---
title: "Define hydrological cycle, runoff, water balance, catchment"
subject: "Engineering Hydrology"
chapter: 1
key: "semester_5/engineering_hydrology:define-cycle-runoff-balance-catchment"
source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/define-cycle-runoff-balance-catchment
site: BCT Engineering
---

# Define hydrological cycle, runoff, water balance, catchment

Engineering Hydrology · Chapter 1: Introduction

- Asked in: 2072 Chaitra, 4 marks
- Video: [🔴Hydrology intro-Catchments-Water Balance || Lecture 1-Engineering Hydrology](https://www.youtube.com/watch?v=fMHCWfADy60) — Africana Hills
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/define-cycle-runoff-balance-catchment
- Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-1

## Question

Define the following terms: hydrological cycle, runoff, water balance and catchment.

## Short answer

The hydrologic cycle is the endless circulation of water among ocean, atmosphere, and land; runoff is the precipitated water flowing over land to streams; water balance equation, P−R−G−ET=ΔS, accounts for inputs, outputs, and storage change; a catchment is the drainage area bounded by ridges.

## Answer

- **Hydrological cycle:** The continuous circulation of water from oceans to atmosphere, to land and back to the oceans through evaporation, condensation, precipitation, infiltration and runoff, driven by solar energy and gravity.
- **Runoff:** The part of precipitation that flows over the land surface and in channels to reach a stream, lake or sea. It includes surface runoff, interflow and base flow, and is usually expressed as discharge (m³/s) or depth (mm) over the catchment.
- **Water balance:** The accounting of inflows, outflows and storage change of a region over a given time, based on conservation of mass: $P - R - G - E - T = \Delta S$.
- **Catchment (watershed or drainage basin):** The area of land that drains to a given point on a stream, bounded by a ridge line called the water divide. All rain falling inside it (apart from losses) flows to that outlet.

## Check yourself

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

1. Runoff is:
   A. All rain falling on a catchment
   B. Water stored in soil
   C. Part of precipitation that flows over land and in channels to a stream, lake or sea
   D. Vapour leaving plants
   Answer: C. It excludes losses like infiltration and evaporation. (Key point: Runoff)

2. A catchment is bounded by:
   A. A river
   B. A road
   C. The coastline
   D. A ridge line called the water divide
   Answer: D. The water divide separates adjacent drainage basins. (Key point: Catchment boundary)

3. Water balance is based on:
   A. Conservation of mass
   B. Conservation of momentum
   C. Darcy's law
   D. Newton's law of cooling
   Answer: A. Inflow minus outflow equals storage change. (Key point: Water balance basis)

4. Runoff includes:
   A. Only surface runoff
   B. Surface runoff, interflow and base flow
   C. Only evaporation
   D. Only rain on oceans
   Answer: B. All three reach the stream. (Key point: Runoff components)

## Related in Engineering Hydrology

- [Hydrologic cycle and water balance equation](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Ahydrologic-cycle-water-balance) — Engineering Hydrology, chapter 1, asked 3×
- [Catchment and factors affecting runoff](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Acatchment-runoff-factors) — Engineering Hydrology, chapter 4
- [Human interference in the hydrological cycle](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Ahuman-interference-hydrologic-cycle) — Engineering Hydrology, chapter 1
- [Hydrological cycle and uses of engineering hydrology](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Ahydrologic-cycle-uses) — Engineering Hydrology, chapter 1
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