---
title: "Flow net discharge, 200 cc/day"
subject: "Soil Mechanics"
chapter: 7
key: "semester_4/soil_mechanics:flow-net-discharge-numerical-200cc"
source: https://www.bctengineer.com/q/semester_4/soil_mechanics/flow-net-discharge-numerical-200cc
site: BCT Engineering
---

# Flow net discharge, 200 cc/day

Soil Mechanics · Chapter 7: Seepage through Soils

- Asked in: 2079 Jestha, 3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/soil_mechanics/flow-net-discharge-numerical-200cc
- Whole chapter: https://www.bctengineer.com/md/semester_4/soil_mechanics/chapter-7

## Question

The discharge through the pervious soil is 200 cc/day. The flow net shows 5 flow channels and 10 equipotential drops. If the net head causing the flow is 2.5 m, calculate the permeability of the soil.

## Short answer

Using q = kh(Nf/Nd), with q=200 cm³/day, Nf=5, Nd=10, h=250 cm, permeability k = (q/h)(Nd/Nf) = 1.6 cm/day ≈ 1.85×10⁻⁵ cm/s.

## Answer

$$
q = k\,h\,\frac{N_f}{N_d}
$$

#### Given

$q = 200$ cm³/day (per unit width, taken as 1 cm), $N_f = 5$, $N_d = 10$, $h = 2.5$ m $= 250$ cm.

#### Calculation

$$
k = \frac{q}{h}\cdot\frac{N_d}{N_f} = \frac{200}{250} \times \frac{10}{5} = 1.6\ \text{cm/day}
$$

$$
k = \frac{1.6}{86400} = 1.85\times10^{-5}\ \text{cm/s}
$$

**Answer: $k = 1.6$ cm/day $\approx 1.85\times10^{-5}$ cm/s.**

## Check yourself

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

1. Which expression gives k from the flow net?
   A. k = q h N_f / N_d
   B. k = (q/h)(N_d/N_f)
   C. k = (q/h)(N_f/N_d)
   D. k = q N_d / (h N_f^2)
   Answer: B. From q = k h N_f/N_d, k = (q/h)(N_d/N_f). (Key point: Rearranged formula)

2. With q in cm3/day, how must h = 2.5 m be used?
   A. As 2.5 cm
   B. As 250 cm
   C. As 25 cm
   D. As 0.25 cm
   Answer: B. Convert to cm for consistent units: 250 cm. (Key point: Unit consistency)

3. What is k in cm/day?
   A. 0.4
   B. 3.2
   C. 1.6
   D. 16
   Answer: C. (200/250) x (10/5) = 0.8 x 2 = 1.6 cm/day. (Key point: Value of k)

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