--- title: "Rivers of Nepal and their features" subject: "Engineering Geology I" chapter: 6 key: "semester_3/engineering_geology_i:rivers-of-nepal-and-their" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rivers-of-nepal-and-their site: BCT Engineering --- # Rivers of Nepal and their features Engineering Geology I · Chapter 6: Physical Geology - Asked in: 2065 Shrawan (old course), 3+3+2 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/rivers-of-nepal-and-their - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-6 ## Question What are the different types of rivers in Nepal? Explain the features developed by rivers with suitable diagram. State their engineering significance as well. ## Short answer Nepal has antecedent rivers (Koshi, Gandaki, Karnali), monsoon-fed Mahabharat rivers, and flashy Siwalik rivers. Features include gorges, teraces, meanders, aluvial fans, and braided channels, significant for hydropower, bridges, irrigation, and flood hazards. ## Answer #### Types of rivers in Nepal 1. **Antecedent (Himalayan) rivers:** the Koshi, Gandaki (Narayani) and Karnali, whose sources lie in the snow of the Himalaya or on the Tibetan plateau. They are fed by snow and glaciers, cut deep gorges through the rising Himalaya and carry water all year. 2. **Rivers from the Mahabharat range:** the Bagmati, Kamala, Kankai, East Rapti, West Rapti and Babai; fed by monsoon rain and springs, with some flow in the dry season. 3. **Rivers from the Siwalik (Churiya):** small, seasonal and flashy; dry in winter, with severe floods in the monsoon and a high sediment load. By pattern, rivers are also divided into straight, meandering and braided. #### Features developed by the rivers **Erosional work** of a river is done by hydraulic action, abrasion, attrition and solution. Features: - **V-shaped valley:** formed by vertical (downward) 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:** form where hard rock lies over soft rock; a plunge pool forms at the base. - **Potholes:** 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:** formed by lateral (side) cutting in the old stage. - **Interlocking spurs:** ridges of the valley sides that project alternately into the winding valley of a young river. **Depositional work** occurs when the velocity and carrying capacity fall (on gentle slopes, at the river mouth, and on the floodplain during 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 sand and coarse silt built along the banks during floods. - **Braid bars and point bars:** sand and gravel bars in the channel (braid bars) and on the inner bank of bends (point bars). - **Delta:** fan-shaped deposit at the river mouth, e.g. the Ganges-Brahmaputra delta. - **Ox-bow lake and meander scars:** cut-off bends. ```text Mountain Foothill Terai gorge -> braided fan -> meanders V-valley (Bhabar) ox-bow, levee ``` #### Engineering significance - **Hydropower:** gorges, high gradient and large discharge in the hills; narrow bedrock valleys suit dams and give a high head, but the high sediment load wears turbines and fills reservoirs. - **Bridges and roads:** terraces are good sites for roads and bridges; braided Terai rivers need long spans and guide bunds. - **Flood control:** levees, embankments and spurs on the meandering and braided reaches, e.g. the Koshi barrage and embankments. - **Construction materials:** river-bed sand, gravel and boulders. - **Water supply and irrigation:** alluvial groundwater and canals. - **Hazards:** landslide dams, GLOF, bank erosion and shifting channels. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which rivers are the snow-fed antecedent Himalayan rivers that flow all year and cut deep gorges? A. Koshi, Gandaki and Karnali B. Bagmati, Kamala and Rapti C. Rapti, Babai and West Rapti D. Small Siwalik streams of the Terai Answer: A. Koshi, Gandaki (Narayani) and Karnali rise in the Himalaya or Tibet and cut gorges through the rising range. (Key point: Antecedent rivers) 2. Which statement fits rivers rising in the Siwalik (Churiya) hills? A. Large, snow-fed and perennial B. Small, seasonal and flashy with high sediment load; dry in winter and flooding in monsoon C. Slow, clear and with steady flow all year D. Fed mainly by glaciers Answer: B. Siwalik streams depend on monsoon rain, so they flood severely and then run dry. (Key point: Siwalik rivers) 3. Which pair are depositional features of a river? A. Gorge and waterfall B. V-shaped valley and pot hole C. Alluvial fan and delta D. Interlocking spur and rapids Answer: C. Deposition occurs when velocity and load capacity fall, building fans, floodplains, levees and deltas. (Key point: Depositional features) 4. How are pot holes formed? A. Waterfalls leave circular pools of hard rock B. Floods deposit round sand heaps C. Solution of limestone by acid rain only D. Swirling pebbles drill circular holes in the river bed Answer: D. Pot holes are erosional features formed by abrasion from swirling pebbles. (Key point: Pot holes) 5. Why do Nepal's hill rivers suit hydropower, and what is the main problem? A. High gradient, discharge and narrow bedrock valleys give high head; high sediment load wears turbines and fills reservoirs B. Flat gradient gives large storage; the problem is low discharge C. Wide braided channels suit dams; the problem is salinity D. Dry winters help construction; the problem is too little sediment Answer: A. Steep gorges give head, but sediment damages turbines and reduces reservoir life. 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