Planning a Water Supply System for the Village of Adi-Gheda, Eritrea

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1 Planning a Water Supply System for the Village of Adi-Gheda, Eritrea Bereket K. Tesfatsion 1 Objective This case study involves the use of mixed integer linear programming to aid in the planning of a water supply system for a rural community, prior to more detailed design of the system. It is based on a real situation with some estimated data and assumed parameters. The problem involves selecting several components of the water supply system, and it is shown that even for a simple system computer programming is required to arrive at a solution quickly. A demo version of LINGO (Schrage, 1999) is recommended to formulate and solve the problem, but other software may be used as well. Background Eritrea is a relatively young country located in the Horn of Africa. Adi-Gheda is a small village located in the southern zone of Eritrea, about 5 km away from a small city called Dubaruwa. As of 2000, the population for the village was about 1,805. The population for the year 2020 is projected to be 3,030. Assuming a water use of 25 liters/person-day, total water use in the village in the year 2020 would be about 76,000 liters/day. As of 2000, the residents of the village did not have a water supply system. However, there are several existing wells in the vicinity (1 to 3 km away) where the villagers fetch water for their use. This takes a lot of valuable time, which could be used for other productive purposes, such as food preparation, child care, and education. Therefore, implementing a water supply project for the village would bring a great return to local development and the nation as a whole. There are two possible water supply sources. The village can either be connected to the water supply system of the nearby city of Dubaruwa or pump water from wells. The wells they use can either be the existing ones, newly dug wells, or a combination thereof. If wells are selected, then proper pump selection must also be made. The material for the elevated storage may be concrete, metal, or PVC. Finally, the number of distribution points and their type (capacity) must be selected. A schematic of the proposed water supply system components is shown in Figure 1. 1 Graduate Student, Department of Civil and Environmental Engineering, Utah State University, Logan, UT ber.kel.tes@aggi .usu.edu 114

2 Figure 1. Proposed water supply system for Adi-Gheda. 115

3 Water Supply System Components Water Sources As shown in Figure 1, Adi-Gheda has two options for a water source: wells or imported water from the nearby town. Currently, the village has two wells in public use, which can be part of the proposed water system. However, since the two existing wells are a bit far from the center of the village where the distribution will take place, the feasibility of constructing two new wells is also considered. Table 1 shows the relevant information on the current and future wells in the village. Table 1. Capacity, cost, and service life of the existing and proposed wells Well ID Current Status Capacity, liters/day Wet-Season Capital, USD Life W 1 Existing 50, W 2 Existing 50, W 3 Proposed 35,000 25, W 4 Proposed 35,000 25, The other water supply source option is installing a longer pipeline to the nearby town of Dubaruwa, 5 km away. It is estimated that Dubaruwa will charge $ per barrel of water, or $62.50 per million liters. For the pipeline to be constructed, a minimum of 100,000 liters/day would be delivered to Adi-Gheda, and the maximum delivery is 250,000 liters/day. The model should help to decide whether to import water or use domestic wells. A combination of these two schemes is expected to be costly; however, the model could help confirm this belief. Pumps Each well selected will require a pump to transmit water to the elevated water reservoir at the center of the village. There are two types of pumps, with different capacity and cost, which can be used in each selected well. Table 3 shows the relevant information pertaining to the pumps. Table 2. and capacity for the two pumps considered for the project Pump Type Operation and Maintenance ($/Million Liters) life Optimum operating Flow, l/s Pump Pump

4 Transmission and distribution pipes Water will be transmitted from each selected well and/or the nearby town of Dubaruwa to the elevated water reservoir. The water will then be distributed to the public distribution points (fountains) as per the plan (Figure 1). Table 3 provides the pertinent information for the transmission and distribution pipelines. Table 3. s of the transmission and distribution pipes Pipe Diameter (mm) Purpose Transmission from Dubaruwa Transmission from Wells Distribution from Reservoir ($/m) life (yrs) Operations and Maintenance, Annual ($/1000m) Reservoir Previous studies conducted in the village have shown that a reservoir capacity of 50,000 liters should be provided to meet the fluctuating daily demand of the population in the year The reservoir can be made of reinforced concrete, plastic, or steel. Table 4 summarizes the pertinent information associated with each option. Table 4. s for the different options for the elevated water tank. ( of routine cleaning is the same for all tanks and is not included.) Type of Material ($) Operation & Maintenance ($/year) life (years) Reinforced Concrete 15, Plastic 10, Steel 12, Distribution points For the rural water supply, a number of carefully located distribution points will be used to distribute water to the community. As can be seen in the preliminary plan (Figure 1), three potential sites have been identified. However, the optimum number of distribution points will be selected by the model. There are two types of distribution points, and the relevant information associated with them is given in Table

5 Table 5. Water demand and population size projections Distribution Type ($) Operation & Maintenance ($/year) life (years) Optimum delivery capacity (liters/day) Type ,000 90,000 Type ,000 60,000 Assignment Using a reasonable discount rate (assume 6%) and all given information for the system components, formulate a mixed integer linear program to select from among the different alternative components of the proposed water supply system. Show the steps involved in formulating the model and solve the model using software such as LINGO, Excel, or LiPS. Present the results clearly, including the number of decision variables and the total number of alternatives for system design. Conclude by recommending an optimal system for Adi-Gheda. Consider the optimization results as a first step for a detailed engineering design which will include drawings, specifications, and quantity estimates. (Optional: Conduct some sensitivity and trade off analyses using your model and consider the results of these analyses in making your final recommendation.) References Bishop, A.B., T.C. Hughes, and M. McKee (2009). Water Resources Systems Analysis (Course Notes). Department of Civil and Environmental Engineering, Utah State University, Logan, UT, Spring Kelati, B., Z. Hailemichael, B. Goitom, and B. Leake (2002). Engineering Design of the Water Supply System for the Village of Adi-Gheda, Final project for diploma in civil engineering, Department of Civil Engineering, University of Asmara, Eritrea. Schrage, L. (1999). Optimization Modeling with LINGO, 5th edition. Lindo Systems, Inc., Chicago, IL, 534 pp. 118

Existing Condition: (Date: May 2000) Evaluation: In good working condition but the facility is not secured.

Existing Condition: (Date: May 2000) Evaluation: In good working condition but the facility is not secured. Atauro 05 - Tangke Cementerio 1998 AusAID Facility: Service reservoir Structure: Concrete Shape: Rectangular Dimension: 2.5m x 3.5m x 2.3m Capacity: 15m 3 Function: Storage Source of Water: Tulai spring