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ADDIS ABABA WATER SUPPLY STAGE III-A PROJECT Ijigneh Sime, Senior Engineer, AAWSA, Addis Ababa 1. Project Background 1.1 Historical Development Addis Ababa was established as the capital city of Ethiopia in 1886 and has grown to become the largest urban and commercial center in the country. During its early years, the principal sources of water were the numerous springs located at the foot of the Entoto mountain range and hand dug wells located in the lower areas. The larger springs were tapped and fed into a number of small tanks for local distribution. Continued growth necessitated the construction, in 1938, of a plant at the foot of Entoto to treat water from a number of springs and the nearby Kechene River, and in 1944 the original Gefersa dam located north west of the city was completed. The Gefersa Dam was raised and a treatment plant built in 1960, while many of the springs were taken Out of service because their quality was deteriorating. In 1966, the raw water storage capacity in the Gefersa watershed was increased with the construction of another small dam north of the existing dam. This dam was also assumed to assist as a sediment trap. At this time primary source of Addis Ababa’s water supply relied on the Gefersa facilities. The supply from Gefersa was transmitted via twin 400mm pipelines to nine service reservoirs for distribution. The next major phase of expansion of the water supply facilities commenced in 1970 with the commissioning of the Legedadi Dam and treatment plant, which was located on the Akaki River east of Addis Ababa. The plant’s output of 50,000 m3/day was transmitted via 900 mm pipe line to the Terminal Reservoir on the city’s Eastern edge and to Meskel Square in the city’s center. To transfer and distribute this additional water additional reservoirs, pumping stations and pipelines were constructed in the eastern and northern areas of the city. These facilities came to be known as the Stage I Water Supply Project. Further development of the water supply facilities was pursued during the l980s under the Stage II Water Supply Project. The First phase included expansion at the Legedadi treatment plant, construction of a new transmission pipeline into the city, the rehabilitation of the Gefersa treatment plant and the construction or upgrading of several reservoirs and pumping stations throughout the city. The second phase included extensive primary and secondary pipeline installations and improvements to the distribution network. The capacity of the supply facilities, of 150,000 and 30,000 m3/day respectively for Legedadi and Gefersa were projected to be adequate to serve the need of Addis Ababa up to 1992. Planning for a Stage III water supply program commenced in the early 1980’s, when a reconnaissance study was undertaken of all potential water supply sources located within a 50km radius. In 1991, feasibility studies and preliminary designs were completed for the development of a number of sources to serve the city to the year 2020. The initial part of the scheduled development was identified as Stage III A and includes those components described later in Section 3. The delay in the implementation of Water Supply Stage Ill-A (WSS Ill-A) project called for an emergency program to fast-track the development of two water supply projects. These are part of the Akaki well field and the Dire dam, which are now under construction, In addition, a program of spring rehabilitation and bore hole drilling has provided improved water supplies to outlying areas of the city not vet serviced by the distribution network Additional programs are underway to reduce leakage losses and to improve operational efficiencies. Implementation of the WSS Ill-A project will quadruple the supply of potable water over existing capacity and will enable the Addis Ababa Water and Sewerage Authority (AAWSA) to meet the needs of the city for some time in an economical and financially sustainable manner.
1.2 Objectives of the Project The broad objective of the Stage Ill-A water supply project is to ensure the continuity in supply of safe and adequate quantities of water for the inhabitants of Addis Ababa. Water is a basic necessity of life; it is also necessary for the economic viability of the city. In the long term, the attainment of this objective will lead to improvements in health and productivity of the population. A secondary objective is to organize a team of Ethiopian professionals for technology transfer and training during the design process. This will provide the Authority in particular, and the country in general, with experienced professional personnel able to implement, manage and operate the proposed facilities as well as to undertake the design of other projects of similar scope
2. Population and Water Demand Project Projections 2.1 Growth and Development of Metropolitan Addis Ababa Addis Ababa has grown from a small village to become the predominant and largest urban center in Ethiopia since being selected as the capital in 1886. The city has grown from an area of some 16 Km with an estimated population of about 100,000, prior to the Italian occupation, to its current size of about 532 km2 and 2.36 Million residents (1997). The first comprehensive municipal census was carried out in 1961 and indicated a population of 450,000. a subsequent municipal census in 1967 reported a population of 680,000. A national census carried out in 1984 and 1994 reported the population of Addis Ababa to be 1,417.200 and 2,112,700 respectively. Although three city master plans were prepared between 1955 and 1967, the plans lacked legal status and there was no effective administrative body to implement them. As a result, development during much of this period continued in a haphazard fashion. Now, development is guided by Addis Ababa Urban Development Plan (AAUDMP), which was completed in 1986 by the National Urban Planning Institute and formally adopted by the government in 1995. Responsibility for implementation of the plan lies with the current Region 14 Administration. The AAU7DMP delineated land use zones both within the administrative boundary of Addis Ababa as demarcated in 1986 - the ‘core’ area which covered 202 kin2, and the ‘expansion areas’ beyond the boundary as required to accommodate future development to the year 2006. Following the introduction of the regional system of local governments, a new boundary was delineated and Region 14 (metropolitan Addis Ababa) now encompasses some 532Km2, including the formerly separate towns of Akaki and Kotebe. The WSS I Il-A project will therefore cover a significantly larger territory in order to provide adequate water supply for the population growth, urbanization and industrialization that is being planned for on a rational basis.
2.2 Population Projections Official census results and future projections of rural and urban population in Ethiopia are prepared by the Central Statistical Authority (CSA). National population censuses were carried out in 1984 and in 1994.
Sample surveys and future projections of population for Addis Ababa have been made by a number of government agencies for their own purposes or for specific projects. Some other relevant projections include those made by the National Urban Planning Institute (NUPI) in conjunction with preparation of the Addis Ababa Urban Development Master Plan in 1986, and a population estimate made by the Addis Ababa Municipality. Other projections based on the data presented by CSA or NUPI have been made for various water supply and sewerage studies. These have presented low, medium and high growth scenarios based on different rates of fertility, mortality, migration, or net annual change. There are some significant differences in these projections.
The CSA 1994 population census and its future population projections were to be used as the basis of design for the WSS Ill-A project. The metropolitan population was obtained by adding the Addis Ababa (core area) population and the expansion area population (Kotebe, and Akaki and rural areas incorporated into Region
2.3 Water Demand Projections Projections of future water demands for domestic, industrial and administrative uses, together with unaccounted for losses such as leakage were made from current demands for each water supply subsystem and their aggregated to determine total water demand projections for the metropolitan Addis Ababa area. The current demands of each subsystem had been derived from 1994-95 water consumption statistics and from the demand-monitoring program carried out in 1995. The population projection used for the project is presented in table 1. Table 1 Population projections used for the project Year Population Consumption Total Demand (L/cap/day) (m3/day) 1994 2,112,000 97 204,000 2009 3,690,000 143 528,000 2018 5,170,000 187 967,000 2019 5,370.000 193
1,034,000
The 1994-95 consumption data obtained from customer billing records were totaled for various categories of users in each of more than 300 kebeles (administrative sub-units) in the city. The consumption subtotals for the kebeles were then allocated to one of eleven existing subsystems and adjusted on the basis of results obtained from monitoring program to derive a synthesized demand. From the 1994 synthesized demand data and other empirical information, future demands were estimated on a kebele and land-use basis for the design horizon years of 2006 and 2020. Demands for other years were interpolated. Factors such as levels of service, existing living conditions, existing and proposed land use (master plan), existing per capita demands, current development trends, and demand values of other third world countries, were used in estimating the future water demands for the following categories of land use: - Future Residential Demand, - Future Government, Institutions and Urban Services, - Future Industry, Work Shops, Business and Trade Land and Irrigated farmland and Formal Green Space. After the analyses, the requirement for potable water to satisfy all demands plus unaccounted for losses was estimated to average 204,000 in/day in 1994. This total is projected to increase to 431,000m/day in 2006 and 1,105,000 m3/day in 2020. It has been assumed that per capita rates will approximately double over the 25 year design horizon as a result of several factors including: improved housing with a greater proportion of indoor plumbing and sanitary facilities; greater awareness of the relationships between cleanliness, good personal hygiene and improved health; increase in commercial and industrial demand; and improved standards of living in general.
Figure 1. Location of the new and old resource developments. 3. Project Description 3.1 General The WSS Ill-A project is one of the largest civil engineering projects to be undertaken in Ethiopia. It includes three components, which are located within the city and the regions to the north and south of Addis Ababa. These components will be integrated with the existing water supply and distribution facilities serving the city. In addition to the design project, two other contracts are being undertaken within the context of the WSS Ill-A project. These are the Geological and Geotechnica1 investigation projects on the dams, reservoir and tunnel sites contracted to the Transport Construction Design Enterprise (TCDE) and the second one drilling of 25 large diameter (17.5f) bore holes for the ground water development, contracted to COMPLANT of China. The design project components and major facilities are described below. Location of the new and old resource development are shown on Figure 1.
3.2 Ground Water Component The Ground Water Component includes the development of an aquifer in the Akaki area south of Addis Ababa. The potential of this aquifer was identified in 1991 when a drilling and testing program for the Akaki town water supply project was carried out. Production wells for the Akaki project were completed in 1995, and drilling for the WSS 111-A project is currently underway. When the presently proposed development is completed, this well field will be able to supply an additional 125,000 m3/day of water to Addis Ababa. This yield is estimated based on an average of about 62 l/sec/well whereas, though the ground water modeling is yet to be completed, from the individual and group pumping tests at 87 l/sec continuous pumping for 72 hours maximum draw-down of 25 cm and 86 cm respectively were observed. This certainly implies that the yield from individual wells could substantially be increased. However, the final figures will be reached at, only after the modeling works are completed. The facilities included under this component consist of wells, collecting pipelines, collection tanks with chlorination equipment, pumping stations, reservoirs and pipelines to service the southern parts of the city. Some facilities are currently being constructed under an emergency program to supply about 40 percent of the projected yield to help alleviate the water shortages now being experienced. The WSS Ill-A project facilities share common sites with the emergency works and include the following.
3.3 Surface Water Component Existing water supply sources serving Addis Ababa are located to the east (Legedadi) and west (Gefersa) of the city. The surface water component of WSS 111-A project includes the development of water~ resources located north of Addis Ababa, together with treatment and transmission facilities. This new development will take place in two phases. the first phase will supply 364,000m3/day of treated water to the city and the second phase will supply an additional 290,000m/day for a total of 654,000m3/day The surface water component is the largest and most diverse of WSS Ill-A project program. It is comprised of six major facilities including: • Gerbi dam and reservoir with gross storage volume of 48.5Mm’ and safe yield of 77,000m3/day. The dam will be located approximately 10 km north of the existing Gefersa dam. • Sibilu darn and reservoir with gross storage volume of 347.7Mm3 and safe yield of 61 1,500m3/day. The dam will be located approximately 2 km Southwest of the town of Chancho. Chancho is 30 km north of Addis Ababa on the Gojam road. • Intake structure and 1.2 m diameter 8.2 km long raw water transmission pipeline from Gerbi reservoir to the treatment plants. • Intake structure, raw water pump station and 1.8 m diameter, 11.3 km long transmission pipeline from Sibilu reservoir to the treatment plant. The pipeline will be twinned in the phase II development. • Wosserbi treatment plant for the water from Gerbi and Sibilu. which will be developed in 2 stages. The first stage capacity will be sized for the Gerbi supply and half of the Sibilu supply; the second stage will be sized for the remaining Sibilu supply The treatment plant site is located on the north side of the Entoto ridge approximately 3 km Southwest of the Sululeta telecommunications station. • Lined tunnel 3.0m diameter, 4.8 km long from the treatment plant through Entoto ridge to convey the water to a terminal reservoir located near the northern limits of Addis Ababa at Shegolle.
3.4 Transfer and Distribution Component The existing water distribution system in Addis Ababa is divided into several distribution sub-systems due to the topography of the city. These sub-systems are interconnected to some extent and supplied from the major sources through separate transfer pipelines. The existing water transfer and distribution system in Addis Ababa has evolved over several decades. The most recent significant upgrading took place in the late 1 980s under the Stage II Water Supply Project in conjunction with the expansion of the Legedadi water treatment plant. At the implementation of the WSS III-A project and the commissioning of the new sources of water at Gerbi and Sibilu, the transfer network must be re-arranged and expanded. In the future, most water will flow by gravity from the upper, northern area of the city to the lower, southern area instead of being pumped in the reverse direction. Primary distribution pipes will also be installed in all sub-systems. This will integrate the delivery and transfer of water from the primary sources to the 31 pressure zones, and improve flow and pressure within the zones. The facilities will include pipelines, service reservoirs; pump stations and modifications to existing works. When completed, this system will be capable of delivering approximately 1,000,000m3/day of water to consumers in all parts of the city, and include the following facilities: • Approximately 250 km of transfer pipelines and primary distribution mains, including appurtenances and tie-ins to existing facilities. The largest transfer pipelines will run from the proposed Shegolle terminal reservoir to the eastern, central and western parts of the core area of the city. Most of the distribution mains will extend service into the expansion areas on the eastern and western fringes of the city. • Thirty one service reservoirs will be installed in the distribution systems to provide peak-balancing and fire-fighting reserve storage. Thirteen booster-pumping stations will be provided to service areas of higher elevation located on the slopes of Entoto in the northern side of the city. • Existing facilities, which will be required in the future, will be rehabilitated and redundant facilities will be de-commissioned. Therefore, the overall operational efficiency and reliability of the system will be improved. In connection with this design work, a comprehensive computer-based model of the entire water transfer and primary distribution network for Addis Ababa has been created. This model is linked with the new digital topographic mapping prepared for WSS 111-A project and with several databases containing land use, population and water consumption information. This model provides AAWSA with a powerful tool to monitor and operate the existing water supply system as well as plan and manage future changes.
4. Socio-economic and Environmental Aspects 4.1 Environmental Impact Assessment A thorough environmental impact assessment is being undertaken to describe and quantify the anticipated environmental effects of the WSS Ill-A project on the natural resources of the project area. The interactions of the project with the environment are being identified and those environmental issues of concern will undergo detailed impact assessments. Key Environmental issues, referred to as Valued Environmental Components (VEC), are being identified by taking into consideration World Bank and African Development Bank Terms of Reference, concerns raised by environmental experts and public concerns. Valued Environmental Components are components of the environment, both natural and socio-cultural, that are valued by society, and upon which the impact assessment will be focused. Scopping is done to limit the assessment so that a meaningful analysis of potential environmental effects arising from the project can be made. The scooping is done based on the following two major study boundaries:
Potential impacts on the Valued Environmental Components are assessed on the basis of a review of literature, consultation with experts and professional judgment. In some instances, making impact predictions is difficult if the available data are limited. Ratings are therefore provided to indicate the level of confidence associated with each impact prediction. Based on the impact analysis, mitigation measures will be developed as required to minimize or reduce the potential impacts of the project. Following the application of mitigation, any remaining residual impacts will be evaluated against the established significance criteria.
4.2 Environmental Management Plan An Environmental Management Plan (EMP) will be developed for the construction of each major project component addressing specific activities that interact with the environment. The EMP is the prime vehicle for implementing mitigation programs, monitoring programs and other environmental protection procedures throughout the life of the project. It is a field document meant to be used by the Authority and integrated into the contract bid documents to be considered in the costing of the work. The EMP will outline environmental monitoring programs to be undertaken to determine the actual environmental effects of the project. Cost estimates for the monitoring and mitigation programs will also be included. Further field studies will also be recommended where more detailed information is required in order to develop a meaningful management plan.
4.3 Socio-economic Impact Assessment The Socio-Economic Impact Assessment (SEIA) process is being carried out for the WSS Ill-A project to identify and evaluate impacts on, benefits to, the local, regional and national human environment (social, cultural, and economic). It has the following objectives: • identify the potential benefits and adverse impacts that may occur as a result of the project; • determine the significance of such effects; • recommend ways to enhance the positive effects, and reduce or eliminate the negative impacts through the development of effective mitigate measures; • determine significance of residual or inevitable impacts that are likely to remain following implementation of these mitigation; and • recommend ways to monitor and report the benefits and adverse impacts and to provide a feedback loop so that mitigation can be adjusted or modified as necessary to accomplish their goals.
5. Implementation Staging 5.1 Water Demand and Expansion of Supply Capacity The total water demands for Addis Ababa (Table 1) must be supplied from the existing and proposed water supply facilities. The existing facilities are now operating at the limits of their capacities, which is less than the present demand. It is therefore necessary to construct new facilities’ to expand the supply capacity and to make up for the shortfall. These include both the Emergency and the Stage Ill-A Water Supply Projects, which are comprised of: • Akaki Ground Water • Dire Dam • Gerbi Dam • Sibilu Dam The safe yields of water which can be expected from the new facilities, except for Gerbi and Sibilu which are revised during the WSS 111-A project design stage, and the order in which these projects are to be implemented have been estimated in previous engineering studies. The Emergency Ground Water and Dire Dam Projects are now under construction and are expected to be completed in 1998. Design of the WSS Ill-A Project components is expected to be completed at the end of 1997 and beginning of 1998. However, several additional years will be required for their implementation, including pre-qualification, tendering, and supply of materials, construction and commissioning. Except for the second phase of the Sibilu development, the implementation of all other WSS Ill-A project components must be commenced as quickly as possible in order to avoid more or prolonged shortages of water in Addis Ababa.
5.2 Stages of Development Anticipated for WSS Ill A. The Water Supply Stage Ill-A project is assumed to be implemented in the following Four Stages. Stage one - Ground water development - Associated distribution system Stage two - Gerbi dam and transmission line
- Entoto tunnel full scale - Related distribution system
Stage three - Sibilu dam and phase one transmission line
Stage four - Sibilu phase two transmission - Treatment plant phases two
The time of implementation and schedule of the WSS Ill-A is determined from the projected supply and demand of the city. A graph showing the demands and available supply for the city on yearly basis to year 2020 is shown in Figure 2.The first component of the WSS Ill-A project to be commissioned will be the ground water component in the year 2000. This will be followed by the Gerbi surface water development to be commissioned in the year 2004, the Sibilu surface water phase one development in year 2005 and phase two in year 2014. The current schedule of implementation is made with the assumptions of the volume of ground water being equal to that estimated in the feasibility study, that is 62 I/sec/well. However if the volume of ground water increases dramatically as individual and group well testing indicated then the timing of the surface water development may be delayed for some time. And in some cases there are possibilities that Gerbi may not be needed at all for the design period aimed at, year 2020.
Fig. 2. Projected water supply and demand of Addis Ababa
5.3 Possible Supply of Materials and Construction Contracts The facilities to be constructed under the WSS UT-A project vary in type, size and complexity, and they are located on several different sites within the city and surrounding areas. It is appropriate to divide the work into several contract packages based on established criteria. Projects of this nature may be divided into categories based on the type of work involved, such as: • Supply of Pipes, Valves and Fittings • Construction of Civil Works • Supply and Installation of Mechanical and Electrical Works The construction of civil works may be divided into sub-categories. For this project the following may be considered. • Dams and Related Structures • Treatment Construction of Civil Works • Pipelines • Tunnel • Reservoirs, Pumping Stations and Related Structures Where possible, the work may also be divided into packages of different sizes. Because of financiers and funds small projects may be less restrictive for local firms than larger complex projects. The final breakdown of the work into specific contract packages has not yet been made.
6. Cost Estimates 6.1 Base Year Capital Costs Preliminary estimates of capital costs for the construction pf the WSS III-A project have been prepared. Quantities have been estimated from the designs currently being prepared. Unit prices have been calculated on the basis of 1996 costs obtained from manufacturers and suppliers, or from general cost indices applicable to particular types of construction. The breakdown between local and foreign currency has not yet been determined. However, the foreign cost component for projects of this type in Ethiopia is typically in the range of 60-80 percent. The preliminary estimates prepared to date indicate the following capital costs: • Ground Water Component -156 Million Birr • Surface Water Component -1,390 Million Birr (Excluding EEPCO power supply) • Distribution Network Component 588 Million Birr • Socio-Economic and Environmental Protection, Enhancement & Mitigation 186 Million Birr Project Total = 2,320 Million Birr. A pretender estimate of costs will be available after the designs have been completed. |
