The City of San Diego Metropolitan sewer system serves a population of 1.8 million generating an annual average daily flow of 190 mgd. The service area includes the City of San Diego and 14 other wastewater agencies. A network of trunk sewers and interceptors ranging up to 114 inches in diameter convey the wastewater to 2 major pumping stations and on to the Point Loma Wastewater Treatment Plant (PLWTP) and ocean outfall. Collection system facilities within the City of San Diego (representing about 70 percent of the total Metropolitan sewer system) include over 2800 miles of sewers ranging in size from 8 to 114 inches, and 82 pumping stations.

The City has recognized that the growing size and complexity of its wastewater system call for ongoing sewer system modeling and continuous planning. This recognition has led to the development of a dynamic hydraulic model to analyze the existing and future systems. The construction of the hydraulic model focused attention on the need to assemble large amounts of data ranging from physical sewer data (eg; lengths, inverts etc.) through to demographic data for population analysis. It became clear of the need to develop a comprehensive data management system that organized, stored and processed both the tabular and graphical data acquired to build the hydraulic model.

 The following sections of this paper describe the processes undertaken to build, calibrate and analyze the hydraulic model using customized tools developed within the ArcView GIS environment.

 A sustainable planning process requires more comprehensive tools for managing information about a system, whether that information be observed flows and rainfall, physical characteristics and condition of sewers and facilities, changing population and land use patterns, or the results of hydraulic analyses. The following are brief descriptions of tools that the City’s modeling team has developed or adapted to support its efforts.

Since most of the information needed for wastewater planning has a spatial component, it is best managed in a geographical information system (GIS) environment. Fortunately, the agencies in the San Diego region were early leaders in adopting GIS technology and that investment has paid dividends for the City’s modeling team. Several different agencies and City departments are responsible for maintaining GIS maps and databases which the modeling team has been able to use productively. Key databases include:

• Extensive land base information such as compressed digital ortho-photos, address-coded streets, political boundaries, parcel boundaries, and topographic contours.
• Sewer system facilities data covering the City’s entire 70,000-pipe collection system, including pipe diameters, invert and ground elevations, materials, etc. This is the database used for producing sewer maps and is also used in the City’s sewer maintenance management system. Due to limitations in the completeness and accuracy of this massive database, the attributes for the pipes included in the models (generally all pipes greater than or equal to 15 inches in diameter) had to be verified from as-built drawings and a separate database of modeling data created. Graphic data was used directly. The modeling team is currently working to integrate the verified attribute data back into the full GIS database and modify the database structure to facilitate future model updates incorporating newly constructed and mapped facilities.
• Population, employment, and land use information (existing and projected) by geographic units (MGRA's) as small as a city block. The data is maintained and updated by the San Diego Association of Governments (SANDAG) and covers the entire Metropolitan sewer service area. SANDAG is responsible for periodically updating the inventory and projections. These data are the basis for automatically computing wastewater flows in all parts of the sewer system.
• Major industrial dischargers’ estimated wastewater flows and other discharge characteristics, maintained by the City industrial permitting group. Although this database is not in a GIS environment, the database includes address information which has been geocoded via address-matching tools. Selected industrial flows are used in the model to better estimate existing flows in certain trunk sewers.
• Flow monitoring sites, as digitized and maintained by the City flow monitoring group and modeling team.

The hydraulic modeling and data management tools developed to assist the planning and sewer modeling team were created using ArcView’s Avenue programming language and Dialog Designer. The resulting scripts and dialogs were compiled into an ArcView extension and distributed to all users. The modeling and data management tools can be accessed from customized menus, buttons and tools all within the standard ArcView View document window.

The first stage of the development process involved designing the database and graphic file structure. The attribute data (eg; pipe size, length, inverts etc.) are stored in separate (DBF) tables and joined to corresponding graphic (SHP) files using a key field. This approach maximizes the use of the SHP files by joining different forms of attribute data to the same graphic SHP file, in effect ‘normalizing’ the tabular and graphic data. The following details the main hydraulic modeling process tools used for constructing and calibrating the City’s sewer model.

This routine performs extensive data validation checks based on specified rules such as missing lengths, sizes, reverse slopes, connectivity errors etc. The results are displayed on the plan view and with error descriptions ‘joined’ to the attribute data.

The Network Trace Manager is used to verify connectivity errors, select profile views, define model network and identify sub-area basins.

The Profile Viewer creates a theme displaying a profile of a selected pipe section. Node and link data can be accessed from the profile view.

This routine extracts a selected portion of the City sewer system for re-formatting and export to the City’s modeling software package (HydroWorks^TM). The routine has the capability of exporting to various model formats.

Import of selected results from the modeling program, for graphical viewing and analysis (e.g., highlighting of problem areas on the sewer map).

Import of selected flow monitoring data and linkage of that data to the monitor symbols on the GIS map, for displaying flow and depth graphs along with modeling results graphs during the model calibration process.

The development of the hydraulic modeling and data management toolkit (ArcADE) enabled the City of San Diego Metropolitan Wastewater Department modeling team to efficiently build and calibrate a dynamic hydraulic model of the entire sewer system. ArcADE provided a modern approach to data processing and modeling activities making full use of the benefits of a GIS. In addition, the GIS provided an excellent means of presenting the data to the management and relevant departments within the City. Finally, processing the sewer, demographic, flows and rainfall data within the GIS environment enabled the modeling team to maximize the use of all available data and build a comprehensive 'data warehouse' used to enhance the City's current GIS data services.