Model Lift Irrigation Scheme (Lecture notes by Dr.S.S.Rao) Contents 1. Introduction... 2 2. Guideline lines for small lift irrigation schemes.... 3 2.1. Lift irrigation on surface water... 3 2.1.1 Size and Location... 3 2.1.2. Command Area / Cropping Pattern... 3 2.1.3 Design... 3 2.1.4. Water Availability... 3 2.1.5 Water Lifting Permission... 3 2.1.6. Soil Characteristics... 3 2.1.7. Power... 3 2.1.8. Civil Works... 4 2.1.8.8. Pumping Machinery... 6 2.1.8.9. Number of Stages... 7 2.1.8.10. Project cost... 7 2.1.8.11. Command Area Map... 7 2.1.9 A typical design of small lift irrigation scheme on surface water... 7 2.2 Groundwater based small lift irrigation schemes... 8 1
1. Introduction A conventional lift irrigation scheme consists of civil works like intake well, intake pipe, jack well, pump house, rising main and distribution system to suit the command area. The lift irrigation schemes can broadly be grouped as Medium / large and single stage and large & Medium with multi stage pumping systems wherein water is pumped more than 50 m height and have a command area more than 40 ha. Small river lift irrigation schemes whose cultural command varies between 10 and 40 ha with a total head of less than 50 m of single stage pumping and which do not require conventional civil works like intake well, intake pipe, jack well, pump house are more user friendly and can be operated by the local farmers themselves without much problem. Generally, the lift irrigation systems have to be designed as per the field requirements considering the land and water availability, the people s participation and their requirement etc. However, it is necessary to design a few models for easy physical and financial planning and making people involve in their projects. Brief guidelines are given below for model small lift irrigation scheme. 2
2. Guideline lines for small lift irrigation schemes. The following guidelines are prepared which would facilitate in designing as well as appraisal of such schemes. These guidelines are only indicative and could be modified to suit the local conditions. 2.1. Lift irrigation on surface water 2.1.1 Size and Location The cultural command area should be restricted up to 20-40 ha only under small lift irrigation schemes. Lift irrigation schemes on surface water source with command area more than 40 ha may be considered as medium / large schemes and the technical and financial appraisal may be carried out as as per the guidelines pertaining to large lift irrigation schemes. The scheme area should be as close to source of water as possible and land holdings are contiguous as far as possible from design optimization point of view. 2.1.2. Command Area / Cropping Pattern The command area has to be demarcated and as far as possible to be adjoining. The cropping pattern has to be fixed and water requirement has to be estimated. 2.1.3 Design The design discharge for small lift irrigation scheme should be assessed based on peak water requirements for envisaged cropping pattern and area of crops during kharif, rabi and summer seasons based on water requirement norms. 2.1.4. Water Availability It is necessary to ascertain the availability position of water from sources like river, canal, ponds, tanks or any other surface water body. It should preferably be perennial in nature and should have adequate flow to support the quantity of water to be pumped for the proposed scheme. 2.1.5 Water Lifting Permission Water lifting permission should be obtained for private individuals or societies from Government Department authorized to issue such permissions. The water lifting permission should indicate the period, area and percentage of different crops in each season. Long duration water lifting permission is required if the implementing agency desires to take loan. 2.1.6. Soil Characteristics Soil characteristic should broadly be known for its suitability for various crops proposed in the scheme. 2.1.7. Power Normally the power availability for large schemes is considered to be 16 hours per day but in case of small lift irrigation scheme up to 40 ha command area, power availability may be considered at maximum of 12 hours. If the command area is less than 10 ha then 8 hours of power supply can be considered on economic considerations. 3
2.1.8. Civil Works 2.1.8.1 Intake Well This is a civil structure required for guiding the water in the sump well / jacks well. In some cases, this structure is necessary even for small schemes to take care of water level fluctuations in the river. It also provides silt free water for the pumping operations. However, for small lift schemes, this need not be insisted upon. 2.1.8.2 Intake Pipe This structure is not necessary for small schemes. 2.1.8.3 Jack Well and Pump House This structure is not necessary for small schemes 2.1.8.4 Suction Pipes for Pump set The following table may be followed in determining the diameter of suction and delivery pipes for various discharge ranges: (lps) Diameter of Suction pipe 5 65 10 80 15 100 20 125 30 150 50 200 100 300 (NABARD) 2.1.8.5 Rising Main Rising main should be designed based on discharge and total pumping head. It is expected that the total pumping head in normal cases will not exceed 50m. The total length of the rising main should not exceed 3000 m. The diameter of rising main recommended for RCC pipes and Rigid PVC pipes for various discharges are given below: 4
(a) RCC Pipes (lps) Dia (lps)* Dia 5 100 55 300 10 150 60 300 15 200 65 300 20 200 70 300 25 225 75 300 30 225 80 300 35 250 85 350 40 250 90 350 45 250 95 350 50 250 100 350 *(lps = litre per second) (b) Rigid PVC Pipes (lps) Dia (lps) Dia 5 90 45 225 10 125 50 250 15 150 55 250 20 150 60 250 25 200 65 250 30 200 70 300 35 200 75 300 40 225 80 300 If direct tapping on the rising main is proposed for drawing partial discharge then such tapping should not exceed 2 numbers. Water hammer control devices in case of large schemes are necessary but in case of small lift irrigation schemes, it may not be required. However, the accessories like air valve, drain valve may be provided as per the topographic conditions. Apart from the PVC and RCC pipes, HDPE and AC pipes of equivalent class and diameter can also be allowed. Cast Iron (CI) and Mild Steel (MS) pipes are not recommended except for road crossing and nala crossing. 5
2.1.8.6. Delivery Chambers The delivery chamber of one minute retention capacity can be provided for release of water in the command area. 2.1.8.7. Distribution System Generally a chak size of 8 ha may be considered while designing the distribution system. If scheme economics does not permit use of underground pipes then open channels can be provided. For schemes up to 8 ha. command area only open channels need be provided. 2.1.8.8. Pumping Machinery Most of the small lift irrigation schemes require centrifugal pump sets for pumping surface water / groundwater. In case the fluctuations between low water level and high flood level is less than 4.5 m, then the puppets can be placed in the pump house subject to suitability of site conditions. If the pump sets are to be operated with shifting arrangements then it should not exceed 20 HP per unit. The permanent pump house can be provided if the water level in the river is more or less constant throughout the year. This may vary from site to site depending upon the stream hydrology. The centrifugal pump sets selected should conform to BIS standard i.e., IS:10804-94 for Complete Pumping System. The usual formulae that may be applied for calculating the horse power of the centrifugal pump sets and discharge required to be pumped are given as under: (a) Break Horse Power BHP = (Q x H) / (75 x e) Where, BHP = Break Horse Power of the Centrifugal Pump set Q = in liters per second H = Total Head in meters (including friction losses) e = Overall efficiency of Pump set (as percentage) (b) required to be pumped: The discharge required for the envisaged command area may be calculated from the following formula: Qr = (28 x A x I) / (R x t) Where, Qr = Required discharge in litres per second (lps) A = Crop area in ha I = Depth of irrigation in cm R = Rotation period in days t = Working hours per day The discharge required to be pumped during different crop seasons can be calculated for kharif, rabi and summer seasons and the peak discharge i.e., maximum discharge should be adopted as the required discharge (Qr). 6
2.1.8.9. Number of Stages From the management point of view, the number of stages should not exceed two. Especially small lift irrigation projects, as far as possible, there should be only single stage pumping. 2.1.8.10. Project cost The project cost of the scheme should be based on the schedule of rates prevailing in the area. 2.1.8.11. Command Area Map A map of the command area showing layout drawing of civil works should be attached to the scheme along with a longitudinal section (L Section) for rising main indicating the Low Water Level (LWL), High Flood Level (HFL) position of fixed foundations, pump set, etc 2.1.9 A typical design of small lift irrigation scheme on surface water A typical design of small lift irrigation scheme on surface water body is given below. The details of the scheme are as under: Basic details of the lift irrigation scheme Details Quantity Command Area (Ha) = 20 Cropping Pattern (ha) Kharif: Rabi: Summer Paddy = 10 Makai= 10 Wheat 8 Gram 5 Makai 2 Makai 5 Static Head (m) = 50 Length of rising main (m) = 3000 No of pumping hours (hrs) 12 The required design is as under: Max discharge (cum/hr= 52.778 Total Head (m) 69.68 Hp of pump sets = 27.24 No of pump sets= 2 Diameter of rising main (m) 0.143 Class of pipes = varies from 2.5 kg to 8 kg of different lengths. 7
Other details are shown in the design. The design varies depending on various factors like, command area, static head, length of rising main, cropping pattern etc. The actual design should be based on the field conditions. 2.2 Groundwater based small lift irrigation schemes If the lift irrigation scheme is proposed on the sub surface flow in a given alluvial/ hard rock formation then the intake well has to be designed as per the design criteria adopted for a dug well determined on the basis of aquifer characteristics. If the source of water is an existing irrigation well, the well discharge and command area to be adopted under small lift irrigation scheme could be similar to one that is as usually considered under a dugwell scheme. For schemes, contemplating well discharge of more than 6 lps in hard rock and 10 lps in alluvial areas, the availability of groundwater from such dug wells has to be ascertained from local groundwater department including stipulations of spacing criteria and clearance of scheme based on categorization of blocks/watersheds etc.. 8