Henrik G. Muller, Sten Lindberg, Danish Hydraulic Institute Agern Alle 5, DK-2970 Horsholm, Denmark, Telephone +45 45 76 95 55, Fax +45 45 76 25 67
Figure 1. MOUSE GIS
Two widely used software tools in the management of urban drainage systems are:
* asset management systems
* numerical hydrodynamic and water quality modelling systems
The asset management systems are used in the daily management of inspections, permits, billings, etc. and most often they contain information about the physical systems at very detailed levels, reflecting the complexity and details of the real systems.
Numerical modelling systems, on the other hand, require a much less detailed description of the physical system when applied for the analysis and planning of extensions and other modification to the drainage system.
Keeping the information updated and consistent at these two different levels of detail is no trivial task. Normally, the responsibility lies within different departments, and there are no formal procedures established to ensure that changes in the layout or dimensions of the sewer system are implemented both in the asset management systems and in the models. Hence there is a great risk that further evaluation of the existing, but recently changed, system's capacity and performance will be incorrect.
The proposed paper describes an ArcView application which bridges the gap between asset management systems and the advanced numerical modelling system, MOUSE. The application allows the user to extract data from a number of different asset management systems, to condense the network automatically - while maintaining consistency in the description of the physical system - and finally to store the data as a model for further analysis in MOUSE. All decisions in the simplification process made by the programme are based on user-specified criteria.
All changes are recorded on a separate file, which can be replayed later if and when the user wants to repeat the process, e.g. after changes in the asset management system. Further, the application enables the user to analyze results from the MOUSE simulations within the ArcView program. CSO points and volumes, exceedence of critical levels, etc. can quickly be identified. By virtue of direct access to the asset management system, the simulation results can also be visualized in combination with parameters describing the actual conditions of the sewer system, e.g. CCTV information.
GIS systems are useful tools for visualising the projected developments in Metropolitan areas, in terms of changes in population, industrial patterns, infrastructural utilities, etc. One very interesting aspect in this context, is the expected future load and behaviour of sewer systems, which convey the foul and industrial waste-water flow to sewage treatment plants.
Large sewer systems are structurally very complex, often with overflow chambers and loops. The hydraulic performance and capacity can only be evaluated by use of comprehensive mathematical modelling tools.
This paper describes one of the main problems when setting up large sewer network models to be used for the urban drainage modelling system, MOUSE.
MOUSE GIS is an ArcView application where the user can interactively select the relevant nodes, pumps and weirs to be included in the final model network.The MOUSE simulation results (extreme filling of pipes, time series plot, etc.) are available to the MOUSE GIS application for graphical display and further analyses.
Geographical Information Systems (GIS) are among the relatively young software technologies which are rapidly finding a role in the management of urban drainage systems. GIS provides an excellent platform for facility management and planning.
As one step towards an efficient integration between the MOUSE modelling system and GIS technologies, DHI has developed the MOUSE GIS application using the ArcView and Avenue from Environmental System Research Institute (Esri). This application offers the user an interactive tool for the definition of sewer network systems to be used for simulation in the MOUSE package.
MOUSE is a professional engineering software package for the simulation of surface runoff, flows, water quality and sediment transport in urban catchments and sewer systems. The programme can be equally successfully applied in other types of pipe networks with alternating free surface and low pressurised flows.
MOUSE is a dynamic, user-friendly modelling tool for the analysis, design, management and operation of both simple and large pipe networks. It provides a complete and effective working environment for sophisticated urban drainage and sewer engineering.
By applying MOUSE it is possible to obtain answers to questions such as:
- what are the return periods for overloading of various parts of the existing sewer system?
- what are the main causes of overloading - backwater or insufficient pipe capacity?
- what are the implications of replacing critical sewers, installing new basins, weirs, etc?
Integrated Modular Structure
The standard MOUSE includes versatile computational models for surface runoff in urban catchments and hydrodynamic analysis of flows in pipe networks.
Add-on modules are available for advanced analyses and design:
- MOUSE NAM - an advanced hydrological model for continuous time series
- MOUSE RTC - for analyses of the potential of Real-Time Control (RTC) applications
- MOUSE TRAP - a suite of computational models for the simulation of sediment transport and water quality in urban catchments and sewer systems
- SAMBA - a simplified model for the computation and statistical analysis of combined sewer overflows
The modular structure offers great flexibility:
- each module can be handled separately
- data transfer between modules is automatic
- coupling of physical processes (eg sediment deposition - hydraulic conveyance) is facilitated
- updating or expansion of existing installations with renewed or additional modules is simple
The Pipe Flow Model performs the computations of unsteady flow in pipe networks. The computations are founded on an implicit, finite difference numerical solution of the 1D, free surface flow equations (Saint Venant). The implemented algorithm provides efficient and accurate solutions in multiply-connected, branched and looped pipe networks.
The computational scheme is applicable to vertically-homogeneous flow conditions which occur in pipes ranging from small-profile collectors for detailed urban drainage to low-lying, often pressurized sewer mains, affected by a varying outlet water level. Both subcritical and supercritical flows are treated by means of the same numerical scheme which is adaptive according to the local flow conditions. Naturally, flow features like backwater effects and surcharges are simulated. Pressurized flow computations are facilitated through the implementation of a narrow 'slot', as a vertical extension of a closed pipe cross section.
The complete non-linear flow equations can be solved for user-specified or automatically-supplied boundary conditions. In addition to the fully-dynamic description, simplified flow descriptions are also available.
Within the Pipe Flow Model, advanced computational formulations enable the description of a variety of pipe network elements and flow phenomena including:
- flexible cross-section database, including standard shapes
- circular manholes
- detention basins
- overflow weirs
- pump operations
- flow regulation
- constant or time variable outlet water level
- constant or time variable inflows into the network
- non-standard headlosses at manholes and basins
- depth-variable friction coefficients
With this description, the Pipe Flow Model can predict the detailed hydraulic conditions throughout the pipe network. Depending on the purpose of the study, the user may concentrate on the following aspects in particular:
- the treatment plant loads (outflow hydrographs)
- combined sewer overflows
- pump activity
- filling of detention basins
- local surface flooding, etc.
MOUSE GIS works in the ArcView environment and consists of two parts:
- the Network Editor
- the Results Presentation.
Both parts support the general features available in ArcView.
The Network Editor allows the user to extract data from a number of different asset management systems, to condense the network automatically and still maintain consistency in the description of the physical system - and finally to store the data as a model for further analysis in MOUSE.
The nodes in the original network could be included or excluded from the final network through the simplication process. This is done by interactive check of a pipe section or an automatic check of the entire network. The criteria that will be used in the simplification process are:
- change in slope (per mille)
- change in pipe diameter (per cent)
- change in flow capacity (degrees)
- change in direction (degrees)
- change in invert level
- change in pipe type/shape
These criteria can be altered by the user if necessary.
Any exceedence of the above-mentioned criteria will include the node in the final network.
Figure 2. MOUSE GIS Selection criteria
The simplification process creates pipes between the included nodes. If more than one pipe section is found between two included nodes, then the new pipe section is based on the pipes found in the original network and the pipe diameter is based on user-specified criteria, like:
- maximum pipe diameter
- minimum pipe diameter
- mean pipe diameter
- unaltered hydraulic resistance
- user-defined diameter
All changes are recorded on a separate file, which can later be replayed if the user wants to repeat the process, eg after changes in the asset management system.
Figure 3. MOUSE GIS Pipe diameter option
The Results Presentation allows the user to present results from the fully dynamic MOUSE simulations combined with other GIS data. CSO points and volumes and exceedence of critical levels can, for instance, quickly be identified.
By direct access to asset management databases, the simulation results can also be visualised in combination with parameters describing the actual condition of the sewer system or any other relevant information from the database.
MOUSE GIS's strengths are:
- quick and automatic simplification of sewer network systems
- presentation of combined MOUSE results and GIS data
- import and conversion of sewer network systems from other formats and databases into MOUSE format
- advanced graphical output
- easy-to-use for ArcView users
- Context-sensitive help available
Henrik G. Muller E-mail, Sten Lindberg E-mail, Danish Hydraulic Institute Agern Alle 5, DK-2970 Horsholm, Denmark, Telephone +45 45 76 95 55, Fax +45 45 76 25 67 DHI's WWW
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