---
title: "Canal discharge for dry and wet crops"
subject: "Irrigation and Drainage Engineering"
chapter: 2
key: "semester_6/irrigation_and_drainage_engineering:kor-discharge-dry-wet-20000-30000"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/kor-discharge-dry-wet-20000-30000
site: BCT Engineering
---

# Canal discharge for dry and wet crops

Irrigation and Drainage Engineering · Chapter 2: Irrigation Water Requirements

- Asked in: 2078 Baisakh, 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-discharge-dry-wet-20000-30000
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-2

## Question

Compute the flow discharge needed of a canal to irrigate dry season crops in 20000 ha and wet season crops in 30000 ha. Kor period and kor depth for dry and wet season crops are 5 weeks, 12.5 cm and 4 weeks, 9.5 cm respectively.

## Short answer

Dry-season discharge is 8.27 m³/s, wet-season discharge is 11.78 m³/s. Seasons do not overlap, so canal discharge is 11.78 m³/s.

## Answer

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

**Dry-season crops:** $A = 20000$ ha $= 2\times10^8$ m$^2$, $T = 5\times7 = 35$ days, $d = 0.125$ m

$$
Q_{dry} = \frac{2\times10^8\times 0.125}{35\times 86400} = 8.267\ \text{m}^3/\text{s}
$$

**Wet-season crops:** $A = 30000$ ha $= 3\times10^8$ m$^2$, $T = 4\times7 = 28$ days, $d = 0.095$ m

$$
Q_{wet} = \frac{3\times10^8\times 0.095}{28\times 86400} = 11.781\ \text{m}^3/\text{s}
$$

The two seasons do not overlap, so the canal is designed for the larger discharge.

**Answer: canal discharge = 11.78 cumec** (wet season governs; dry season needs 8.27 cumec).

## Check yourself

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

1. How is the kor period used in the formula?
   A. Weeks are converted to days (5 weeks = 35 days) and multiplied by 86400 s
   B. Weeks are used directly
   C. Weeks are converted to hours only
   D. Weeks are multiplied by 365
   Answer: A. Q = A d /(T x 86400) needs T in days, so 5 weeks = 35 days and 4 weeks = 28 days. (Key point: Kor period conversion)

2. Which season governs the canal design and what is the discharge?
   A. Dry season, 8.27 cumec
   B. Wet season, 11.78 cumec
   C. Both together, 20.05 cumec
   D. Dry season, 11.78 cumec
   Answer: B. Wet: 3e8 x 0.095/(28 x 86400) = 11.78 cumec, larger than dry 8.27. (Key point: Governing season)

3. Why are the dry and wet season discharges not added?
   A. Adding gives too small a value
   B. Wet season crops need no canal water
   C. The two seasons do not overlap, so the canal is designed for the larger discharge
   D. The formula already includes both
   Answer: C. Kor waterings occur at different times of the year, so the maximum single-season demand controls. (Key point: Why not add)

## Close variants set in other exams

- [Canal discharge for dry and wet crops (30000/40000 ha)](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Akor-discharge-dry-wet-30000-40000) — Irrigation and Drainage Engineering, chapter 2, asked 2×