---
title: "Canal discharge for dry and wet crops (30000/40000 ha)"
subject: "Irrigation and Drainage Engineering"
chapter: 2
key: "semester_6/irrigation_and_drainage_engineering:kor-discharge-dry-wet-30000-40000"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/kor-discharge-dry-wet-30000-40000
site: BCT Engineering
---

# Canal discharge for dry and wet crops (30000/40000 ha)

Irrigation and Drainage Engineering · Chapter 2: Irrigation Water Requirements

- Asked in: 2071 Magh, 8 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-discharge-dry-wet-30000-40000
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-2

## Question

Compute the flow discharge needed for a canal to irrigate dry season crops in 30000 ha and wet season crops in 40000 ha. Kor period and kor depth for dry and wet season crops are 6 weeks and 14.8 cm and 4 weeks and 11.5 cm respectively.

## Short answer

Dry-season discharge is 12.24 m³/s, wet-season discharge is 19.01 m³/s. The canal is designed for the larger wet-season discharge of 19.01 m³/s.

## Answer

**Formula:** $Q = \dfrac{A\,d}{T\times 86400}$ with $A$ in m$^2$, $d$ in m, $T$ in days.

**Dry-season crops:** $A = 30000$ ha $= 3\times10^8$ m$^2$, $T = 6\times7 = 42$ days, $d = 0.148$ m

$$
Q_{dry} = \frac{3\times10^8\times 0.148}{42\times 86400} = 12.235\ \text{m}^3/\text{s}
$$

**Wet-season crops:** $A = 40000$ ha $= 4\times10^8$ m$^2$, $T = 4\times7 = 28$ days, $d = 0.115$ m

$$
Q_{wet} = \frac{4\times10^8\times 0.115}{28\times 86400} = 19.015\ \text{m}^3/\text{s}
$$

The seasons are different, so the canal is designed for the larger of the two.

**Answer: canal discharge = 19.01 cumec** (wet season governs; dry season needs 12.24 cumec).

## Check yourself

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

1. In Q = A d /(T x 86400), what units must A, d and T be in?
   A. A in m^2, d in m and T in days
   B. A in ha, d in cm, T in weeks
   C. A in m^2, d in mm, T in seconds
   D. A in ha, d in m, T in days
   Answer: A. The 86400 converts days to seconds, and A d is a volume in m^3, so A must be in m^2 and d in m. (Key point: Formula and units)

2. Dry season: 30000 ha, 6 weeks, 14.8 cm. What is the discharge?
   A. 19.01 cumec
   B. 12.24 cumec
   C. 8.16 cumec
   D. 2.04 cumec
   Answer: B. 3e8 x 0.148/(42 x 86400) = 12.235 cumec. (Key point: Dry season discharge)

3. Wet season: 40000 ha, 4 weeks, 11.5 cm. What is the discharge?
   A. 12.24 cumec
   B. 25.5 cumec
   C. 19.01 cumec
   D. 7.2 cumec
   Answer: C. 4e8 x 0.115/(28 x 86400) = 19.015 cumec. (Key point: Wet season discharge)

4. Which discharge is adopted for the canal and why?
   A. 31.25 cumec, the sum of both
   B. 12.24 cumec, the smaller to save cost
   C. 15.6 cumec, the average
   D. 19.01 cumec, because the seasons differ and the larger governs
   Answer: D. Non-overlapping seasons means the canal is sized for the larger of the two. (Key point: Design value)

## Close variants set in other exams

- [Canal discharge for dry and wet crops](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Akor-discharge-dry-wet-20000-30000) — Irrigation and Drainage Engineering, chapter 2, asked 2×

## Related in Irrigation and Drainage Engineering

- [Canal design discharge at 0, 1, 2, 3 km](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-design-discharge-along-reach) — Irrigation and Drainage Engineering, chapter 4