinder with external supports to which the plastic is glued. The primary problem with previous microcosm designs is their structural instability resulting in destruction during rough water conditions. The purpose of this paper is to report a strong and easily-assembled microcosm system. The microcosm design used 0.0152-cm (6-mil) clear polyethylene plastic heat sealed into a cylinder 0.776 m in diameter. The plastic cylinder was supported from inside by aluminum rings 0.0381-m wide, 0.0025-m thick, and 0.76-m in diameter. The rings were coated with spray plastic to negate leaching of aluminum and possible toxicity during experiments. The bands, which supported the microcosms at 1-m intervals, were held in place from the outside of the plastic cylinder by a second band similar to a large hose clamp. The microcosms performed well under extreme conditions, including winds to 110 km/hr, during water quality investigations at Lahontan Reservoir, Nevada.

Verification of a numerical beach water quality model

A dynamic two-dimensional finite difference water quality model was developed to predict the fecal coliform densities at the Toronto, Ontario, Eastern Beaches resulting from storm-water discharges. There are 10 storm-water and 2 combined sewer overflows discharging to the beach. Site-specific data were collected for use in the model. This data included local bathymetry, currents, dispersion, fecal coliform mortality rates, winds, receiving water fecal coliform densities, and discharge pollutographs. Specially designed field fecal coliform surveys were required to calibrate and verify the model since the storm effects are very dynamic in both time and space. The verified model was then used to estimate the reduction in fecal coliform densities at the beaches for different intensity storms for different remedial works. The improvements resulting from the different remedial works were quantified as the number of hours when the fecal coliform densities exceeded 100 counts/dL. Key words: beach fecal coliform predictions, storm runoff, water quality, numerical modelling, verification.

A dynamic one-dimensional water quality model : Huizinga, P., 1985. CSIR Res. Rept, S. Afr., 562:23pp. plus 33 figures

A dynamic one-dimensional water quality model : Huizinga, P., 1985. CSIR Res. Rept, S. Afr., 562:23pp. plus 33 figures

Dynamic Estuary Water Quality Model and its Applications

In this paper a few problems arisen from the use of dynamic water quality model are discussed. some special applications are proposed. It shows that under certain situations the dynamic model is needed for giving some more useful information.

St. John's Harbour water quality model

A dynamic two-dimensional numerical water quality model was developed for St. John's Harbour, Newfoundland, to assist in providing direction for a water quality enhancement program. The model input parameters were adjusted until the model outputs of water levels, currents, and water quality concentrations matched collected field data which included measurements of the sewer discharges. The tidal stage for the most degraded harbour water quality was identified. This stage was used to compare the harbour water quality enhancements and degradations for different management scenarios which included combining and relocating discharges, partial treatment of some discharges, and some direct ocean discharge. By using the model in a comparative manner, the requirements for model verification are reduced as are some of the errors in the modelling process. Key words: St. John's Harbour, dynamic numerical water quality model.

Erratum: “Dynamic Advective Water Quality Model for Rivers” by Keith W. Bedford, Robert M. Sykes, and Charles Libicki (June, 1983)

Erratum: “Dynamic Advective Water Quality Model for Rivers” by Keith W. Bedford, Robert M. Sykes, and Charles Libicki (June, 1983)

MATHEMATICAL MODELLING OF WATER-QUALITY FOR LONG TIME PERIODS

This paper presents a one-dimensional dynamic water-quality model suitable for long-term application to estuaries. The computation techniques used in the model are very simple, but very good results have been obtained both for theoretical test cases and from applications to estuaries when compared with prototype measurements.

SENSITIVITY OF PHYTOPLANKTON SIMULATIONS TO VARIATIONS IN THE HALF SATURATION CONSTANTS1

ABSTRACT In many impoundment dynamic water quality models, the growth of two or more ecologic groups of phytoplankton may be simulated. These ecologic groups are differentiated by growth rates, temperature tolerances, settling rates, and the Michaelis‐Menten half saturation constants for necessary nutrients. In this investigation, the effect of variations in the Michaelis‐Menten half saturation constant for the limiting nutrient when two competing ecologic groups of algae are simulated is examined. In an idealized case, it is demonstrated that uncertainty in the half saturation constant for the limiting nutrient for one ecologic group of algae can significantly affect the simulation results and in some cases could lead to a poorly designed impoundment restoration program.

Dynamic Advective Water Quality Model for Rivers

A dynamic water quality model for storm induced flows in rivers is presented. The hydrodynamic portion is solved by a four‐point implicit Newton‐Raphson procedure, while the water quality code is formulated with a Holley‐Preissmann nonlinear formulation. The water quality model represents the effects of biodegration by plankton, sedimentation, and diffusion of material into the benthos by a single turbulence dependent decay term. Eight constituents are employed and the effects of light shading are considered. Two simple tests were used to provide simple initial calibrations. The first test, the propagation of a Gaussian wave, demonstrated the necessity of higher order treatment of the water quality numerical analog. The second test was a steady state test of the water quality model against data from the Olentangy River. The minimum kinetic structure required for Ohio streams should include CBOD, organic nitrogen, ammonia nitrogen, nitrate nitrogen, and orthophosphate.

Some limitations of water quality models for large lakes: A case study of Lake Ontario

Some of the problems encountered in the design of a predictive water quality model for a large lake are discussed with reference to Lake Ontario and within the framework of a simple dynamic phosphorus model which incorporates the essential mechanisms of complex plankton models. By fitting the model to a seasonal data base it is shown that equally satisfactory simulations are obtained with a variety of parameterizations and regardless of conditions of annual periodicity imposed on the solution. By comparison of model output with long‐term observations it is demonstrated that seasonal verification studies of dynamic models by themselves are not sufficient to diagnose the utility of such models for predicting long‐term trends. It is concluded that the uncertainty surrounding the formulation of sedimentation and nutrient regeneration, in conjunction with the sensitivity of models to assumptions regarding dynamic balance between lake concentrations and nutrient loadings, undermines the predictive capability of dynamic water quality models.

A dynamic water quality model of Lake Biwa — a simulation study of the lake eutrophication

Lake Biwa is the largest lake in Japan and is the origin of the Yodo River which supplies drinking water to 12 × 10 6 people and industrial water to the economic center of western Japan. Recently, serious environmental problems, especially eutrophication, have become evident in Lake Biwa. This paper treats the eutrophication of Lake Biwa as a dynamic process related to nutrient, mainly nitrogen and phosphorus influx, and the effect this influx has on aquatic ecosystems, water quality and the internal nutrient cycle. For purposes of simplification, Lake Biwa has been treated as a five-block system consisting of three geographical blocks and two of which are divided into two layers. The main objectives of the research reported in this paper are to construct a dynamic eutrophication model of Lake Biwa and to provide basic information for the future exploration of water quality management.