Rainwater harvesting for peri-urban poor
E. Mangore * , L. B. Ndlovu and N. L. Kutshwa
Department of Civil and Water Engineering, National University of Science and Technology, Box AC
939 Ascot, Bulawayo, Zimbabwe
*Corresponding author email: enmangore@gmail.com (E. Mangore
ABSTRACT
Study and design of low cost water harvesting technologies for peri-urban poor was investigated in
Bulawayo, Zimbabwe. Due to scarcity of water in the area there was need to look for other sources of water, and rainwater was an alternative that was welcomed by most households.
The rainwater harvesting systems were designed taking into consideration the local rainfall patterns, other physical parameters such as length, slope, area and type of the catchment area and material that was available for construction. The Rational Method was used to estimate the peak flows from the various catchment surfaces i.e. the courtyard, thatched roof and corrugated roof.
Manning’s Formula was also incorporated to come up with the dimensions of the water conveying structures i.e. the gutter, channels and downspouts. Design of storage devices was depended on the amount of rainfall anticipated. Construction procedures carried out were related to the workmanship and materials that are available in the community.
Rain water was collected all the days that the site received rains. The amount of water that was collected from the different surface areas was recorded. The largest amount of rain water was harvested from surface runoff and the least from the thatched roof. 83% of all the water harvested was collected from surface runoff, 16% was collected from the corrugated roof and only 1% was collected from the thatched roof. The results suggested that the amount of water collected was dependent on the catchment area as well as the type of the surface. Good quality drinking water was collected from the corrugated and thatched roofs. Laboratory investigations indicated that water from surface runoff was unsuitable for drinking because it contained faecal coliforms.
Key words: alternative, catchment, materials, rainwater harvesting, workmanship
1.0
Introduction
It is widely accepted that water is an essential part of life yet many people lack adequate access to this basic commodity. The Southern African region is characterised by frequent droughts, floods and erratic, unevenly distributed rainfall. Zimbabwe has not been spared by these force majeure as these have magnified the already existing challenges in the provision of increasing populations with adequate and sustainable water services. Ekern (2000) argues that for the world to develop it needs to devote greater attention to the needs of the rural poor since the world’s poor live in the countryside.
We therefore dare not overlook the billions who still live in the rural areas, especially in Africa. In
Zimbabwe, 65% (Central Statistical Office (CSO), 2002) of the total population of 11 631 657 million people live in rural areas.
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There is a need to develop appropriate technologies in a view of coming up with: Sustainable rain fed agriculture, Sustainable water supply systems, Sustainable sanitation, Sustainable rain water harvesting, Sustainable shelter delivery, Sustainable use of renewable energy sources, Sustainable health delivery systems, Sustainable education policies and systems, Access to wireless internet and
Small industries to make rural areas better places to live in. Halving the number of people without sustainable access to safe drinking water and basic sanitation by 2015 is one of the targets of the
Millennium Development Goals (MDG). Rain Water Harvesting (RWH) is one of the methods than can be pursued vigorously to help achieve this MDG targets.
RWH is the small scale interception, collection and storage of rain water runoff for beneficial use, i.e for domestic, agricultural and small scale commercial activities. The intercepted rainwater can be collected for storage, slowed down, or routed through the site landscape using water harvesting structures. At household level the water is collected from rooftops, parking area, court yard or any surface and stored in storage devices for use within the household. In addition to roof and surface runoff collection, the other main groups of water harvesting systems are; in situ moisture conservation
(soil and water conservation) and the concentration of runoff in the field (Falkenmark and Rockstrom,
2004). Due to the above various types of run-off, there are a number of storing devices that could be chosen for storing harvested runoff such as reservoirs , farm dams, check dams, ground –water recharge systems, tanks and bunds (which confine water in fields) (Winnar et al, 2007).
Improved water supply systems can thus generally improve the well being of rural people. RWH has the potential of improving water availability and land productivity in semi arid areas. Supplemental irrigation of rainfed crops is a viable option of increasing water and land productivity. RWH has the potential to supplement rain water and thus increase crop yields and reduces crop failure risks. The other potential impacts of RWH are that less time is spent in collecting water from sources far away from homesteads, potential to supply water of better quality at household level and thereby reducing water related diseases and an improved health status as excess water is used for vegetable and crop growing in small gardens. In Zimbabwe 25% of the population is infected with HIV/AIDS, with some are in the rural areas such that provision of water nearby nourishes nutrition gardens and this is very beneficial to them healthwise as well as having a water close by. More benefits include improved economic status from the income of vegetables and crops, increase in households annual water consumption by 50% while reducing the fetching time by 70%, RWH systems are simple and easy to install, operate and maintain, affords homesteads to have total control over their own systems, RWH has few negative environmental impacts compared to other water supply project technologies, water collection and storage capacity can be increased depending on the capacity of the household, and more time is freed for education and personal development particularly for young girls as time saved is now used for school attendance and homework.
1.1
Background
RWH is an old technique that has been used as a major source of water during rainy season. Although unfavourable socio –economic conditions led to a decline in the use of the systems over the last , the increased scarcity of water in most dry areas has resulted in renewed interest and revival in the technique. Other contributing factors towards the urge / drive to harvest rain water especially in rural; areas are the increased use of small scale water supply for productive and economic purposes, decreased in quality and quantity of ground water, absence of piped water supply systems, the flexibility and adaptability of rain water harvesting technology and the increase in the availability of affordable tanks.
Different techniques and systems have been developed in different parts of the globe e.g. North
America, Middle East, Africa, China and India. In Asia rainwater harvesting started around the 9 th or
10 th century whereby rain water was collected from roof tops. In Thailand rain water was collected from the eaves of the roof tops into traditional jars and pots almost 2000 years ago. In China rain water harvesting has long been used in the loess plateau regions of China. Storm water ponds of
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various sizes lined with red clay at the bottom to minimize seepage were also used. Traditionally in
Uganda and Sri Lanka rain water is collected from trees of banana leaves or stems as temporary gutters, up to 200 litres may be collected from a large tree in a single storm. In India rain water harvesting dates back to the third millennium BC. Simple stone rubble structures for impounding rain water were used (Argarwall and Naran 1997).
In the northen African countries of Libya, Tunisia, Egypt, Sudan and Jordan, and Syria in the Middle
East, indigenous RWH systems are still practiced to increase crop production (Prinz, 1994). Various harvesting systems exist throughout Sub-Saharan Africa. These are predominately soil water conservation techniques. Rockstrom (2000) states that potential improvements for adoption of runoff storage types RWH systems are possible. In Tanzania, farmers widely practice RWH to such an extent that most of the rice produced in the country emanates from cropfields where RWH technologies are practiced (Mbilinyi, 2007). In rural South Africa rooftop RWH practice is spreading thanks to financial assistance from the Department of Water Affairs and Forestry. The money is for the purchase of tanks and related works (Kahinda, et al, 2007).
RWH is practiced in semi – arid Zimbabwe. Kahinda (2004) on his study on six Districts (Insiza,
Beitbridge, Zvishabane, Chivi, Gwanda and Umzingwane) in the semi arid regions of Zimbabwe found that the use of RWH for supplemental irrigation increased the water productivity i.e. the relative quantity of crop yield per unit of water produced, and stabilises crop yield. However despite its obvious benefits as claimed by farmers and researchers, there is still a lack of quantitative data on the extent of its use in the country and scientific information on how the various techniques are performing (FAO, 2005). There is a need for cost effective RWH techniques to be applied at household level. The implementation of rain water harvesting techniques in Zimbabwe has the potential of alleviating spatial and temporal water scarcity.
In Zimbabwe the potential of rain water harvesting has not yet been fully explored. This paper presents results of a study conducted to evaluate existing rain water systems and how they could be improved in a cotemporary rural area.
Also presented here are ways of increasing the uptake of the RWH systems.
1.2
Study Area
The study was carried out in St Peters communal area (peri-urban of Bulawayo). St Peters is part of the Hyde Park Estate which lies to the north of the Bulawayo City, the second largest city of
Zimbabwe. Administratively it falls under the Umguza Rural District Council and politically under the Tsholotsho South Constituency.
St Peters is at an altitude of 1350m. The area lies in the Natural Region IV, where rainfall is erratic, low and there are high incidences of drought and intraseasonal dry spells (Kahinda et al, 2007). The mean annual rainfall for the area is 555mm. Geologically, the area is covered with massive granite.
The predominant soils are subsequently sandy clay loams.
The main source of livelihood for the area is proceeds from rain fed agriculture although there are villagers who are formally employed in Bulawayo. Mixed farming system is practiced here and is dominated by crop and livestock production.
Currently a combination of water sources is used in the area as a means of meeting the water demand.
Firstly, St Peters is supplied with treated piped water by the Bulawayo City Council. However not everyone is connected to the piped water system as only institutional premises such as schools and clinics and a few homesteads have tap water. The main water source at St Peters are boreholes equipped with Bush Pumps/hand pumps. Vandalism of equipment at these water points has reduced their reliability. A very small percentage of the villagers own personal hand dug shallow wells. All these wells are not protected and they provide water for domestic and agricultural purposes. A substantial number of villagers own Ferro-cement tanks that store water harvested from roof tops. The capacity of these tanks range from 4 000 to 6000 litres. The owners of these tanks are beneficiaries of a Zimbabwe Project Trust program to promote rainwater harvesting in rural areas.
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2.0 Methods and Materials
The case study research methodology was the basic frame adopted in this study. It provides an in depth description and analysis of the RWH in our area of study. A baseline survey was carried out to come up with the mapping of physical elements of the area namely, geological formation such as rock and the type of soil and the vegetation, flows and elements i.e. checking on any naturally existing channels on courtyards and availability of slope, soil type, percentage of the impervious cover, runoff coefficients, storm event, Data acquired was relevant to local resources and the local environment.
Information about the rainfall, existing water resources, and availability of material, housing and roof types was taken note of. Other type of data collected included the livelihoods issues of the community, socio-economic drivers in the area, existing RWH practices, cost and efficiency of existing systems, local people’s opinion about usefulness and quality of water from these systems as well as the safety of the designed systems. This is important because many developmental programmes fail because they ignore indigenous knowledge systems (Pacey and Cullis, 1989).
Rainfall data for the period 2007 and 2008 was collected from historical rainfall data obtained from rain gauges in the local area. Water quality analysis was carried out on water collected from existing
RWH systems. Microbiological analyses was carried out on the water collected. The collected was tested for the presence of faecal coliforms that could cause harm to human health. Water was collected from the site was only allowed to stand for less than 24 hours. MacConkey broth was used to test for faecal coliforms. A single broth was prepared by adding 40g of powdered broth to 1 litre of distilled water. A membrane was placed in a Petri dish with the grid on the uppermost centrally in the
Petri dish. Forceps were used to place the membrane in the dish and was impregnated with water to be tested. Broth of1ml is placed in the Petri dish with the sample and the whole set up is closed with a lid. The dish is then placed in a rack ready for incubation. It was incubated for approximately 16hrs.
If present bacteria grew into visible colonies that were counted manually. Petri dishes and forceps were autoclaved to ensure sterility.
Design approaches for sizing tanks for thatch roofed and corrugated roofed houses as well for courtyard and underground tanks was done. Appropriate water harvesting technology for the corrugated roof, thatched roof and land surface (courtyard) were designed. Information was prepared for the home owners to encourage water harvesting. Also spelt out are the maintenance procedures as well ways of reducing diseases associated with RWH.
3.0 Results
3.1 Rainfall Data
For the year 2007 it rained for all the months except in May, July, August and September. The peak monthly rainfall was 162.2mm in December and the recorded annual rainfall for year 2007 was
514.6mm. Figure 1 shows the monthly rainfall distribution. This is the rain fall data that was used to size RWH storage devices. Rainfall data was collected from St Peter’s Village Hyde Park Estate.
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Figure 1. Monthly rainfall distribution for St Peter in 2007
3.2 Water Quality from RWH Systems
Because of the essential role played by water in supporting human life it also has if contaminated, great potential of transmitting a wide variety of diseases and illness. The major objective in water quality control is to reduce the incidence of water related diseases. The rain water harvested for drinking purposes has to be free from excessive colour, visible suspended matter, taste, odour and bacteria indicative of faecal pollution. The quality of the harvested and stored rain water depends on the characteristics of the considered area such as the weather conditions, topography, types contaminants found in the locality, proximity to polluting sources, type of catchment area, type of water tank and the handling and management of the water (Kahinda, et al, 2007).
From the microbial test carried out, it was found out that all water samples from underground water tanks had some faecal coliforms present. Results of 3 – 5 colony forming units (cfu) per 100ml of sample were recorded. No faecal coliforms were detected from rooftop RWH systems samples. These results buttress the point that rain water collected from ground catchment systems is subjected to higher levels of microbial contamination. This is because the surface runoff has a contamination path very similar to that of other water bodies. The zero faecal coliform count does not mean that water from rooftop RWH systems meet portable water standards. This is because other WHO drinking water parameters were not tested for. Possible sources of potential pollutants in rooftop RWH systems are bird droppings, micro-organisms entering the storage device, dust from soil, tree leaves, chemical deposits e.g. from roof paints, algae and thermal pollution that can upset oxygen balance.
To ensure the improved water quality from RWH systems and at the same time safeguarding the consumer’s health, appropriate techniques must be adopted and alternative water treatment technologies be applied at household level. Periodic cleaning of the catchment area, the interior of the water tank, diverting the first few millimetres of rainfall and installing a screen between the collection device and storage tank to keep out debris can suffices. Depending on the pollution levels of the water the following processes can de adopted to effectively reduce contamination levels; water retention, filtration, disinfection by Ultra Violet (UV) radiation, Sodium Hydrochloride and Moringa Oleifera.
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Water storage devices must be designed such that stored water will not be accessible to mosquitoes and other insect vectors. Pipes conveying water should not allow water to collect in them. Ponding around the tank should be avoided as well.
3.3 Design of tank sizes
Although all the water storage devices will be located in the same area, which has the same mean annual rainfall, there are other factors that are not uniform but are important for the RWH system.
These are rock and soil type, catchment area, surface type, intended use of water, required storage period, water requirements, and affordability levels. The main types of catchment surfaces were considered. These are the soil surface runoff and the roof top runoff. Thatch roofing and modern materials roofing (corrugated Asbestos Cement and corrugated Galvanised Iron) make up the roof top surfaces. Thatch is the dominant roofing material with more than 80% of all the houses having this material as roof cladding. Table 1 shows the steps undertaken in the sizing of storage tanks for domestic water uses. The stages are the determination of water requirements, water availability and the consideration of technical and construction issues.
Table 1: Stages involved in the sizing of domestic RWH tanks.
Stage 1 Stage 2 Stage3
Water Availability Technical issues Determination of water requirements
-per capita demand
-number of people within the homestead
-other water uses
-storage requirements
-use of rational formula to calculate runoff
-rainfall distribution and intensity
-catchment area size
-Surface type
-Slope
-sizing the tank
-placing tank underground or over ground
-roof height
Stage4
Construction issues
-Availability affordability materials and of underground tanks of
-Availability of labour
-Soil type – Avoid clay soils for construction
For the sizing of the three storage systems a commonly accepted minimum amount of water of
20litres per head per day was adopted. The minimum storage capacity was give as the product of the number of people in the homestead, water used per capita per day and the period in which water is to be stored over the dry months. An estimated amount of water required for economic and productive purposes is added to the above product to give storage for all uses. For St Peters Village an average of five people per household and a dry period of 4 months (120 days) were adopted. Table 2 shows the parameters that were used for sizing tanks from the three catchment surfaces. However the economics of storage tanks is not proportional to its size as smaller can be filled and emptied whilst bigger ones are rarely emptied. Costs, availability of resources and construction methods are therefore important factors for the design of storage devices.
Table 2: Input parameters for sizing RWH tanks
Table 2.
Input parameters for sizing RWH tanks
Surface Area Slope C Tank Q Location of tank
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m 3 size m 3
12 m 3 /s
Ground surface
0.0003 0.03 0.4
Thatch roofing
Corrugated roof
0.000016 0.488 0.035
0.000028 0.0213 0.8
12
12
0.0051
0.0000253 On ground
0.001008
Underground
On ground
During the period of one six months, extending from October 2007 to March 2008, the volumes of water collected from different surfaces was recorded. Figure 2 shows the relative cumulative results for a sixth month period for each catchment area.
Figure 2: Relative amount of water that was collected from each surface
Figure 2 shows that very little water was collected from the thatched roof. This was due to the catchment area and the rainfall intensity. It was observed that it takes about twenty minutes for water to start running down the roof if it is raining heavily. The greatest amount of water was collected from surface run off.
Rainwater harvesting using ground or land surface catchment areas is a less complex way of collecting rainwater. Land surfaces provide greater opportunities for harvesting water because they have a larger surface area. The challenge is to reduce water losses due to infiltration and improving the water quality.
4.0 Conclusion
4.1 Conclusions
RWH has the potential of alleviating water problems in peri-urban and rural communities. The idea of
RWH was not new to the rural community of St Peters as a number of homesteads were already
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practicing the technique, mostly from corrugated roofs. However its potential is not yet fully appreciated in the village as other surfaces like thatch roof tops and courtyard surfaces are not utilized as yet. Water from various surfaces can be utilized in different ways depending on the quality requirements. However because of the scarcity of water in the region the community was eager to learn more about ways of collecting water and storing water for later use.
4.2 Recommendations
NGOs to capacity build communities need to look at communities as partners and not just as donation beneficiaries. This will allow communities to be actively involved and be part of programs that will improve their livelihoods and subsequently reduce dependence syndrome.
The community needed to be educated on the concepts of water harvesting i.e. the construction of the system and most important appreciating its value at home. On a broader scale, the implementation of
RWH in rural Zimbabwe requires an all inclusive approach, where technical, institutional aspects are all taken into consideration. The government, local authorities, NGOs and all other key stakeholders including the locals must work together for the improved uptake of RWH system.
5.0 Acknowledgement
The authors of this paper would like to acknowledgement to all those who made the research and the subsequent writing of the paper a success. Their comments and contributions are greatly appreciated.
6.0 References
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Falkenmark, M., and Rockstrom, J., 2004, Balancing water for humans and nature: The new approach ecohydrology. Earthscan, London, London. UK.
FAO, 2005, Irrigation in Africa in figures: AQUASTAT survey 2005. Food and Agricultural
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Kahinda, J, M., 2007, Rainwater harvesting to enhance water productivity of rainfed agriculture in semi-arid Zimbabwe. Physics and Chemistry of the Earth. Volume 32, Issues 15-18.
Mbilinyi, B, P., 2007, GIS-based decision support system for identifying potential sites for rainwater harvesting. Physics and Chemistry of the Earth. Volume 32, Issues 15-18.
Mwenge Kahinda, J., 2004, Water productivity and yield gap analysis of water harvesting systems in the semi-arid Mzingwane catchment, Zimbabwe, MSc Thesis, University of Zimbabwe, Harare,
Zimbabwe Unpublished, pp 1- 102.
Pacey A. and Cullis A. (1986), Rain Water Harvesting
Prinz, D., 2004, Water harvesting and sustainable agriculture in arid and semi-arid regions. In:
Proceedings of CIHEAM Conference, Land and Water Resources management in the Mediterranean
Region, 04 08 September, 1994 Valencano (Bari). III, pp. 745-762.
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Rockstrom, J., 2007, Water resources management in smallholder farms in Eastern and Southern
Africa: An overview. Physics and Chemistry of the Earth25 (3), 275 -283.
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