HyGIS-Qual2E: Flexible Coupling of Water Quality Model with GIS Sung-Ryong HA*, In-Hyeok PARK Abstract This paper aims to develop a program HyGIS-Qual2E by which an input data file of the river water quality model, Qual2E provided by U.S. EPA can be prepared automatically. A flexible coupling scheme is applied to compose of the program. As a spatial analysis engine, HyGIS based on GDK that is one of the commercial based program package of GIS provides several convenient spatial analysis components and it is coupled with QUAL2E model. Major results obtained are follows. The program reduces significantly the data preparation time to set up the input file of QUAL2E and gives the model users to be convenient handling of the model. Because of a component based program development, users of the program can cope with the difficulties to expend the utilities of the program to wider application areas. Keywords : Flexible Coupling, Pre-Processing, Coupling with GIS 1. Introduction The application of GIS has been starting progression since 1990 s (Goodchild, Parks, and Steyaert, 1993; Kemp, 1993). It inspired to realize the needs of GIS introduction to the simulation modeling field because of the finding that the preparation of necessary parameters for the modeling is complicate and also, the results from the same model application and the same studyarea still might be conflicted. Therefore, the coupling of GIS and an environmental model is focused to be able to carry out modeling effectively and to minimize spent time for collecting and analyzing for source data (Hassan and Benjamin, 1996). * Professor, Dept. of Urban Engineering Chungbuk National University 12Gaeshindong, Heungdukgu, Chungbuk, Rep. of Korea Tel. / Fax. (+)82-43-275-2497 e-mail : simplet@cbucc.chungbuk.ac.kr Nowadays, there are three types of coupling methods such as the loose coupling & tight coupling (Stuart & Stocks, 2003), the flexible coupling (Choi, 2001), and the full coupling (Bo and Bin, 2002). Loose Coupling is the most fundamental method which relies on transferring of data files between GIS and environmental models. The advantages of this approach lie in the fact that both systems can be developed or used independently. However, the disadvantage is the requirement of additional operation for analyzing when two systems are coupled and the operation is troublesome (Bo & Bin, 2002). Tight Coupling is coupled with GIS after developed to models using advanced programming languages. It is able to extract the necessary result with on direct access to database of GIS. However, it sometimes causes serious communicative problems due to models and GIS established using different programming languages. It is also noted that the finding
of an error is difficult (Bo and Bin, 2002) and models developed by different systems are not compatible with the GIS software used. On the other hand, Flexible Coupling applies GIS software for only preparing an input and output data file as a pre-process as well as a post-process of environmental models. Therefore it is also necessary to develop the special interface program to connect simulation models of water quality and GIS software. It has an advantage to more convenient than Loose Coupling as well as reducing spent time for development. While, Full Coupling scheme combines the water quality simulation models and GIS using a macro development language provided by vendor of the GIS software used. It has been reported that this coupling scheme causes less errors than the Tight Coupling one. Anyhow, it takes a deal of time for the development of the program to combine the water quality model and GIS software and the application of the program coupled is still limited for other application models of water quality. With the context mentioned, this paper aims to develop a program HyGIS-Qual2E by which an input data file of the river water quality model is prepared automatically. 2. Methodology 2.1 Water Quality Model: Qual2E Qual2E model is a steady-state water analysis program based on the uniform flow consumption. Therefore the study river has to be divided into several consecutive reaches in which hydrological, hydraulic and pollution properties are homogeneous. For the calculation of longitudinal dispersion of water quality constitutions, the reach is divided into the elements with a same spatial step. On the Figure 2, the calculation step of QUAL2E model is schematized. 2.2 HyGIS-QUAL2E The HyGIS (Hydrological Geographic Information System) is a GIS-based system development engine established by the Sustainable Water Resource Research Center of 21st century frontier R&D program and used to develop the program, HyGIS-Qual2E. The program can automatically construct the required spatial information. This engine is based on GEOMania package (MST, Korea, 2004). While Figure 1 shows the concept of flexible coupling used for the development of the program HyGIS-QUAL2E. Figure 1. A Concept Sketch of Flexible Coupling Figure 3 is the schematic diagram of HyGIS-Qual2E coupled with GIS. The middle processor linked to GIS package, denoted in the dashed box in the figure conducts to determine the water quality model parameters through accessing to GIS database and create the input file of QUAL2E model in ASCII format. Using this file, QUAL2E model is operated and, then results in the calculation outputs in ASCII format and produces the off-printed records as well as on-line ones. Especially, the HyGIS-Qual2E system is developed into a component based program and integrated to a data base management system (DBMS) for the convenience of the accessibility as well as the systematic maintenance of the program. Furthermore, the program expansion to the other application model becomes easier.
Figure 2. A Traditional Process of Qual2E Modeling & Strategies of Development for HyGIS-Qual2E 2.3 A Process of Generating Stream Network Generation of a stream network requires a digital elevation model (DEM) scheme. In this research, the components provided by HyGIS for instance, Fill Sink, Remove Flat Area, Flow Direction, and Flow Accumulation are used to delineate the stream network from the DEM data of the study watershed. 2.4 Division of the Reach and the Element Figure 3. A Concept of HyGIS-Qual2E Program Division of the reach consists of two steps. One is to apply the Flow Accumulation component to the stream network in a grid format and, then calculate the length of a main stream line. Next step is to determine the stream distance in which hydraulic condition has uniform flow on the basis of hydraulic calculation
results from HEC-RAS program by U.S. Army Corps of Engineers and identify the hydraulic coefficients of the cross-section of the stream. And the element, longitudinal distance step for the water quality dispersion is divided from each reach. Each element is assigned the same ID number with that of the reach for recognition individually. the pollution loads in terms of point and diffuse sources. This process is conducted using the Flow Path component developed after combine Layer included characteristic information with River Basin Diagram. 2.5 Allocation of Sub-Catchment to the Reach and Pollution Loads Sub-Catchment division is done using the GIS components designed for the allocation of subwatershed area to the specific stream reach divided previously. Figure 4 denotes the process of the allocation of pollution loads established on the based of administrative boundary to the watershed basis. Figure 4. Division Reach a. Watershed b. Pollution c. Overlaying Figure 4. Overlaying Watershed Map and Regional Pollution Map of Government 3. Result & Discussion Figure 5 is the result obtained from the execution of the component of the Division of stream reach using the HyGIS-Qual2E system. Figure 6 denotes the results of allocation of the sub-watershed division and Figure 5. Division Element & Pollution Load into Element Figure 7 shows the sub-watershed division result and assign a delivery coefficient for the calculation of pollution loads reached to the stream reach. Figure 8 is the result of the input data file developed using the program established. From the figure we can find that the program to build the input file of QUAL2E is operated effectively. In addition, Figure 9
shows the result of simulation of water quality modeling using the developed program, HyGIS- Qual2E. Figure 7. Input file Generated for modeling Figure 6. Division Watershed & Calculate Delivery Coefficient Figure 8. Calibration & Verification Table 1. A Data Sheet of Watershed Table 1 is an example of the data record and field assigned for providing input data details through integration of databases combining operation. 4. Conclusion This paper aims to develop a program HyGIS-Qual2E by which an input data file of the river water quality model, Qual2E can be prepared automatically. A flexible coupling scheme is applied to compose of the program. As a spatial analysis engine, HyGIS based on GDK that is one of the commercial based program package of GIS provides several convenient spatial analysis components and it is coupled with QUAL2E model as a water quality simulation tool. Major results obtained are follows. The program reduces the data preparation time to set up the input file of QUAL2E and gives the model users to be convenient handling of the model. Using the program developed with a component based development tool, the program users can cope with the difficulties to expend the utilities of the program to wider application areas.
Acknowledgements Authors would like to express sincerely thanks for financial supports from the KICT through the Sustainable Water Resource Research Center of 21st century frontier R&D program (Grant No: M106KI010004-06K0901-00430, 1-2-2) prospects(pp.33-51), Computers, Environment and Urban systems, Vol. 23. References Choi, Y. W., A Study on the integration of GSIS and water quality model for the management of stream water quality, Thesis for Master Science, Chonbuk National University, 2001. Bo, H., Bin, J.(2002), AVTOP : a full integration of TOPMODEL into GIS (pp..261-268), Environmental Modeling & Software. No. 17. Goodchild, M. F.,Parks, B. O., & Steraert, L. T.(1993), Environmental modeling with GIS. New York: Oxford University Press Hassan, A. K. & Benjamin, H. H.(1996). Evaluating Strategies for Integrating Environmental Models with GIS : Current Trends and Future Needs. (pp.413-425). Comput., Environ. and Urban Systems, Vol. 20, No. 6 Kemp, K. K.(1993). Environmental modeling with GIS : A strategy for dealing with spatial continuity. SantBarbara : National Center for Geographic Information and Analysis, Department of Geography, University of California. Stuart, N., & Stocks, C. Hydrological modeling within GIS; An integrated approach. Application of Geographic Information Systmes in hydrology and water resources(pp.319-329). IAHS pub. no. 211. Velp, Netherlands: IAHS Sui, D. Z., Maggio, R. C.(1999). Integrating GIS with hydrological modeling : practices, problems, and