GIS Applications for Water, Wastewater, and Stormwater Systems - Chapter 11

CHAPTER 11 Modeling Applications GIS and H&H model integration allows the users to be more productive. Users can devote more time to solving the problems and less time on the mechanical tasks of inputting data and interpreting reams of model output. More than just text outputs, models become automated system-evaluation tools. GIS integration saves time and money. GIS integration is ideally suited to solve the computer modeling puzzle. Copyright © 2005 by Taylor & Francis LEARNING OBJECTIVES The learning objectives of this chapter are to classify the methods of linking water, wastewater, and stormwater system computer models with GIS, and to understand the differences between various linkage methods. MAJOR TOPICS · GIS applications in H&H modeling · Modeling application methods · Interchange method · Interface method · Integration method · Examples and case studies of the preceding methods LIST OF CHAPTER ACRONYMS AML Arc Macro Language BASINS Better Assessment Science Integrating Point and Nonpoint Sources COE Corps of Engineers (U.S. Army) DEM Digital Elevation Model GUI Graphical User Interface H&H Hydrologic and Hydraulic HEC Hydrologic Engineering Center (U.S. Army Corps of Engineers) HSG Hydrologic Soil Group HSPF Hydrologic Simulation Program — FORTRAN NPS Nonpoint Source NRCS Natural Resources Conservation Service (U.S.) SCS Soil Conservation Service (U.S.) (Now NRCS) SWAT Soil and Water Assessment Tool SWMM Storm Water Management Model TMDL Total Maximum Daily Load TR-20 Technical Release 20 VBA Visual Basic for Applications WMS Watershed Modeling System This book focuses on the four main applications of GIS, which are mapping, monitor-ing, modeling, and maintenance and are referred to as the “4M applications.” In this chapter we will learn about the applications of the third M (modeling). TEMPORAL-SPATIAL MODELING IN WESTCHESTER COUNTY GIS software Modeling software ArcInfo Rational method and kinematic wave model Copyright © 2005 by Taylor & Francis GIS data Study area Organization Land use (from low-altitude infrared color photography), USGS DEM (1:24,000 scale), NRCS soils (1:12,000 and 1:24,000 scales), streams, and watersheds 0.14 mi2 (0.36 km2) Malcolm Brook watershed, Westchester County, New York New York City Department of Environmental Protection Lateral flow is an explicit component of the kinematic wave routing equation, yet some kinematic wave models such as HEC-HMS do not include lateral flow. The lateral flow component can be accounted for by using GIS. Until recently, it was considered impossible to conduct time-varying computations within a GIS. In this case study, lateral flows were derived from GIS output for each segment of the stream and at each time interval of the rain storm and were routed using the kinematic wave routing method. Rather than a raster GIS that uses a constant cell size, a vector GIS was used to define hydrologic response units that divide the stream channel into segments that vary in size according to the combined characteristics for land use, slope, and soil type. This approach permitted vector-based spatially distributed modeling of stream flow during storm events. GIS was used to map and visualize contributing areas around a stream channel. During each calculation of the discharge, a graphical image of the watershed and contributing areas was captured as a Graphics Interchange Format (GIF) image. A series of these images were displayed in sequence to produce a continuous animation (Gorokhovich et al., 2000). H&H MODELING No one said mathematical modeling would be easy, but the preparation of input data and interpretation of output results required by the ever-changing complexities of sophisticated hydrologic and hydraulic (H&H) models have been mind boggling. The good news is that model building and interpretation of results are now easier than ever before thanks to recent advances in computer hardware and software. The assembly of model input data by traditional, manual map measurements is just too time consuming and difficult to justify, now that personal computers are affordable and powerful. It is much easier to see a color-coded map of surcharged sewers to pinpoint the areas of flooding and surcharging than to digest reams of computer output, especially for nonmodelers. Nonmodelers are those people who are not expert modelers but who need to know the modeling results, such as clients of consulting firms, project managers, elected officials, and regulatory agencies. After all, as advocated in Chapter 1 (GIS Applications), GIS technology is an effective means of bridging the gap between information and its recipients. Rapidly developing computer technology has continued to improve modeling methods for water, wastewater, and stormwater systems. GIS applications provide an accurate and manageable way of estimating model input parameters such as node demands, sewage flows, and runoff curve numbers. GIS-based modeling, as a side benefit, also provides an updated database that can be used for nonmodeling activities such as planning and facilities management. Copyright © 2005 by Taylor & Francis There are two fundamental requirements in most H&H modeling projects: a suitable model and input data for the model. It is often difficult to select a modeling approach because of trade-offs between models and data. For instance, a detailed model requires a large amount of input data that is often too difficult to obtain or is too expensive. On the other hand, a simple model that requires little data may not provide a detailed insight into the problem at hand. Modelers must, therefore, use an optimal combination of model complexity (or simplicity) and available data. The recent growth in computational hydraulics has made it increasingly difficult for practitioners to choose the most effective computational tool from among a variety of very simple to very complex H&H models. Fortunately, thanks to the advances in GIS applications, creation of input data sets is easier than ever before. This chapter serves as a guide to help professionals select the most appropriate GIS applications for their modeling needs. It presents an overview of the GIS and computer modeling integration approaches and software. The chapter also shows how to estimate the physical input parameters of H&H models using GIS. The chapter largely uses watershed hydrologic modeling examples to explain modeling integration concepts. However, the integration methods presented here are equally applicable to modeling of water and wastewater systems. Water system modeling applications and examples are presented in Chapter 12 (Water Models). Sewer system modeling applications and examples are presented separately in Chapter 13 (Sewer Models). APPLICATION METHODS There are two types of hydrologic models: lumped and distributed. Lumped-parameter models lump the input parameters of a study area over polygons and use vector GIS applications. Distributed models distribute the input parameters of a study area over grid cells and use raster GIS applications. Application of GIS technology to H&H modeling requires careful planning and extensive data manip-ulation work. In general, the following three major steps are required: 1. Development of spatial database 2. Extraction of model layers 3. Linkage to computer models H&H models, databases, and GIS applications are critical in efficiently and effec-tively completing large modeling studies. The models and GIS can be linked to other databases for data sharing purposes. For example, data can be imported from other sources like AutoCAD, edited and modified within the application, and exported or linked to other databases. Database files can be saved in .dbf format and linked or imported into Microsoft Access for further data manipulation. For example, ArcView GIS provides Open Database Connectivity (ODBC) features that can be used to link ArcView tables with other tables and queries in Microsoft Access or other database programs, without actually going through any import and export exercises. Such procedures eliminate the data redundancies and user errors typically associated Copyright © 2005 by Taylor & Francis Figure 11.1 Three methods of GIS applications in H&H modeling. with such cumbersome tasks. This has proven to be beneficial and time-saving during alternative analysis of systems where a large number of scenarios are modeled and reviewed using the same data connectivity and templates for maps (Hamid and Nelson, 2001). A useful taxonomy to define the different ways a GIS can be linked to computer models was developed by Shamsi (1998, 1999). The three methods of GIS linkage defined by Shamsi are: 1. Interchange method 2. Interface method 3. Integration method Figure 11.1 shows the differences between the three methods. Each method is discussed in the following text with the help of examples and case studies. As described in Chapter 1 (GIS Applications), advanced applications such as the capa-bility to automatically create a model input file always require writing a computer program using a scripting language like Visual Basic for Applications (VBA). INTERCHANGE METHOD Preprocessing is defined as the transfer of data from the GIS to the model. Postprocessing is defined as the transfer of data from the model to the GIS. The interchange method employs a batch-process approach to interchange (transfer) data Copyright © 2005 by Taylor & Francis ... - tailieumienphi.vn