K.L.L. Premanath (7219127)

Tissa Liyanapatabendi (7219130)

English

Loughborough University Institutional Repository

PLENARY SESSIONS: PREMANATH and LIYANAPATABENDI1120th WEDC Conference Colombo, Sri Lanka, 1994AFFORDABLE WATER SUPPLY AND SANITATIONGroundwater depletion due to agrowellsK.L.L. Premanath and Tissa Liyanapatabendi, Sri Lanka.NATIONAL WATER SUPPLY & Drainage Board with financialand consultancy (COWIconsult) assistance from DANIDAcarried out a study to prepare a Master Plan Report onwater and sanitation needs of the Anuradhapura Districtduring February 1992 to March 1993. AnuradhapuraDistrict is located in the dry zone of Sri Lanka having anaverage annual rainfall of about 1200mm. Main occupationof the people in the district is agriculture.The ground water in Anuradhapura District is pres-ently being used for both domestic and irrigation. Waterfor irrigation is pumped from agrowells. However, therecharge of groundwater from infiltrated rainwater setsthe limits for how much water that can be extractedannually. There were 5720 agrowells constructed withinthe district by the end of year 1992. Out of these anestimated 2500 nos were private wells whereas the re-maining wells have been constructed with governmentsubsidies. A detailed study was carried out to monitoragrowells in the district with respect to the fluctuation ofwater levels and varieties in the chemical qualities.Methodology used in the study of agrowells are (a)Field survey of agrowells collecting technical and agricul-tural data (b) Interviews with agricultural authorities anddistrict administration (c) Establishment of a data base (d)Analysis of data.179 nos of agrowells, covering the whole district wereidentified for monitoring purpose. Data collected fromwells show that a typical agrowell is 6.4m deep, has adiameter of 5.4m and a mean water level 3.5m belowground level. Over the year the water level varies be-tween 1.9m and 5.0m below ground level. It is con-structed by the owner by hand/mechanical digging andis lined on the inside by cement blocks or bricks. Con-struction cost excluding own labour and pump has beenabout Rs. 29000.00. Pump capacities vary typically be-tween 27m3/hr and 45m3/hr.The government of Sri Lanka commissioned the agri-cultural development authority (ADA) through the Min-istry of Agriculture Development and Research to imple-ment a nationwide agrowell programme. Hence, theADA started implementation of an agrowell programmein Anuradhapura District in 1989. Although the aim of theprogramme has been to assist farmers to cultivate crops atand around their homesteads and in highland areas wherecultivation depends on rainwater, it is however now seenthat farmers establish agrowells to support paddy culti-vation in areas, where it is felt that gravity irrigation fromthe tanks needs supplementing.In Anuradhapura district three different implementa-tion modes are in existence. They are implementation ofthe nationwide programme supported by either ADA,the programme supported by the provincial council of theNorth Central Province, and  there is a substantial numberof agrowells being established privately without relationto the official programmes. The number of agrowells andthe plans for further well construction at the end of theyear 1992 are given in table 1.It appears from above that a substantial number ofagrowells have been already established. Further, alltrends point in the direction of a considerable economicsuccess for the programme and it must be assumed thatwells may be established at a minimum, at the same rateas planned for 1993.The beneficiaries of the programme are to a large extentthe poor peasants who used to cultivate a single season(Maha) with rainwater and abandon the Yala cultivationdue to inadequacy of irrigation water (Ariyabandu 1989).Even the maha crop was subjected to severe water short-age towards the end  of the season. Today these farmersare benefitting from full cultivation seasons and in a fewcases even a short third season between two major sea-sons. The cultivation comprises of cash crops such aschillies, Bombay onions, Red onions and vegetables asindicated by  the field survey. Farmers with agrowellshave increased their income substantially and in somecases up to ten times. Peasants who often had to migrateas labourers are now full time employed in their cultiva-tion areas. Incomes in the range of Rs 20000.00 to Rs40000.00 per season per acre have reportedly been gener-ated.The development of agrowells takes place in a ratherhaphazard way without a general assessment of thehydrogeological environment, the possible yield and arational siting.In order to assess the sustainability of agrowells and thepossible conflicts with other water demands a roughevaluation of the irrigation water requirements was madebased on the most common cultivation such as Chilliesand Bombay onions. Water requirement from agrowellcalculated on the basis of crop evapo-transpiration fig-ures  from development of agriculture and crop factors atvarious growth stages is given in table 2.Sustainability of the system of lift  irrigation usingagrowells as the source depends on the recharging of thegroundwater resource and the variations in recharge overthe years. The recharge depends fully on the hydrologicalPLENARY SESSIONS: PREMANATH and LIYANAPATABENDI12Table 1. Present number of agro-wells constructed and planned (Ada, Anuradhapura district).Year of Agricultural Provincial Private (estimate)construction development authority councilBefore 1990 100 1591990 159 2381991 919 3401992 1005 300Plans for 1993 1000 400Subtotal 3,183 1,437 2,500TOTAL 7,120regime and the soil conditions. The recharge may differfrom the highland areas to the valley bottoms, where thepaddy cultivations are found.Potential conflicts are many when there is an over-exploitation of the groundwater resource either on thelocal or on the regional scale taking place. Indiscriminategroundwater withdrawal will cause depletion ofgroundwater reservoirs. This will first be observed as afalling groundwater table, a perceived need to deepen theagrowells and a high frequency of wells running dry. Theagrowells will interact and the deepest will deprive theother wells of water. Drinking water wells will likewiserun dry and natural rivers and streams will suffer fromextended dry spells.Master Plan Study calculations show that for each acreirrigated there has to be 34 acres where recharge takesplace in order to have a sustainable situation in highlandareas. Similarly for low land areas corresponding area is17 acres. The table 3 summarises the calculated rechargeand the consequences in terms of maximum numbers ofstandard agrowells.Under the assumption made,it appears that safe numberof agrowells has been vastly exceeded as most develop-ment has taken place in the highland areas. It must beexpected that serious depletion problems will occur andthat agrowells will frequently run dry. They will affecteach other in such a way that the deepest wells will makethe other wells run dry. Further, nearly domestic waterwells will also be drying up. There is thus an urgent needto bring the situation under control in order to avoid asituation like that in Tamil Nadu, where indiscriminatesinking of agrowells has caused a permanent depletion ofthe ground water resource. From the results of the datacollected for the Master Plan, the  figure 1 shows thedecline in ground water level if present level of construc-tion and use continues and if new construction of agrowellsis stopped (Freeze).Based on the very serious consequences that the contin-ued pumping from the agrowells will have, the situationmust be brought immediately under a tight control. Pres-ently there is nothing to stop a farmer on private landfrom exploitingthe national groundwater resource at his will.The following immediate steps are recommended.• An urgent freeze of subsidies.• An urgent programme of registration of the details ofall agrowells, location, the irrigated area, pumping,etc.• An urgent implementation of a ground water levelmonitoring programme in areas with clusters ofagrowells.• Immediate enforcement of criteria for distance be-tween wells.• Identification of legal framework for intervention inparticular regarding privately constrcuted agrowells.• Implementation of a regulatory system of water rights.• Attaching responsibility for allocation of water rightsto an independent agency which should also act as asupervising agency.• Draw up standard construction details for agrowellsthat limits the rate of groundwater abstraction.• Agricultural agencies should be instrumental in ad-vising farmers on the optimal use of the water with-drawn and should collect information on the con-struction and use of agrowells.ReferenceMaster plan for water supply and sanitation Anurad-hapura district - June 1993.PLENARY SESSIONS: PREMANATH and LIYANAPATABENDI13Table 2. Water requirement from source (AGRO-WELL) for most common crop(figure in mm).MAHA YALACrop water requirementA=ETxkc 703 916B =Application Efficiency 55 % 55 %C = Conveyance  Efficiency 80 % 80 %Water requirement at sourceD=A/B/C 1597 2082R = rainfall 970 477E = Rainfall Efficiency 70 % 70 %Effective rainfallF=RxE 679 334Water Requirement at sourceadjusted for effective rainfall W=D-F 918 1748Figure 1. Decline in ground water level of construction and use continue and if new construction ofagro-wells is stopped (freeze).Table 3. Summary of recharge and “safe” number of wells assuming a cultivable highland area of 30,000 ha(75,000 acre) where agro-wells can be established and that agro-wells are desirable also within the presentlyirrigated lowland area.Highland (30,000 ha) Lowland (irrigated are 110,000 ha)Recharge 54 109Required ratio between recharge area and irrigated area 34 17Maximum no. of “standard” agro-wells (0.81 ha) 1090 7971Present no. of “standard” agro-wells (0.81 ha) 7,120(4,272 in highland and 2,848 in lowland)

Groundwater depletion due to agrowells

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Groundwater depletion due to agrowells

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