Wadiso

Sewsan

Swift

Albion

Introduction

Sewsan 2 Sewsan 3 Sewsan 4

Sewsan is a computer application to simulate and analyse flow through sanitary sewer systems. The hydraulic simulation is based on the contributor hydrograph method. The contributor hydrograph for each pipe is made up of the following flow components:

• The local inflow to the pipe defined by the number and type of unit land parcels served by the pipe.
• Storm water ingress
• Infiltration
• Leakage

The hydrographs generated by each pipe are accumulated and routed downstream using time-lag routing. Bottlenecks in the system are identified at structures (manholes) where overflow occurs.

The Sewsan system is an analysis tool coupled to a CAD interface. All the model entities (pipes, manholes etc.) are stored in an internal database, and are displayed in a CAD drawing. The system data and results can also be viewed in tabular format in spreadsheets. Sewsan therefore consists of the following components:

• The sewer model representing the physical components of the sewer system
• Data and result tables
• The CAD interface

The program is extremely user friendly, with a menu driven structure and easy-to-use-and-understand interface between the graphical display/edit model, and the model database and results.

Sewsan is available in 3 modules:

• A basic Capturing Model, which allows the user to capture the sewer network and check the integrity of the model.
• An Analysis Module in which the flow through the system can be simulated and the results of the simulation viewed. Bottlenecks in the system can be identified and the resulting overflow calculated.
• A Planning Module, which can be used to estimate required pipe diameters where bottlenecks in the system occur, pump capacities and rising main capacities.

Sewsan has been used for sewer system analysis and planning by GLS Consulting and other consultants in more than 50 major applications. Some of the more significant projects are:

• City of Tshwane
• City of Cape Town
• City of Johannesburg

Theory

Contributor hydrograph theory was originally developed by Shaw. The concept is very similar to using unit hydrographs for storm water system design. Each contributory unit (normally a single pipe in the sewer network) "contributes" a 24-hour sewer flow hydrograph to the system.

This hydrograph consists of:

• Local Inflow, contributed by the land parcels serviced by the pipe
• Leakage from plumbing into the system
• Storm water ingress into the system
• Ground water infiltration into the system

User supplied hydrographs representing the flow where other networks join the network being analysed, where pumps discharge into the network, or where a large system has to be fragmented

The local inflow to a pipe can be very accurately determined in Sewsan if the water consumption of the land parcels connected to the pipes is known. Sewsan then used the annual average daily demand (AADD) inflow calculation method. Alternatively the unit hydrograph peak inflow calculation method can be used.

The two methods differ in the calculation of the volume of the inflow hydrograph. The unit hydrograph peak method uses the expected peak flows associated with the landuse types to calculate the volume of the input hydrograph where as the AADD method bases the volume of inflow on the annual average daily water demand of all the land parcels serviced by the pipe.

The 24-hour contributor hydrograph for each pipe is routed down the network to the outfall manhole using time-lag routing. The time-lag is calculated using full-flow velocities in the pipes according to the Manning formula.

Modelled Components

The following structures can be accurately modelled in Sewsan:

• Gravity Pipes and Siphons
• Rising Mains and Pumps. Multiple rising mains may be linked to a pump structure
• Diversion structures. The percentage of flow routed through each of the pipes downstream of the structure is defined according to the total inflow to the structure
• Manholes and End Manholes

GIS Compatibility

The open input and output data structures (ASCII, Dbase IV, Paradox, Microsoft MDB) of Sewsan provides for easy interfacing with other application software, including most GIS applications, specifically the ESRI shape file standard and REGIS/Autodesk World FEA format. An interface between the GIS and the Sewsan database typically allows:

• Updating and editing of the model characteristics and parameters
• Updating of water demands, if there is a link between the sales records and the GIS
• Updating reports on the analysis results directly from GIS

User Interface

Sewsan features characteristics that provide for easy, informative use. These include:

• Modeless, user friendly interface
• Seamless transition between modules, e.g. Graphics to Analysis to Tabular Results
• Graphical display, input and editing of any network element
• Non network data may also be displayed as background, e.g. parcel and street layouts
• Data for all entities required for modelling (pipes, rising mains, manholes, pumps etc) is included in the database, with extra fields for other attributes
• Graphical display of results and data, through color coding, arrows on pipes, different line thickness, different node sizes, etc., is available
• Graphical display is always geographically correct, and not schematic.
• Bitmap images can also be imported as backdrop.
• Detailed tabular data and result presentation with filtering capabilities

Model-CAD Interface

The Sewsan system is an analysis tool coupled to a CAD interface. All the model entities (pipes, manholes etc.) are stored in an internal database, and are displayed in a CAD drawing. Sewsan therefore consists of:

• The sewer model representing the physical components of the sewer system
• The CAD interface, used to display the modelled data and results

By using the layer functionality of the CAD environment various background drawings/images can be imported into the current drawing so that the system can be displayed against this background information. Such drawings/images include for example:

• The cadastral layout of the study area
• GIS shapefiles
• A bitmap image of the aerial photograph
• Contours of the study area

The CAD interface provides a user friendly, interactive environment for capturing system data and setting up a model. The CAD interface is used to:

• Convert a drawing of a system into a model
• Capture text from a drawing into the corresponding model parameter
• Display the system graphically
• Easily edit the topology of the system by adding, moving or deleting the entities
• Interrogate (and edit) the data and results of a model entity
• Select model entities either manually or by querying the data or results
• Edit a selection of model entities
• Perform comprehensive queries on the system data and results
• Print accurate plans of the system, including any background drawings which might be necessary

Model Population and Swift

Sewsan models can be directly linked to Swift in order to populate the model with accurate flow data. Swift populates the flow (AADD) associated with each manhole in the system for 5 different flow scenarios. Swift also populates the fields representing the land parcels which discharge into the pipes.

Calibration and Summaries

The simulated flow hydrographs can be compared to calibration hydrographs. Any number of calibration hydrographs can be linked to the system at the relevant nodes.

In order to facilitate the calibration of the sewer network system summaries can be made. The summaries can be made for the entire system, the system upstream of a selected manhole or for a selection of manholes and pipes.

• The system summary table tabulates information in the system regarding the
• Pipe Topology: Length, type and number of pipes,
• Structure Topology: The number and type of structures and pumps
• Volumes produced by each component of the contributor hydrograph and user hydrographs
• Detailed breakdown of the number of land parcel units associated with each unit hydrograph and the volume contributed for each.

The volumes are theoretical volumes based on the input hydrographs and may differ from the simulated volumes due to the nature of the system (lag) and the time step at which the system was analysed. However, this gives a useful and accurate indication of the flow in the system

Result Presentation

Sewsan provides for an extremely flexible query system in order to map data and results. For both nodes and links additional data can be included in user-fields. This allows for the inclusion of information pertaining to age, material and classifications etc. of pipes, present and future allocation of stand numbers etc. to nodes, over and above the normally required data defining the component.

A link and node legend is provided, in which the color coding parameters for any one of the link or node data fields can be specified. Maps can therefore be produced showing output data such as the spare capacities, flow, flow velocities etc with different color coding and different line widths.

In graphical display it is possible to turn on and off either the node display, so that only pipes are mapped, or the pipe display so that only nodes are mapped.

Text from the different fields can also be annotated to the nodes and links. Specific fields can be selectively annotated, e.g. the link number and pressure, or diameter.

Graphs

Graphs can be displayed for the results of any link or any node, for the entire time period. Graphs of the unit and user hydrographs as well as the simulated flow in any pipe or manhole can also be displayed.

The different components of the simulated flow hydrographs can also be displayed. These include:

• The total flow in the structure
• Infiltration into the system upstream of the structure
• The average flow contributed to continuous pumps upstream of the system
• The capacity of the pipe

Tabular Reports

The presentation of tabular reports is as flexible as that of mapping. Again, specific fields can be selected for both nodes and links, and range categories set, just as in the case of mapping. The difference being that for mapping, only a single field is selected and for tabular reporting all fields, or only the important fields, can be selected.

In the mapping, the line width or node size can be set to zero if a specific category of link or node should not be displayed - in the tabular reports a flag is set in a dialogue box in order to specify whether or not that specific category should appear in the report. This makes it possible, for instance, to print a report on only those pipes with spare capacities less than 30 percent.

Long Sections

User selected long sections of the system can be graphically presented in the CAD environment. The ground level, invert levels and cover levels are drawn in the long section. Any of the data or result parameters associated with the manholes, pumps or pipes in the long section can be tabulated with the long section drawing.

Model Size Requirements

The number of pipes that can be simulated in Sewsan is unlimited and depends solely on computer memory and the option purchased. The possibility therefore exists to build large models, including all pipes in a system, thus improving modelling accuracy.

History of Changes

(To be updated)