INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 3, No 3, 2014 © Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0

Research article

ISSN 0976 – 4399

Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila Institute of Human Settlements Studies, Ardhi University, Dar es Salaam, Tanzania P. O Box 35473, Dar es Salaam [email protected] doi:10.6088/ijcser.201304010032 ABSTRACT Rural water supply has been a challenge in most developing countries including Tanzania. Portable water from the available sources is not in sufficient amounts such that that combination of several sources and technologies seem to be most practical. Rainwater harvesting is one of the options that can be considered to supplement the available water sources and is nowadays implemented in most communities. Through the Kisarawe water project “Enhancing access to safe and clean water” we managed to provide some 11 institutions with rainwater harvesting systems that had no alternative sources of water. This was facilitated through community participatory approaches where the community indicated their needs and their proposals before start of implementation The systems consisted of Ferro cement tanks and a guttering system and through the analysis made, it was found that the technology is relatively cheaper by 20% as compared to reinforced concrete, and 38% as compared to polyethylene tanks. The other comparable advantages of using ferro cement tanks included its ability to withstand water pressure as compared to plastic tanks its ease to construct as it could be done using local masonry. Apart from the findings from the case study for Kisarawe, a review of rainwater harvesting technologies and water quality for rainwater is also presented in this paper. Key words: Rain water harvesting, Ferro cement tanks, Kisarawe, Tanzania 1. Introduction Rainwater harvesting appears to be one of the most promising alternatives for supplying freshwater in the face of increasing water scarcity and escalating demand. The pressures on rural water supplies, greater environmental impacts associated with new projects, and increased opposition from NGOs to the development of new surface water sources, as well as deteriorating water quality in the already constructed surface reservoirs, constrain the ability of communities to meet the demand for freshwater from traditional sources, and present an opportunity for augmentation of water supplies using this technology (UNEP, 2002). Rainwater harvesting is becoming an important source of water and has been adopted in many parts of the world where conventional water supply systems have failed to meet the needs of the people (Handia, et al., 2003). It is already implemented in several countries such as South Africa whereby it has contributed to meeting the Millennium Development goals (Kahinda, et al., 2007); China where it has been adopted due to the lack of reliable surface and ground water. Rainwater harvesting has played a prominent role in farmers’ domestic usage and agricultural irrigation (Zhu, et al., 2004). It has been reported to be a tradition in Zambia (Handia, et al., 2003) and in Tanzania as well where is used to supplement the existing water source. Received on November, 2013 Published on February 2014

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

The term rainwater harvesting is usually taken to mean “the immediate collection of rain water running off surfaces upon which it has fallen directly” so the runoff from land watershed into streams, rivers and lake is excluded in this definition (Wateraid, 2009). In other perspectives rainwater harvesting has been considered at all levels including runoff collection in dams and ponds. For instance, it has been considered as the traditionally developed systems such as excavated bunded basin as traditional rainwater harvesting systems (Mbilinyi, et al., 2005). In whatever perspective is taken, rainwater harvesting is considered to be the water resources development with medium capital cost and low running cost as compared to the other water resources development alternatives (Wateraid, 2009). This paper provides a review of some of the technologies that can be used for rainwater harvesting and presents the Ferro cement tank construction technology as the most reliable and affordable option for rural communities using the Kisarawe case study. Other aspects of rainwater harvesting such as the quality of water from rain harvesting have also been presented. 2. An overview of the existing rainwater harvesting technologies The rain harvesting system consists of the catchment area, the collection device, and the conveyance system. In most cases where roof is used as a catchment the parts that needs to be installed is the storage system and the conveyance system. Installation of the storage and conveyance systems is the most cost involving components in Rain water harvesting whereas the storage tank is the most expensive component. (TWDB, 2005). In this section, the rainwater harvesting technologies are briefly discussed with a more focus on the storage system –the tanks. The tanks are usually constructed using Concrete, galvanized sheet metal, polypropylene/plastics, fiberglass and ferrocement. 21. Concrete tanks Concrete tanks are either poured in place or prefabricated. They can be constructed above ground or below ground. Poured-in-place tanks can be integrated into new construction under a patio, or a basement, and their placement is considered permanent. Concrete may be prone to cracking and leaking, especially in underground tanks in clay soil. Leaks can be easily repaired although the tank may need to be drained to make the repair. Involving the expertise of a structural engineer to determine the size and spacing of reinforcing steel to match the structural loads of a poured-in-place concrete cistern is highly recommended. 2.2 Plastic tanks Plastic tanks are usually prefabricated and are made of different sizes to suit different uses and requirements. Material used for these include polyethylene or polypropylene. Polyethylene is a high quality thermoplastic that has outstanding resistance to both physical and chemical attack. The overall general toughness and excellent chemical resistance to a wide array of wet and dry industrial chemicals and food products make polyethylene ideally suited for storage tanks and containers. Polyethylene is translucent and its natural color ranges from slightly off white to creamy yellow, depending on wall thickness and type. Ultraviolet light stabilizers are usually added for use in outdoor applications. Plastic tanks are often employed by water supply organisations, as they are quick to install and are known to work reliably (usually backed by a manufacturers guarantee). Consumers International Journal of Civil and Structural Engineering Volume 3 Issue 3 2014

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

also like the tanks and see them as the most up-to-date method of storing water, however problems of cleaning and the water heating up in the black tanks have been identified (DTU, 2007). 2.3 Ferro cement tanks Above ground level, tanks are constructed with a plain or reinforced concrete base, cylindrical walls of Ferro cement and a roof of Ferro cement, or sometimes mild steel sheeting. The construction of Ferro cement walls is carried out by first assembling a cylindrical mesh of chicken wire and/or fence wire reinforcement, with or without the aid of formwork. On to this, a cement-rich mortar of 3:1 sand:cement is applied by trowel and built up in layers of about 15 mm to a finished thickness of between 30 to 100 mm, depending on wall height and tank diameter. Thicker walls may have two layers of mesh. The mesh helps to control local cracking and the higher walls may call for the provision of small diameter vertical steel reinforcing bars for bending resistance. Sometimes barbed fence wire is wound spirally up the wall to assist with resistance to ring tension and stress distribution. Effective curing of the mortar between the trowelling of each layer is very important and affects the durability of the material and its resistance to cracking. Mortar should be still green when the next layer is placed. This means that the time gap between layers should be between 12 and 24 hours. The finished material should then be cured continuously for up to 10 days under damp hessian, or other sheeting (Wateraid, 2009). Ferro cement is the technology of choice for many rainwater harvesting programs, the tanks are relatively inexpensive and with a little maintenance can last indefinitely. One of its advantages is that the cracks are arrested quickly and are usually very thin resulting in a reliably watertight structure, it has a high tensile strength. Within reasonable limits the material behaves like a homogeneous elastic material (DTU, 2007). 3. Rainwater quality and treatment Rainwater is valued for its purity and softness. It has a nearly neutral pH, and is free from disinfection by-products, salts, minerals, and other natural and man-made contaminants (TWDB, 2005) In a study done in Kefalonia Island Greece it was concluded that the chemical quality of harvested and stored rainwater is satisfactory and there in no parameter detected above the corresponding maximum allowable concentration for drinking purposes (Sazakli, et al., 2007). In Zambia sample from roof water system showed that the water can be used for drinking (Handia, et al., 2003). It can generally be said that rainwater is suitable for drinking purposes, however it must again be noted that the quality of water from rain harvesting depends on the type of the catchment used. For roof catchments, the material used for roofing can have some impacts on the quality of water. In the analysis done by Efe using various roofing materials such as aluminum sheets, asbestos, corrugated iron and thatch, the results showed variability in levels for turbidity, pH, total dissolved solids (TDS), Total suspended solids (TSS), Hardness, Bicarbonate, Calcium, iron and Salinity though within the acceptable limits but was not within the acceptable limits for pH, TSS and Iron (Efe, 2006). Some other study on the microbiological quality of rain water indicated the presence of microbial indicators making the necessity for some sort of treatment before used for drinking purposes (Sazakli, et al., 2007).

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

It is therefore good to think of the quality of water when making a choice for catchment, type of storage and collection system and that ways to improve the quality of water should be considered during the design and installation of rainwater harvesting system. 4. Experience from a case study-Kisarawe district Tanzania Kisarawe is located in the coastal region of Tanzania (map 1) and comprises 4 divisions Sungwi, Maneromango, Chole and Mzenga. The administrative headquarters is located 40 km west of Dar es Salaam. The total population is 95,323 and the majority resides in rural areas (80,817). Approximately 98% are peasant farmers who depend on subsistence agricultural. Most families live in small houses built of mud and pole walls and roofed with grass, those closer to the roadside and in the institutions may have corrugated roofs. Income per capita in the Coast Region is US $ 60 (Compared to the National Average of US $ 560) and an economic review carried out by the region in 1998 ranks the region as the least developed district in the country. Economic status of the people has implications on their ability to contribute in improving supply of safe potable drinking water.

Map 1: The location of Kisarawe area Due to acute shortage of water in the district, Plan Tanzania made an intervention in support to the Government efforts to reduce the problem. A three years funded project named “Enhancing access to clean and safe water in Kisarawe” was initiated in July 2005 and it aimed at providing water to the communities within Kisarawe District. This was funded by “The Charitable Foundation (TCF)” and was a support from Plan Australia. The coverage of the project was only to some villages as the funds were not enough to cover the whole district. However priority was given to the villages identified to have serious water shortage and to the institutions where water collected would save the majority. International Journal of Civil and Structural Engineering Volume 3 Issue 3 2014

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

Different alternatives for provision of water were considered for implementation. In addition to drilling of boreholes in some of the villages where it was possible to identify sources, rainwater harvesting was the only alternative in villages with no alternative water sources. The project was implemented using the rural participatory approach where the communities are involved in the project cycle staring from design of the project to its evaluation. However depending on the nature of its project itself, technical expertise was needed in various stages to help the community members make the appropriate decisions. After the community mobilization and the preliminary preparatory works, implementation of activities started in early 2006. The implementation started with situation analysis where it was revealed that the institutions within the villages such a schools and health centers had an acute water shortage that they called for urgent help. The project therefore utilized some project funds for provision of water to 8 schools and 3 Health centers/dispensaries selected based on the needs assessment and the community requests. The selected schools were, Kibasila primary school, Gumba primary school, Kitanga primary school, Mloganzira primary school, Maguruwe primary school, Kibuta primary school, Chole secondary school, Janguo secondary school, Mzenga health centre, Mafizi dispensary, Kihare dispensary. Analysis of the available tanks construction technologies to aid in the decision of the technology to be adopted s was done. The idea was to have units of 25m3 or 50 m3 as per design to provide storage for the rainwater collected from the roof catchments. Three technologies that were analyzed which are the reinforced concrete tanks, plastic tanks, and Ferro cement tank. The considerations were made on the advantages and disadvantage of the systems (Table 1) as well as the cost for installation (Table 2). Table 1: Merits and demerits comparison of selected tanks for rainwater harvesting #

Reinforced concrete tank

Ferro cement tanks

Sim/poly tanks (Plastic)

Advantage

Advantage

Advantag e Easy to install-just buy and install Many units so

1

Structural more stable

2

Can safe space as bigger units are constructed

3

Disadvanta ge Expensive

Need skilled labour

Procuremen t of skilled contractor may delay implementa tion

Technology available from local masonry Less cost for construction

Disadvantag e High risk of failure if not properly constructed

More u units that when one fails the other can still save the purpose

Disadvanta ge Takes much space

Less durable and seem to be unsuitable for pupils Buying and installation costs higher than the rest of the options

Table 2: Cost analysis of the tank technologies #

Institution

Reinforced concrete tank (Sizes 25m3 and 50m3 per unit) Number Cost (Tshs)

Ferro cement tanks (sizes, 25m3 per unit )

Sim/poly tanks (Size 15m3 per unit)

Equivale

Eq

Cost (Tshs)

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Cost (Tshs)

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

1 2 3 4

Mafizi dispensary Kihale dispensary Janguo Secondary Chole secondary

8,000,000

numbe r of units 3

13,098,000

1 (50m3)

10,005,116

nt number of units 2

1(50m3)

10,205,116

2

8,000,000

3

13,098,000

2(50m3)+ 1 (25m3) 3 (50m3)

28,578,602

5

20,000,000

8

34,928,000

30,615,348

6

24,000,000

9

39,294,000

Based on this scenario, Ferro cement tank technology was taken as the best option and was implemented using the local masonry who trained to do the job. 4.1

Important stages used in constructing Ferro cement tanks 1. Precast some segments using the cement mortal. The segment is to be 1 inch width or more (Figure 1 ) 2. Dig a trench for foundation the depth of the trench depends on the soil type. For clay soil the depth becomes significantly larger as compared to other types of soils. Fill in sand if necessary (especially when the site soil is no strong). Apply a concrete layer (mixing ratio should be 1:2:6) of about 6 inches. Lay a foundation wall using bricks (the width of this wall should be at least 6 inches). Fill in the base of the tank with stones, then a wire mesh followed by cement mortal on top (Figure 2) 3. Join the pre cast segments using binding wire and align then in a circular wall with the help of chick wire (Figure 3) 4. Clothe once again the wall with square mash using steel wire as an aid in fixing it to stabilize it and apply a cement mortal for about 1 inch inside and outside that tank (Figure 4) 5. Apply more cement mortal paste to increase the wall width at least to 150mm (Figure 5) 6. Arrange some supports for the roof construction (Figure 6), align some steel bars 12mm at a spacing of 1ft each and fix them with steel bars and paste the concrete layer for the roof. 7. Make a good finishing to the wall as desired (Figure 7)

4.2

Lessons learnt

Project implementation enabled to draw some important lessons that can be used for future projects. Some of these lessons are in the list below. 1. The use of local masonry in construction process under supervision of technical personnel has proved to be cost effective as compared to use of contractors who have to mobilize to the sites from urban areas. This in turn has been a source of employment creation and community empowerment. It does support the efforts of both the local government and Plan Tanzania of improving the well being of the community as a whole. International Journal of Civil and Structural Engineering Volume 3 Issue 3 2014

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

2. The use of the Ferro cement tank technology has proved to be the most affordable option in terms of costs for construction. The analysis from table 2 indicates that Ferro cement tank is relatively cheaper by 20% as compared to reinforced concrete, and 38% as compared to polyethylene tanks. Again the technology has got other comparable advantages than the rest of the option as it indicated in table 1. 3. Community involvement in project management brings positive results both in terms of technology and quality of services. Community member’s willingness to offer their time in monitoring and assisting project construction activities assured of the better that the quality of the works.

Figure 1: Pre cast segments

Figure 2: Base of the tank

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

Figure 3: Segments joined and aligned to form a wall

Figure 4: Square wire rotated and cement mortar applied

Figure 5: Cement mortal applied to make the tanks wall

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

Figure 6: Support put to allow construction of the roof

Figure 7: A finished tank 5. Conclusion For small institutions where the water needs can be obtained from rainwater harvesting, ferrocement storage tank is the optimal technology in terms of the cost of installation and ease to construct and durability. However its implementation must go in hand with a suitable catchment area and properly installed and maintained collection system to minimize water quality deterioration. The possibility for rainwater contamination do exist therefore the use of rainwater for drinking purposes should be done after some sort of treatment. Involvement of community members at all stages of project implementation ensures the success of the project plus the proper operation and maintenance of the installed system. Acknowledgement Plan Tanzania is acknowledged for implementation of the project and making possible this publication to be made. 6. References 1. DTU, (2007), Rainwater harvesting. University of Warwick.Coventry

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Rainwater harvesting using Ferro cement tanks an appropriate and affordable technology for small rural Institutions in Tanzania Jacob Kihila

2. Efe, S. I., (2006), Quality of rainwater harvesting for rural communities of Delta State Nigeria. Environmentalist, 26, pp 175-181. 3. Handia, L., Tembo, J. M. and Mwiindwa, C., (2003), Potential of rainwater harvesting in urban Zambia. Physics and Chemistry of the Earth, 28, pp 893-896. 4. Kahinda, J. M., Taigbenu, A. E. and Boroto, J. R., (2007), Domestic rainwater harvesting to improve water supply in rural South Africa. Physics and Chemistry of the Earth, 32, pp 1050-1057. 5. Mbilinyi, B. P., Tumbo, S. D., Mahoo, H. F., Senkondo, E. M. and Hatibu, N., (2005), Indigenous knowledge as decision support tool in rainwater harvesting. Physics and Chemistry of the Earth, 30, pp 792–798. 6. Sazakli, E., Alexopoulos, A. and Leotsinidis, M., (2007), Rainwater harvesting, quality assessment and utilization in Kefalonia Island, Greece. Water research, 41, pp 2039– 2047. 7. TWDB, (2005), The Texas manual on rainwater harvesting. Texas Water Development Board (TWDB).Austin 8. UNEP, (2002), Rainwater Harvesting and utilisation, an Environmentally sound approach for sustainable urban water management: An introductory guide for decision-makers. UNEP, 9. Wateraid, (2009), Water harvesting. Technical brief,Wateraid, 10. Zhu, K., Zhang, L., Hart, W., Liu, M. and Chen, H., (2004), Quality issues in harvested rainwater in arid and semi-arid Loess Plateau of northern China. Journal of arid environments, 57, pp 487–505.

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