---
title: "Outlet discharge: wheat and rice, 10000 ha"
subject: "Irrigation and Drainage Engineering"
chapter: 2
key: "semester_6/irrigation_and_drainage_engineering:kor-outlet-discharge-wheat-rice-10000ha"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/kor-outlet-discharge-wheat-rice-10000ha
site: BCT Engineering
---

# Outlet discharge: wheat and rice, 10000 ha

Irrigation and Drainage Engineering · Chapter 2: Irrigation Water Requirements

- Asked in: 2080 Chaitra, 5 marks
- 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/kor-outlet-discharge-wheat-rice-10000ha
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-2

## Question

A culturable command area for a minor channel is 10000 ha. Irrigation intensity is 30% for wheat and 15% for rice. The KOR period for wheat is 4 weeks and rice is 3 weeks. KOR watering depths for wheat and rice are 135 mm and 190 mm, respectively. Estimate outlet discharge.

## Short answer

Discharge for wheat is 1.67 m³/s and for rice is 1.57 m³/s. Since kor periods occur in different seasons, the outlet is designed for 1.67 m³/s.

## Answer

**Method.** The kor (critical) watering must be given to the crop within the kor period, so the outlet discharge for a crop is

$$
Q = \frac{A\,d}{T\times 86400}
$$

where $A$ = area of the crop (m$^2$), $d$ = kor depth (m) and $T$ = kor period (days).

**Areas:** wheat $= 0.30\times 10000 = 3000$ ha; rice $= 0.15\times 10000 = 1500$ ha.

**Wheat** ($T = 4\times7 = 28$ days, $d = 0.135$ m):

$$
Q_w = \frac{3\times 10^7\times 0.135}{28\times 86400} = 1.674\ \text{m}^3/\text{s}
$$

**Rice** ($T = 3\times7 = 21$ days, $d = 0.19$ m):

$$
Q_r = \frac{1.5\times 10^7\times 0.19}{21\times 86400} = 1.571\ \text{m}^3/\text{s}
$$

Wheat (rabi) and rice (kharif) are grown in different seasons, so their kor periods do not overlap and the outlet is designed for the larger discharge.

**Answer: outlet discharge = 1.67 cumec** (wheat governs; if both crops had to be watered together, the total would be 3.24 cumec).

## Check yourself

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

1. Which formula gives outlet discharge for a crop from the kor watering?
   A. Q = A x T / (d x 86400)
   B. Q = A x d / (T x 86400), with T the kor period in days
   C. Q = d x T / (A x 86400)
   D. Q = A x d x T / 86400
   Answer: B. The kor depth over the crop area must be delivered within the kor period, so volume/time with T in seconds. (Key point: Kor discharge formula)

2. With CCA 10000 ha, what are the wheat and rice areas?
   A. 30 ha and 15 ha
   B. 300 ha and 150 ha
   C. 3000 ha wheat and 1500 ha rice
   D. 7000 ha and 8500 ha
   Answer: C. Area = intensity x CCA: 0.30 x 10000 and 0.15 x 10000. (Key point: Areas)

3. Why is the outlet designed for the larger of the two discharges (1.67 cumec) instead of the sum?
   A. Rice needs no water at all
   B. The sum is always too small
   C. Outlets can carry only wheat water
   D. Wheat and rice are grown in different seasons, so their kor periods do not overlap
   Answer: D. Rabi and kharif kor periods fall at different times, so the outlet only has to carry the larger demand; wheat governs at 1.674 cumec. (Key point: Design discharge)

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