USING GIS IN WATER SUPPLY AND SEWER MODELLING AND MANAGEMENT

HENRIETTE TAMAŠAUSKAS*, L.C. LARSEN, O. MARK DHI Water and Environment, Agern Allé 5

2970 Hørsholm, Denmark

*Corresponding author, e-mail: htt@dhigroup.com

Abstract

Geographical Information Systems (GIS) are becoming the universal backbone in most information systems managing data for water and wastewater systems. Using GIS is a great aid in graphically presenting geo-referenced information and providing the necessary tools to accurately locating needed information and linking water supply and sewer modeling systems using the spatial position as the main indexing mechanism. The user can also retrieve related information without the need to find or enter tedious information. This ability to work with vast amounts of spatial data in a visual and easy to understand way means that otherwise slow and cumbersome processes such as building hydraulic models of water or sewer network systems can become much more efficient. This presentation will describe examples of how GIS can be a good partner for hydraulic modeling and integrating with asset management systems to form an efficient work bench for building, maintaining, and graphically presenting accurate water supply and sewer models.

Keywords

GIS, MIKE URBAN, data management, asset management systems, water supply and sewers modelling, hydraulic modelling Introduction Geographical Information Systems (GIS) are becoming the universal backbone in most information systems managing data for water and wastewater systems. Using GIS is a great aid in graphically presenting geo-referenced information and providing the necessary tools to accurately locating needed information and linking water supply and sewer modeling systems using the spatial position as the main indexing mechanism. This ability to work with vast amounts of spatial data in a visual and easy to understand way means that otherwise slow and cumbersome processes such as building hydraulic models of water or sewer network systems can become much more efficient. DHI’s modelling tool MIKE URBAN combines DHI’s 20 years of innovation in urban water distribution and collection system modelling with ESRI’s ArcGIS technology, thus providing a complete urban water modelling environment based on GIS. Management and display of data spatial data hence takes place in a GIS environment, allowing MIKE URBAN to utilize GIS features for building, maintaining and graphically presenting accurate water supply and sewer models.

Integration of GIS functionality and hydraulic models The open architecture of ArcGIS makes it an ideal connectivity tool for the many applications that are used in the management of data related to urban water infrastructure. As MIKE URBAN uses the ArcGIS Geodatabase as the central data repository, the different types of applications can easily exchange data and combine information that originates from separate applications. The MIKE URBAN data model is open and documented and data can be accessed and even managed through other GIS applications. At the same time, MIKE URBAN can obviously use whatever other relevant data that the user may be storing in her GIS system, eg land use data, aerial photographs, digital elevation data, etc as background information for the modeling. Simulation models need information about the physical properties of the pipe network - pipe sizes, materials, hydraulic structures, pumps, valves, etc. Such information is typically managed in an asset management system. The integration with GIS functionality and enhanced update functionality is a major step ahead in data management for hydraulic models. For many years the main efforts among the vendors has been on development of tools for building of the hydraulic models. However many modelers are realizing that they are more or less forced to re-build the models every 4-6 years in order to keep them up to date with the reality. The reason is simply because updating the existing models with all changes in the past period demands handling of large amounts of data, which are both tedious and often results in errors that can be very difficult to detect.

With MIKE URBAN the lifetime of the model can be extended dramatically by allowing the user to maintain the data in the existing GIS system and then update the model whenever needed. The key is to “recognize” the elements, which has been changed in GIS and then update the corresponding elements in the hydraulic models. This way the model can often be used for a significant longer period before re-calibration is needed, and at same time the management of the geometry for the networks data in the organization are significantly improved.

In addition to this some of the Asset data which is normally only accessible from GIS can be handled directly in the model. There are simply two or more synchronized tables in the database for each data type. One table handles the model data while the other handles asset data. This overlap between the data structures in GIS and models are a great help in the daily work where a lot of time is often spend managing data from several sources. Examples A few examples of where the GIS and the hydraulic modelling and integration with asset management systems form an efficient work bench for building, maintaining and graphically presenting water supply and sewer models are: • Water demands can be developed from the customer information systems and billing databases • Asset management systems may be linked to MIKE URBAN using MIKE URBAN’s powerful

database linker • Automated network geometry import and topology errors • Automatic discovery of network topology errors • Automatic generation of node elevations from digital terrain models Validating and correcting erroneous data When starting to build a model, the original data used for building up the model often display missing values along with erroneous values. For a modeller the first steps therefore are to validate data and then listing and correcting these errors. The data validation features in MIKE URBAN include:

! Database consistency check (the project check tool) • Checks database for logical errors • Illegal or unlikely values

! Tracing Tools • Disconnected sections • Loops • Wrong connections

! Visual Checks

The project check tool allows you to validate your data. The consistency of the setup will be checked against a large number of rules. Rules are combined so that both the data structure as well as the values of attributes are checked. You find the errors by group (nodes, links, catchments etc) and the errors are then listed as seen in Figure 1. The errors may then be corrected manually or by using the interpolation and assignment tool. The tool may also be used as a logbook for displaying errors yet to fixed.

Figure 1 The project check tool provides a list of errors and warnings for data used in the setup The tracing tools e.g. allow you to check network connectivity, see e.g. Figure 2, in an easy and convenient way as well as finding (unwanted) loops and wrong connections.

Figure 2 Tracing tools allow for easy detection of unconnected parts of the network Assigning and interpolation values The interpolation and assignment tool in MIKE URBAN is a powerful tool – both used alone or in conjunction with the project check tool. It allows you to perform tasks like the following:

• Assign values to Ground Elevation from a raster layer representing the DEM • Assign the diameter of manholes to be equal to the largest pipe entering the manhole • Interpolate pipe levels by interpolating values following the network (pipes) • Assign a value to construction year based upon a polygon theme giving city areas Basically, you can use any kind of layer for assigning values, so in the case that relevant GIS layers are available you can use these. Interpolations in space and network can also be used to correcting erroneous data. Say you have identified a section in the longitudinal profile where certain data is either missing or obviously wrong, one possible workflow could then be to use the project check tool to identify the errors and then the interpolation and assignment tool to correct the values. In below example the project check tools provided a list of errors for nodes and links in the system, see Figure 3.

Figure 3 The list of errors and the longitudinal profile of the path with missing invert levels. The interpolation and assignment tool allows to assign the missing data in various ways, see Figure 4. The result of assigning the invert levels by performing a linear interpolation along the network path is seen in Figure 5. This is just one example of the various interpolation possibilities. The assignment of values can be done in a number of ways, also using values from external data sources.

Figure 4 The various assignment methods in the Interpolation and Assignment tool

Figure 5 Using the Interpolation and assignment tool for correcting the longitudinal profile along a network path. MIKE URBAN data flags You can choose to keep track of your changes done when interpolating or assigning data values. The scenario manager allows for tracking of changes on an attribute level and reporting of differences between the original setup and the setup after clean up of missing data and correction of obvious wrong data. However, you might also want to flag either the record or the attribute (e.g. the invert level of the manholes) with a user defined specified status code. In the example seen in the previous section you could choose to change e.g. the status of the manholes affected to e.g. ‘interpolated’. The flags can be viewed in the GIS system and also provide a map for e.g the survey team when they verify the data that has now just been assigned or interpolated by the model team. A special tool for setting status flags based upon selections is included in MIKE URBAN. This tool will mark all selected records with the status code chosen by the user. Both record level and attribute flags may be assigned using this tool, see Figure 6.

Figure 6 The flagging tool works on individual layers and is based on the selections in these The flags can, however be set in a number of ways, the most straightforward way in relation to the previous example is to set the flags directly when making the interpolation (or assignment), see Figure 7. An example of a resulting map is seen in Figure 8.

Figure 7 The interpolation and assignment tool allows to set flag values on both record and attribute level.

Figure 8 Horizontal plan displaying the various flags. The flagging can be used for a numerous things. Another example could be to compare ground elevations with invert levels to identify all manholes with unrealistic depth, mark them and then schedule a survey. MIKE URBAN and Asset Management Systems MIKE URBAN can use information from Asset Data systems as background data sets as well as creating hyperlinks between e.g.. CCTV and photos and the model elements. It is, however, also possible to create direct links to asset databases and hence bring in information from e.g. your Asset Management system without actually transferring the data to the MIKE URBAN database. MIKE URBAN can also be extended with user customized tool to suit your specific needs, by e.g. linking to your work order system, CCTV records etc. In below example a link is setup to a database containing information on work orders for the system. This means that when working with the model you can e.g. easily identify which records already have inspections jobs – or even look at the inspection report for specific pipes. Once the user customized tool has been written it is simply activated from within MIKE URBAN, see Figure 9.

Figure 9 The user tool as seen from within MIKE URBAN Opening the tool will then allow you to retrieve work orders for the system, making it possible to query manholes and pipes with inspection results, e.g. you can select all manholes and pipes with recent video inspections. You can then select jobs to show what has been inspected, resulting in the pipes being selected in MIKE URBAN, see Figure 10. Or you can select the area of interest in MIKE URBAN and the job list will then only show the inspection jobs on those selected pipes.

Figure 10 Selecting inspection jobs will select the nodes and manholes in MIKE URBAN – and vice versa If you double click on an inspection job with an attached report, the corresponding report will be opened. This is just one example of the convenient and easy way of linking between MIKE URBAN and your asset management system of choice. Conclusions The price of modelling consists of hardware prices, software prices – and the price of building the model, maintaining the model and running the model. The latter part often is the most expensive part, hence tools that support this process in the most efficient way will save costs. As GIS is becoming the universal backbone in most information systems managing data for water and wastewater systems, the integration and ability to retrieve and (re)use information between GIS/Asset Management systems and the hydraulic models makes building and maintenance of the hydraulic models of water or sewer network systems much more efficient. This presentation has shown some examples of how this interaction is achieved seamlessly with MIKE URBAN.