The following general information’s are required for designing a drip irrigation system:
- WATER SOURCE:
The source of water is usually a well or a tank storing rainfall runoff.
- TYPES OF CROPS:
Different crops required different plant spacing and irrigation requirement. The general layout of the system and especially the emitter were depending on the type of soil and type of crop.
- TOPOGRAPHIC CONDITION:
It is necessary to know the general land slope determine the size and location of mainline and sub main.
The soil infiltration rate, water holding capacity, texture and structure and bulk density must be known when selecting emitter type, determining spacing and setting up irrigation schedules.
- CLIMATE RECORDS:
The climatic records will show when and how often irrigation is needed in various season of the year.
STEPS IN DESIGN OF DRIP SYSTEM AT FARM
- SELECTION OF DRIPPER
- SELECTION AND DESIGN OF LATERAL
- SELECTION AND DESIGN OF SUB-MAIN
- SELECTION AND DESIGN OF MAINLINE
- SELECTION OF PUMP
- SELECTION OF DRIPPER:
The selection of type and number of drippers per plant, is based on Peak water requirement of crop and soil type. Consideration for dripper selection- an ideal of perfect emitter would meet that following four objective. 1. It should be compact, serviceable and inexpensive to keep the system cost low. 2. It should have relatively low discharge to keep the system cost low. 3. It would not vary significantly with pressure this will give good uniformity of distribution.
- SELECTION AND DESIGN OF LATERAL:
Lateral carries water from sub –main and feeds to drippers. Generally one lateral for each row of orchard plant and one lateral for two rows of vegetables is used. The size and length of lateral is decided by using poly plots.
- SELECTION AND DESIGN OF SUB-MAIN:
PVC pipes of size 40 mm X 8 kg/cm2, 50 mm X 6kg/cm2, 63 mm X 4 kg/cm2 , 75 mmX 4 kg/cm2 can be used as a Submain.
- DESIGN OF MAINLINE:
The size of mainline is decided by referring the PVC friction loss chart, All PVC pipes for irrigation are outer diameter controlled.
Pipe mm = Size inch = Class = Flow lit/sec = Range = lit/sec
- 20 = 1/2 = 4 = 0.07 = 0.13
- 25 = 3/4 = 4 = 0.13 = 0.25
- 32 = 1 = 4 = 0.25 = 0.50
- 40 = 1 and 1/4 = 3= 0.50 = 1.0
- 50 = 1.5 = 3 = 1.0 = 1.8
- 63 = 2 = 2 =1.8 = 3.0
- 75 = 2.5 = 2 = 3.0 = 5.0
- 90 = 3 = 2 =5.0 = 8.0
- 110 = 4 = 2 = 8.0 = 15.0
- 140 = 5 = 2 = 15.0 = 20.0
- 160 = 6 = 2 = 20.0 = 30.0
- 180 = 7 = 2 = 30.0 = 40.0
- 200 = 8 = 2 = 40.0 = 50.0
Pressure rating of pipe is determined by PVC material used and dimension ratio. They are generally available in class 1 to 4 corresponding to 2.5, 4.6 and 10 kg /cm2.
- SECTION PUMP:
Total head= (Suction + Delivery) + filter losses + Mainline loss + Operating of drip irrigation system + fruiting loss + Ventury head+ elevation difference. Where, Suction head is the vertical distance between water level to the center of pump. Delivery head is the vertical distance between the centres of pump to the outlet.
Filter loss are assumed to be 2m for screen filter and 4m for sand plus screen filter. Operating pressure is approximately 1kg/cm2 at the last dripper of lateral.
Filter loss: assumed 2m. Ventury loss assumed to be 5 m. Elevation = Upward slope of ground.
Note: Downward slope of mainline and plot should be considered while calculating the total head of the pump.