Ceylon Journal of Science (Physical Sciences) 19 (2015) 01 – 15 Environmental Sciences
SUSTAINABLE RAIN WATER HARVESTING SYSTEM FOR RURAL COMMUNITY: A CASE STUDY FROM DEDURU OYA BASIN IN SRI LANKA
H.A.H. Jayasena1 and P.B. Kulasekera2
1Department of Geology, University of Peradeniya, Peradeniya, 20400, Sri Lanka.
2School of Environmental Sciences, University of Guelph, Guelph, ON, N1G 2W1 Canada.
(*Corresponding author’s email:).
(Received: 03September 2014/ Accepted after revision: 04 January2015)
ABSTRACT
Rural communities in the dry regions are continuously struggling with the meagre water resources available to satisfy their daily household and agricultural needs. A pilot study conducted among 250 households from Aladeniya, Hedeniya, Weerakodiyana, Rakogama and Chilaw in the Deduru Oya basin during the period from 2002 to 2005 revealed that 80% of their daily needs are met with groundwater obtained from dug wells and tube wells. Approximately 82% of their average per capita daily domestic water consumption of 110 L was utilized for bathing while the remaining 18% was used for drinking, cooking, washing and toilets. The socio economic inputs show that the household income varies from SLRS. 5,000 to 15,000per month. Their willingness to pay for a reliable water supply system is little over 1.5% of their income, which is encouraging but very low to implement a modern water supply scheme. The average annual rainfall is 1600 mm, however geohydrologic environment is not conducive for extensive groundwater extraction. Therefore, rain water harvesting (RWH) systems with simple and affordable technology transfer could be implemented to supplement the existing supply of water without major difficulties. As the baseline survey is indicating a positive approval for a community driven long term RWH program, a combined water supply system operated by alternative energy technologies could be considered for implementation through a community based water supply scheme.
© University of Peradeniya 2015
Jayasena and Kulasekera /Ceylon Journal of Science- Physical Sciences 19 (2015) 01-15
INTRODUCTION
Water shortage within the dry regions in many parts of the world need specific attention since community development and consequent water requirement in these areas is currently thriving. A significant proportion of the world population of 7 billion people (UN day, 2011) is living within the developing dry regions (UNU INWEH, 2009). In United States, approximately 40 percent of its population growth during the period from 1960 to 2000 occurred in its arid and semiarid states (US Census Bureau, 2004). Similar examples could be identified from Middle East
ern countries, Australia, China, Africa and Central Asia (Jiang, 2009; Fayez et al., 2009; Tassabehji, 2011). The water scarcity problem faced by the development activities in such dry regions are characterized by significantly high potential evapotranspiration (ET) which surpass its mean annual precipitation (UNESCO, 1979). However such water scarcity related environmental problems are not similar to the other rainfall related environmental problems observed in the desert regions. The communities in the dry regions mostly depend on availability of resources such as water and food while sustainable measures need to be incorporated as a way forward for then communities to thrive in the desert areas.
In semi-arid environments, water plays a crucial and decisive role for future development. River discharge is expected to decrease substantially under changing climatic conditions (de Wit and Stankiewicz, 2006). Since water supply is highly intermittent, understanding the spatial and temporal variability while predicting the behaviour of water cycle are essential for better water management. Few studies exist on the availability of water in semi-arid mountain ranges (Chaponniere et al., 2005; de Jong et al., 2005a, b). Especially considering the present conditions an analysis of natural and anthropogenic influences on water availability is urgently required. Although water is an important resource in these areas it can also form a hazard in terms of flash floods and high erosion rates. The effects of global warming may accelerate or decelerate the expansion or contraction of the communities in the dry regions depending on the socio-technical initiatives adopted by the modern society.
The Global and Sri Lankan Scenario
The precarious nature of the global water scenario appears to threaten world’s future socio-economic development. World Bank estimates that by year 2030, the demand for water will exceed supply by 40%. UN Water suggests that 1.8 billion people would live in regions already classified as water scarce. Another count indicate that two thirds of the global population could experience water stress by 2025 (uk.oneworld, 2011). In a new ranking among 186 countries, the water stress index rates 17 countries at ‘extreme risk,’ wjhere the Middle East and North African (MENA) nations of Bahrain(1), Qatar(2), Kuwait(3) Saudi Arabia (4) Libya(5), Western Sahara (6), Yemen(7), Israel(8), Djibouti(9) and Jordan(10) topping the ranking (Tassabehji, 2011). Furthermore, in Yemen, the annual per capita water availability is only 200 m3, well below the international water scarcity threshold of 1,700 m3 (Photos and Montanari, 2011). The country is one of the four in the world to have been designated water short. “It is one of the most water-scare countries in the world,” the World Bank stated in 2005 (Tassabehji, 2011).
Sri Lanka is an island located about 50 km away from the southern tip of India between latitudes 5° 55’- 9° 51’ N and longitudes 79° 41’– 81° 53’ E. The island has a central mass of highlands and mountains surrounded by rolling land with rock knobs. The country has an appreciable quantity of fresh water resources to satisfy the needs of its 20 million inhabitants though the dry zone areas are faced with spatial and temporal water shortages (Department of Census and Statistics Sri Lanka, 2011). The annual rain fall varies from a very small amount in the dry lowlands to 5000 mm in the wet hilly regions. The mean annual rainfall varies from less than 1900 mm in the dry zone to more than 2500 mm in the wet zone (Fig. 1). Based on the average annual seasonal rainfall, the country has been divided in to the “dry zone” with rainfall less than 1250 mm isohyet and the “wet zone” above it (Domrose, 1974). However, recent advances based on factor solutions favoured four spatiotemporal rainfall modes – weak southwest (SW) mode (March–April), strong SW mode (May–October), strong northeast (NE) mode (December–February) and mixed mode (November) (Wickramagamage, 2010). The estimated annual per capita water availability is 2300 m3 (Samad, 2005; Imbulana and Neupane, 2003) and it falls well above 1700 m3 which is the Falkenmark national stress indicator value (Falkenmark et al., 1990), demonstrating that the island is under no water shortage. However, recent investigations pointed out that the water stress is high in the dry zone of Sri Lanka and communities are faced with significant water shortages (Amarasinghe et al., 1999) and Sri Lanka was ranked at the 40th position in water stress index according to a recent survey by Center for Environmental Systems Research (2000). Therefore, Sri Lanka would face a water shortage especially during the dry months of the year. However, the annual rainfall received in these areas may be sufficient enough to meet the annual domestic and agricultural requirements of the community, provided that adequate measures are adapted to harvest and manage this rainwater in addition to existing water resources in the region. Therefore, objective of this paper is to investigate the current domestic water needs, possible future water supply options, and the willing to pay (WTP) for a reliable domestic water supply scheme by the rural community in the Deduru Oya basin.
Figure 1: Sri Lanka showing major climatic zones, broader geologic formations and study locations. 1. Weerakodiyana, 2. Rakogama, 3. Hedeniya, 4. Aladeniya 5. Chilaw
METHODOLOGY AND DATA COLLECTION
Four hamlets and Chilaw town from the Deduru Oya basin were selected for this study. A sample of fifty families was randomly selected with the support of the village headmen. A questionnaire was prepared and locally tested before carrying out a detailed field survey during 2003 to 2005 period. The data used in this analysis were collected as a part of a large water management study using a relevant subset of questions and answers in a questionnaire. The questions were based on family income, water usage, willingness to pay for a reliable water supply scheme and who should be given the authority to such an operations. Data were statistically analysed to obtain social indices based on sustainability. The enumerators were asked to select key informants, either from a respectable community or among the educated personnel of the village community, to clearly express the goals of the survey. The inception criteria as discussed above play a catalytic supported at the crucial entry point to the village community when the survey was started. Several teams comprised with a male and a female were employed to carry out the survey. In addition, data on hydrological and hydrogeological framework as well as possibilities on rainwater harvesting were also collected from previous studies and the analysis was used to come up with final recommendations (Singh and Jayasena, 1984; Jayasena, 1989; Jayasena, 1993; Jayasena, 1995; Gangadhara and Jayasena, 2005; Gangadhara and Jayasena, 2006; Jayasena and Gangadhara, 2006; Jayasena et al., 2008).
The study areas and its hydrogeologic environment
The study was conducted in the Deduru Oya basin located is the fourth largest river in Sri Lanka and traverses about 115 km from the headwater in Hedeniya village in the Kandy district and discharges its water into the sea at Chilaw in the Puttalam District. Five areas from the Deduru Oya basin were selected (Fig. 1) on the basis of communities living at different location within the Deduru Oya basin. Chilaw is an urban town with significant fishing community living in and located in the lowest end of the drainage basin. Weerakodiyana is an agriculture based village in the flat lower part of the basin where a more conservative society is living. Rakogama is a more rural village in the NE part of the basin in which elevated dry conditions are prevailed and tank irrigation is practiced. Hedeniya and Aladeniya both are located in the mountainous headwater areas while Aladeniya is considered as a peri-urban town. The demography and ethnic complexion are other criteria we used to select these areas.The basin has tropical humid climate with seasons changing due to monsoonal rains. The daily average temperatures are varying from 22° to 32° C whereas relative humidity changes from more than 80% close to the coastal Chilaw to around 70% in the central mountain mass where Aladeniya and Hedeniya are located. Except Chilaw town, the water supply is mainly through private wells, reservoirs, Dedru oya and its tributaries. However recent advances in development had introduced tube well constructions through many government and donor driven initiatives (Singh and Jayasena, 1984; Jayasena, 1989; Jayasena, 1993; Jayasena, 1995). Even though tube wells provided some relief for these dry regions, it usually depends on the hydrogeological feasibility based on the fracture distribution in the hard Precambrian rocks or the thickness of the regolith and the overburden in the region.
Water Resources in the Deduru Oya
Basin
Water resources in Deduru Oya basin is currently faced with spatial and temporal water scarcity, though aggregate water availability indicates sufficient quantities. The resource can be differentiated into rainfall catch by the web of tanks, surface flow along the network of channels and groundwater. Average annual rainfall is 1609 mm for Deduru Oya basin (Somaratne et al., 2003). Rainfall has a bimodal distribution due to northwest and southeast monsoons (Fig. 2). In the lower plain, a cluster of village tanks distributed in the cascade system and run of diversion canals supplemented the water scarcity.
Deduru Oya starts from mountains in the central region (peaking at 850 m above MSL), and flow through a dissected plateau extending into the NW coastal plain (Jayasena et al., 1986). The estimated discharge varies from 1130 (Amarasinghe et al., 1999) to 1500 MCM/year (ECL, 1999). Several streams contribute to the discharge of the Deduru Oya viz: Maguru Oya, Kimbulwana Oya, Kuda Oya and Kolamunu Oya (Fig. 1). Runoff coefficients for the basin vary from 50 to 83% and runoff ratios vary from 39.8 to 63.7% for Yala (dry) and 50.7 to 80.5% in Maha (wet) seasons respectively (Somaratne et al., 2003). During rainy seasons, it is common to see flash floods overtopping embankments in the lower segments of Deduru Oya. However, during the drought seasons only a trickle passes through, and this situation is clearly indicated by the overall monthly discharge variations (Fig. 3).
Groundwater availability is diverse and spatial and temporal variations are seen in the basin area. The total basin area is 2622 km2, of which about 80% is covered with regolith and alluvium. Bedrock-bearing hinterlands account for the remaining portion of the basin. Contribution from groundwater to the household water requirement is estimated at 57300 m3/day (ECL, 1999). Groundwater occurs mainly in the regolith, alluvium, coastal sands and fractured and fissured hard rocks (Balendran, 1970; Singh and Jayasena, 1984, Panabokke and Perera, 2003). Infiltration of 8% (Athavale, et al., 1980) to 10% (Rai and Singh, 1992; Molden, 1997) of rainfall indicated 840-1050 million m3 of groundwater per annum. However, these values are arbitrary and infiltration varies from 1.6% to 22.8% based on Tritium tracer techniques (Dharmasiri and Dharmawardena, 1980). By measuring the discharges through different water bearing formations, the groundwater availability in the basin have been estimated at 2050 million m3 (ECL, 1999). Deduru Oya basin is not considered to be a hydrologically closed system.
Water balance studies for the basin show water shortage with a value of 333mm (Jayasena, 1998) to excess water as uncommitted out flow with values vary from 683 to 1818 MCM for both Yala and Maha seasons in 1996 and 1997 (Molden and Shakthivadivel, 1999; Somaratne et al., 2003). Current in basin storage in Deduru Oya has been estimated as 22% of the rainfall (Imbulana and Neupane, 2003). As per the forgoing discussions the water resources distribution interact with many environmental factors while significant spatial and temporal influences play a major role controlling availability and supply of water.
Sustainable Water Harvesting Systems for Rural Community
Sustainable water harvesting system supported by community participation could be utilized in a positive manner as to overcome the water scarcity in the dry regions. Recent investigations pointed out that the water security of dry lands in the world is continuously being threatened by haphazard land use patterns and excessive depletion of groundwater resources due to over utilization (Bruins, 2002). Scarcity of water for household consumption and agricultural needs affects the development of rural
Jayasena and Kulasekera /Ceylon Journal of Science- Physical Sciences 19 (2015) 01-15Figure 2: Bimodal distribution of monthly rainfall (mm) at Ridibendi Ela gauging station within the Deduru Oya basin
Figure 3: Mean monthly discharge within 95% Confidence Intervals (CI) given at Chilaw gauging station from 1991 to 1998 (After Jayasena and Selker, 2007)
Jayasena and Kulasekera /Ceylon Journal of Science- Physical Sciences 19 (2015) 01-15communities in many ways. The poor health conditions, and malnourishment linked to food shortages related to crop failures during droughts have raised concerns among the organizations working on food security. In view of the future water and food demands of the world, a clear necessity has stand up to develop and use water resources equitably (van Hofwegen, 2001). This has resulted in more resources being diverted to improve water management efficiency in rural areas where the accessible water resources are scarce. Today the focus on recharging of groundwater reserves, rain water harvesting and encouraging efficient utilization of water in households and agriculture have grown in order to ensure water security among rural communities in dry regions of the world.
Water is a basic human need and efficient management of the resources in all possible ways should be achieved to have more sustainable water supply schemes for the communities around the world. Water availability in many rural areas in the developing world is adversely affected by climatic extremes and social unawareness. The domestic water supply schemes even in the urban areas of these countries are facing with difficulties. The situation in Sri Lanka is same and only a 36% of the urban population in Sri Lanka receives pipe-borne water (DHI, 1999), while in Deduru Oya basin it is only 9% (Imbulana and Neupane, 2003). Therefore, a plausible water management mechanism should be introduced to enhance the domestic water supply schemes under present sociotechnical framework in Sri Lanka. Several possibilities and mechanisms have been proposed in the subsequent sections together with difficulties and problems encountered when implementing such a scheme under present scenario.
RWH systems
Rain water harvesting (RWH) has been popular among the rural communities around the world as a safe source of water supplementing their existing water resources. Evidence of reduced diarrhoea among the communities using rainwater has been observed in developing countries (Garrett et al., 2008). Rainwater collected from rooftops and grey-water generated from households other than toilets are used for non-potable domestic and agricultural water requirements in the rural homes (Zhang et al., 2010). Therefore, a system utilizing a combination of rainwater of acceptable quality and grey-water generated from households may reduce the cost of water in rural households while contributing to conserving existing water resources. However, if not properly managed and maintained cost effectively, these systems might not yield the desired outcome.
Surface Reservoirs and diversion schemes
Surface reservoirs are the key component in the rain fed runoff harvesting system in dry regions of Sri Lanka. These are common in areas where rainfall is generally less than 1800 mm (Fig. 1). About 32000 surface reservoirs have been identified in Sri Lanka out of which more than 18000 located in the dry zone are currently in use (Fernando and Silva, 1984). Water shortage and management problems associated with these systems had been identified. However, even with such water shortage, thriving dry zone agriculture is evident in the north and north eastern to south eastern parts of Sri Lanka. The current water management methods consisting of Irrigation tank cascade systems and large diversion schemes had proved the ability to overcome many water shortage problems in hand.