---
title: "Stream flow from current meter data"
subject: "Engineering Hydrology"
chapter: 4
key: "semester_5/engineering_hydrology:current-meter-0-035-0-74n"
source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/current-meter-0-035-0-74n
site: BCT Engineering
---

# Stream flow from current meter data

Engineering Hydrology · Chapter 4: Surface Runoff

- Asked in: 2071 Chaitra, 8 marks
- Video: [Hydrology - Flow measurements using a current meter | Eng.Tony Chabz |.](https://www.youtube.com/watch?v=zTcgbKqyMB8) — Engineering and Graphics With Tony Chabz
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/current-meter-0-035-0-74n
- Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-4

## Question

Compute the stream flow from the following data. The calibrated equation of current meter is: $V = 0.035 + 0.74 N$, where V is in m/sec and N is revolution/sec.

| Distance from bank (m) | 0 | 0.6 | 1.5 | 2.5 | 3.5 | 5.0 | 6.0 | 7.0 | 7.5 |
|---|---|---|---|---|---|---|---|---|---|
| Water depth (m) | 0 | 0.3 | 0.75 | 1.2 | 1.7 | 1.3 | 0.7 | 0.3 | 0 |
| No. of revolutions | 0 | 15 | 95 | 110 | 120 | 110 | 80 | 20 | 0 |
| Time (sec) | 0 | 45 | 85 | 95 | 90 | 100 | 70 | 40 | 0 |

## Short answer

Using mid-section method, velocity from v = 0.035+0.74N (N=rev/s), the summed discharge is 6.006 m³/s. Stream flow ≈ 6.01 m³/s.

## Answer

The mid-section method is used with $v = 0.035 + 0.74N$, where $N$ = revolutions / time (rps). The depths are small (max 1.7 m), so the meter reading is taken as the mean velocity of the vertical.
$$
q_i = v_i\,d_i\,\frac{b_{i+1}-b_{i-1}}{2}
$$

| Distance (m) | Depth d (m) | N = rev/time (rps) | v (m/s) | Width w (m) | Area $w\,d$ (m$^2$) | $q = v\,w\,d$ (m$^3$/s) |
|---|---|---|---|---|---|---|
| 0.6 | 0.3 | 15/45 = 0.333 | 0.282 | 0.75 | 0.225 | 0.063 |
| 1.5 | 0.75 | 95/85 = 1.118 | 0.862 | 0.95 | 0.712 | 0.614 |
| 2.5 | 1.2 | 110/95 = 1.158 | 0.892 | 1 | 1.200 | 1.070 |
| 3.5 | 1.7 | 120/90 = 1.333 | 1.022 | 1.25 | 2.125 | 2.171 |
| 5 | 1.3 | 110/100 = 1.100 | 0.849 | 1.25 | 1.625 | 1.380 |
| 6 | 0.7 | 80/70 = 1.143 | 0.881 | 1 | 0.700 | 0.616 |
| 7 | 0.3 | 20/40 = 0.500 | 0.405 | 0.75 | 0.225 | 0.091 |
| **Total** | | | | | **6.812** | **6.006** |

Total area $= 6.81$ m$^2$; mean velocity $= 0.882$ m/s.

**Answer: Stream flow $Q \approx 6.01\ \text{m}^3/\text{s}$.**

## Check yourself

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

1. Why is a single reading used as the mean velocity of each vertical?
   A. Time is short
   B. Velocity is uniform
   C. Meter is inaccurate
   D. Depths are small (max 1.7 m)
   Answer: D. For small depths the meter reading is taken as the vertical's mean velocity. (Key point: Single point)

2. At 0.6 m: 15 revolutions in 45 s, V = 0.035 + 0.74N gives
   A. 0.282 m/s
   B. 0.035 m/s
   C. 11.1 m/s
   D. 0.74 m/s
   Answer: A. N = 0.333 rps, V = 0.035 + 0.74 x 0.333 = 0.282 m/s. (Key point: Velocity calculation)

3. The strip width at the 1.5 m vertical (neighbours 0.6 m and 2.5 m) is
   A. 1.9 m
   B. 0.95 m
   C. 1.0 m
   D. 0.4 m
   Answer: B. (2.5 - 0.6)/2 = 0.95 m. (Key point: Strip width)

## Close variants set in other exams

- [Stream flow from current meter, V=0.045+0.76N](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-0-045-0-76n) — Engineering Hydrology, chapter 4, asked 2×

## Related in Engineering Hydrology

- [Discharge from current meter at 0.6d, stream gauging data](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-0-32n-0-032-2) — Engineering Hydrology, chapter 4
- [Discharge from current meter at 0.6 depth](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-0-32n-0-032) — Engineering Hydrology, chapter 4
- [Mid-section method discharge from current meter data](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Amidsection-0-3n-0-004) — Engineering Hydrology, chapter 4
- [River discharge with current meter constants a and b](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-a0-51-b0-03) — Engineering Hydrology, chapter 4
- [Current meter discharge, rating equation](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-0-53n) — Engineering Hydrology, chapter 4
- [Discharge from multi-point current meter data](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acurrent-meter-two-point-0-3n) — Engineering Hydrology, chapter 4

## Related in other subjects

- [Stream discharge from current meter revolutions (V = 0.51N + 0.03)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Astream-gauging-revolutions-0-51) — Hydro Power, chapter 2, asked 2×
- [Stream discharge from current meter revolutions (v = 0.55N + 0.04)](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Astream-gauging-revolutions-0-55) — Hydro Power, chapter 2, asked 2×