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Agriculture:- Model Bankable Projects in India Minor Irrigation : Dugwells Part 2

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CHAPTER II : MODEL FOR A SCHEME OF DUGWELLS IN HARD ROCK AREAS 1.0. INTRODUCTION Formulation of a scheme is explained in the subsequent paragraphs taking the case of a model block.The scheme aims to provide financial assistance for construction of 150 dugwells with pumpsets to individual farmers for irrigation development through groundwater sources. These wells would mostly benefit small and marginal farmers in the area where at present irrigation facilities either by surface or groundwater sources are inadequate. Dugwells are the most suitable stuctures for the hydrogeological conditions obtaining in the area and would be constucted by local contractors using conventional methods. Infrastructural facilities like road, powerlines and extension services by the state government are available for successful implementation of the minor irrigation programme.

2.0. SELECTION OF SCHEME AREA The block in the district has been selected to formulate model scheme for minor irrigation development. The block has a geographical area of 17,500 ha of which 14,000 ha are cultivable. It is located 15 km from the district headquarter town. It has an undulating topography and the elevation ranges from 300 m to 400 m above mean sea level . A canal of 9 km length with wetted perimeter of 2.5 m flows for about 90 days during the non-monsoon period. An area of 9200 ha is presently irrigated from canal and 1157 existing irrigation wells. 3.0. SOILS Soils in the scheme area are of black cotton type and suitable for growing jowar, wheat, vegetables and cash crops like sugarcane and groundnut. 4.0. CLIMATE AND RAINFALL The scheme area in general has a sub-humid to tropical climate. The monsoon season extends from mid-June to September end. About 90% of the total annual rainfall of 750 mm occurs during this period only. The average temperature and humidity are 27o C and 65% respectively. The fair weather season extends from mid October to February during which a winter rainfall of about 60 mm is recorded. The temperature during the months of December and January comes down to about 18oC. The hot weather conditions last from March to mid June and are characterised by high evaporation with temperature going upto 36oC. The rainfall pattern varies from year to year and on an average there is a dry spell once in 5 years. As per IMD records, the normal annual rainfall in the area is 760 mm. 5.0. HYDROGEOLOGY The area comprises of basaltic rocks with an aggregate thickness of over 100 m. The individual basaltic lava flows vary in thickness from 10 to 15 m and are made up of alternating massive and vesicular units. The massive units are hard and compact but highly weathered upto a depth of 10 m and are jointed and fractured upto a depth of about 50 m. Vesicular units are generally soft and make upto 30% of the total thickness of individual lava flows. These individual flows are sometimes separated by beds of red clays. Groundwater in the scheme area occurs under water table conditions. The weathered and jointed zones in massive units and vesicular zones are the main water bearing formations. These aquifers are inter-connected forming a type of multi-layered system but show lateral and vertical variations due to heterogenity of aquifers which governs the well yield. Hydrogeologically, aquifers in the scheme area are good and are suitable for construction of dugwells. Their hydraulic conductivity as estimated by the state groundwater department varies from 8 to 12 m/day. Dugwells in the area vary in diameter from 4 to 6 m and in depth from 15 to 20 m. These wells give a discharge of 4 to 6 litres per second for a pumping period of 4 to 6 hours per day for a draw down of 2 to 3 meters. The well recoups by next day. 6.0. GROUNDWATER AVAILABILITY 6.1. Recharge The state groundwater department (SGD) has estimated the available annual recharge by water table fluctuation and specific yield method. This includes recharge from monsoon rainfall and from supplementary sources like canals and tanks, re-cycled irrigation water, non-monsoon rainfall etc. The available recharge as estimated by SGD in the block is given below. Total Annual Groundwater Recharge(ham)4200 Net annual groundwater availability (ham)3780. After allowing for the existing and projected demand for drinking water and industrial use, the balance groundwater recharge available for irrigation is estimated at 3570 ham.

6.2. Draft

Irrigation by electric and diesel operated pumpsets is the common method of groundwater extraction in the area. The average draft of a dugwell with pumpset is about 1.2 ham/year. Thus the total annual groundwater draft is about 1326 ham and is given in Table 1 below.

Table 1. Draft from Existing Minor Irrigation Structures

Sr. No. MI Works Nos Unit Draft (ham) Gross Yearly Draft (ham) Monsoon Non-monso-on Yearly 1 Dugwell 114 0.65 22 52 74 2 Dugwell with pumpset 1,043 1.2 376 876 1,252 Total 398 928 1,326

6.3. Water Balance Net annual Groundwater availability for future irrigation development use is 2244 ham. 6.4. Stage of Groundwater Development The stage of groundwater development is defined by ratio of existing gross annual groundwater draft to net annual groundwater availability and expressed as percentage. From the groundwater estimates by the state groundwater department, the stage of groundwater development in the block is 41%. Further the long term behaviour of water levels in the observation wells as recorded by the state groundwater department, does not show any progressive decline during past 10 years. Accordingly, the block is categorised as white (safe) and new well programme in the block is feasible. 7.0. PHYSICAL PROGRAMME A programme of 150 dugwells with pumpsets is proposed under the scheme. The unit gross draft of a dugwell is taken as 1.2 ham per year. The gross draft works out to be 180 ham, against a water balance of 2244 ham. Thus the proposed programme in the block is feasible. The stage of groundwater development after financing the proposed programme would be within 70% and the block would remain in the white (safe) category. 8.0. SPACING The spacing between two dug wells as based on aquifer performance test conducted by the SGD works out to be 120 m. However, spacing on economic considerations has also been examined. A dugwell with pumpset can irrigate an area of about 2 ha and thus, on economic considerations, the spacing would be 150 m. Thus, spacing between two wells would be kept at 150 m. 9.0. GROUNDWATER QUALITY As per report of the state groundwater department, groundwater in the block shows low values of total dissolved solids (TDS less than 700 ppm) with Sodium Adsorption Ratio (SAR) less than 10. The water is therefore, suitable for irrigation purposes. 10.0. WELL DESIGN In the scheme area a saturated thickness of about 6 m is available in a well depth of 15 m. The water table aquifers in the weathered and jointed zones, vesicular units have good hydraulic conductivity and are capable of yielding about 5 to 6 lps. The state groundwater department has recommended a well of 5m diameter and 15m depth in the scheme area and the same is adopted. Predictably, within this depth, atleast 2 m of water column would be available in the wells during summer season. 11.0. CROPPING PATTERN AND COMMAND AREA The crops grown in the scheme area under irrigated conditions are jowar, wheat, vegetables, groundnut and sugarcane. The command area of a dugwell varies from 1.5 to 2 ha. The well discharge can meet the crop water requirement for such a farm model. The cropping pattern and water requirement for a 1.6 ha farm model are given below in Table 2.

Table 2. Cropping Pattern and Water Requirement

Command Area = 1.6 ha Working Period = 4 hrs/day

Season Crop Area (ha) Number of Irrigations (nos) Irrigation Interval (days) Depth of Irrigation (cm) Kharif Vegetables 0.4 4 20 5 Groundnut 0.8 2 30 7.5 Sugarcane 0.4 4 15 7.5 1.6 Rabi Jowar 0.8 4 30 7.5 Wheat 0.4 6 20 7.5 Sugarcane 0.4 12 12 8.75 1.6 Summer Groundnut 0.4 10 12 7.5 Sugarcane 0.4 12 10 10 0.8

Cropping Intensity 200% Irrigation Intensity 250% 12.0. Discharge Required The discharge required has been calculated from the following formula: Q = ( 28 AxI ) / ( Rxt ) where, A = Crop area in ha I = Depth of irrigation in cm R = Rotation period in days t = Working hours per day Q = Required discharge in lps The discharge required during the different crop seasons is calculated below: KHARIF Q = 28 [ (0.4x5) / (20x4) + (0.8x7.5)/(30x4) + (0.4x7.5) / (15x4) ] = 3.50 lps RABI Q = 28 [(0.8x7.5)/(30x4) + (0.4x7.5)/(20x4) + (0.4x8.75)/(12x4)] = 4.49 say 4.5 lps SUMMER Q = 28 [( 0.4x7.5) / (12x4) + (0.4x10)/(10x4)] = 4.55 lps Considering water losses at 20% (irrigation efficiency at 80%) the required discharge would be: Kharif = 4.4 lps Rabi = 5.6 lps Summer = 5.7 lps The discharge required during the Rabi and Summer season is 5.6 lps and 5.7 lps respectively, say 6 lps. This can be met from the design of well proposed under the scheme. A discharge of 6 lps is therefore taken for selection of pumpset. 13.0. PUMPSET SELECTION A centrifugal pumpset is suitable for installation on dugwells. This type of pumpset, both electric and diesel are also commonly used in the scheme area. The pumpset has been selected as per IS-10804-1994 keeping in view the discharge and the total pumping head and the pump/motor efficiencies as observed from the relevant tables and curves. 13.1. Discharge Required The discharge required is 6 lps for a daily pumping period of 4 hrs. 13.2. Total Pumping Head The total pumping head to meet peak demand (5.7 lps) in summer season is likely to be 15.4 m (apprx) with 65 mm dia GI pipe. This includes total static head, friction losses in pipes, allied fittings, foot valve and offset pipe as per norms on suction and delivery side. The required HP of the pumpset under these conditions works out to be 3.0. This includes 10% additional input to nominal pump input to take care of tolerance on pump efficiency and variation in duty.  Accordingly, pumpsets of 3 HP are considered under the scheme. 13.3. Pumpset Specifications The specifications of the electric pumpset selected for the scheme area are as below: a) Centrifugal Pump Total Head (H) = 16.3 m Discharge(Q) = 6 lps Efficiency (n) = 54% b) Piping System Suction/Delivery pipes = 65 mm Foot valve = 65 mm ( K = 0.8 m) Straight length = 17 m of 65 mm GI pipe Long radius bend (65 mm) = 2 Nos. c) HP of pumpset (electric/diesel) = 3 The complete pumping system would be installed as per IS 10804 - (1994). 14.0. COST ESTIMATE The cost estimate for the well with suggested design is made on the basis of prevalent schedule of rates. The unit cost works out to Rs.37000/-. The cost estimate of the dugwell in the scheme area is given below in Table 3.

Table 3. Cost Estimate of a Dugwell (Indicative Only)

Dia (m): 5 Steining (m) : 0.35 Depth (m): 15 Depth (m) : 4.5 Type : Brick Masonry

S.N.r No Item of Work Qty. (m3) Rate (Rs/m3) Amount (Rs) 1 Excavation a. Soil and Murum (0 to 2.5 m) 116.35 24 2,792.4 b. Hard Murum (2.5 to 4.5 m) 70.47 30 2,114.1 c. Soft Rock (4.5 to 6 m) 29.44 33 971.52 d. Soft Rock (6 to 7.5 m) 29.44 80 2,355.2 e. Soft Rock (7.5 to 9 m) 29.44 85 2,502.4 f. Weathered Jointed Rock (9 to 10.5 m) 29.44 85 2,502.4 g. Hard Rock (10.5 to 12 m) 29.44 165 4,857.6 h. Hard Rock requiring blasting (12 m to 15 m) 58.40 185 10804.0 28,899.62 2 Steining a. Lining in Cement Mortar (1:6) 0.35 m thick upto 4.5 m 26.46 201 5,318.76 b. Lining in Cement Mortar (1:6) for parapet wall of 0.90 m 5.30 201 1065.30 3 Dewatering During Excavation LS 1,500 7,884.06 Total cost of well 36783.68 sayRs.37000/- 4 Pumphouse 2.5 m x 2.5 m x 2.1 m 7000 5 Pumpset 3 HP (electric/diesel) pumpset conforming to ISI standards including accessories, piping system,transportation and installation charges etc.

The above unit cost is as approved by NABARD regional office Unit Cost Committee. 15.0. TOTAL Financial Outlay The unit cost of a dugwell with 3 HP pumpset is Rs.59000 (Rs.37000 + Rs. 7000 + Rs.15000). The financial outlay of the scheme for 150 dugwells with pumpsets is Rs.88.50 lakhs. 16.0. Economics The scheme economics is given in Annexures III and IV. It is seen therefrom that the net incremental income is Rs.26,870 per year and the IRR works out to be 49%. Thus, the scheme is considered economically viable. 17.0. INFRASTRUCTURAL FACILITIES Adequate extension services are available in the scheme area. The beneficiaries having irrigation facilities have adopted modern cultivation practices. A good net work of low tension/high tension power lines exist and energisation of pumpsets can be expected without any delay. A sugar factory is located in the nearby block and marketing of sugarcane produce will not be a problem. A market yard exists within 3 km for marketing the agricultural produce and there are good all weather roads for transport of agricultural produce. 18.0. Supervision and Technical Guidance The technical officer of the sponsoring bank would look after the supervision and implementation of the proposal and also extend technical guidance wherever necessary. 19.0. Lending Norms Majority of beneficiaries (70%) are in the small and marginal farmers category. 20.0. Repayment Period For small and marginal farmers, the loan repayment period of a dugwell would be 11 years excluding a gestation/grace period of 23 months and for pumpset 9 years. The beneficiary may, if he so desires, repay the loan instalment with interest earlier than the stipulated period. For other farmers, the loan repayment period would be 9 years. 21.0. Rate of Interest The present (2003-04) refinance rate to the financing bank for minor irrigation investments is 5.50% for NE region including Sikkim, A&N Island, whereas for other regions, it is 5.50% and 6.25% respectively for loansizes upto Rs. 50.000/- and above Rs. 50,000/-. The minimum down payment would be 5%.

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