A WINDOWS-BASED SIMULATOR FOR YANGON WATERSHED ENVIRONMENT MANAGEMENT

Ruan Xiaohong¹ and Wang Deguan²

¹Department of Environmental Engineering, Hohai Univ., Nanjing, 210024, China

²Department of Environmental Engineering, Hohai Univ., Nanjing, 210024, China

Abstract: Since the relation between the pollution source and the receiving water body was established by the water quality model, recently water quality model has become one of the most important tools for watershed environment management planning. As a planning tool, water quality model should be composed on the basis of full understanding of the complex physical, chemical, biological processes of water systems, able to provide real-time and visible information on watershed environment, and easy to apply for practical purpose. Interactive computer simulation techniques are expected suitable to the composition of water quality model with above functions. In this study a Windows-based simulator of the water environment of Yangong watershed in combination with Geographic Information System (GIS) has been developed. The simulator can quickly and interactively provide both digital and graphical information necessary for controlling water pollution of Yangong river and watershed management.

Keywords: water quality model, GIS, environment management

1    INTRODUCTION

Water quality model is a tool for simulating the movement of rain fall and pollutants from the ground surface through pipe and channel networks, storage treatment units and finally to the receiving water bodies. The advances in the basic sciences such as biology, chemistry and physics have improved water quality model in model structure, analytic methods, and parameter estimation techniques. Both single-event and continuous simulation may be performed on watershed, for prediction of flows and pollutant concentrations. Each water quality model has its own unique purpose and simulation characteristics.

Recently, researches have focused on combining water quality model with the GIS, and making model easier to use for practical purposes. GIS can provide relatively easy access and extraction of information, including map production and table generation. The GIS import/export information capabilities can be used to automate the preparation of the input data and the model parameters for water quality model and to give graphically intuitive outputs of the simulation results. The GIS table generation makes the model more easily to use. ARC/INFO software, developed by Environmental Systems Research Institute, USA, is one of the wide-used softwares in watershed management. Using GIS has enhanced the famous water quality models such as WASP4 and QUAL2E.

The objective of this study is to develop a Windows-Based simulator. The simulator has three main functions: management and decision-making information acquisition, watershed modeling automation and water management strategy selection. The use of Windows interface has made the systems user-friendlier. An input menu is provided for preparing model inputs and executing the model. It also provides on-screen-graphical display of input data and model results. The main features of the system are as follows.

l        Visualization and convenient operation interface

l        Easy information acquisition and watershed modeling automation

l        Real-time and visual result display

2    DEVELOPMENT OF WINDOWS-BASED SIMULATOR

For the purpose of water pollution control of Yangong River, the simulator, which combined water quality models with a GIS (Mapinfo), has been developed to provide the information necessary to the watershed environment management. The simulator was designed to facilitate the water quality model in accomplishing the various data exchange and model linkage. The features built into the simulator include relevant database management and simulation system (model input/output, model scenario manager, model calibration/verification, and model linkage assistance). The above features are built into a software package. The structure of the software package is shown in Fig.1.

Fig.1    Structure of the Simulator

Fig.2    The main user interface

The user interface is screen menu written in VB language as shown Fig 2. A series of help/explanation windows are included in this interface. It links the databases with model packages. It allows system users to display calculated and modified parameters for the models as well as to display different scenarios of the future management. The interface was designed on the basis of "question-answer" communication format. It guides a user to all necessary steps.

The simulator is designed mainly for application in small watersheds, its software (model) package has a compact size, which can be run on a computer such as PC-computer (32MB RAM) with input/output facilities (printer, plotter). Furthermore, Visual Basic language is used as simulator platform in Window98 to provide a more flexible user interface and easier input/output data processing.

2.1    Database development

The database building is one of the most important parts in the simulator development. The information in the simulator database includes:

(1) Topographic and hydrographic characteristics (stream, location, watershed topography, landuse, soil distribution, precipitation and water quality)

(2) Drainage system data (size, location, network composition)

(3) Social and economical development data (population, industry and agriculture productions and economical growth)

The simulator data is so huge and complex that it is necessary to be classified and organized reasonably. In this study, the data is divided into the spatial data that are relevant to geographic features, and the attribute data including all of the remains. The two kinds of data are stored in two components of the database: the first is in a spatial component and the second is in an attribute component. The database management software links the attribute data to spatial data and allows for manipulating the attribute data. The output of the database can be displayed as maps or data tables either on the computer monitor or as hard copy output to a plotter or printer.

The data acquisition inventory is developed to facilitate the inspection of the above data. There is a "Background Information" menu in the main interface (Fig. 2). It consists of 9 thematic sub-inventories such as 'distribution of pollution source', 'criteria', etc. All thematic sub-inventories contain database layers corresponding to metadate text files. Metadate files allow users to check necessary documentation for the menu.

2.2    Automation of watershed modeling

The model package in the simulator includes a series of generalized water quality simulation tools for providing necessary information for watershed management by describing qualitatively the relationships between organic pollution loads in the watershed and distribution of the organic materials in the Yangong River. It consists of a water quality model, a hydrodynamic model and a pollutant loads model.

    The water quality model is composed for well-mixed, dendritical and tidal streams. It can simulate the major reactions of nutrient cycles, carbonaceous demand and their effects on the dissolved oxygen balance. The mass balance equation can be expressed as follows:

Where: A: cross-section area, m²

C: concentration of water quality constituent, mg/l

U_x: longitudinal average velocities, m/s

E_x: longitudinal diffusion coefficient, m²/s

S_L: direct loading rate, mg/m³/s

S_B: boundary loading rate, mg/m³/s

S_K: total kinetic transformation rate, mg/m³/s

X: distance, m

T: time, s

This equation represents the three major classes of water quality processes-transport, loading, and transformation by the three terms on the right side of the equation respectively. The finite-difference method is applied for the numerical analysis of this equation.

The hydrodynamic model is capable of simulating variable tidal cycles and unsteady flows. It is based on the famous one-dimensional de Saint-Venant equation. The solution of the equation is also through the finite-difference method. The model gives outputs of flows, velocities, volumes and average water depths, all of which will necessary as the inputs to the water quality model.

Pollutant load model simulates the generation and runoff processes of the point sources and non-point sources from both rural and urban area of the watershed. The discharge of the point sources loads usually are regulated by local environment protection agencies in China and monitored monthly. Estimating of non-point pollutant loads is more complex than that of the point sources loads. Typical methods for estimating pollutant loads include continuous flow measurements and some methods of automated sampling that is either timed or triggered by some features of the runoff hydrograph. But these kinds of methods are not practical in this time in China. Non-point pollutant load depends on precipitation, land-use, basin storage capacities, and watershed topographic characteristics. In this study, the method of estimating the non-point source loads is based on the concept of distribution coefficient, that is, two watersheds with similar land-use patterns and geological conditions in the same region should have the same specific non-point source load. In terms of above assumption the total annual mass of loads is obtained by identifying land-use and the utilization of the fertilizer and pesticide, it is possible to evaluate the changes of non-point source loads and consequently water quality in the future. The distribution coefficients are calculated from hydrological flow and stream pollutant concentration. In this study, total annual COD load is estimated by the above method and applied in water quality model.

Fig.3  The water quality-modeling interface

The execution of the above mathematical models in a watershed scale usually requires a cascading linkage of several models. The output from one model is used as input for the next model. Secondly, water quality models requires effective acquisition, storage, organization, reduction and analysis of model input data and manipulation, interpretation, reporting, and display of model output data. Finally, model calibration, verification, and application are also performed automatically.

The water quality-modeling interface is developed in terms of VB language, as shown in fig.3. The calibration, verification and application of the models are carried out through operation interface. The main role of database is to integrate various kinds of information for model input. The functions such as altering of input data by users are also built in database. These functions are very important for model calibration and verification. The model outputs of water quantity and quality is displayed spatially and temporally by taking advantage of the GIS capabilities.

3    THE SIMULATOR APPLICATION

The Yangong watershed, as shown in Figure 4, is located at the Ninhei country, Zhejiang province. It occupies an area of about 86 square kilometers with complicated land use. The river system contains a main stream and 13 tributaries with tree-like structure. The main stream, Yangong River is 17.5 kilometers long and about 20-30 meters wide, flows through the city of Ninhei and joins East China Sea at Huangden harbor.

Fig.4  Yangong watershed scale

The Yangong River systems receives industrial and domestic point pollutant loads that come from the combined sewers of the urbanized upper stream basin, and non-point pollutant loads that originate from various kinds of activities within the watershed. According to a rough estimation made in 1998 by the Ninhei Environment Protect Agency (1998), the total of annual COD pollutant load discharged into river system is about 2338 tons. The results of pollutant source assessment indicated that the pollution problem of the Yangong River is mainly caused by the organic materials in domestic wastewater. The domestic wastewater accounts for about 84% of the total wastewater discharged into the river. Because the wastewater is not treated by any kind of plants and discharge directly into the river, the water quality level is very low presently.

The watershed model was applied to evaluate the relation between COD contamination of the river and COD pollutant loads discharge from Yangong watershed. The Ninhei Environment Monitor Station provided flow, water quality and point pollutant sources data from March 1, 1998 to March 1, 1999. The models were calibrated, verified by above data. Based on the calibrated water model, the effects have been evaluated of various pollutant sources within the watershed on COD concentration in the Yangong River. The model simulation results can be summarized as follows.

(1) The point sources account for 58% of the total annual pollutant COD loads, and non-point sources for another 42%.

(2) If all point pollutant loads of the presently were treated to second degree (treatment efficiency 0.80), the water quality would reach the water quality standard of local environment protect agency.

(3) In the year of 2010, even all point pollutant loads are treated to second degree, the water quality will not be able to meet the standard if non-point pollutant loads discharge continually because of the limited self-purification capability of water bodies.

It can be seen from above conclusions that a comprehensive control strategy is necessary for water environment management in Yangong River, which is especially important for the water environment management in the future. The comprehensive control strategy from engineering view point could include installation of sewerage treatment plants, improvement of urban drainage system, and water project from reservoir to the river through the existing canal.

The sewerage treatment will be built by stages. The construction plan is shown in table 1. The quantity of water diversion is planned to be 0.5-1.0 m³/s because of water the limitation of water source availability and canal capacity.

Table 1    The plan of builds sewerage treatment plant

The simulation of the above alternatives has provided the possible water quality level of Yangong River and construction fees for each case. After a comprehensive interpretation and comparison of the results, the following water quality control program has been proposed finally.

(1) The construction plan of the treatment plant as shown in table 2 is possible.

(2) The diversion water quantity of 0.5 m³/s is reasonable.

(3) The separate sewer system for the newly-developed area of the city is necessary.

4    SUMMARY

This study develops a windows-based simulator for water quality control in Yangong River. The simulator is constructed to provide all necessary information for watershed environment management. It includes a model package that can simulate flow and water quality, and provides the means of viewing model outputs. The Windows interface of the simulator have made the simulator use-friendly. The philosophy and the methodology of the simulator are especially suitable for small watershed.

Acknowledgements

We would like to thank the Environment Monitor Station for offering all data for this study. This work is a part of the study project the estimation of non-point pollutant load, which was funned by Jiangsu Provincial Nature Science fund (Project No.BK97151).

References

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[2] Chang, M.Z. and Ruan, X.H.(1993). Study on Water Quality Model of Non-point Source, Shanghai Environmental Sciences, 107,16-19.

[3] Chang, M.Z. and Ruan, X.H.(1991). Water Quality Model Comprehensive Assessment of Tidal River, Shanghai Environmental Sciences, 81,44-46.