---
title: "Rating curve and factors affecting runoff"
subject: "Engineering Hydrology"
chapter: 4
key: "semester_5/engineering_hydrology:rating-curve-runoff-factors"
source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/rating-curve-runoff-factors
site: BCT Engineering
---

# Rating curve and factors affecting runoff

Engineering Hydrology · Chapter 4: Surface Runoff

- Asked in: 2067 Shrawan (old course), 2+4 marks
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/rating-curve-runoff-factors
- Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-4

## Question

What is rating curve? What are the factors affecting run off? Explain.

## Short answer

A rating curve is a stage-discharge relationship (Q=C(G-a)^b) that converts stage records to discharge. Runoff is affected by climatic factors (rainfall intensity, duration, antededent moisture), catchment properties (area, slope, land cover, soil), channel geometry, and human influences (urbanisation, dams).

## Answer

#### Rating curve
A **rating curve** is the graph (or equation $Q=C(G-a)^b$) that gives the discharge of a river corresponding to the stage at a gauging section. It is used to convert the observed stage record into discharge.

#### Factors affecting runoff
**1. Climatic factors**
- Rainfall intensity, duration and areal distribution; direction of storm movement.
- Antecedent moisture (soil wetness), temperature, evaporation and snow-melt.

**2. Catchment factors**
- **Size and shape:** large area gives more volume; fan-shaped basins give sharp peaks.
- **Slope and elevation:** steep slopes give fast runoff and less infiltration.
- **Land use and vegetation:** forest increases interception and infiltration; urban areas and bare soil increase runoff.
- **Soil and geology:** permeable soils give less runoff; clay and rock give more.
- **Drainage density** and **storage** (lakes, ponds, depressions) which delay and reduce peaks.

**3. Channel factors:** cross-section, roughness, slope and bank storage.

**4. Human factors:** dams, diversions, irrigation, drainage, urbanisation.

## Check yourself

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

1. What does a rating curve do?
   A. Gives rainfall for a given runoff
   B. Gives velocity for a given depth
   C. Gives evaporation for a given temperature
   D. Gives discharge for a given stage so stage records can be converted to discharge
   Answer: D. It is the stage-discharge relation Q = C(G-a)^b. (Key point: Rating curve)

2. How do land use and soil affect runoff?
   A. Forest and permeable soils reduce runoff; urban areas, bare soil, clay and rock increase it
   B. Forest increases runoff and urban areas reduce it
   C. Soil type has no effect
   D. Permeable soils give more runoff
   Answer: A. Infiltration and interception reduce runoff; impervious surfaces increase it. (Key point: Catchment factors)

3. Which statement is correct?
   A. Fan-shaped basins give flat peaks; lakes sharpen peaks
   B. Fan-shaped basins give sharp peaks; lakes and depressions delay and reduce peaks
   C. Steep slopes increase infiltration
   D. Large area always gives less volume
   Answer: B. Shape controls concentration time and storage attenuates flood peaks. (Key point: Catchment shape and storage)

## Related in Engineering Hydrology

- [Catchment and factors affecting runoff](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acatchment-runoff-factors) — Engineering Hydrology, chapter 4
- [Rainfall-runoff relationship, factors affecting runoff](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Arainfall-runoff-relation-factors) — Engineering Hydrology, chapter 4
- [Runoff using Horton's curve and pan data](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Ahorton-pan-runoff) — Engineering Hydrology, chapter 3
- [Phi-index from mass curve, 3.5 cm runoff](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Aphi-index-3-5cm-runoff) — Engineering Hydrology, chapter 3
- [Rating curve definition and uses](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Arating-curve-define-uses) — Engineering Hydrology, chapter 4, asked 2×
- [Zero-discharge stage of a smooth rating curve](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Astage-zero-discharge-23-37) — Engineering Hydrology, chapter 4, asked 2×

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