Rainwater Harvesting: A Key to Drinking, Irrigation, Disaster Prevention and Poverty Alleviation in the Mountains of Nepal

Bhuwani Paudel

Proceedings of Unfolding Futures: Nepalese Economy, Society, and Politics
Friday-Sunday, Octobet 5-7, 2007, Ottawa, Canada

ABSTRACT

Despite bestowed with abundance of water resources, rainfalls, and precipitation, Nepal seems to be a country in dire need of clean drinking water and irrigation for its people. The mountainous region of Nepal has so many places where water resource utilization is considered as technically and economically not feasible for irrigation. In absence of new technology and in face of harsh geographical challenges, peoples in the mountains regions are living with their conventional irrigation practices, which have not undergone through improvements for ages.

Immense fresh water, on an average precipitation of 1400 mm per year, that falls over Nepal runs off without effective use and largely drains as monsoon flood. Such marvelous natural gift is barely able to improve the quality of life of people due to an absence of appropriate techniques or technologies for its sustainable use. Improvement of conventional ponds and development of water-harvesting reservoirs with exploitation of locally available impervious natural materials is a crucial demand of the time. Construction of numerous but reasonably sized water harvesting reservoirs have a greater potential for transforming Nepal than small number of massive reservoirs, which are potential environmental hazards.

Development of environmentally non-invasive rainwater harvesting reservoirs constructed from locally available materials integrated with novel techniques for its consumptive use are important for bringing people of the mountains into the development mainstream. However, developing knowledge, technology, and methodology, and taking them to people in the form of standards, guidelines, and operational manuals is not an established practice in Nepal to this date. Works in this front are urgently required if Nepal is to enable its people to appropriately harvest and utilize rainwater. This paper outlines some key elements that must be parts of such guidelines, and it highlights prime areas for further research.

Introduction

Conventional resources of portable water is depleting in mountainous region of Nepal year after year due to receding glaciers and other environmental changes that are beyond Nepal’s own control and there are causes induced by human activities born within the country. Therefore, rainwater harvesting does not only carry relevance today but also into the distant future for fulfilling a portion of required water quantity for the inhabitant of Nepal. Rainwater collection and its utilization at the times of need require proper technical know-how, social awareness and commitment. Components such as collection, conveyance to storage, conveyance to distribution system and environmental protections are parts of technical fields. Similarly, land’s effective utilization, sharing of harvested water, and sharing catchments are parts of social fields.

Some researchers have already begun to stress the importance of rainwater harvesting and have formed some international alliance for this purpose in Nepal [8]. World water day of March 22, 2007 also celebrated as a rainwater-harvesting day in Nepal [9]. A rainwater harvesting National Steering Committee was formed in 2006. From the activities conducted in national level, at this moment, it shows that rainwater harvesting is focused for application of drinking only. Harvesting for other purposes such as recreation and irrigation has not gone past investigative stage. Not only feasibility of rainwater harvesting for irrigation is initiated but also other application of rainwater harvesting is ignore. However, a remarkable part of rainwater use can be found in these areas. A guideline with responsibility of different agencies, communities and people for implementation of rainwater harvesting work should develop for sustainable development of rainwater in fragile mountains of Nepal.

Experiences generally tell that economic development works usually undermine the natural environment. Haphazard construction of rural roads is an example of this phenomenon. Rural roads are source of sediment in rivers and causes of landslides and flooding every season in Nepal. In addition, the increase in the numbers of landslides over the past years has been linked to these activities. Indirectly road construction has become a cause of death and loses of property of Nepalese people for some years. Rainwater harvesting could be another cause of environmental destruction if further precaution is not timely taken.

Before investing in this field, a policy level work must be carried out. Legislation should be issued for environmental protection measures, which can control size, location, technical soundness and social acceptance of the project. Technical guidelines should be developed and adopted for sustainable use of rainwater for different purpose. More area should be address for collection and conveyance for large-scale rainwater harvesting project such as for irrigation.

Rainwater harvesting could potentially be a key ingredient for employment generation. Recreation and irrigation uses of rainwater have more potential for involving more people and in garnering investment capital. There should be a provision and planning for rainwater harvesting and consumptive use for recreation and irrigation, the area that is discarded. Rainwater harvesting could accommodate people and capital in different sector and remove a shadow of unemployment [7, 10].
Nepal Rainfall Pattern

Importance of rainwater harvesting

Due to lack of infiltration zones and extraction more than recharging capacity, groundwater levels are deepening in Nepal’s urban area every year [4]. Conventional springs (eg dhunge dharas) are going to dry due to these reasons and most time of the year there is dry or very low discharge in existing springs. This trend of water depletion is increasing year after year. It is due to concreting in the city, collection of rain runoff through drainage and discharge to rivers – reducing subsurface infiltration area. Existing natural flow runoff areas are occupied or destroyed by new infrastructures that caused change of surface runoff morphology. Therefore, rainwater harvesting is a prime means for solution of these problems. Effective harvesting and consumptive use for appropriate purposes also support for solving runoff related flood problems.

Various committees are formed for development of rainwater harvesting in different levels. International non-governmental organizations (INGO) and national government organizations (NGOS) are involved for rainwater harvesting and consumptive use since many years. Unless a national guideline and technical expertise in this field, investing time and money do not make much effective.

Rainwater harvesting and proper utilization support to make a green environment. Rainwater harvesting for drinking, recreation and irrigation covers mostly entire daily activities of unemployed people. Influx of drinking water, food, and recreation make both people and the environment healthier. Rainwater harvesting brings many good aspects in the society such as reduce flooding in cultivated area, solve food deficit problem and provide job opportunity to unemployed people. Rainwater harvesting can help control pollution to groundwater resources, infiltration of chemical from industrial area and retard peak flooding period in uncontrolled rivers. Rainwater harvesting controls erosion from slope surface and sedimentation with flooding in plan area that is prevailing problem in Nepal. There are other direct and indirect benefits from rainwater harvesting which support the country economy. It is also a means for poverty alleviation [12].

Social and political commitment

Data related to rainfall infiltration and crop water requirements are necessary to work on rainwater harvesting, therefore, a government commitment for establishment of such information centre all over the country for recent global temperature change condition is necessary. A network among the rainwater users for fair share of rainwater and marketing of products should be developed. A committee can be formed among the users to serve theses purposes. Committee help to distribute their reserve water for effective use among their members and serve for farming and marketing. Committee can develop rules and regulation within their jurisdiction.

Poverty alleviation

Rainwater is a means of poverty alleviation. There are examples of using only 300 to 400 mm annual rainfall precipitation to bring food sufficiency and embark new economic activities in China for more than 21 millions people [19]. In Nepal, precipitation is not less than 1000 mm per year in any part of the country, Figure 1. This amount of precipitation is ample for generation of employment in any area of the nation. Rainwater harvesting and irrigation cause erosion control, conditions soils, innovate new farming practices, and also balances ground water rechargeable system.

Before artificial irrigation system was developed, most part of the country depended on either rainfall or river inundation for irrigation. Still many part of hilly cultivated land is depends on rainfall for irrigation. Due to lack of rainwater harvesting techniques and resources, these areas are still practicing ages old techniques that have not been improved over time. Proper utilization of such resources exploits human resources and certainly up lifts the country’s economy.

At the beginning, focus should be given to middle hill region of Nepal because middle hill is highly populated, unemployed and its economy is based on agricultural products only. Middle hill covered 41.7% of total area of Nepal. The potential area of irrigation in this region is 33.2% of total irrigable land in Nepal [2].

Application of rainwater for irrigation involves lots of resources. Application of such resources certainly support to generate employment in deprive mountainous region of Nepal.

Various Aspects of rainwater harvesting

Feasibility Study

Feasibility study of rainwater harvesting is as similar as feasibility study of other infrastructure projects. Based on purpose of work such as drinking, recreation or irrigation and available rainfall runoff information, the size of rainwater harvesting system can be decided. For drinking water small system will be sufficient while for irrigation all components in large scales are necessary. For estimation of monthly or annual average precipitation in any area, precipitation information of at least nearby three measuring stations and their distance form the interest site are required. For preliminary design purposes, precipitation of near by measuring station can be taken. The precipitation depends on location, vegetation, orientation of hill and other factors. The precipitation vary from place to place so that precipitation estimation of any areas based on near by station may not be correct. Therefore, error on estimation should be adopted for deciding size of various components of rainwater harvesting system.

Same as rainfall and runoff, infiltration is also required for feasibility study, if collection is in large scale and ground surface runoff is considered for collection. Decision for required volume of water, medium of collection, reservoir capacity and conveyance system for collection and distribution should be conformed and tested with general engineering practice and related field experience.

For effective operation, a good social structure is required. Managing collection area, location of reservoir and conveyance systems as well as distribution of harvested water is a challenging work in social aspect. A good relation among the users internally and good net work among the other group provides social harmony of effective use of resources.

Right of water collection for particular person at particular area should be based on precipitation in the area and water requirement for survival. The equivalent amount of water required to survive a person is 1700 m3 per year. This amount includes all purposes such as raising pet and cultivating food. In country like Nepal available water quantity is as less as 500m3 [17]. A lower bottom of 500m3 per year can be used as a datum for computation of survival quantity of water. This problem will not arise for drinking and small scale collection for other purposes but for large scale collection runoff area and person benefited from that area should be match each other.

Drinking water

Total water requirement per person for personal use per year is 37.5 to 75 m3 on an average 56 m3 [17]. This amount is equal to 10*(3.5 to 5)*1.25 m size of reservoir. Rainwater supplement will be for dry days of the year when other sources are not available. The capacity of reservoir can be decided based on number of people for serving and length of dry period. Area of catchments can determine based on precipitation in the proposed area. Roof top is a best catchments area for drinking water collection.

Ground surface runoff in any area depends on intensity of precipitation and type of ground surface. Detail precipitation and runoff relation should be developed for runoff collection from ground surface. Efficiency of natural conveyance system can be taken only 60%, however for pipeline and other close conduct system it will be higher. Distribution system after reservoir may not have full efficiency. Reduction on efficiency of conveyance and distribution system should be incorporated in the capacity of the reservoir. It is understood that 90 m3 capacity of reservoir will be sufficiently retain water for a person for all round the year.

Water should met the required standards for drinking therefore water harvesting for drinking required extra care to avoid contamination. Rainwater can be harvested from roof top or from a conventional Padelo. Some other artificial collection surface such as plastic roof etc can be constructed for rainwater harvesting. For drinking purpose 20 litres per day will be adequate for one person [1]. The capacity of the tank can be decided based on dry period and available roof top area. The quantity required to clean roof top gutters and collection tank could be some 20% of the total rainfall. The rest of the water can collect matching with required capacity. On an average rain fall is 1400 mm (Figure 1) but effective from roof top will be one third about 500 mm only for initial computation purpose. Immediate evapo-transparation and conveyance losses should be incorporated in the total capacity. These losses are considered and implemented in rainwater harvesting work successfully in some part of Nepal [4, 5].

Nepal Human Development Report [16] mentioned that only 71.6% people of Nepal have access of clean and fresh drinking water. As importance of rainwater harvesting is unfolded people are celebrating world water day with rainwater harvesting [9] instead of demanding water supply system in various parts of Nepal. Quality of rainwater also attracts developed countries like US and Australia for rainwater harvesting. Australia is an example of large rainwater user for drinking purpose. In Australia, 42% people drink water from rainwater and only 40% people drink water from main water supply system [13]. Government should invest resources, develop guidelines and make policies for rainwater harvesting so that Nepal will be another forefront as a large rainwater user in the world.

Rainwater harvesting is more effectively used in urban area in the world [11]. Rainwater harvesting supports to improve ineffective drainage system, retard flooding, and provide quality water for drinking in urban area. At present many people are drinking arsenic contain water in Nepal. Drinking from rainwater avoid from such mineral borne diseases. Rainwater harvesting program should be effectively implemented in the area where drinking ground water contain arsenic. Identification and implementation of such program in arsenic prevailing area is crucial at the moment.

Guide lines for rainwater use are issues in different cities in the world, water quality guide lines for different use should be issued. Different technique [11] to construct rainwater harvesting tanks cost effectively is important to minimize initial investment in rainwater harvesting.

Irrigation and recreation

Rainwater application for irrigation purposes includes more large size components. Therefore, each part of this process required extra care and appropriate management. Large size and greater number of reservoir and conveyance systems creates extra space management and investment. Detail technical report for these components is necessary.

Type of crop and area of irrigation influences the required size of various components. Before planning to harvest rainwater for irrigation detail study of type and area of crop and crop water requirement should be known. For an example, rice is not feasible for crop selection in any part of Nepal because of high crop water requirements. Potato and similar type of crops that have high yield and less water requirement are better options. As mentioned above, if potato is a better option for rainwater harvesting crops for any area, combination of available water for storage and crop water requirement for potato can analyse area to be cultivated. Identification of crops, which required less water but high yield, is a subject of further research in Nepalese context.

Efficiency of systems and application methods are important for effective use. Irrigation efficiency can be increased from correct watering schedule with required quantity of water in one side and uniformly distribution of irrigation water in the cultivation area in other side [3].

Water simultaneously can use for recreation such as bathing, drinking water for cattle, small gardening and other purposes together with irrigation. Ground surface runoff water can collect and treat for this purpose. Water used for flushing also can recycle to use in irrigation [11] and other purpose but this practice may socially or culturally unacceptable in Nepal.

Rainwater harvesting pond connection with small perennial spring provides both effective recreation and irrigation. An example of such application can be taken as a fishpond and vegetable garden along its bank.

Reservoir construction

Construction materials for reservoir material should be free from any contamination and chemicals such as lead and arsenic [14]. Rainwater is a free marvellous gift of nature and free from all contaminations. Size of the reservoir decided after the purpose of the rainwater harvesting. Some percentage such as 80 to 90 can be taken for factor of safety for size of the reservoir for security of deficit. Degree of security for drinking water can keep small because of the small quantity.

Small Ferro-cement tank or Gagro (water retain pot) can use to collect water for drinking purpose. Conventional water treatment practices should adopt for drinking water after collection.

Runoff collected water should filtrated with conventional sedimentation and filtration system before storing. Based on acceptable size of the particle in water, size of the sediment tank can be decided. Personnel who have knowledge and experience of prevailing engineering practices in this field should conduct design and treatment work.

Precaution should be taken for design and implementation of reservoir and conveyance system for large-scale rainwater harvesting system because a lesson from rural road development and their impact on erosion and landslides are unforgettable and unrecoverable in the past. Therefore, emphasize should be given to small scale harvesting system. For Irrigation purposes, also emphases given in small reservoir but large reservoir may be required based on the local situation and supporting perennial source. Capacity of the reservoir can decide as give below.

Capacity of reservoir = runoff * time =(rainfall – infiltration) * time

Capacity of reservoir = (Crop area * number of watering per crop * required water depth per watering) &$150; (Rainfall during the crop season)

The area of crop cultivation can be decided from available water in the reservoir. Crop water requirement from rainwater harvesting can be decided from required crop water difference with rainfall in the area in that season. For selection of crop area to cultivate, the worst case, no rain should be adopted in the dry season. Rainfall and infiltration of required catchments is necessary to calculate available water from those catchments. An efficiency of 80 to 85 % or 24 mm depth of precipitation of water for wetting loss should be taken for roof top catchments collections. For surface runoff, small scale efficiency, around 60% should be taken. For either of purpose, drinking, irrigation or recreation reservoir should be covered all the time. Above is an example only, a detail study should be carried out by the personnel working in this field for formulation and design of each project individually.

New technology can incorporate to effective consumption of rainwater. Drip irrigation provides very good efficiency for crop water requirement. Small perennial source connection with rainwater harvesting tank also help to counteract with the water loss through evaporation.

Local materials are useful for reservoir construction. Plastic, concrete and ferro-cement tank are useful for small-scale rainwater harvesting applications.

For medium scale reservoir construction, a core, mixture of clay cement and sand (6:2:1 to 9:3:1) is also a good water retained material for seepage control in reservoir. This material can not stand or retain water pressure so that outer mud walls or a concrete wall from local material is necessary. This material can fill within the structured wall to reduce seepage. If cement is not available fine silty clay with clay contain more than 60% will be applicable as a core material.

For large reservoir construction, an earthen pond can construct with local materials. Silty clay is easily available earth material in Nepal. If silty clay or clayey silt is not available or available in matrix form with sand or gravel, a standard sieve (Sieve no 200) can use to separate fined and coarse material from the matrix (size 0.075mm opening). Sieve can be used to test and select clay quarry where clay content is appropriate or more than 60 % for reservoir core construction. Sand and silt can mix with 60% clay to make an impervious paste, which can compact in optimum moisture content. Clay core is equally important material for simple conventional pond or engineered reservoirs due to not only its low cost but also impervious and flexible nature. A 10 cm thick clay core can retain water for 4 months without seepage. Conventional stone and mud can use to construct wall of the reservoir but core thickness should decide based on the properties of core materials. A detail research on design and construction aspect of reservoir from local material is required.

Evapo-transporation is one of the major factors for loss of harvested water therefore a perfect surface seal is required to protect water evaporation. As reservoir can not keep open, a plastic sheet will be a better option to use for covering the reservoir.

Gravity flow is better for conveyance after collection. Location of the reservoir is better at the higher portion of the field whether the purpose is either irrigation or other. This location will reduce lots of cost and easy to operate. Mostly reservoir placed below the ground level so that ground besides the reservoir would not shock water from the tank and does not seep outside. Seepage is another major means of water loss through underground.

A detail design of collection and distribution system is necessary. If HDPE pipe line system is used for distribution or collection system, pipe line should buried underground with required depth. Required check and supply valves should be installed for proper operation and maintenance.

Capacity and collection process should be re- evaluated every year to make sure the system is compatible with required purpose.

Recent Developments in Nepal

Nepal is rich in water resources but is facing shortage of water for drinking and irrigation. The problems stemming from the lower quantity of usable drinking water are further aggravated by the lack of quality [7]. Amidst this situation, there are signs of encouragement due to build up of knowledge on rainwater harvesting as seen in recent seminars and symposiums. Recently, governmental officials agreed to build a rainwater harvesting tank in every government building. Department of Urban Development and Building Construction (DUDBC) is responsible to implement an already passed legislation for construction of rainwater harvesting tank in government buildings [10]. Rainwater resource centre is established within the DUDBC. Legislation is coming for compulsory construction of a rainwater tank in every house in urban area. UN HABITAT organized a program to develop national strategies for rainwater harvesting for drinking purpose. More research in rainwater harvesting application in recreation and irrigation area is expected to come in near future.

Some organizations are intensively working in rainwater harvesting field in urban area (Ngo forum for urban water supply and sanitation is also working specially for water and sanitation in Kathmandu valley). Such organization will extend their activity beyond Kathmandu and beyond the limited use of drinking only [10]. There is an existing national level committee formed through representation of eleven organizations. This committee can play a leading role to develop required network for further extension of rainwater application in irrigation and recreation. International rainwater catchments association is going to prepare guidelines [14] that can be useful for rainwater development in Nepalese perspective.

Recommendations

Rainwater harvesting should be addressed in national plan with specific initiatives and targets for short term and long term development. As water is an important for human development and human existence, the state should take initiatives for awareness campaigns on rainwater harvesting and its effective utilization for improvement of living standards. For irrigation, rainwater harvesting should be coordinated with every year’s cropping plan.

Rainwater harvesting is more technical than social work. Feasibility study, water collection, quality grading, treatment, and appropriate field application are better handled by technically trained people than a social scientist. It is necessary that any organization that wants to work in rainwater harvesting should have competent and certified technical personnel to carry out feasibility studies, structural design, construction supervision, and consumptive consultations.

Mini weather stations should be established throughout the country to measure rainfall, temperature, wind, and other factors so that more reliable meteorological statistics could be developed. They could collect data on rainfall, runoff, temperature, day light hour, air velocity and temperature in the area. This is more so important in Nepal because geographic factors have great influence in rainfall, runoff, and evapotranspiration patterns. Further, those weather stations should also be used for assessments like estimating crop water requirements, conducting infiltration tests, selecting proper rainwater harvesting techniques for the area, and so on.

Research on micro irrigation system should be done for effective use of rainwater. Programs such as watershed management should be implemented to avoid slope movement and landslides due to water harvesting work. Without proper scientific assessment of impact on environment, economy and society, no structural development work should be done on the name of “development”. Further research is also required to develop detailed technical guidelines and to recommend incrementally develop suitable legislations for implementation of rainwater harvesting programs to cope with increasing technical complexities that could be overlooked in the early stages.

Because scientific knowledge and education are paramount for further innovation and sustainability, education on nature, natural resources, and their sustainable utilization should be formally taught as compulsory subjects in school curriculum. Rainwater harvesting should be an important subject in the higher secondary level education.

Technicians working in VDC level should be trained and equipped with knowledge and skills for effective utilization of water, rainwater, and soil for technical consultation and leadership at local level.

Reference

  1. http://www.unep.or.jp/ietc/Publications/techpublications/TechPub-8e/community.asp
  2. http://unapcaem.org/Activities%20Files/A07/Country%20paper-Nepal%202(Hanoi%2004).pdf
  3. http://www.ag.uidaho.edu/potato/research/files/Volume%2038/Stark1.pdf
  4. http://www.bspnepal.org.np/rainwater_harvesting.htm
  5. www.RAINfoundation.org.
  6. http://www.rainfoundation.org/index.php?menuid=3000&lang=en&cl=blue&q=
  7. http://ww2.unhabitat.org/nepal_2006.asp
  8. http://www.irha-h2o.org/index.php?option=com_content&task=view&id=21&Itemid=57
  9. http://www.worldwaterday.org/
  10. http://www.ngoforum.net/index.php?option=com_content&task=view&id=58&Itemid=6
  11. http://www.harvesth2o.com/Bookreview_Brad.shtml
  12. www.ircsa.org
  13. http://www.unep.org/GC/GCSS-VIII/Kenya%20%20Expert%20-%20IRCSA.pdf
  14. http://www.ircsa.org/factsheets/HawiiRainHarv.pdf
  15. http://www.ircsa.org/factsheets/Cunliffe.pdf
  16. http://www.matchinggrants.org/grant388.html
  17. Basic Water Requirements for Human Activities : Meeting Basic Needs Perer H. Gleick, M. IWRA, Pacific Institute for Studies in development environment and security
  18. http://www.icrisat.org/gt-aes/text/Nepal/Nepal-Imgs5.htm
  19. Rainwater Harvesting in Mainland China http://www.eng.warwick.ac.uk/ircsa/factsheets/ChinaRWH.pdf

One thought on “Rainwater Harvesting: A Key to Drinking, Irrigation, Disaster Prevention and Poverty Alleviation in the Mountains of Nepal

  1. I first heard about rain barrels not too long ago from a cookewrr. We are looking into getting our own! During the summer months in Kansas, it can get pretty dry. Usually we have a pretty wet spring. Although the weather has been very messed up so who knows! I love the idea of preserving what the Lord gives us through rainfall and just being less wasteful. Blessings, Nicole

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