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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Some Countries in Asia>

5.6 Daungha Rainwater Collection Water Supply Project, Nepal

Introduction

Rainwater harvesting is an old practice in Nepal. People have been collecting rainwater for washing clothes and utensils, and for watering animals, for years. However, most of the people in the rural communities will try to avoid using water that has been stored overnight for drinking. They believe that the stored water is stale compared to flowing water. Thus, the practice of using rainwater catchment systems (RWCS) to supply drinking water (and water for other domestic uses, where possible) is of fairly recent origin. The Gulmi District is one of 75 districts in Nepal and lies in the hill region in the western part of the country. Its topography ranges from 600 m to 3 000 m above sea level, and its climate ranges from a warm to a cool temperate climate, depending upon the altitude and the presence of deciduous monsoon forest.

The Gulmi District is also one of 15 districts included in the Western Development Region. There are 79 villages in this District. Daungha is one of these villages, situated about 26 km southeast of the District Headquarters at Tamghas. The nearest roadhead is at Lumchha Hardeneta, which has a 25 km earthen road link with Tamghas, and a 50 km earthen road link with Tansen via Ridee Bazar. The Village of Daungha, administered by the Village Development Committee (VDC), is situated at an altitude of between 785 m and 1 350 m. There are three springs in the vicinity of the Village:

a. Hingaha Mul, Q = 0.85 lps, elevation 408 m, Ward no. 1

b. Nishi Mul, Q = 0.053 lps, elevation 885 m, Ward no. 5

c. Dharapani, Chinne and Kayanko Kunchnir Mul, Q = 0.08 lps, elevation 855, Ward no.5

These springs are used for domestic purposes by about 1 500 people in about 150 households in Ward nos. 1, 5 and 6. People spend about 4 to 5 hours per day fetching water from these springs. The remaining population of the Village, located in other areas, face severe hardships in fetching water, as the few other available springs are not easily accessible. Due to the lack of other surface water resources, the Village has adopted rainwater harvesting as the most suitable technology for meeting the demand for freshwater. The District Water Supply Office (DWSO) of Gulmi has been the lead agency concerned with the introduction of rainwater harvesting, and has constructed four ferrocement storage tanks, each with a capacity of 20 m3, during fiscal year 2046-47 (1989-90). A total of eleven tanks have been constructed through fiscal year 1994-95. Over 300 students and teachers, and more than 250 other people, have benefited from these construction projects.

Technical Description

Rainwater is collected from the rooftops of the buildings within the Village using corrugated galvanized iron sheeting as roofing materials. A gutter constructed of a half cut HDPE pipe and HDPE downpipe are used for collecting the rainwater in a storage tank. The storage tanks are 20 m3 ferrocement tanks, some of which are fitted with separate tapstands.

Extent of Use

The rainwater harvesting system was introduced in Daungha during the fiscal year 2045-46 (1988-89). As a pilot-scale project, one 20 m3 ferrocement tank was built to collect water from the roof of the middle school. This system helped to meet the drinking water demands of about 300 students and teachers at the school. The success of this system encouraged the villagers to build additional systems, and three more 20 m3 tanks were installed during 1989-90 (one additional tank at the middle school, one at the VDC Office, and one at the Mohare Primary School). The interest and active participation of the villagers have helped to promote the use of rainwater harvesting systems. Seven further storage tanks have been constructed and there are now eleven ferrocement tanks for rainwater storage in the Village.

Operation and Maintenance

Operation and maintenance requirements of this technology include the regular cleaning of the rooftops and gutters, the frequent cleaning of the storage tanks, and the periodic inspection of the gutters, feeder pipes and valve chambers to detect leakage. These tasks have been handed over to the users committee, who bear the overall responsibilities for the operation and maintenance of the systems. Required works that are beyond the capacities and means of the users committee are carried out by the DWSO.

Level of Involvement

Both the community and the Government have been involved in this project.

Costs

The total cost of the project was $24 620, or $121 per capita. The project was financed through a cost sharing arrangement with His Majesty's Government providing $22 560 and the Village providing $2 060. The Village contribution was primary used for financing the cutting and back filling of trenches used to contain the piping that conveys the water from the rooftops to the storage tanks. The present rainwater harvesting system provides a total volume of 1 224 l/day. The cost of a 20 m3 ferrocement tank is $2 000. Although the operation and maintenance cost of the system is negligible, the capital cost is too high for individual households and a rural community to invest independently in such a system.

Effectiveness of the Technology

A total of 183 m3 of rainwater is collected annually in the storage tanks from the 160 m2 rooftop catchment area in Daungha. Assuming the average rate of water consumption, for drinking purposes only, is 73 m3/year, this system can provide sufficient water to sustain 34 people. The ability of the rainwater harvesting scheme to service Village needs, shown in Table 35, was estimated on the following basis. It was assumed that the available catchment area was 160 m2 (the combined area of the rooftops of 5 houses, each 8 m x 4 m), and that 75% of the total rainfall would be available for potential storage in the 20 m3 storage tank (rainfall of less than 20 mm/month was not considered to contribute to the total rainfall available for storage). It was further assumed that the maximum monthly rate of consumption of water for drinking purposes was 6.12 m3/person. Over the design period of 10 years, a 2% annual rate of growth in population from the design population of 28 persons (using the relationship pn = pn (1+r)n) would result in a total population served 34 persons.

TABLE 35. Indicative Rainwater Collection at Daunghaa.

Month Total rainfall
(mm)
Catchment (m2) Quantity of water entering the tank (m3) (75% of rainfall) Consumption (m3) Quantity of water in the tank at the end of the month
August 312.33 160 37.48 6.12 20.00
September 103.07 160 12.37 6.12 20.00
October 67.93 160 8.15 6.12 20.00
November 14.33 160 - 6.12 13.88
December 67.70 160 8.12 6.12 15.88
January 11.67 160 - 6.12 9.76
February 27.87 160 3.34 6.12 6.98
March 15.80 160 - 6.12 0.86
April 72.13 160 8.66 6.12 3.40
May 90.40 160 10.85 6.12 8.13
June 461.73 160 55.40 6.12 20.00
July 319.60 160 38.35 6.12 20.00

Advantages

The main advantage of this project is the time saved in fetching water, which may be utilized for other economic activities. Women especially benefit by having more free time for child care, social activity and income generation. Rainwater also has the advantage that it is considered to be free of contamination.

Disadvantages

The disadvantage of this technology is its high capital cost to implement.

TABLE 36. Monthly Precipitation at Ridee Bazar, Gulmi District, Nepal.

Table 36

Source: HMG/DHM 1992. Precipitation Records of Nepal, DHM: Ridee Bazar,
Gulmi District: Elevation, 442 m

TABLE 37. Storage Tank Size Determination

Month Rainwater
Available(Q),m3
Demand (D), m3 Difference (Q-D),m3 Cumulative Difference (Q-D),m3
January 1.08 4.2 -3.22 -3.22
February 1.16 4.2 -3.04 -6.26
March 1.84 4.2 -2.36 -8.26
April 1.12 4.2 -3.08 -11.70
May 3.88 4.2 -0.32 -12.02 (T)
June 7.12 4.2 2.92 -9.10
July 20.75 4.2 16.55 7.45
August 14.16 4.2 9.96 17.41 (P)
September 3.44 4.2 -0.76 16.65
October 1.56 4.2 -2.64 14.01
November 0.16 4.2 -4.04 9.97
December 1.04 4.2 -3.16 6.81
Annual Total 57.31 50.4 -- --

Further Development of the Technology

Although rainwater is generally considered free of contamination, requiring little or no treatment prior to potable use, the roofs and gutters used to collect the rainwater need to be regularly cleaned, and the rainwater flowing off the roof at the beginning of rainy season should not be collected in the tank. While roofs are commonly used as catchment, ground catchments have the advantage of providing larger surface areas enabling greater volume of water to be collected. Ground catchments also are cheaper to construct. However, the use of ground catchments in Nepal is rare due to the limited availability of suitable land. Flat roofs with tiles or plastered concrete may be used, with floor traps instead of gutters, but sloped roofs are better as they are accessible for cleaning and repair, and the rainwater has less chance of being contaminated. Asbestos cement roofing and sheet metal roofing coated with lead based-paints should be avoided, as they may be dangerous to human health.

The storage tank is the most expensive part of any RWCS. The method used to determine the most appropriate storage capacity for any given locality, and the optimal size of catchment area needed to provide a reliable supply of rainwater for storage, will critically affect both the cost of implementing this technology and the amount of water available for use. In order to determine the potential rainwater supply for a given catchment, reliable rainfall data (mean annual rainfall and its distribution) are required for a period of at least 20 years.

Information Sources

Mr. I. Sainju, Civil Engineer, Department of Civil Aviation, Maintenance Branch, Tribhuvan International Airport, Kathmandu, Nepal.

Mr. R.B. Tamang, Department of Civil Aviation, Repeater Station, Phulchoki, Lalitpur, Nepal.

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