The Dynamic Master Planning Process Integrated and continuous updating and planning of sewer systems.

Transcription

1 The Dynamic Master Planning Process Integrated and continuous updating and planning of sewer systems. K.Fair 1, B.F Loubser 1, H.E.Jacobs 2 *, J van der Merwe 1 1 GLS (Pty) Ltd, 11 Electron Street, Technopark, Stellenbosch, South Africa 2 Department of Civil Engineering, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa. *Corresponding author, hejacobs@sun.ac.za ABSTRACT In a developing nation such as South Africa, with its mix of first and third world service levels, effective sewer and water master planning is vital. However, as backlogs are identified and services are provided the sewer master plans are in need of regular updating. In this continuously evolving system the challenge has been to maintain the accuracy of the models of the existing systems as well as the relevance of the master plans. It has been found that in certain instances updates of complete master plans are required at intervals as short as a month. The authors report on the integrated strategy which they have developed and implemented to update sewer master plans on a monthly basis. The same principles are also used to update the water master plans. Using the City of Tshwane as a case study for illustration purposes, the paper discusses key aspects of a dynamic master plan, which include the systems, processes and software which have been put in place to continuously efficiently and semi-automatically update the master plan on a monthly basis. Aspects discussed include: Organisation and inclusion of as-built information as it becomes available for the pipe networks The use of billing system information, linked to GIS coverage, to populate the models with up to date and accurate water consumption data and subsequent theoretically estimated sewer flows The continuous modification of information regarding to future development areas as services are implemented The adaption of the master plan as required when spatial development frameworks are amended and extended The methods use to assess township applications as and when they occur Prompt and accurate responses to ad-hoc queries regarding system improvements when permission is requested to develop land The paperless reporting system. KEYWORDS Sewer networks; hydraulic modelling; infrastructure planning; master planning; Fair et al. 1

2 INTRODUCTION In South Africa, water and sewer master planning has taken the form of establishing a model of existing infrastructure followed by the preparation of a master plan defining future improvements to the system to meet the requirements for expected developments. The master plan typically includes a capital expenditure programme that is used for budget purposes and project prioritisation by the service provider. Traditionally the process is repeated and updated every two to five years, depending on the rate of development in the study area. Over the last decade in South Africa there has been a government drive to provide basic services to all residents. This, in combination with the upbeat economy, has resulted in considerable development within certain areas of the country, evident in Figure 1 which shows the total length of sewer pipes over the last four years for the City of Tshwane (previously known as Greater Pretoria). The City of Tshwane has a population of approximately 2.2 million people and covers an area of 2350 km 2. Unless newly constructed infrastructure elements are captured regularly, the model of the existing system soon becomes outdated. The continuing interest in development and approximately 300 applications for development have been made since The City of Tshwane has a population of approximately 2.2 million people and covers an area of 2350 km 2. There are properties of which are occupied. Of these occupied properties are residential. In addition to the formal properties there are approximately ha of informal areas which house approximately households where services are still to be installed. The sewer system consists of 7 300km of gravity pipes, 53 pump stations, 38 km of rising mains and 10 waste water treatment plants with a total capacity of 560 Ml/day and a measured flow of 330 Ml/day Length (km) Total Length Figure 1. The total length of sewer pipes in the City of Tshwane ( ). Not only are the number of applications significant but it has recently been experienced that the number of units and associated theoretically calculated sewer flow for which applications are made, exceed that used in the initial master planning studies. Due to densification within the City, rather than development outside of the boundaries, increased densities should be considered during master planning. Once verified and accepted, the trends should be accommodated in future planning, with corresponding adjustments to the capacities of the planned infrastructure. The challenge has been to develop a strategy to manage, capture and utilise information, to keep the models up to date, to plan for the future and revise the planning given new information. Up to date information should be available from the model at any time to 2 The Dynamic Master Planning Process

3 facilitate decision making for both the existing and future systems, allowing for prompt and accurate responses to queries and applications for new developments. BACKGROUND TO SOUTH AFRICAN PRACTICE In South Africa sewerage networks are designed to convey waste water flow exclusively. Various design guidelines are available (Little, 2004; City of Tshwane, 2003; Council for Scientific and Industrial Research, 2003). Separate storm water drainage systems exist in parallel for drainage of storm flows, but some groundwater as well as storm water will ingress the sewerage system (Stephenson and Barta, 2005) and are allowed for in design criteria. The peak dry weather flow is used in South Africa for system modelling and an allowance of spare capacity is then stipulated to compensate for storm water ingress during wet weather flow (Little, 2004). A comprehensive discussion regarding the determination of the sewer flow volume is beyond the scope of this text. To aid further discussion readers should note that sewer flows in master plans by the authors are based on monthly water consumption data of individual consumers. The latter is readily available from the South African National Water Consumption Archive (Van Zyl and Geustyn, 2007) and is often reported as an annual average daily water demand (AADD). Detailed sewer flow monitoring is conducted in the field at strategic points in the system for pre-determined time periods prior to hydraulic modelling. In conjunction with "typical" diurnal flow patterns, compiled by the project team over many years, the sewer flow for each land use type in the area to be modelled are obtained by calibrating the modelled flows to measured flows at the strategic points. In other words, the sewer flows are calculated as a percentage of the AADD linked to a manhole and distributed over a 24 hour period according to the hydrographs applicable for the relevant landuse categories. Infiltration into the system is also reckoned in during this procedure. This process is more complex and accurate than guidelines suggesting mere estimates for sewer flow. After a master plan item has been identified it is addressed by the service provider. A detailed design is made and the work is put out for tender. Construction of the infrastructure element follows during which time construction drawings are available. Once construction is complete a final set of drawings are compiled by the Consulting Engineer. These drawings are commonly called "as builts" in South Africa and are considered to be the most accurate representation of what is under the ground. Unfortunately some system elements are very old and it is often hard to obtain the original as built drawings. With new developments as built information is readily available. COMPONENTS OF THE DYNAMIC MASTER PLANNING MODEL The various components of the system are listed and described below. Their interrelationships are shown in Figure 2 and discussed in detail in the following sections. The numbers in brackets following the headings refer to the items as shown in Figure 2. The Hydraulic Modelling Software Sewsan (GLS Software, 2008a) was chosen to model the sewer system. It is a commercially available software package which operates in a CAD/GIS environment and is used to simulate, analyse and plan sewer systems. It is used extensively in South Africa for sewer system master planning Fair et al. 3

4 Existing system model (1) The existing model is the hydraulic model of the sewer system. It contains all information required for accurate hydraulic simulation of the existing system. The model is populated with topological and hydraulic information captured from as-built drawings at 3 monthly intervals. Figure 2. The Dynamic Master Planning Process The model is populated on a monthly basis with water consumption and landuse information obtained from the municipal billing systems. Two development scenarios are maintained for the model of the existing sewer system: An operational flow scenario to simulate the existing sewer flow in the system: The model is populated with the AADD of water sales as recorded in and extracted from the municipal billing systems. This model is used for verification and calibration purposes. Bottlenecks and problems experienced in the field can be compared to the simulated conditions in the model to evaluate their cause. 4 The Dynamic Master Planning Process

5 A fully developed model populated according to landuse or zoning: For this scenario all occupied as well as vacant stands are assigned a theoretical unit water demand according to their registered landuse or zoning. The model represents the system as if all of the vacant stands were occupied. Construction Information (1a) Construction drawings for projects being implemented are also captured and shown in the reporting software along side the existing system model. Once the project is complete and the as-builts plans are available, the pipes are moved from the construction model, to the as-built model (see below) where they reside until they are joined to the existing system model. As built model (1b) This is a sub-set of the existing system model. It represents the sewer system which has been captured from as-built information, but which has not yet been connected to the existing system model. It contains all the information contained in the existing system, except for the flow and landuse information as it has not yet been linked to the billing system records. Existing Landuse and Billing Data Analysis (2) A software programme Swift (GLS Software, 2008a) was developed to obtain information from water sales records held in municipal billing systems. Swift is used to, inter alia, populate sewer models with accurate flow and landuse information. The software includes the following features and capabilities: For each stand or land parcel in a town, it establishes: o Whether it is occupied or vacant o The land use and zoning o The number of existing water meters o The annual average daily demand (AADD) and total demand (TWD) o The link to the GIS cadastral shapefile o The user defined geographical region in which it is located o The bulk water meter zone(s) in which it is located o The manhole in the hydraulic model to which it is linked. Thereafter it updates various land use and flow scenarios in the sewer models o To that actually recorded o To the theoretical flows based on land use or zoning By comparing water sales to bulk water meter inputs for each water meter zone a water balance is conducted, thereby verifying the water consumption information. Various reports regarding water consumption and unaccounted for water can be generated to show statistics per landuse category and geographical area or bulk meter zone on o the number of stands, both vacant and occupied o the total AADD, TWD and sewer flows o unit AADD's o theoretical (fully occupied) AADD. Future Landuse and Flow Data (3) Research by Sinske and Zietsman (2001) led to a GIS-based approach to sewer master planning and reporting being implemented by the study team, also in Tshwane. In addition, a GIS based module (Swift_Future) was developed in 2008 to include land use and flow data for future developments and for areas of densification or rezoning. The input to this module is generally obtained from the spatial development framework compiled by the town planners. It Fair et al. 5

6 consists of a shapefile defining the future development areas, linked to a database of expected landuse, densities and unit water demands. From this information the expected number of units which will be developed and their combined water demand and sewer flow are determined. The information is then used to populate the future development model with theoretically estimated future sewer flows. The module was designed to allow the user to easily update both the shape of a development area as well as the data associated with it, so that changes to the future development could easily be applied to the model. The Ultimate Future Model (4) This is the hydraulic model representing the system required for the ultimate future flow scenario, with all future areas fully developed and with every existing stand occupied and where applicable sub-divided or re-zoned. The model is maintained in three parts to allow each of the parts to be easily updated and maintained and most importantly to ensure that all recent changes and additions to the existing model are incorporated into the future model. By merging the parts of the models together and deleting redundant elements from the existing part of the model, the ultimate future model (4) is created, comprising the following components: The existing system network representing pipes and sewer system components as they currently exist (1), with sewer flow and landuse information for two flow scenarios, including that representing the flows for those areas already developed The schematic pipes which represent the sewer system in the future development areas (4a) Reinforcements to the existing system and major works which will be required to upgrade the existing system to handle the ultimate future flow scenario (4b). In order to have an accurate and up-to-date representation of current and imminent developments in the future models the future development model (4a) and reinforcement model (4b) include the construction information (1a). The flow information in the model is populated semi-automatically by Swift for the area where water sales are included and by the Swift_Future module for the areas where future developments must still take place. Master Plan Details (5) The improvements to the existing system that are included in the ultimate future model are labelled with unique master plan item numbers. The sewer modelling software uses this information and user defined cost functions to determine the cost of each planning item. A master plan table can then be generated which includes: The master plan item number A description of the infrastructure upgrade(s) that are needed Comments Cost estimates of the work to be completed. Each item is also linked to a master plan project number in the project management software. In this way modifications to the master plan items are implemented and accounted for in the project management software. 6 The Dynamic Master Planning Process

7 Additional Data Other important data which is used in the master planning process and which requires regular updating includes cadastral shapefiles, aerial photographs and digital terrain models. Additional output from the master planning includes plan books of the layout of the system with user required information, GIS shape files of the drainage areas and related information such as sewer flow, water demand and landuse summaries. Summary tables of infrastructure upgrades and costs are also generated. Reporting and Management Information System (6) After consideration of the following factors it was decided that the reporting system should be paperless and integrated with the management information system: The dynamic nature of the planning process The frequency at which updates would have to be issued The number and skill level of individuals to whom the updates would be issued The large volume and various different components of data to be reported on. All information on the existing system, existing landuses, zoning, water sales and flows, future developments, future system and master plan items, projects and costs is presented in a user-friendly GIS based, but GIS independent, management information system (called IMQS). Information and results are posted in IMQS in the form of pre-defined maps, graphs and tables, allowing for easy access for various levels of management and staff at the City of Tshwane. THE PROCEDURES This section describes how the master plan is created and updated. As-Built Information (i) As-built information is continuously received, via courier, , FTP or via communication through the reporting software (IMQS). The data is checked by the capturing team for completeness and against existing data. The data is further categorised according to whether it is a new network in a new development or whether it pertains to the replacement or reinforcement of existing network elements. Pertinent data which is captured for the sewer systems includes: Pipe layouts with diameters, materials and manholes Pipe vertical alignment, e.g. inverts or slopes Additional information including material, nominal and inside diameters Special elements e.g. pumps, siphons, bridges Connections to stands or land parcels. Unfortunately there are no standard or norms regarding the format of as-built data, with the result that as-built information is supplied in various formats including electronic drawings (*.dwg/*.dxf), GIS shapefiles, PDF documents or hard copy paper drawings. The software team has developed various functions to facilitate the conversion of electronic drawings to hydraulic models by for example importing text semi-automatically into the model space, rather than manually entering the information. The authors have found that a GIS representation of pipe layout is seldom at the same standard as that required for a model. The sewer simulation software vendors have made every effort to automatically identify and Fair et al. 7

8 correct the typical problems in the data although a trained capturer s assessment is often required. Once a particular set of as-builts has been captured its model is merged with that of the other as-builts which have been captured. The as-built model continues to grow until it is joined to the existing system model. When the as-built model is merged to the existing system, the following procedures take place: The as-built model is cleared of all elements If necessary the corresponding future development area is adjusted to exclude the recently developed area and the related database is updated accordingly The corresponding elements which represent the as-built information in both the future development model and the reinforcement model are removed Updates to the plan books of the system are prepared and issued Where necessary the shapefiles of the existing system drainage areas are updated The master plan items corresponding to the now deleted future required works are removed from the master plan tables and the project manager information is updated. Population of the existing system with flow and landuse information (ii) The existing system model is now complete with the hydraulic information required for simulation. The next step is to populate it with updated flow and landuse information from the billing system: The required data is exported from the billing system and imported into Swift. The water meter recordings are processed to determine an AADD for every stand. Summary reports per geographical area are produced, unit water demands are calculated and checked. Bulk water meter readings are obtained and imported into Swift. Bulk input to each meter zone is determined and compared to sales in the zone to calculate unaccounted for water (UAW) per meter zone. Summary reports per bulk meter zone are produced. Each record in Swift is linked to the GIS cadastre of the town and to a manhole in the existing system sewer model. The existing system model is populated with flow and landuse information for two flow scenarios (operational, fully developed based on landuse, fully developed based on zoning). Population of the Future Development Model with flow and landuse information (iii) The future development areas in the future development shapefile must be updated: The shapes must be either removed or adjusted where the development is complete and the as-built information has been captured and merged to the existing model. Changes to the spatial development framework must be implemented in the future demand model. Differences between existing information and that applied for by developers should be updated in the database. The future development shapes and database should be extended to include any approved applications for development outside the existing future development areas. Once the areas, densities, dominant landuse and unit water demand are updated the new sewer flows are calculated for each development area and are applied to the future development model. 8 The Dynamic Master Planning Process

9 Merging the model components to produce the ultimate future model (iv) At this stage each of the sections of the model are completely populated with the topology and slope information. They must be merged together to form the fully populated future model. During the merging process various processes must be applied to different model elements: Unless otherwise flagged the existing model must be maintained. The future development model and reinforcement model must be merged to the existing elements with proper connectivity being established. Existing elements which are to be decommissioned must be removed from the model. Future planning (v) The fully populated model of the future system has now been established and the flows are simulated and additional reinforcements are identified or previously planned future reinforcements are adjusted where required. Once the future model meets the hydraulic design criteria the table of master plan items is updated and the project information is sent to the project management software. Evaluation of an application for development In the City of Tshwane developers must apply for a connection to the sewer system before land can be developed. Subsequently a study must be performed to determine the availability and capacity of the existing services as well as the required upgrading, if any, to the existing system. The study must: Evaluate the existing sewer network systems in the vicinity of the development in terms of available spare capacity to accommodate the new development Evaluate the effect of incorporating the proposed new development on the rest of the sewer system in terms of maximum flow capacity Identify the required infrastructure upgrades, if any, to accommodate the proposed development Identify the effect of the development on the previously planned required works Compile reports and drawings summarising the outcome of the study. In the simplest case the proposed development will comply with one of the future development areas which has already been accounted for in the future model. The future model will therefore contain the works required before the development can take place. In a more complex case the proposed development does not comply with and/or falls outside a development area identified in the spatial development framework. In these cases the sewer flow has to be determined and the effect of the flow on previously defined required works has to be assessed. The findings must be reported to the authorities and a decision must be made as to whether the development can be approved, or not. If it is allowed the future development database as well as the future model must be adjusted to ensure that future planning is correct. Until the construction drawings for the development are submitted the application is represented as an area in the application shapefile so that it is easily visible and can be considered when other applications are made and future planning is to be updated. FUTURE RESEARCH South Africa is a water scarce country. Water demand management (WDM) strategies are being compiled by those service providers who do not already implement WDM measures. Subsequently reduced water use will result in reduced sewer flows with infrastructure Fair et al. 9

10 elements optimally sized with conventional master planning becoming oversized if allowance is not made in the process for sewer flow reduction due to increased WDM implementation. End-use models i.e. the modelling of micro-components of water use have been used in South Africa to model residential consumers' water demand and sewer flow (Jacobs and Haarhoff, 2004a; Jacobs and Haarhoff, 2004b). On the international front the end-use approach has been used to assess changes in sewer flow brought about by WDM measures (Lauchlan and Dixon, 2003). This concept could be extended to South Africa and could potentially become an integral part of the master planning process, allowing for "what if" scenarios to be included in the analyses. CONCLUSION The authors have been involved with master planning in Tshwane since The dynamic master planning process has evolved through necessity over the years and is currently fully operational in the City of Tshwane. Benefits which have been realised are that all information pertaining to the existing sewer system, current developments and the future system remain up to date. An added advantage is that a continuous awareness of development trends and their effect on the existing system and future systems is created with engineering consultants, town planners and the City staff. ACKNOWLEDGEMENTS The authors would like to acknowledge the following organisations for the contribution to successfully instituting the dynamic master planning process: The staff and directors of GLS (Pty) Ltd, GLS Software and IMQS for the customisation of software, input and invaluable experience. To Benjamin Harper, for developing Albion, the GIS/CAD based platform on which the modelling software runs To the staff and management of the City of Tshwane REFERENCES City of Tshwane (2003). City of Thswane Metropolitan Municipality: Sanitation By-Laws. Available online at (accessed February 2008) Council for Scientific and Industrial Research (2003). Guidelines for Human Settlement Planning and Design, A report compiled by the CSIR Building and Construction Technology under the patronage of the South African Department of Housing, (2003) GLS Software 2008a. Overview of Sewsan. and Sewsan User s Guide Available online at (accessed February 2008). GLS Software 2008b. Overview of Swift. and Swift User s Guide Available online at (accessed February 2008). Jacobs H.E. and Haarhoff J. (2004b). Application of a residential end-use model for estimating cold- and hot water demand, wastewater flow and -TDS concentration. Water SA, 30(3), Jacobs H.E. and Haarhoff J. (2004a). Structure and data requirements of an end-use model or residential water demand and return flow. Water SA, 30(3), Lauchlan C. S. and Dixon A. (2003). Modelling of water discharges for houses with conventional and low water use appliances. In: Maksimovic, C, Butler, D and Mermon, FA (eds.) Advances in Water Supply and Management 2003, Swets and Zeitlinger, Lisse, Little, C.J. (2004) A comparison of sewer reticulation system design standards gravity, vacuum and small bore sewers. WaterSA 30(5), Sinske, A.S. and Zietsman, H.L. (2001). Sewer-system analysis with the aid of a geographical information system. WaterSA, 28(3), Stephenson, D. and Barta B (2005) Guidelines on reduction of the impact of water infiltration into sewers. South African Water Research Commission Report No.TT239/05. Van Zyl, J.E. and Geustyn, L.C. (2007) Development of a National Water Consumption Archive, South African Water Research Commission Report No.1605/1/ The Dynamic Master Planning Process