--- title: "Catchment and factors affecting runoff" subject: "Engineering Hydrology" chapter: 4 key: "semester_5/engineering_hydrology:catchment-runoff-factors" source: https://www.bctengineer.com/q/semester_5/engineering_hydrology/catchment-runoff-factors site: BCT Engineering --- # Catchment and factors affecting runoff Engineering Hydrology · Chapter 4: Surface Runoff - Asked in: 2076 Asoj, 1+5 marks - Video: [Runoff and Factors affecting Runoff || Hydrology || Irrigation Engineering || Civil Engineering](https://www.youtube.com/watch?v=UHIkQ8kXoB8) — Mukesh Kumar - Answer checked by Claude Sonnet 5.5 on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/engineering_hydrology/catchment-runoff-factors - Whole chapter: https://www.bctengineer.com/md/semester_5/engineering_hydrology/chapter-4 ## Question Define catchment. What are the factors affecting runoff from a catchment? ## Short answer A catchment is the land area draining to a point. Runoff is affected by rainfall intensity/duration, antecedent moisture, catchment size, shape, slope, land use, soil type, drainage density, storage, channel characteristics, and human activities. ## Answer #### Catchment A **catchment (drainage basin, watershed)** is the area of land which drains the surface runoff from precipitation to a common outlet (a river or a point on it) through a connected system of streams. Its boundary is the water divide (ridge line). #### Factors affecting runoff from a catchment **1. Climatic factors** - Type of precipitation (rain, snow, hail). - **Rainfall intensity:** an intensity above the infiltration capacity gives more runoff. - **Duration** and **areal distribution** of the storm; direction of storm movement relative to the drainage network. - **Antecedent precipitation (soil moisture):** wet soil gives higher runoff. - Evaporation, temperature, wind and snow-melt. **2. Physiographic (catchment) factors** - **Size:** a larger area gives larger total runoff but a lower specific peak, and a longer lag time. - **Shape:** fan-shaped or circular basins produce high, sharp peaks; elongated basins produce lower, flatter peaks. - **Slope:** steep slopes give quick runoff, higher peaks and less infiltration. - **Land use and vegetation:** forest and crops intercept and infiltrate water; urbanisation and bare land increase runoff. - **Soil type and geology:** the permeability of the soil and rock governs infiltration; sandy soil gives low runoff, clay gives high runoff. - **Drainage density and stream pattern:** a high density gives quick drainage. - **Topography, elevation and orientation:** these affect rainfall, snow and temperature. - **Storage:** lakes, ponds, depressions, wetlands and reservoirs reduce and delay peaks. **3. Channel factors** - Cross-section, roughness and slope of the channels; presence of check dams and bank storage. **4. Human factors** - Dams, diversions, irrigation, drainage works and land-use change. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A catchment is best defined as A. The land area draining surface runoff to a common outlet, bounded by a water divide B. The area receiving rainfall above 100 mm C. Any area covered by a river D. The area of a reservoir Answer: A. A catchment drains runoff to a common outlet through connected streams and is bounded by its ridge-line water divide. (Key point: Catchment definition) 2. How does antecedent precipitation (soil moisture) affect runoff? A. Dry soil gives higher runoff B. Wet soil gives higher runoff C. It has no effect D. Wet soil gives lower runoff Answer: B. Wet soil has less infiltration capacity left, so more rainfall becomes runoff. (Key point: Antecedent moisture) 3. Which basin shape gives a high, sharp flood peak? A. Narrow strip B. Elongated C. Fan-shaped or circular D. Any shape equally Answer: C. Fan-shaped or circular basins bring flow to the outlet together; elongated basins give lower, flatter peaks. (Key point: Catchment shape) 4. What is the effect of lakes, ponds and wetlands in a catchment? A. They increase infiltration only B. They have no effect on peaks C. They raise and hasten peaks D. They reduce and delay peaks Answer: D. Storage attenuates and delays the flood peak. 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