--- title: "Geological work of running water and its landforms" subject: "Engineering Geology I" chapter: 6 key: "semester_3/engineering_geology_i:geological-work-of-running-water" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geological-work-of-running-water site: BCT Engineering --- # Geological work of running water and its landforms Engineering Geology I · Chapter 6: Physical Geology - Asked in: 2078 Bhadra, 3 marks; 2075 Chaitra, 1+2 marks; 2081 Chaitra (new course), 3 marks; 2069 Chaitra, 4 marks; 2072 Chaitra, 3 marks (asked 5 times) - Video: [How Rivers Shape the Landscape: Crash Course Geography #23](https://www.youtube.com/watch?v=CDEj62HGNkk) — CrashCourse - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/geological-work-of-running-water - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6 ## Question Give a full account of the geological work of running water and the (erosional and depositional) landforms/features it develops. ## Short answer Running water erodes by hydraulic action and abrasion, transports by saltation and suspension, and deposits onto floodplains and deltas. Erosional landforms include V-valleys, gorges, and terraces; depositional landforms include alluvial fans, floodplains, and deltas. ## Answer Running water (rainwater, streams and rivers) is the most important agent of landscape change. Its work has three parts. #### 1. Erosion Done by **hydraulic action** (force of water), **abrasion** (carried load scrapes the bed), **attrition** (load wears itself) and **solution**. Erosion is vertical in the youth stage and lateral in old age. #### 2. Transportation - *Solution:* dissolved salts. - *Suspension:* clay and silt. - *Saltation:* sand bouncing along the bed. - *Traction:* pebbles and boulders rolled along the bed. #### 3. Deposition Occurs when velocity falls (gentle gradient, river mouth, floods). #### Landforms **Erosional work** of a river is done by hydraulic action, abrasion, attrition and solution. Features: - **V-shaped valley:** vertical cutting in the youth stage, in the hills. - **Gorge and canyon:** deep, narrow valley in hard rock, e.g. the Kali Gandaki gorge. - **Waterfall and rapids:** hard rock lying over soft rock; the plunge pool forms at the base. - **Pot holes:** circular holes drilled in the bed by swirling pebbles. - **River terraces:** step-like old floodplain levels left after the river cuts down again. - **Meanders and ox-bow lakes:** side cutting in the old stage. - **Interlocking spurs:** ridges between bends of a young river. **Depositional work** occurs when the velocity and load capacity fall (at gentle slope, at a mouth, in floods). Features: - **Alluvial fan:** cone-shaped deposit where a mountain stream meets a plain, e.g. the Bhabar zone at the foot of the Siwaliks. - **Floodplain:** broad flat valley floor built by flood deposits. - **Natural levees:** low ridges of coarse silt built along the banks during floods. - **Braided bars and channel (point) bars:** sand and gravel bars inside the channel. - **Delta:** fan-shaped deposit at the river mouth (Ganges-Brahmaputra delta). - **Ox-bow lake and meander scars:** cut-off bends. #### Stages of a river | Stage | Gradient | Main work | Landforms | |---|---|---|---| | Youth | Steep | Vertical erosion | V-valley, gorge, waterfall | | Mature | Moderate | Balanced erosion and deposition | Meanders, wider valley | | Old | Gentle | Deposition | Floodplain, ox-bow, delta | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What are the three parts of the geological work of running water? A. Weathering, folding and faulting B. Erosion, metamorphism and deposition C. Solution, melting and cooling D. Erosion, transportation and deposition Answer: D. Running water erodes, transports and deposits. (Key point: Three parts) 2. Which load is moved by saltation? A. Sand bouncing along the bed B. Dissolved salts C. Clay and silt held in the flow D. Boulders rolled along the bed Answer: A. Saltation is the bouncing of sand; traction rolls pebbles and boulders; suspension carries clay and silt. (Key point: Transport modes) 3. When does a river deposit its load? A. When velocity increases on a steep gradient B. When velocity falls, e.g. at gentle gradient, river mouth or in floods C. Only in the youth stage in gorges D. When the river cuts vertically Answer: B. Reduced velocity lowers carrying capacity so the load settles. (Key point: Deposition) 4. Which stage is dominated by vertical erosion giving V-valleys, gorges and waterfalls? A. Mature stage B. Old stage C. Youth stage D. All stages equally Answer: C. The steep youth stage cuts downward; the old stage deposits to build floodplains, ox-bows and deltas. (Key point: River stages) ## Related in Engineering Geology I - [Erosional and depositional landforms of glaciers](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aerosional-and-depositional-landforms-of) — Engineering Geology I, chapter 6, asked 3× - [Geological work of wind and its landforms](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageological-work-of-wind-and) — Engineering Geology I, chapter 6, asked 6× - [Geological agent and features of running water](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Ageological-agent-and-features-of) — Engineering Geology I, chapter 6 - [Erosional and depositional features of river and glacier](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aerosional-and-depositional-features-of) — Engineering Geology I, chapter 6, asked 2× - [Erosional feature of running water and wind](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aerosional-feature-of-running-water) — Engineering Geology I, chapter 6 - [Erosional features of glacier and underground water](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aerosional-features-of-glacier-and) — Engineering Geology I, chapter 6