---
title: "Steps for rice irrigation requirement"
subject: "Irrigation and Drainage Engineering"
chapter: 2
key: "semester_6/irrigation_and_drainage_engineering:rice-irrigation-requirement-steps"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/rice-irrigation-requirement-steps
site: BCT Engineering
---

# Steps for rice irrigation requirement

Irrigation and Drainage Engineering · Chapter 2: Irrigation Water Requirements

- Asked in: 2075 Baisakh, 4 marks; 2070 Chaitra (old course), 4 marks; 2069 Bhadra, 5 marks; 2063 Asoj (old course), 4 marks (asked 4 times)
- Video: [Irrigation Calculation Made Simple | GCA, CCA, IP & Discharge](https://www.youtube.com/watch?v=M3EkYhmMVks) — CiviTube
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/rice-irrigation-requirement-steps
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-2

## Question

Write down the steps for calculating irrigation requirement for rice crop.

## Answer

**Irrigation water requirement (IWR) of rice** is the water that must be supplied by irrigation, after deducting effective rainfall, to meet crop evapotranspiration, field losses and land preparation needs.

#### Steps
1. **Collect data:** climate (temperature, humidity, wind, sunshine), rainfall, soil type (percolation), crop calendar (nursery, transplanting, growing stages, harvest).
2. **Reference evapotranspiration ($ET_o$):** compute by Penman, modified Penman or Blaney-Criddle method for each month or ten-day period.
3. **Crop coefficient ($K_c$):** select $K_c$ for each growth stage of rice (initial, development, mid, late) from FAO tables.
4. **Crop evapotranspiration:** 
$$
ET_c = K_c \times ET_o
$$
5. **Seepage and percolation (S&P):** estimate daily loss from the standing water (e.g. 2-6 mm/day depending on soil).
6. **Land preparation water (puddling):** estimate water for soaking and puddling, typically 150-250 mm, spread over the preparation period; also nursery requirement.
7. **Water layer (WL):** water needed to establish and maintain standing water, e.g. 50-100 mm at transplanting.
8. **Effective rainfall ($P_e$):** estimate by dependable rainfall (75% probability), USDA SCS or fixed percentage method.
9. **Net irrigation requirement:**
$$
\begin{aligned}
NIR = ET_c + S\&P + WL + LP - P_e
\end{aligned}
$$
10. **Gross irrigation requirement:**
$$
GIR = \frac{NIR}{\eta_{overall}}
$$
where $\eta_{overall}=\eta_c\times\eta_a$ (conveyance and application efficiencies).
11. **Convert to discharge:** the peak monthly GIR gives the canal capacity (l/s/ha, or $m^3/s$ for the command area).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Crop evapotranspiration is:
   A. ETc = Kc + ETo
   B. ETc = ETo / Kc
   C. ETc = Kc x ETo
   D. ETc = Pe x Kc
   Answer: C. Kc is selected by growth stage. (Key point: ETc)

2. Net irrigation requirement for rice is:
   A. ETc - S&P - LP + Pe
   B. ETc + Pe
   C. GIR x efficiency
   D. ETc + S&P + WL + LP - Pe
   Answer: D. Rainfall is deducted; losses and land preparation are added. (Key point: NIR)

3. Gross irrigation requirement is:
   A. NIR / overall efficiency
   B. NIR x efficiency
   C. NIR - efficiency
   D. NIR + Pe
   Answer: A. Overall efficiency = conveyance x application. (Key point: GIR)

4. Land preparation water is typically:
   A. 5-10 mm
   B. 150-250 mm
   C. 1000 mm
   D. 0 mm
   Answer: B. Needed for soaking and puddling. (Key point: Puddling)

## Related in Irrigation and Drainage Engineering

- [Irrigation water requirement of rice](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Arice-irrigation-requirement-definition) — Irrigation and Drainage Engineering, chapter 2
- [Steps of crop water requirement calculation](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acrop-water-requirement-steps) — Irrigation and Drainage Engineering, chapter 2, asked 2×
- [Crop coefficient curve for rice](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acrop-coefficient-curve-rice) — Irrigation and Drainage Engineering, chapter 2
- [Crop water requirement and its factors](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acrop-water-requirement-factors) — Irrigation and Drainage Engineering, chapter 2
- [Reservoir capacity: rice, wheat, sugarcane](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Areservoir-capacity-areas-71bh) — Irrigation and Drainage Engineering, chapter 2
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