Agriculture:- Model Bankable Projects in India | Minor Irrigation : Tubewells Part 2 --- www.nabard.org
| CHAPTER- III LLUSTRATIVE MODEL FOR SCHEME OF 'SHALLOW TUBEWELLS IN ALLUVIAL FORMATIONS'
2.1 Introduction
Formulation of a scheme is explained in the subsequent paragraphs taking the case of a model block.The scheme gives details about availability of groundwater, its present stage of development, existing number and type of minor irrigation works with a view to finance construction of additional shallow tubewells in private sector in the block for development of minor irrigation.
The block is located in the Indo-Gangetic alluvial terrain. The total geographical area of the block is about 16,739 ha. It has a flat topography with elevation ranging from 200m to 220m above mean sea level. Certain parts of the block are already provided irrigation facilities through surface and groundwater sources. A canal of 110 km total length with average wetted perimeter of 8m in the block flows for about 120 days during the non-monsoon period. The canal length in the block is about 48 km.
2.2 Soil
In the scheme area the soil is mostly sandy loam. It also has large patches of clayey loam. Wheat, paddy, maize and gram are generally grown in the area.
2.3 Climate and Rainfall
The climate of the area is typical of the North Indian sub-continent. It is characterised by large seasonal fluctuation in temperatures.A temperature of about 400 C is common between April to June and about 80 C between December to January. The normal yearly rainfall in the scheme area is about 1060 mm out of which 930 mm (89%) is received from South West monsoon during the monsoon period from June to September and 129 mm during the non-monsoon period (winter rainfall) from November to January.
2.4 Hydrogeology
2.4.1 Exploration Data
Quaternary alluvium of considerable thickness occurs in the area. Exploratory drilling carried down to a depth of 450 metres have not indicated presence of any bed rock. The alluvial complex principally consists of fine to medium sand, silt and clay. Beds of gravel or very coarse sand are uncommon. Kankar, an impure deposit of calcium carbonate of secondary origin, is very often associated with the sediments. The finer parts of alluvium generally consist of sandy or silty clay. Thick horizons of pure clay are uncommon.
The lithology of alluvium, as inferred from the study of lithological and geophysical logs show heterogeneous character of sediments in the transverse and downstream directions. Clay zones are distributed at random. Although there are local concentrations of fine grained sediments of considerable thickness, individual strata are generally lenticular and have little horizontal or vertical continuity.
Two major aquifer systems separated by silty clay are encountered within 100m depth. The first aquifer, developed extensively by private tubewells, occurs in the depth range of 15 to 45 m. It has an average thickness of about 12 m. The second aquifer occurs in the depth range of 50 to 95m. Deep tubewells constructed by the State government tap this unit. The lower aquifer is separated from the upper one by a thick confining clay layer. Shallow tubewells in the top aquifer are capable of giving a discharge of about 8 lps at a drawdown of about 3m. The average hydraulic conductivity of unconfined aquifers as estimated by the SGD is about 30 m per day and the radius of influence is about 100m.
2.5 Groundwater availability
2.5.1 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) 6200
Net annual groundwater availability (ham) 5580.
After allowing for the existing and projected demand for drinking water and industrial use, the net annual groundwater available for irrigation is estimated at 5270 ham.
2.5.2 Draft
The existing gross annual groundwater draft for all uses in the block,as estimated by the state groundwater department is 2742 ham.
2.5.3 Water Balance
Net annual groundwater availability for future irrigation development is estimated by the state groundwater department as 2560 ham.
2.5.4 Stage of Groundwater Development
The stage of groundwater development is defined by ratio of existing gross annual groundwater draft for all uses to net annual groundwater availability and expressed as percentage. From the above groundwater estimates by the state groundwater department, the stage of groundwater development in the block is 49%. 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 technically feasible.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.5.5 Physical Programme
A programme of 300 shallow tubewells with pumpsets is proposed under the scheme. The unit gross draft of a shallow tubewell is taken as 1.5 ham per year. The gross draft works out to be 450 ham, against a water balance of 2560 ham. Thus the proposed programme in the block is technically 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.
2.6 Groundwater Quality
As estimated by the State Groundwater Department the electrical conductivity of groundwater in the scheme area is 1500 micro mhos/cm and the Residual Sodium Carbonate 1.5 ppm. Therefore, groundwater in the scheme area is of good quality and suitable for all crops.
2.7 Spacing
In the area, the spacing norm between two shallow tubewells is 150 m as prescribed by the State Ground Water Department, and the same would be adopted in the scheme area.
2.8 Well Design
In the scheme area, an aquifer thickness of about 12 m in a boring depth of about 45 m is available. Therefore, shallow tubewells of 45m depth with strainer length of 12 m would be provided. The diameter of wells would be 100 mm and they would be capable of giving a discharge of about 8 lps.
2.9 Cropping Pattern and command Area
The irrigated crops in the scheme area are paddy, maize, wheat, potato and gram. The average available command area with the farmers in the scheme area is about 1 ha. The cropping pattern and water requirements for a 1 ha model are given inAnnexure II. The peak discharge required during the Rabi season is 2.5 lps. This can be adequately met from the well designed for the scheme area (in fact, as indicated above, it is capable of giving upto 8 lps). The discharge of 2.5 lps is also taken for selection of an appropriate pumpset.
2.10 Pumpset Selection
A centrifugal pumpset would be suitable for installation on shallow tubewells. This type of pumpset is also commonly used in the scheme area. The pumpset has been selected keeping in view the discharge and total pumping head.
a. Required discharge
The discharge required is 2.5 lps for an average daily pumping period of about 6 hrs. on the days of irrigation.
b. Total Pumping Head
The total pumping head including static head, lowering of water level during pumping (drawdown) and friction head losses will be 16.5 m. The friction losses are considered as per norms i.e. not exceeding 10% of the total static head.
For the groundwater regimen prevalent in the area, the total pumping head is calculated as under.
Peak water requirement period Rabi
Total static head (m) 12.5
Drawdown (m) 3.0
Friction losses in pipes, valves etc.(m) 1.0
Total 16.5
Therefore a pumpset for a discharge of 2.5 lps and total head of 16.5 m has to be selected.
c. Horse power of the prime mover
The horsepower required after taking into consideration the pump efficiency as 50% and for discharge and head as indicated above is calculated below :
HP =(Q x H) / (75 x e)
Where
Q = discharge in lps
H = head in meters e = pump efficiency in fraction
2.5 x 16.5
HP = -------- = 1.1 75 x 0.5
add 40% extra cushion for diesel pumpset
HP = 1.1 + 0.4 = 1.5
However, from practical considerations including that of market availability,it is proposed to provide 5 HP diesel pumpset (If electricity is available, a 3 HP electrical pumpset may be provided wherever required).
The specification of complete pumping system selected for the scheme should be as per BIS:10804. The details are as follows
1. Centrifugal pump
Discharge (Q) = 2.5 lps
Total head (m) = 16.5 m Efficiency = 50%
2. HP of diesel engine = 5
3. Suction pipe = 100mm
Delivery pipe = 100 mm
Reflex valve = 100 mm other accessories = as per requirement | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.11 Cost Estimates
The cost estimates for the suggested shallow tubewell design are indicated below as per prevalent rates. The unit cost for the shallow tubewell and pumpset works out to Rs.36200.00. The cost of pumphouse may be considered as an optional item.
Diameter (mm) : 100 Type : PVC Strainer well
Depth (m) : 45 Plain pipe : 33 m Slotted pipe : 12 m | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||
2. RCC pit for installation of centrifugal pump : 6.5 m depth
(RCC rings 1.25 m dia. x 0.6 m height) @ 800/- per m depth 5200.00
3. Diesel Pumping system @18000/- 18000.00
Belt, shaft and pully arrangement 2000.00
Hence, the total cost of Shallow Tubewell with pumpset will be Rs. 36200.00
Optional Structure
Pump house (2.5m x 2.5m x 2.1m) @10000/- per unit Rs. 10000.00
2.12 Financial Outlay
The unit cost of a shallow tubewell with 5 HP Diesel pumset is Rs.36200.00. The total financial outlay of the scheme of construction of 300 shallow tubewells with pumpsets would thus be Rs.108.60 lakhs.
2.13 Economic Analysis
The same has been done as per details below.
2.13.1 Interest Rate for Ultimate borrowers
Banks are free to decide the rate of interest within the overall RBI/NABARD guidelines. However, for working out the financial viability and bankability of the model project, we have assumed the rate of interest as 12% p.a.
2.13.2 Repayment Period
The repayment period of loan for pumpset may be kept as 9 years, and for shallow tubewells, 11 to 13 years excluding 11 months grace period. However,for the purpose of this model project, 12 years has been taken.
2.13.3 Security
Banks may take a decision as per the RBI guidelines.
2.13.4 Pre and Post Development Incomes
The annual incremental income works out to be Rs. 12,480/-.The details are indicated in Annexure – III.
2.13.5 Projected Cash Flows
The discounted cash flows are indicated in Annexure – IV , from where the following values of BCR,IRR and DSCR are observed.
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||
2.14 Interest Rate for Refinanace from NABARD
As per circulars of NABARD issued from time to time.
2.15 Supervision and Monitoring Arrangements
The financing bank has the necessary staff to give guidance to farmers in regards to long term and crop loans. Services of the concerned government department would also be availed for successful implementation of the programme.
2.16 Availability of Technical and Extension Services
The bank shall ensure that all technical conditions stipulated by NABARD under the scheme would be followed during the scheme implementation. The services of State groundwater department and state agriculture department are also available as and when required.
Agriculture Extension Officers at block level would provide necessary extension services to farmers through village level workers and gram sevaks by arranging camps and through audiovisual aids. This would include extension services for agronomical practices, crop-calender, fertilizer, pest control and marketing.
The following general guidelines would be followed for selection of site of Shallow Tubewells :
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||
No comments:
Post a Comment