---
title: "Hydrologic cycle with sketches and its need"
subject: "Engineering Hydrology"
chapter: 1
key: "semester_5/engineering_hydrology:hydrologic-cycle-sketch-need"
source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/hydrologic-cycle-sketch-need
site: BCT Engineering
---

# Hydrologic cycle with sketches and its need

Engineering Hydrology · Chapter 1: Introduction

- Asked in: 2075 Chaitra, 3+2 marks
- Video: [The Hydrologic and Carbon Cycles: Always Recycle! - Crash Course Ecology #8](https://www.youtube.com/watch?v=2D7hZpIYlCA) — CrashCourse
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/hydrologic-cycle-sketch-need
- Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-1

## Question

Explain hydrologic cycle with neat sketches and justify its need in Engineering Hydrology.

## Short answer

The hydrologic cycle is the continuous movement of water via evaporation, condensation, precipitation, and runoff, forming the framework for water balance. Its study is essential to quantify components for design floods, water availability, and sustainable planning.

## Answer

#### Hydrologic cycle
The hydrologic cycle is the continuous movement of water between the ocean, atmosphere and land through evaporation, condensation, precipitation, runoff and infiltration. It is driven by solar energy and gravity.

```text
   Sun's energy
      |
  Evaporation          Condensation -> Clouds
  + Transpiration  ^        |
      ^            |        v
 [Ocean]---------->|   Precipitation
      ^                     |
      |    Surface runoff   v
      +----- Rivers <--- [Land/Catchment]
      |                     |
      +--- Groundwater <----+  (infiltration,
           flow to sea          percolation)
```

**Land-phase sketch of a catchment**

```text
        Precipitation (P)
   \ \ \ \ \ \ \ \
    Interception   Evapotranspiration
   -------------------------------------
    Depression storage | Surface runoff -> River
    Infiltration  \    |
   ~~~~~~~~~ Water table ~~~~~~~~~~~~~~~~
      Groundwater flow -> River / sea
```

**Processes:** evaporation, transpiration, condensation, precipitation, interception, infiltration, percolation, surface runoff, groundwater flow and snowmelt.

#### Need of the hydrologic cycle in engineering hydrology
- It is the **framework of hydrology**: every topic (precipitation, losses, runoff, streamflow) is a part of the cycle.
- The **water balance** of a basin ($P - R - ET - G = \Delta S$) comes from the cycle and is used to find water availability.
- Engineers estimate **design floods, yield and droughts** by quantifying the cycle components.
- It shows how **human activities** (dams, deforestation, urbanisation, pumping) change evaporation, runoff and recharge.
- It helps in **planning water use** for supply, irrigation and hydropower in a sustainable way.

## Check yourself

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

1. Why is the hydrologic cycle called the framework of hydrology?
   A. It only describes oceans
   B. It replaces statistics
   C. It is only for groundwater
   D. Every topic like precipitation, losses and runoff is a part of the cycle
   Answer: D. All hydrology topics are components of the cycle. (Key point: Framework)

2. What equation comes from the cycle?
   A. P - R - ET - G = ΔS
   B. P x R = ET
   C. P + ET = R
   D. ΔS = R/P
   Answer: A. The basin water balance follows from the cycle. (Key point: Water balance)

3. What do human activities like dams and urbanisation do?
   A. Nothing to the cycle
   B. Change evaporation, runoff and recharge
   C. Only change solar energy
   D. Only change gravity
   Answer: B. The cycle helps show these effects. (Key point: Human effect)

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- [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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