Wastewater Infrastructure Planning Using GIS Kapil Chaudhery Spatial Decisions Email: kapil@spatialdecisions.com Eram Rizvi Spatial Decisions Email: eram.r@spatialdecisions.com Robert Despault KITABOSHI Consulting Ltd. Vancouver British Columbia Email: kita@uniserve.com Introduction Operation of wastewater management is one of the most expensive utilities for the urban population. Expanding and maintaining a very large and rapidly aging wastewater collection system is a major problem facing many large cities in Uttar Pradesh. The rapid growth of population in the major towns of Uttar Pradesh and an ever increasing pollution load in the rivers called for an attention of the responsible government bodies to look into the matter of assessing the capacity of present sewerage system and to plan the same for future. Populations in the cities studied exceed 1 million and are expected to double during the next 30 years. The existing collection and treatment systems must be expanded to reduce pollution to the environment and to improve living conditions in urban centers. This paper deals with the concern of applying the technology of remote sensing and GIS for assessing and improving the sewerage infrastructures of an urban area. Evaluation of present sewerage facilities in respect to the present current population and planning and installation of new units with enhanced capacity to fulfill the need of estimated population of the target year. The ultimate goal being sewerage planning for the entire city for the target year 2030. The study discusses the strategy to bring all the existing sewage works into an orderly operation and provide new works to the necessary population in an effective and economical manner to assure the conservation of the environmental qualities. The software used in this study were basically developed on using ESRI suite and Auto CAD. The study initiated with the detailed inspection of existing population, past population, the development pattern of the city and the growth trend. On the basis of collected information population projection was done for each of the four cities. Properly managed water supply and sewerage services are essential for the maintenance of public health and ensuring the well-being of communities. Poorly managed water supply and sewerage services threatens public health and result in environmental harm. To ensure that these services are properly managed a significant legislative and regulatory framework must be complied with by those responsible for the provision and management of these services it is important that planners are aware of the legislative and regulatory framework relating to water supply and sewerage services. This paper seeks to answer all these issues through use of remote sensing and GIS for assessing and improving the sewerage infrastructures of an urban area. GIS in Sewerage Infrastructure Planning Geographic Information System (GIS) provides logical approach to understand the location significance of the information with its spatial location also referred as “spatial information”. An accurate map and a related list of information linking to the points, lines, polygons and symbols in the map can be considered as the principles of the GIS system. GIS has been an integral part of the wastewater system planning process. The analysis capabilities of GIS coupled with satellite imagery allowed engineers to develop sewer system master plans more quickly than previous traditional methods. A computerized base-map of the GIS system can provide vital data for the design of sewerage by locating the nodes of connection between buildings to the sewerage pipe network. The population number or the measurement of the floor-space areal size of the buildings provide the flow-rate.GIS base maps and data developed during the project provide a foundation for the development of future planning and management tools such as hydraulic modeling, infrastructure mapping, maintenance management, and integration with GPS and field survey data. Objective : The intent of the study and all the efforts put in was to evaluate the present sewerage facility of an city of Uttar Pradesh in respect to its population and to propose the additional infrastructure for the target year that was decided as 2030. Database Used : The data used in this study was in form of maps, figures and oral information from the government officials of responsible organization.
One of the largest data gaps that sewerage engineers had to overcome was the lack of detailed topographic information. Collector sewers are generally layed out to work by gravity and engineers typically work with detailed contour maps at 1:15,000. Since these contour maps were not available, engineers relied more heavily on satellite imagery, looking at natural drainage patterns to provide clues on the lay of the land. In this case 5m resolution made it difficult to interpret, and several time consuming field visits were required to observe and confirm natural drainage boundaries. The process could have been simplified by using higher resolution imagery or better yet by having a specialized software package interpret satellite imagery and generate the topographic contours. Neither of these options was adopted mainly because of budgetary constraints. Methodology : Sewerage Planning Procedure The planning of sewerage systems with GIS uses the same procedures that civil engineers traditionally use to evaluate and design sewers: (1) Prepare a base map (2) define a sewer service area and divide it into smaller collection basins (3) estimate wastewater flows based on populations and water consumption in the basin(4) identify potential treatment plant sites (5) define and compare alternative configurations for sewerage system (6) define potential collector sewer alignments. (7) Calculate sewer sizes and treatment plant loads. (8) Prepare engineering drawings for sewer system. I Preparation of Base Map The base map is the foundation of any infrastructure planning project. This is particularly true when using GIS. Digital base maps for the project cities did not exist and had to be created from the only available data: Survey of India topographic maps at 1:25,000. Although outdated, these maps were used as the starting point. The maps were scanned and digitized, then compared to satellite imagery and updated to show new features. The city level base map was prepared with the help of recent satellite imagery supplemented with topo sheets of SOI for each town. The satellite image was processed and georeferenced before interpretation and feature extraction. This base map had
Preparation Of Sewerage Facility Map The same map was then used to prepare the sewerage facility map on which all the existing sewerage infrastructure was marked. Initially the location was based on record drawings which in most cases were often inaccurate and could not be accurately geo-referenced. In later stages of the study, alignment and leveling surveys were carried out on some of the critical trunk sewers that needed to be rehabilitated under the project. These surveys were geo-referenced to benchmarks and the GIS database and base map was corrected. The map finally had all the information on
II Future Design Population Distribution Analysis of Census Data (Population Projection) It initiated with the study of past and existing population to project the same for the target year. City population was organized into the population within municipal boundary and population outside the municipal limits but within the development boundary of the city. Census data of 1991 and 2001 were the source of the information that provided data for the municipal wards and data for the adjacent towns and development area. Different statistical methods of estimating growth of the urban population of the cities like linear, weighted averages, and simple regression were applied for population projection for the project cities. Projected population data was also provided by Nagar Nigam and Jal Nigam, which was used for validating and cross checking the projection done by the study team. The geographic limits of wards was defined by Nagar Nigam which was brought into the GIS platform that was again verified for precision by superimposing those boundaries on high resolution satellite imagery. The master plan documents and boundaries were provided by Development authority and Town and Country Planning department. The master plan had past growth trends that were used to guide the future projections. 
To develop the sewerage master plans the need was to define the population within the sewerage catchments. For this purpose the city was divided into major sewerage catchments keeping in mind the drainage area, topology and the population therein. The major catchments were again divided into sewerage sub districts so that the population of each district can be easily ascertained and the pollution load could be established. Allocation of population to the sewerage districts was the task which was made very easy by the application of GIS which otherwise would have been a tedious and a time taking process as there were numerous iterations before any final decision were made on the location of sub district boundary. The ward boundaries were allocated the population growth in the city among the municipal wards and the areas beyond was given the population density which was arrived at by the analysis of satellite imagery .A differential growth rate was applied to each ward due to the differences they had in developable areas, nature of existing development, and availability of infrastructure. Calculation of population density The distribution of population, population density, and the location of other users such as commercial and industrial facilities were determined to a great extent by the land-use plan and zoning regulations of the city. The same was verified by information extracted from satellite image. Interpretation of satellite image was done to extract the developed areas, open spaces, water bodies and potential developable areas within the wards. 
The exclusion of broad undevelopable area from the total ward area gave a residual area for each ward, which was later on used for calculation of a normative population density for each ward. This population density was then used to determine the population in each sewerage sub district. 
III Calculation Of Pollution Load Define a Sewer Service Area In a GIS environment the determination of the service area is a simple process once the population density has been mapped out. Collector sewers are typically extended into all urban areas where population densities are greater than 125 persons per hectare. This is considered to be the threshold level below which sewerage is no longer cost effective means of wastewater disposal. Visual presentation of data, made possible by GIS, identified several hotspots were population densities were the highest. Not surprisingly the most densely populated areas tended to be in the old central core already served by sewer systems. The density maps also identified population corridors linking these hotspots, generally along major transportation arterials. This visual interpretation provided engineers with clues on how to layout the major arterials of the sewerage system. 
After defining the sewer service the planning process consists of dividing a large area into smaller sewer basins, each one draining to a treatment plant. The amount of wastewater collected and thus the size of treatment plant will depend on the population and the water consumption within the sewer basin. The basin boundaries are fixed primarily on the basis of topographical features. The most important feature is natural drainage because engineers are trying to achieve flow by gravity to reduce energy costs. Natural drainage boundaries were derived by interpreting satellite images and topographic maps. In a GIS environment project engineers were able to merge the imagery and base map in order to derive populations within the sewer basins. Estimate Wastewater Flows Wastewater flows are estimated on the basis of population in the basin, average water consumption (including allowances for industry) and a return factor ranging between 0.7 and 0.8 of the water used. The sewerage district boundaries were intersected with the ward boundaries to get the population of each sewerage district. Wastewater flows were estimated for each sewer basin and compared to field measurement of flows in nalas. In some cases there were large differences between calculated and measured flows. Sewer basins with discrepancies were examined in more detail during follow-up site visits. In some cases the population densities had to be adjusted to balance flows between adjacent basins and in other cases it was found that the basin boundary did not match the full reach of the nalla. Adjustments, which happened several times during the study, were relatively quick and simple using GIS. For base year: Pollution Load = Population(existing) X per capita waste water consumption X return factor( 0.7 to 0.8 ) For Target year: Pollution Load = Population(projected for 2030) X per capita waste water consumption X return factor( 0.7 to 0.8 ) Define and Compare Alternative Layouts In every city there are many possible alternatives for interconnecting sewer basins with treatment plants. A smaller number of treatment plants (i.e. centralized approach) generally results in economies of scale. However a centralized approach results in longer, larger, and deeper pipelines therefore increasing the cost of laying trunk sewers. Finding the most cost-effective configuration involves comparison of many alternatives. GIS made the work much easier by providing engineers with the ability to quickly recalculate populations for different sewer basin combinations thereby making the planning process more efficient. It also provided engineers with a toll to carry out a more complete analysis of potential options. Identify Potential Treatment Plant Sites The project included site selection for several treatment plants with land requirements ranging from 50 to over 100 ha. Selecting a suitable site for a treatment plant is a time consuming task that involves a number of technical, environmental and social considerations. Good sites are generally in lower lying areas, near a natural water course or large drain, and downstream of the water supply intake. One of the key issues in selecting a site is to minimize the social impact caused by land acquisition. Using GIS and satellite imagery, engineers selected sites that would meet the technical requirements for sewerage and also minimize relocation or disruption to nearby settlements. Initially the type of treatment process was selected and the land requirements for each treatment plant were calculated. Potential treatment plant sites were then identified by selecting areas that appeared to be sparsely populated or areas that did not appear to be productive agriculture. Satellite images provided engineers with a big picture view that also indicated potential problem areas which might be environmentally sensitive to the discharge of treated effluent. For selected sites, a rectangular polygon representing the required land area was superimposed on the satellite image along with latitude and longitudinal coordinates. During subsequent field reconnaissance visits, engineers located the site using hand held GPS devices and modified the perimeter boundaries depending on their assessment of conditions on the ground. Having verified conditions in the field the next task was to identify individual land parcels and owners. Here again the use of GIS proved to be a time saving tool. Revenue maps corresponding to the site were digitized however these drawings are ancient and not to any recognizable scale. Field surveys with GPS were able to provide engineers with coordinates for key land parcels thereby making it possible to transfer the revenue maps to the base map. Final treatment plant site boundaries were then determined and surveyed. Define Potential Collector Sewer Alignments The road network and its attribute like the width in GIS database was very essential for planning the future sewerage infrastructure. The base map along with the sewerage facility map was decisive in identifying potential sewer alignments along roads that appear wider than other roads Trunk sewers are generally laid along road alignments using open trench excavation. Finding a suitable route for large diameter trunk sewers in densily populated cities can be time consuming and difficult task. Most roads are typically too narrow or too congested with traffic. GIS provided sewerage planning engineers with a means to expedite the process. The precisely mapped location and network of various existing sewerage facilities assisted in putting up of new facilities. Before doing any field reconnaissance, engineers worked with satellite imagery to identify roads that appeared wider and thus more suitable for potential sewer alignment. These roads were then identified on the GIS base map with existing and proposed sewer networks. The process was like piecing together a jigsaw puzzle until a pattern of potential sewer alignments began to emerge. These alignments were then verified on site and adjusted to suit observed traffic conditions. Calculate Sewer Sizes And Treatment Plant Loads Although not done for the study, GIS provides the framework for integrating sewer attribute data and mapping with hydraulic network modeling tools. The area of sewerage sub district and the pollution load determined the pipe sizing of the gravity sewers and the rising mains. Observed Constraints To Implementing GIS The project experienced two major constraints to the effective implementation of GIS:
Conclusion Sewerage is part of the city planning in the technical terms because the size and the network of the system is strongly related to the spatial location of the population and its density. GIS base provides an integrative platform for urban planning and sewerage system planning exercise. thus an attempt has been made to apply the technology of GIS and Remote Sensing in the planning of sewerage infrastructure. The development and maintenance of a comprehensive sewer system inventory should be regarded as an essential undertaking for all sewerage authorities. In the initial stages of the project, engineers decided that satellite images with 3 m resolution would provide sufficient detail for master planning purposes. However, at later stages of the project it became apparent that higher resolution images could have greatly reduced the amount of time spent in the field selecting sites for treatment plants and alignments for collector sewers. |