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

Bereket K. Tesfatsion1

Objective

This case study involves the use of mixed integer linear programming to aid in theplanning of a water supply system for a rural community, prior to more detaileddesign of the system. It is based on a real situation with some estimated data andassumed parameters. The problem involves selecting several components of thewater supply system, and it is shown that even for a simple system computerprogramming is required to arrive at a solution quickly. A demo version of LINGO(Schrage, 1999) is recommended to formulate and solve the problem, but othersoftware may be used as well.

Background

Eritrea is a relatively young country located in the Horn of Africa. Adi-Gheda is asmall village located in the southern zone of Eritrea, about 5 km away from a smallcity 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 of25 liters/person-day, total water use in the village in the year 2020 would be about76,000 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 forother productive purposes, such as food preparation, child care, and education.Therefore, implementing a water supply project for the village would bring a greatreturn to local development and the nation as a whole.

There are two possible water supply sources. The village can either be connected tothe 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 combinationthereof. If wells are selected, then proper pump selection must also be made. Thematerial for the elevated storage may be concrete, metal, or PVC. Finally, thenumber of distribution points and their type (capacity) must be selected.

A schematic of the proposed water supply system components is shown in Figure 1.

1Graduate Student, Department of Civil and Environmental Engineering, Utah State University,Logan, UT 84332. E-mail: [email protected]


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


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Water Supply System Components

Water Sources

As shown in Figure 1, Adi-Gheda has two options for a water source: wells orimported water from the nearby town. Currently, the village has two wells in publicuse, which can be part of the proposed water system. However, since the two existingwells 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 therelevant information on the current and future wells in the village.

Table 1. Capacity, cost, and service life of the existing and proposed wells

WellID

CurrentStatus

Capacity,liters/day

Wet-Season

Capital Cost,USD

UsefulLife

W1 Existing 50,000 0 25

W2 Existing 50,000 0 25

W3 Proposed 35,000 25,000 25

W4 Proposed 35,000 25,000 25

The other water supply source option is installing a longer pipeline to the nearby townof Dubaruwa, 5 km away. It is estimated that Dubaruwa will charge $0.0125 perbarrel of water, or $62.50 per million liters. For the pipeline to be constructed, aminimum of 100,000 liters/day would be delivered to Adi-Gheda, and the maximumdelivery is 250,000 liters/day.

The model should help to decide whether to import water or use domestic wells. Acombination of these two schemes is expected to be costly; however, the model couldhelp confirm this belief.

Pumps

Each well selected will require a pump to transmit water to the elevated waterreservoir at the center of the village. There are two types of pumps, with differentcapacity and cost, which can be used in each selected well. Table 3 shows therelevant information pertaining to the pumps.

Table 2. Cost and capacity for the two pumps considered for the project

PumpType

FixedCost

Operation and MaintenanceCost ($/Million Liters)

Usefullife

Optimum operatingFlow, l/s

Pump-1 4500 15 15 1.5 - 3

Pump-2 5500 20 30 1.2 2.5


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Transmission and distribution pipes

Water will be transmitted from each selected well and/or the nearby town ofDubaruwa to the elevated water reservoir. The water will then be distributed to thepublic distribution points (fountains) as per the plan (Figure 1). Table 3 provides thepertinent information for the transmission and distribution pipelines.

Table 3. Costs of the transmission and distribution pipes

Pipe Diameter(mm)

PurposeCost

($/m)

Usefullife (yrs)

Operations and MaintenanceCost, Annual ($/1000m)

100Transmission

from Dubaruwa3 30 50

80Transmissionfrom Wells

2 30 40

60Distribution

from Reservoir1 30 20

Reservoir

Previous studies conducted in the village have shown that a reservoir capacity of50,000 liters should be provided to meet the fluctuating daily demand of thepopulation in the year 2020. The reservoir can be made of reinforced concrete,plastic, or steel. Table 4 summarizes the pertinent information associated with eachoption.

Table 4. Costs for the different options for the elevated water tank. (Cost of routinecleaning is the same for all tanks and is not included.)

Type ofMaterial

FixedCost ($)

Operation & Maintenance($/year)

Useful life(years)

ReinforcedConcrete

15,000 250 35

Plastic 10,000 0 25

Steel 12,000 500 40

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 numberof distribution points will be selected by the model. There are two types ofdistribution points, and the relevant information associated with them is given inTable 5.


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Table 5. Water demand and population size projections

DistributionType

FixedCost

($)

Operation &MaintenanceCost ($/year)

Usefullife

(years)

Optimum deliverycapacity

(liters/day)

Type-1 5000 100 10 70,000 90,000Type-2 3000 75 10 40,000 60,000

Assignment

Using a reasonable discount rate (assume 6%) and all given information for thesystem components, formulate a mixed integer linear program to select from amongthe different alternative components of the proposed water supply system. Show thesteps involved in formulating the model and solve the model using software such asLINGO, Excel, or LiPS. Present the results clearly, including the number of

decision variables and the total number of alternatives for system design. Concludeby recommending an optimal system for Adi-Gheda. Consider the optimizationresults as a first step for a detailed engineering design which will include drawings,specifications, and quantity estimates. (Optional: Conduct some sensitivity and tradeoff analyses using your model and consider the results of these analyses in makingyour final recommendation.)

References

Bishop, A.B., T.C. Hughes, and M. McKee (2009). Water Resources SystemsAnalysis (Course Notes). Department of Civil and EnvironmentalEngineering, Utah State University, Logan, UT, Spring 2009.

Kelati, B., Z. Hailemichael, B. Goitom, and B. Leake (2002). Engineering Design ofthe Water Supply System for the Village of Adi-Gheda, Final project fordiploma in civil engineering, Department of Civil Engineering, University ofAsmara, Eritrea.

Schrage, L. (1999). Optimization Modeling with LINGO, 5th edition. Lindo Systems,Inc., Chicago, IL, 534 pp.

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