KEY TERMS: ArcView, ARC/INFO, GIS, sewer systems, computer mapping, hydraulic modeling.
Mapping, monitoring, modeling, and maintenance are the four most important activities in effectively managing a stormwater and wastewater collection system. Since these activities begin with the letter "M", a management practice which utilizes them can be referred to as a "4M" management approach. A Geographic Information System (GIS) can be used to implement or improve the 4M management strategy. This paper describes how the desktop GIS, ArcView, can be used to implement the 4M approach for the management of stormwater and wastewater collection systems.
The mapping work can be best managed by developing a Computer Mapping Program (CMP) which can be defined as a comprehensive package of data collection, mapping, and data management services. A CMP can produce infrastructure maps that are complete, accurate, up-to-date, and affordable. Since a CMP provides accurate and up-to-date information, responding to emergencies is much faster. A CMP uses GIS technology to incorporate comprehensive information about an infrastructure gleaned from interviews with staff, from an inventory of records, and from field and airborne investigations.
Monitoring is an expensive activity. It is very costly to monitor all the potential sampling sites. The monitoring work requires selection of representative monitoring sites which can be accomplished by gaining a sound understanding of the collection system and its surrounding features. GIS coverages for watersheds, sewersheds, receiving waters, roads, municipal boundaries, demographic characteristics, and land use provide a sound basis for optimal monitoring site selection.
Modeling helps us to study the collection systems in ways that would not be practical, or even possible, by other means. Mathematical models are used to understand the system and evaluate strategies for the efficient operation of a system. Development of complex models which are capable of simulating detailed hydraulic processes of a collection system is a very labor oriented task. Interpretation of model results which can span hundreds of pages, is just as hectic. GIS can be used to facilitate model development and interpretation.
Maintenance activities require an accurate and up-to-date date system inventory and maps. GIS can provide a computerized maintenance management system capable of automatically creating work orders from sewer inspections, customer complaints, and identified problem sewers. This can be accomplished by linking a utility's existing maintenance module and GIS.
Most GIS packages are designed for technicians who perform heavy duty production work on work stations, and therefore, are not very user friendly for the casual PC users. Some of the leading GIS products are ARC/INFO by Environmental Systems Research Institute (ESRI), Geo/SQL by Generation 5 Technology, GENEMAP by Genasys, and MGE by Intergraph. ARC/INFO, PC ARC/INFO, ArcCAD, Geo/SQL, GENEMAP, and MGE are complex software systems that require substantial technical skills. The sewer system operators and managers often do not have the technical expertise to develop, run, and maintain a complex GIS.
In the past decade, powerful workstations and sophisticated software combined to bring mapping capability to any desktop. In the last five years, computers have become so powerful that mapping software will now run on off-the-shelf PCs. Once the province of cartographers and CAD technicians, desktop mapping and GIS are ready to infiltrate almost all areas of water and wastewater utility operations and management. ESRI's ArcView is a sophisticated desktop mapping and GIS application which promises to bring the power of GIS to the average PC user. The main features of ArcView are:
The above features make ArcView a cost-effective tool for implementing the 4M management approach. A limitation of ArcView is that it is not intended to support a GIS production shop. The paper maps cannot be digitized directly in ArcView. ArcView has limited feature editing capability. Therefore, ArcView's best applications lie in management, manipulation, and modification of existing GIS coverages. The coverages can be produced in ARC/INFO and imported to ArcView. The users who do not have an in-house ARC/INFO site can hire consultants for converting the existing maps to ARC/INFO coverages by scanning and digitization. The widespread use of ARC/INFO among government agencies, coupled with the wide range of exchange formats supported by ARC/INFO, makes it highly probable that most third-party data providers will be running ARC/INFO and as such be able to directly supply data in either ARC/INFO coverage or ArcView shape file (ArcView's native format). If spatial data in whatever format is available for your project, it can be converted to ArcView format via ARC/INFO (Hutchinson and Daniel, 1995). ESRI publishes a catalogue of ArcView compatible data sources called "ArcData." ArcData is a collection of digital information products developed cooperatively by ESRI and more than 30 data providers. Included are data sets for such applications as urban and transportation planning, natural resources, environmental, agriculture and demographics. Some specific example of ArcData are: Digital Line Graphs (roads, railroads, rivers, lakes, streams, wetlands, contours, states, counties, cities, etc.), TIGER files (census blocks, census block groups, roads, railroads, hydrography, political boundaries, etc.), and Climatedata (monthly summaries of the meteorological data). The ArcView coverages illustrated in this paper were created in ARC/INFO.
There are three main types of computer mapping systems available today for developing a CMP: Computer Aided Design and Drafting (CADD) based Computer Aided Mapping (CAM), Automated Mapping and Facilities Management (AM/FM), and GIS. The commonly accepted definition of a GIS is, "a computer-based system used to capture, store, edit, display, and plot geographically referenced data." Unfortunately, this definition applies to CAM and AM/FM also. However, all the three technologies have distinctly different characteristics and applications and no single system offers all of them. For instance, you can't simply use a CAM or AM/FM system as a GIS. It is important to understand the distinctions between CAM, AM/FM, and GIS systems, listed in Table 1. CAM and AM/FM systems do not permit spatial analyses. A GIS has the capability to relate data across layers to allow spatial analysis (Dueker, 1987). A CAM map does not have the graphical intuition of human eye and can't, for example, tell which drainage area is adjacent to which (Berry, 1994). A GIS map does not have this limitation because the spatial relationship among its features or topology are simply a part of the map intelligence.
A commercial map atlas company may use a CAM system since its applications are primarily for cartographic products. A telephone company will use an AM/FM system to support its telephone system operations and maintenance, as it must be able to quickly trace a cable network and retrieve its attributes (Korte, 1994). For the management of a sewer system, a GIS based CMP is most suitable because it must conduct many types of spatial analyses, asking questions like how many customers, by type (residential, commercial, industrial), are located within 1,000 ft of a proposed sewer line. Most importantly, in addition to sewer system management, a CMP must also support other applications of the municipality. For example, the planning department must be able to generate 200 ft notification lists as part of its plan review process. The public works department must be able to conduct maintenance tracking and scheduling. The public safety department must be able to perform crime location analysis. Thus, if the sewer system is owned and operated by a city rather than a sewer authority, its CMP should be designed to simultaneously address the mapping needs of all the city departments. Like most other computer-based technology, the combination of more powerful PCs, better quality graphics, and more flexible software have made GIS capability affordable. Thus, a GIS based CMP is the most suitable technology to meet all the mapping and management needs of a municipality.
Table 1. CAM and AM/FM Versus GIS
Feature CAM AM/FM GIS Layers Yes Yes Yes Spatial relationship (Topology)No No Yes Network analysis No Yes Yes Lines Yes Yes Yes Nodes No Yes Yes Polygons (areas) No No Yes Attributes No Yes Yes Actual locations Yes/No Yes Yes Map intelligence No No Yes
The Board of Public Works of the Borough of Ramsey (the Board), New Jersey, is responsible for the operation and maintenance of water distribution and sanitary sewer collection systems throughout the Borough. These operations necessitate the daily use of a variety of map products and associated geographically referenced information resources. Geographically referenced or georeferenced is information describing or relating to a specific location, such as a land parcel, manhole, sewer segment, or building. More than 70% of all information processed by local governments is georeferenced. In an effort to more efficiently manage its geographically referenced data, the Board started to explore the benefits and applications of GIS technology and computer mapping in early 1993. As a first step, with the assistance of Chester Engineers, the Board started a GIS Pilot Project. The goals of the pilot project were:
The GIS Pilot project has produced a GIS Needs Assessment report, a GIS Implementation Plan, and a functioning GIS demonstration system for a selected portion of the Borough. Whatever the range of mapping requirements, the CMP base map must be suitably accurate and detailed to support the application with the most demanding application, requiring map accuracies of better than 2 (0.6 m) ft. Utility asset location also requires mapping that depicts specific small features such as manholes and catch basins. These requirements can be met by a map scale of 1'=50' (1 cm = 6 m). To meet the recommendations of the system design, a digital orthophoto produced from stereo aerial mapping photography was used as the base map. Digital orthophotos have been widely accepted as an optimal land base for GISs. A digital orthophoto is a computer compatible raster image derived from aerial photography which has been scanned at very high resolution. The image is corrected to remove distortions due to attitude of the aircraft at the time of exposure, image displacement due to topographic relief, and the distortion introduced by the camera (Michael, 1994). Digital orthophotos are very detailed, can be easily interpreted, and provide excellent accuracy which can be easily quantified and verified.
The GPS technology offers a promising solution to placing current data on maps (Lewis, 1993). GPS technology was used in the pilot project to verify the locations of valves, hydrants, and manholes. A GPS represents a space-age revolution in GIS data collection. GPS systems utilize a constellation of satellites orbiting the earth twice daily transmitting precise time and position signals. GPS receivers read signals from orbiting satellites to calculate the exact spot of the receiver on earth. The new line of GPS receivers brings technology to GIS practitioners who can populate maps with the location of features such as manhole covers, catch basins, and overflow points.
ARC/INFO and ArcView were the two main softwares used in the pilot project. ARC/INFO is a complex software and requires substantial technical expertise. Since, the Borough did not have the technical staff to run and maintain an ARC/INFO CMP, the CMP production was conducted by the consultant using ARC/INFO. Due to its low cost, ease of use, and compatibility with the ARC/INFO file format, ArcView was installed in the Borough for routine display and plotting of maps and querying the CMP database.
With the knowledge and experience gained from the Pilot Project, the Board will be prepared to pursue a broader implementation of GIS technology. The pilot project was completed in one year and costed approximately $40,000. To accomplish the pilot project task of presenting a functioning GIS demonstration system several maps were produced. Figure 1 shows an ArcView screen displaying the sewer system overlayed on the street map. The sewer lines have been classified according to pipe diameter. Classification by attribute value is the cornerstone of thematic mapping and GIS. This was achieved in ArcView by classifying the "sewers" theme based on the values of the attribute "diameter". Figure 1 also shows ArcView's attribute table for the sanitary sewers and an "Identify Results" window which displays the feature attributes in response to the user queries.
Figure 1. ArcView's User-friendly Work Space Showing Sewer Map and Attributes
The City of Huntington, West Virginia, has a combined sewer system with 23 Combined Sewer Overflow (CSO) discharge points permitted under the National Pollution Discharge Elimination System (NPDES) program. The sewer system is operated by the Huntington Sanitary Board (HSB). One of the CSO requirements specified in the NPDES permit is to monitor each CSO event for cause, frequency, duration, quantity and quality of flow. As a first alternative to comply with this requirement the feasibility of monitoring all of the 23 CSO locations was studied. This option required purchase, installation, monitoring, and maintenance of flow monitors, water quality samplers, and rain gages for each CSO site. This option was ruled out because of its excessive cost, estimated at over a million dollars, and other problems such as adverse environmental conditions in the CSO structures, difficult access issues, and new federal requirements for confined space entry. The second option consisted of a combination of monitoring and modeling. In this option, a representative subset of CSOs can be monitored temporarily to collect sufficient calibration data and develop a calibrated model for each monitored CSO area. Calibrated model parameters could subsequently be applied to the models of unmonitored CSO areas. CSO models can eventually be used to predict quantity and quality of CSO discharges from observed rainfall data. This option, costing approximately one-third of the first option, was preferred by both the HSB and the EPA (Region V) and was selected for implementation.
ArcView was used to select a representative subset of the 23 CSO sites to be monitored. Selecting the representative sites is a complex process. The objective is to maximize the extent and value of the data for use in model calibration and provide a uniform distribution of flow meters, samplers and raingages throughout the system so that all parts of the service area are equally covered. Other factors such as providing coverage to all land uses, known problem CSO areas, and all types of diversion chambers; and access for installation and maintenance of monitoring equipment should be thoroughly studied. Using these selection criteria, a total of six were finally selected for sampling and monitoring. Figure 2 presents an ArcView plot showing the monitored versus unmonitored CSOs and CSO areas. The map clearly indicates that by monitoring only 25 percent of the total number of CSOs, approximately 70 percent of the study area was covered.
Figure 2. Selecting Representative Monitoring Sites
As mentioned in the previous section, HSB selected an approach which combined both monitoring and modeling to comply with the CSO regulations. U.S. Environmental Protection Agency's Storm Water Management Model (SWMM) was selected for modeling the collection system. SWMM (Huber and Dickinson, 1988) was developed in the early 1970s and has been continually maintained and updated. It is perhaps the best known and most widely used of the available urban runoff quantity/quality models. SWMM is a large and complex model which simulates the movement of precipitation and pollutants from the ground surface through pipe and channel networks, storage treatment units and finally to receiving waters. Both single event and continuous simulation may be performed on sewersheds or natural watersheds for predicting flows and pollution concentrations. SWMM can be used for both planning and design. The planning model is used for studying the urban runoff problems and abatement options. The design model performs event simulations using a detailed sewershed schematization and shorter simulation time steps.
Minimum input data for modeling dry weather quantity and quality consist of demographic data (dwelling units, persons per dwelling unit, market value of average dwelling unit, and average family income), land use (single and multi-family residential, commercial, industrial, and open space), and diurnal and daily quantity/quality variations. Commercial and industrial dry weather flows are not computed by SWMM and their estimates must be provided by the user. Minimum input data for modeling wet weather quantity and quality consist of observed or synthetic hyetographs, watershed's physical characteristics (area, imperviousness, slope, width), watershed's hydraulic characteristics (Green-Ampt or Horton infiltration parameters, surface and stream channel roughness coefficients, surface depression storage, and stream channel geometry), and surface pollution characteristics (land use; total curb length; catch basin volume and initial pollutant concentrations; street sweeping interval and efficiency; dry days prior to initial precipitation; dust/dirt and/or pollutant fraction parameters for each land use; initial pollutant surface loading; and washoff coefficients).
Figure 3 shows an ArcView plot of Land Use. The land use coverage was used to estimate percent imperviousness for the CSO areas which is an parameter for SWMM. The land use information was also used to select the representative monitoring sites, as described in the previous section.
Figure 3. Land Use Map
Computerized maintenance management permits more comprehensive planning and scheduling of preventive and corrective tasks. Also, potential maintenance backlogs can be identified quickly and scheduled by priority. Most large utilities already have computer programs to detect maintenance problems by tracking and scheduling maintenance. Repair histories can be tracked and repair costs accumulated by each piece of equipment (Renner 1993). Maintenance work can be managed efficiently if the problem areas and the maintenance work can be displayed on maps. This can be accomplished by linking a utility's existing maintenance module and GIS. Maintenance and inspection histories of the sewers can be extracted from the maintenance database and transferred to the sewer coverage of a GIS. The link can graphically track the maintenance activities and identify areas where rehabilitation or capital improvements may be necessary (Hardin, 1995). Color-coded thematic maps may be generated highlighting sewer segments in terms of their capacity, condition, and maintainability (Johnson and Bockemeier, 1991).
An example of integrating a computerized maintenance management module with ArcView is CASS WORKS (RJN Group Inc., Wheaton, Illinois). CASS WORKS is an integrated infrastructure management software for water distribution, sanitary sewers, storm drainage, treatment facilities, parks and recreation, GIS, and AM/FM applications. Integration is accomplished through a module called GeoCAD that can integrate the maintenance module with the leading GIS software programs that use ORACLE. This integration allows the maintenance module to run within GIS programs. Using ANSI SQL RDBMS standard, RJN has integrated CASS WORKS with ARC/INFO and ArcView. The ability for both systems to access the same database increases the value of the data, eliminates database inconsistencies, allows for both graphic and nongraphic representation of data, and eases implementation issues and costs. Figure 4 shows the Borough of Ramsey sanitary sewer lines, manholes, catch basins, cleanouts, and problem areas plotted on the digital orthophoto base map. Figure 4 also shows a problem area movie being launched from ArcView. This video clip was imported from a video tape of the internal TV inspection of the sewers. This movie is displayed using ArcView's "hot link" function. Hot links allow the user to point and click on a map feature to view photos, schematics, etc., or launch other applications from ArcView, such as run a video clip. Thus, whenever a problem sewer segment is clicked on the sewer map, its video clip is automatically started.
Figure 4. ArcView's Hot Link Displaying TV Inspection Video of Sewers
ArcView is a user-friendly and affordable desktop GIS program. It can be used by system operators and managers for implementing a collection system management program involving mapping, monitoring, modeling, and maintenance activities. ArcView has limited feature editing capability, and therefore, it is neither suitable for developing new GIS coverages nor it is intended to support a map production shop. ArcView's optimum applications are in the management, manipulation, and modification of the existing GIS coverages which have been created elsewhere, preferably using the ARC/INFO GIS.
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Hardin, D., 1995. Computer Tools Simplify Sewer Planning, Management. Water Environment and Technology, WEF, July, pp. 34-35.
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Huber, W.C., and R.E. Dickinson, 1988. Storm Water Management Model. User's Manual, Version 4, Environmental Research Laboratory, U.S. Environmental Protection Agency, Athens, Georgia.
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Renner, D.C., 1993. Establishing a Maintenance Program, WATER/Engineering and Management, February, pp. 26-36.
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