Hello everyone,
After my first post on basics of drip irrigation design, Now I am going further to technical aspects of drip irrigation design and another method to draw a drip irrigation design for a field.
Before deicide a particular drip irrigation design for any field one have to take several points in to consideration. This points are,
- Head (mtr)
- Discharge (Q) of the water (m3/hr.)
- Irrigation Rate (mm/hr.)
- Irrigation Time for one shift (hr.)
- Water requirement in Field/ No. of Shifts a day
- Area Flow (m3/hr.)
- Irrigation time for one shift
- No. of shifts a day
Now I am proceeding to the further details,Note: I’ve explained the meaning of all the above aspects in detail in my previous thread.
1.Total Head (mtr):
Head contains various aspects like, suction of the pump, delivery and availability of water etc.
So first you have to calculate the head for operating your drip irrigation system. You can calculate it by the following method,Total Head = Head of System + Depth of water level (mtr) + Distance of water source from the field
Where, System Head = Suction + Lift + Head of Pipes (main & sub main) + Head of Lateral
2. Discharge Q (m3/hr):
It is the water available from the main water source. We can calculate it by the following formula,
Discharge (Q) = Motor HP X 75 X Pump Efficiency (%)
--------------------------------------------
TOTAL HEAD (mtr)
Where,
- Pump efficiency (%) = 50 to 60 (if using electric motor)
- Pump efficiency (%) = 60 to 65 (if using submersible pump)
“Please note that the discharge we can get from the formula above is approximate. The actual flow may vary according to water availability in the particular season.”
3. Irrigation Rate (mm/hr):
Irrigation rate is the amount of water supplied to one hector of land in a single watering period.
Irrigation rate can be drawn from the following formula,
Irrigation Rate = Dripper discharge (LPH)
-------------------------------------------------------
Lateral Spacing (mtr) X Emitter Spacing (mtr)
4. Water Requirement of field:
For running perfect and effortless irrigation system we must have to know the actual water requirement of our field and the water available to our water source. If one get more water then the water required in the field than you have to divert water according to the exact need of your field and wise a versa.
For this we have to divide our field in to the shifts. So all the area of the field can irrigate with the proper amount of water. We can decide the field shift with the following formula,
Water Requirement = Irrigation Rate X 10 X Area (ha)
(No. Of shifts) ---------------------------------------------
Discharge (m3/hr)
Note: If you get the figure like 1.2 then the no. of shift will be 2. Always move to the next figure from the first figure.
The above method for calculating shift may be vary according to the type of field. It is possible that you have to put more shifts in a uneven land or typical elevated field.
To calculate the water requirement of the particular Shift, one can get if from the formula below,
Shift Flow (m3/hr) = Area (ha) X 10 X Irrigation Rate
Note: Always set the total flow of shifts irrigated at the same time, lesser than the available flow at the water source.
5. Irrigation Time for one Shift:
After all the above calculation we have to still count a major part of the design and that is,how much to irrigate a shift ? It is depend upon the water requirement of the crop you have grown and the area of the shift.
You can get the peak period water requirement of mostly grown crops in India from the following chart,
Sr. No.
|
Name of the Crop
|
Water Requirement(mm/day)
|
1
|
Mango
|
2.30
|
2
|
Sapota
|
2.30
|
3
|
Coconut
|
2.5
|
4
|
Sweet Orange
|
3
|
5
|
Acid Lime (Lemon)
|
3
|
6
|
Citrus
|
2.91
|
7
|
Aonla
|
1.85
|
8
|
Guava
|
3.5
|
9
|
Papaya
|
6
|
10
|
Cashewnut
|
3
|
11
|
Grapes
|
5.5
|
12
|
Pomegranate
|
4.9
|
13
|
Custard Apple
|
3
|
14
|
Banana
|
6.5
|
15
|
Ber
|
3.3
|
16
|
Vegetables
|
6.5
|
17
|
Medicinal & Aromatic Plants
|
7
|
18
|
Patchouli
|
4
|
19
|
Mulberry
|
5
|
20
|
Sugarcane
|
7
|
21
|
Castor
|
6
|
22
|
Cotton
|
6
|
23
|
Groundnut
|
6
|
24
|
Pulses
|
5
|
25
|
Tobacco
|
6
|
26
|
Potato
|
5
|
27
|
Strawberry
|
7.6
|
28
|
Onion
|
7.6
|
You can find out the irrigation time from one shift by the following formula,
Irrigation Time = Evaporation Equivalent of the Crop
------------------------------------------------
Irrigation Rate
For Example:
If we have Evaporation Equivalent of 6.0 mm /day and Irrigation rate of 3.57 mm/hr, then
Irrigation Time = 6 / 3.57 = 1.68 hrs.
“But how can you find out how much time is equal to 1.68 hour ? “Note that the Value we get from irrigation time is always in fraction of 100. So we have to convert it in to the hour format. For this you have to do the following,
1.68 = 1 + 68 * 60/100
= 1 + 4080 / 100
= 1 + 40.8
= 1 hour 40 minutes
6. Total No. of Shifts a day:
After getting all the necessary information on designing a drip irrigation system. Still we have a question that if we have limited power source and we have large field that how can we irrigate a field at the same time?
Well for this we have to count the total number of shifts per day to irrigate the particular part of the field. You can simply find out numbers of shift according to power availability in your region by following,
No. of shifts per day = Time available for Irrigation
------------------------------------------
Irrigation time of one shift
Some more necessary information
Well that’s all about the drip irrigation design aspects but some more information you have to needed is,
How much plants are there in the field?
No. of plants in the field =
(Total area * 10,000) / lateral spacing * Emitter Spacing
Conversations
LPS= (m³/hr. X 1000) / 3600
LPM = (m³/hr. X 1000) / 60
M³/hr. = (LPM X 60) / 1000
How many laterals are going to be used in the field?
Lateral Length = Area (sq. mtr) / Row spacing
Distance Measures:
| 1 m | = | 3.28 feet |
| 1 hector | = | 2.47 Acre or 10000 Sq. mtr. |
| 1 m³ | = | 1000 ltr |
These are the basic things to decide and draw a suitable drip irrigation design for your field. You can use some of the Software like Auto cad for this.
All the above calculations are bit hectic, So I've prepared an excel sheet for easy calculations.
You can download it from HERE (Irrigation Data Calculator).
Lets see it in details as under,
Irrigation data calculator looks like below,
You can get almost all the necessary data with this calculator sheet. for this you have to enter some details like,
- Area of the plot/ field (in hector)
- Lateral spacing / Spacing between two rows of crop (in meter)
- Spacing between two emitters / drippers (in meter)
- Emitter discharge (LPH)
- Motor/Engine HP
- Water source depth (in meter)
This will give all the data like available flow, total number of plants in the field, required flow by the crop in the field, number of shifts to irrigate the field, irrigation rate etc.
You have to select your crop in the crop cell to get peak water requirement and operation hours per shift like below,
Other parts like Water carrying capacity of PVC, Hydraulic Calculation are explained in the posts below,
- Basic aspects of drip irrigation system design
- Drip Irrigation Component Installation
- Head loss & Velocity in irrigation pipes
- Video Tutorial on drip irrigation systems design
- Water carrying capacity of irrigation pipes
Or scan a QR code here,
- Hardip Gajjar
(hrdpgajjar@hotmail.com)
