CHAPTER 13 Sewer Models GIS saves time and money in developing sewer system models for simulating flows and depths in the collection system. GIS also helps to prepare maps of the model results, which can be easily understood by nonmodelers. GIS-based sewer models bridge the gap between information and its recipients. 2097_C013.fm Page 257 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis LEARNING OBJECTIVES The learning objectives of this chapter is to understand how GIS can be applied in developing sewer system hydraulic models, and to understand how GIS can be used to present modeling results MAJOR TOPICS • Representative sewer models • Storm Water Management Model (SWMM) • Graphical user interface (GUI) • SWMM applications • Data preparation • Interface development steps • GIS application case studies LIST OF CHAPTER ACRONYMS CMOM Capacity, Management, Operations, and Maintenance CSO Combined Sewer Overflow DSS Decision Support System EPA (U.S.) Environmental Protection Agency GUI Graphical User Interface HEC Hydrologic Engineering Center HGL Hydraulic Gradient Line LTCP Long-Term Control Plan (for CSOs) NMC Nine Minimum Controls (for CSOs) NPDES National Pollution Discharge Elimination System ODBC Open Database Connectivity OLE Object Linking and Embedding SHC System Hydraulic Characterization (for CSOs) SSO Sanitary Sewer Overflow SWMM Storm Water Management Model MAPINFO ™ AND SWMM INTERCHANGE In the late 1990s, Portland’s Bureau of Environmental Services (BES) developed a suite of GIS and database tools to develop data for SWMM models. Model data were Application area Basement flooding modeling using the Interchange GIS Linkage Method described in Chapter 11 (Modeling Applications) GIS software MapInfo Modeling software SWMM Other software Microsoft Access GIS data Sewer pipes, aerial photographs, buildings and parking lot polygons GIS format Raster and vector Study area City of Portland, Oregon Organization Bureau of Environmental Services, City of Portland, Oregon 2097_C013.fm Page 258 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis developed from maps and databases with automation of many of the steps for data extraction, variable assignments, and model building. Detailed collection-system models of basins were developed to analyze local areas. These models contained essentially all of the pipes in the collection system and utilized two subcatchment definitions to place runoff into the system in the correct location. Surface water subcatchments were defined as the areas that flowed into the sewer through street inlets in the public right-of-way. Direct connection subcatchments were defined as the areas that contributed to sanitary and stormwater drainage through service laterals. A GIS tool was developed to predict flooding of individual parcels by overlaying modeled hydraulic gradient lines (HGLs) with estimated finished floor elevations obtained from a DEM. Detailed SWMM RUNOFF and EXTRAN models were developed from facility maps and photogrammetric data with the use of a MapInfo GIS and a Microsoft Access database. The SWMM model showed that many of the system capacity problems were in the local areas at the upstream ends of the system and that the local collection system tended to hold water back from the downstream trunk sewers in the system. This better understanding of where flooding was likely to occur and where system capacity constraints actually occurred allowed BES a top-down view of the basin during alternatives analysis. Local inflow control alternatives were considered first, and pipe upsizing along with passing the problem downstream was the second alternative. Figure 13.1 shows a thematic map showing flooding risk and historical complaints (Hoffman and Crawford, 2000). GIS APPLICATIONS FOR SEWER SYSTEMS GIS applications for sewer systems include (Shamsi, 2002): • Performing H&H modeling of collection systems, including: • Automatic delineation of watersheds, sewersheds, and tributary drainage areas Figure 13.1 Thematic map showing flooding risk and historical complaints (map courtesy of Computational Hydraulic Int.). 2097_C013.fm Page 259 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis • Model simplification or skeletonization to reduce the number of manholes and sewers to be included in the H&H model • Estimating surface elevation and slope from digital elevation model (DEM) data • Estimating dry-weather sewage flow rates from land use, census data, and billing records • Estimating wet-weather sewage flow rates from land use, soil, surface impervi- ousness, and slope • Creating maps for wastewater National Pollution Discharge Elimination System (NPDES) permit requirements (as described in Chapter 9 [Mapping Applica- tions]), such as: • U.S. Environmental Protection Agency’s (EPA) combined sewer overflow (CSO) regulations, such as System Hydraulic Characterization (SHC), Nine Minimum Controls (NMC), and long-term control plan (LTCP) • U.S. EPA’s sanitary sewer overflow (SSO) regulations, such as capacity, man- agement, operations, and maintenance (CMOM) • Documenting field inspection data (as described in Chapter 15 [Maintenance Applications]), including: • Work-order management by clicking on map features • Inspection and maintenance of overflow structures and manholes • Television (TV) inspection of sewers • Flow monitoring and sampling • Smoke-testing, dye-testing, and inflow/infiltration (I/I) investigations • Performing and planning tasks such as assessment of the feasibility and impact of system expansion In this chapter, we will focus on the sewer system H&H modeling applications of GIS. SEWER SYSTEM MODELING INTEGRATION Tight integration between a sewer model and a GIS is highly desirable. The GIS applications in sewer system modeling are developed by using the three application methods (interchange, interface, and integration) described in Chapter 11 (Modeling Applications). These methods facilitate preparation of model-input data and mapping of model output results similar to their application for water system models described in Chapter 12 (Water Models). Transfer of data between a GIS and a sewer model is handled differently by different software vendors. Some products offer nothing more than a manual cut- and-paste approach for transferring data between a GIS and the model. Others offer a truly integrated package. Obviously, tight integration between the sewer model and the GIS is desirable. However, it should not be assumed that a tightly integrated model is the best modeling tool. For example, the interchange or interface capability of a comprehensive sewer model might be more useful for some users compared with a tightly integrated model having limited modeling capability to simulate complex situations such as surcharged sewers. 2097_C013.fm Page 260 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis SOFTWARE EXAMPLES Sewer system modeling software is used to compute dry- and wet-weather flow for hydraulic analysis and design of collection systems and wet-weather control facilities such as storage tanks and equalization basins. Table 13.1 lists representative sewer system modeling packages and their GIS capabilities, vendors, and Web sites. The salient GIS features of some programs are described in the following subsections. What is common among the recent software developments is a transferability of fundamental database information, also referred to as a decision support system (DSS). Under a DSS framework, neither the GIS nor the model is central to the process. Both perform satellite functions for a central master database. (Heaney et al., 1999). SWMM Numerous hydrologic models were created in the U.S. during the 1970s, including the U.S. EPA’s legacy computer program SWMM and the U.S. Army Corps of Engineers’ Hydrologic Engineering Center’s HEC series of models (HEC-1 through 6). Two of the most popular models, HEC-1 and HEC-2, have been updated and renamed HEC-HMS and HEC-RAS. Collection system hydraulics can be characterized by using an H&H computer model such as SWMM. SWMM is a comprehensive computer model for analysis of quantity and quality problems associated with urban runoff. Both continuous and single-event simulation can be performed on catchments having sanitary Table 13.1 Representative Sewer System Modeling Software Software GIS Linkage Method Vendor Web Site SWMM Interchange U.S. Environmental Protection Agency (EPA) www.epa.gov/ceampubl/ swater/swmm/index.htm CEDRA AVSand Integration CEDRA Corporation www.cedra.com H 2 OMAP Sewer H 2 OVIEW Sewer Interface and Integration MWH Soft www.mwhsoft.com InfoWorks CS and InfoNet Interface and Integration Wallingford Software www.wallingfordsoftware.com Mouse GM and MIKE SWMM Interface DHI Water & Environment www.dhisoftware.com PCSWMM GIS Integration Computational Hydraulics Int. www.computationalhydraulics .com StormCAD and SewerCAD Interface Haestad Methods www.haestad.com XP-SWMM Interchange and Interface XP-Software www.xpsoftware.com 2097_C013.fm Page 261 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis sewers, storm sewers, or combined sewers and natural drainage, for prediction of flows, stages, and pollutant concentrations. SWMM is one of the most successful models produced by EPA for the waste- water environment. SWMM was developed from 1969 to 1971 as a mainframe computer program and has been continually maintained and updated. Versions 2, 3, and 4 of SWMM were distributed in 1975, 1981, and 1988, respectively. The first batch-mode microcomputer version of SWMM (Version 3.3) was released by EPA in 1983. The first conversational-mode user-friendly PC version of SWMM, known as PCSWMM, was commercially distributed in 1984 by Computational Hydraulics, Inc., of Guelph, Ontario (Computational Hydraulics, 1995). The first PC version of EPA’s SWMM was Version 4, which was distributed in 1988 (Huber and Dickinson, 1988; Roesner et al., 1988). An excellent review of SWMM’s development history can be found in the book by James (1993). SWMM is regarded as the most widely used urban H&H model in the U.S. (Heaney et al., 1999). SWMM continues to be widely used throughout the world for analysis of quantity and quality problems related to stormwater runoff, combined sewers, sanitary sewers, and other drainage systems in urban areas, with many applications in nonurban areas as well. From 1988 through 1999, the EPA Center for Exposure Assessment Modeling in Athens, Georgia, distributed approximately 3600 copies of SWMM. The University of Florida distributed roughly 1000 copies of SWMM in the late 1980s. Third-party interfaces for SWMM, such as MIKE- SWMM, PCSWMM, and XP-SWMM, have several thousand users. The number of subscribers to the SWMM Users Group Internet discussion forum (Listserv) on the Internet is nearly 10,000 (EPA, 2002). The current version (4.3) was released by EPA in May 1994 for the 16-bit MS-DOS operating system. Professor Wayne Huber of Oregon State University, one of the authors of SWMM, has developed several updated versions of SWMM 4. His latest version (4.4H) was updated in March 2002. All of these and previous SWMM versions were written in the FORTRAN programming language. None of them have a user interface or graphical capability. Users must provide ASCII text input and rely on ASCII text output. EPA is currently developing an updated version of SWMM referred to as SWMM 5. Written in the C++ programming language, SWMM 5 will incorporate modern software engineering methods as well as updated computational techniques. The modular, object-oriented com- puter code of SWMM 5 is designed to simplify its maintenance and updating as new and improved process submodels are developed. The new code will also make it easier for third parties to add GUIs and other enhancements to the SWMM engine. This approach follows the same approach used by the highly successful EPANET model from EPA (described in Chapter 12 [Water Models]), which analyzes hydraulic and water quality behavior in drinking water distribu- tion systems (Rossman, 2000). SWMM simulates dry- and wet-weather flows on the basis of land use, demo- graphic conditions, hydrologic conditions in the drainage areas, meteorological inputs, and conveyance/treatment characteristics of the sewer system. The modeler can simulate all aspects of the urban hydrologic and quality cycles, including rainfall, snow melt, surface and subsurface runoff, flow routing through drainage 2097_C013.fm Page 262 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis network, storage, and treatment. Statistical analyses can be performed on long- term precipitation data and on output from continuous simulation. Figure 13.2 shows a conceptual schematic of SWMM. This figure shows that SWMM is a complex model capable of modeling various phases of the hydrologic cycle using different blocks (modules) such as RUNOFF, TRANSPORT, and EXTRAN. SWMM can be used both for planning and design. Planning mode is used for an overall assessment of the urban runoff problem or proposed abatement options. SWMM is commonly used to perform detailed analyses of conveyance system performance under a wide range of dry- and wet-weather flow conditions. These days, SWMM is frequently used in the U.S. for modeling wet-weather overflows including CSO, SSO, and stormwater discharges from collection sys- tems. As such, it is the model of choice for use in many collection-system modeling studies. For example, SWMM can be used to develop a CSO model to accomplish various tasks leading to the development of a CSO Plan of Actions mandated by EPA. These tasks include characterizing overflow events, develop- ing the CSO vs. rainfall correlation, maximizing the collection-system storage, and maximizing the flow to the treatment plant. The CSO model can also be used to develop the EPA-mandated LTCPs to evaluate various CSO control options. Sizing of CSO control facilities such as a wet-weather equalization tank requires CSO volume and peak discharge, both of which can be modeled using SWMM. The use of SWMM to model wet-weather overflows is particularly advantageous for the following reasons: • SWMM produces estimates of present and future dry- and wet-weather flow rates. Flow estimates can be prepared based upon present and future land-use Figure 13.2 SWMM conceptual schematic. 2097_C013.fm Page 263 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis conditions, topography, sewer characteristics, and selected meteorological con- ditions. The model can be calibrated against measured flow rates. • SWMM models the performance of the conveyance system under a range of dynamic flow conditions. • Using SWMM, it is possible to assess hydraulic capacity in response to wet- weather input. This characteristic can be very useful for analyses related to abatement of overflows. SWMM is flexible enough to allow for different modeling approaches to the same area. An approach that adequately describes the service area and accurately computes and routes the flows at reasonable computing time and effort should be adopted. The following modeling strategy is generally used for modeling wet- weather overflows: • Delineate sewersheds (the drainage areas tributary to overflows, also referred to as subareas or subbasins). • Use the TRANSPORT Block to generate sewershed dry-weather flows. • Use the RUNOFF Block to generate sewershed wet-weather flows. • Combine dry-weather and wet-weather flows to generate combined sewershed flows. • Use the EXTRAN Block to route the flows through the collection and interceptor system. USEFUL SWMM WEB SITES SWMM Graphical User Interface Most users have now become accustomed to modeling in a point-and-click computing environment that provides a user-friendly graphical user interface (GUI). A GUI is a computer program that acts as an interpreter between users and their computers. It is designed to minimize (but not eliminate) the need for human experts and to guide the modeler through the intricacies of a particular numerical model. A GUI provides a suite of tools to create a decision support system for the numerical model that has been adopted. It also stimulates user interest and facilitates interpretation of model results. A GUI improves produc- tivity by increasing the efficiency of data entry, eliminating data errors through expert-checking, and the use of decision-support graphics and interpretation tools. It replaces difficult-to-remember text commands by interactive computer graphics consisting of menus, dialogue boxes, input and output windows, and icons. The main goal of using GUIs is to develop user-friendly computer applications or to SWMM4 www.epa.gov/ceampubl/swater/swmm/index.htm SWMM5 www.epa.gov/ednnrmrl/swmm/ Oregon State University ccee.oregonstate.edu/swmm/ SWMM-Users Internet Discussion Forum www.computationalhydraulics.com/Community/ Listservers/swmm-users.html SWMM-Online www.swmm-online.com 2097_C013.fm Page 264 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis add user-friendliness to existing command-line-driven applications. For example, Microsoft Internet Explorer is a GUI for user-friendly access to the Internet. Modern software offer pull-down menus, toolbars, icons, buttons, dialogue boxes, hypertext, context-sensitive online help, etc., which are not available in legacy computer programs including SWMM 4. Many commercial modeling packages now offer on-screen point-and-click drawing and editing of drainage network maps, but unfortunately some legacy programs still rely on ASCII text input and output files. SWMM was developed in an era when input files were created on punched cards. After 30 years, SWMM 4 now runs on personal computers, but it is still a text-based, nongraphical DOS program. It reads ASCII input to produce ASCII output, which is most suitable for mainframe line printers. SWMM’s ASCII format output is long, boring, difficult to interpret, and not very useful for nonmodelers. Creating computer models and reviewing the model results is often slowed by our inability to see the system being modeled. It is up to the modeler to review SWMM’s voluminous output and construct a mental image of the physical system being modeled. Often, the limitation in understanding the model output has been the modeler’s own comprehen- sion of the output, not the model itself. Quite frequently, it is impossible for the modeler to absorb the large amount of information contained in the model output (TenBroek and Roesner, 1993). A GUI and a GIS can be employed to overcome SWMM’s input/output defi- ciencies. Two types of GUIs can be employed for GIS applications in SWMM modeling (Shamsi, 1997; Shamsi, 1998): • An input interface (also called a front-end interface or preprocessor) extracts SWMM input from GIS layers and creates SWMM’s traditional ASCII text input file. The input GUIs can also provide graphical tools to draw a network model that is subsequently converted to SWMM’s ASCII input file. For example, an input interface may extract sewer-segment lengths and manhole coordinates from the sewer and manhole layers. • An output interface (also called a back-end interface or postprocessor) converts text to graphics. It can convert SWMM’s traditional ASCII text output file to graphs, charts, plots, and thematic maps that can be easily understood by everyone. With the help of these GUI/GIS tools, everybody can understand the model output. These tools help one to see storm-surge progress through the sewer system and pinpoint areas of flooding and surcharging. More than just reams of computer paper, such models become automated system-evaluation tools. Other benefits of GUI/GIS tools are: • Preparation of network schematics is not essential. Digitized plots of sewers and subarea boundaries can be used to create a drainage network diagram on a com- puter screen. • Zoom and pan features make it possible to display even the largest networks conveniently on the screen. • Connectivity data errors are easily detected and can be edited while still in the program. Instabilities in the model output, often the most difficult errors to find, are also easily located. 2097_C013.fm Page 265 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis • Flow and depth data from SWMM output can be displayed in either plan or profile view, providing an animated display of the HGL during the simulation time steps. • Flow and HGL time-series plots can be displayed for any conduit or node in the hydraulic network. • Field-collected flow and depth data can be displayed along with the model output for model calibration and verification. • Network graphics and modeled hydrographs can be exported to word processors to aid in report preparation. XP-SWMM and XP-GIS XP-SWMM by XP Software (Belconnen, Australia and Portland, Oregon) is a full-fledged 32-bit Microsoft Windows application. The program has been enhanced by the addition of a graphics database, and an adaptive dynamic wave solution algorithm that is more stable than the matrix method used in the original SWMM. The program is divided into a stormwater layer, which includes hydrology and water quality; a wastewater layer, which includes storage treatment and water quality routing for BMP analysis; and a hydrodynamic/hydraulics layer for sim- ulation of open or closed conduits (Heaney et al., 1999). XP-SWMM is also included in Visual SWMM from CaiCE Software Corp. (Tampa, Florida). Basically, XP-SWMM and Visual SWMM are GUI programs for SWMM. The user-friendly GUI is based upon a graphical representation of Figure 13.3 Visual SWMM screenshot. 2097_C013.fm Page 266 Monday, December 6, 2004 6:08 PM Copyright © 2005 by Taylor & Francis [...]... translated between most CAD and GIS software systems using the interchange method CAD or GIS files can also be used as a backdrop for the system being modeled Although XP-SWMM is not linked or integrated to a GIS package, it provides an optional utility called XP -GIS to extract model input data from the existing GIS database tables XP -GIS is a module for linking XP-SWMM to GIS databases Its main purpose... to facilitate the import and export of modeling data from GIS and other data sources such as spreadsheets, asset management software, and OLE/ODBC compliant databases It also allows for the inclusion of Shapefiles as background layers and for data to be viewed and manipulated in an XP-SWMM graphical environment GIS Data for SWMM GIS layers for land use, elevation, slope, soils, and demographics can be... tables shown in Table 13. 4 These look-up tables are based on the data provided in SWMM’s users manual (Huber and Dickinson, 1988) GIS APPLICATIONS FOR SWMM Representative GIS applications in SWMM modeling are given in the following subsections AVSWMM Shamsi (1997) developed an ArcView GIS interface called AVSWMM for collection-system and wet-weather overflow modeling Both RUNOFF and EXTRAN Blocks were... sewer and stormwater modeling software The GIS contained sanitary sewers and land-use layers, and was utilized as the raw data source for developing a sewer model for master planning purposes To facilitate this process, a customized GIS data management interface was developed using ArcView GIS as the graphical interface between the City’s GIS and the sewer model This interface included several project-specific... successfully using GIS applications for modeling their sewer systems The software Copyright © 2005 by Taylor & Francis 2097_C 013. fm Page 292 Monday, December 6, 2004 6:08 PM examples presented in the chapter indicate that many public-domain (e.g., SWMM) and commercial-off-the-shelf software packages (e.g., MOUSE) are available to help users benefit from sewer system modeling applications of GIS CHAPTER QUESTIONS... capabilities It integrates with GIS, desktop office systems, hydraulic modeling systems, maintenance management systems (MMS), field data systems, SCADA, and corporate databases Data exchange interfaces have been designed not only for import and export purposes but also to connect directly with GIS (ArcView and MapInfo), hydraulic modeling systems (InfoWorks), SCADA, and logger systems InfoNet has been designed... displays SWMMDUET, therefore, uses the integration method of GIS applications described in Chapter 11 (Modeling Applications) Data-entry sheets and forms eliminate the need for the modeler to know detailed ArcInfo processing techniques Similarly, feature selection, spatial joins, and processing commands and options of ArcInfo are specified and executed for the user Hyetographs are related to rain gauges where... tedious and error-prone work in the early phases of modeling projects MOUSE GM reads and writes the SWMM file formats It can be used as the ArcView GIS link and model-simplification tool for all SWMM modeling packages that apply the Copyright © 2005 by Taylor & Francis 2097_C 013. fm Page 287 Monday, December 6, 2004 6:08 PM standard SWMM data formats With MOUSE GM, MIKE SWMM users can link to GIS databases and. .. management systems, spreadsheets, and ESRI Shapefiles For example, the Shapefile Connection Wizard provides import and export capabilities to transfer data between GIS and sewer models SEWER MODELING CASE STUDIES Representative case studies of GIS applications in sewer system modeling are given in the following subsections XP-SWMM and ArcInfo Application for CSO Modeling Application Study period GIS software... impervious field to the landuse polygon layer and will prompt for the percent impervious value for each land use type Landuse grid layer Subarea polygon layer Adds or updates field containing percent impervious, PERIMP, to subarea layer 5 Set Soil Look-up Tables Function Function Input Layers Output Joins the look-up tables for soil infiltration parameters for the Green-Ampt method (Huber and Dickinson, 1988) . alternative. Figure 13. 1 shows a thematic map showing flooding risk and historical complaints (Hoffman and Crawford, 2000). GIS APPLICATIONS FOR SEWER SYSTEMS GIS applications for sewer systems include. to compute dry- and wet-weather flow for hydraulic analysis and design of collection systems and wet-weather control facilities such as storage tanks and equalization basins. Table 13. 1 lists representative. also allows for the inclusion of Shapefiles as background layers and for data to be viewed and manipulated in an XP-SWMM graphical environment. GIS Data for SWMM GIS layers for land use, elevation,