This chapter describes the planning procedures and the data required to follow and prepare the preliminary layout. Section 2.2 explains the planning stages of the sewerage and drainage system, while Section 2.3 describes the system layout implementation, which presents the process of locating the preliminary routes.
2.2 PLANNING FOR SEWAGE AND DRAINAGE SYSTEMS
This section describes the steps that should be taken in order to develop a sewage layout. These steps can be summarized as follows:
2.2.1 Existing Information
The first task in the planning process is to collect all available information about the area to be served. In this project, most of the data were provided by Hyder Consultant Middle East Ltd. and Abu-Dhabi Town Planning Department. Topographical maps and zoning distribution (commercial, residential, and industrial; for flow rates), shown in Figure 2.1 in Appendix A are examples of existing information, and any maps showing the routes of existing drains and sewers should be collected. Based on this information, the proposed location of the wastewater treatment plant can be determined as shown in Figure 2.2 in Appendix A.
The second discharge for drainage and rain water disposal would be collected in the outfall near the deep channel GIC southern direction, as shown in Figure 2.3 in Appendix A. These maps were needed to define the area to be served in order to locate the overall pipe layout. This information was available on a number of maps and plans. Detailed plans and profiles containing base map or street elevations, location of building and major centers, and other utilities, such as water, gas, electric and telephone, were required in order to avoid pipe lines clashing during construction. This information was presented in the service reservation or the service corridor map in Figure 2.4 in Appendix A.
Area to be Included 2.2.2
The next task was to decide the area to be included in the scheme. There were two possible situations and this project used the design for an exclusively local system. The main task to determine the routes of the main sewers and the points at which they will discharge, to a treatment site or existing sewer, as shown in Figures 2.2 and 2.3 in Appendix A.
The important point was to ensure that the overall situation was taken into account, as defined by natural drainage areas, the location of existing sewers and possible treatment/disposal locations. The sewered area is flat and much less obvious because the topography is flat. After choosing the sewered area, the boundaries and the type of each building was obtained to prepare a population survey, which will be discussed in Chapter 3.
2.2.3 Development of a Draft Sewerage Plan
The first step was to decide the routes of the main public collector sewers and then consider how local lines can be joined to them. In general, public collector sewers were designed to include flows from all parts of the drainage area that are likely to be sewered.
Once the routes of the main public collector sewers were decided, preliminary proposals was made for the routes of buildings system.
Note that the main collector sewer was routed along roads, keeping as close as possible to the natural drainage routes that were determined by the contour analysis as shown in Figures 2.5 and 2.6 in Appendix A.
The accuracy with which sewer layouts were plotted at this stage depended on the accuracy of the available plans and the availability of the information at ground level.
2.3 SYSTEM LAYOUT IMPLEMENTATION
After gathering all the information needed for the draft drawing, the data were integrated with each other to appear as search tools in order to locate the pipelines and manholes at different coordinates inside the area’s base map. GIC consists of three
areas: main center, residential area and industrial area, as shown in Figures 1.1 to 1.4 in Appendix A.
Each area has various requirements, but the main goal was to convert the flow from different buildings to the wastewater treatment plant for sewage flow, and to the outfall for storm water flow. The sewer and drainage systems were kept separate, thus achieving the long life span, about 50–60 years for the systems, to avoid the
additional loads from the flow combination. Separate systems were used for the following two reasons:
1) Rainwater would not enter the public sewer system as this can overload the
capacity of the sewer and cause flooding.
2) Wastewater would not enter the rainwater sewer system or an infiltration
drainage system intended only for rainwater, as this will cause pollution. Therefore, the flow was directed to the existing services throughout the manholes by calculating the invert level of each manhole in order to connect the final pipe using suitable invert level to serve the area. The main trunk lines were drawn through the major and continuous roads across the GIC to make sure that all blocks or buildings were served and easily connected in future in case of house connections through the client. The layout took the following consideration into account:
1. Best use of available reservations with short length was made to ensure
economy of design and avoid unproductive lengths.
2. The route and depth of a new sewer should take account of land where there
is a possibility of future development.
3. Adequate access provision for maintenance.
The same considerations were taken into account for the drainage system. The proposed networks are shown in Figure 2.5 in Appendix A. for sewage and in Figure 2.6 for drainage systems.
2.3.1 Proposed Sewage and Drainage System Layout
2The GIC was approximately 40 Km, and from the contour lines it was noticed that
the area is flat with a slight slope at certain places. But the pipes were run from high to low level because the flow is acting under gravity. For storm water pipes, the line is at the lowest part of the road to make sure that the water goes through the system following the ground profile, but the sewers are at the opposite level.
The sewerage collection network was designed to handle the projected range of flows estimated over the design life of the project. Flows were estimated based on a combination of factors such as population, rate of development, type of development and per capita sewage generation rates.
For current design projects in Abu-Dhabi, the design year is 2020. Therefore, it’s
necessary to emphasize that future development is expected for the next 17 years. The proposed sewage network comprises 20 km of new sewer pipes ranging from 200 mm to 900 mm in diameter, with 400 manholes. The final sewer line in this site was connected to a nearby existing wastewater treatment plant, constructed previously for this purpose with 95.2 m invert level.
Abu-Dhabi’s drainage collection network was designed to remove runoff from catchments within GIC. The proposed drainage network comprises 16 km of new drains ranging from 250 mm to 1200 mm diameter, with 300 manholes.
The drainage system from this site was then connected into nearby outfall at the edge of the deep channel, constructed previously for this purpose with 96 m invert level. The service reservation was used; each system followed the corridors to achieve an economical design and avoid clashing of pipes or conflict during construction.
Distances between manholes in the trunk line were 60-130 m and in the branches. Manholes are located as required to permit access to the system and to ensure controlled transition in hydraulic flow. Manholes were installed as shown in Figures 2.5 and 2.6 in Appendix A, at the following points throughout the collection system:
; Change in pipe gradient.
; Change in pipe diameter.
; Change in pipe alignment.
; Junction of two or more pipes.
; Distance greater than 100 m.
; End of each lateral sewer.
After laying the pipelines and manholes at the area’s base map, it was necessary to
ensure that all blocks and buildings were served for easily future connection. The aim of this layout was to serve and convert the flow from the buildings, factories and roads to the wastewater treatment plant and outfall.