--- title: "Cross drainage works favourable in hilly areas" subject: "Irrigation and Drainage Engineering" chapter: 8 key: "semester_6/irrigation_and_drainage_engineering:cd-works-hilly-areas" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/cd-works-hilly-areas site: BCT Engineering --- # Cross drainage works favourable in hilly areas Irrigation and Drainage Engineering · Chapter 8: Cross-Drainage structures - Asked in: 2076 Bhadra, 1+2+1 marks - Video: [Cross Drainage works | cross drainage works in hindi](https://www.youtube.com/watch?v=oDcOSADN1jo) — Engineer's Coach - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/cd-works-hilly-areas - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-8 ## Question Define cross drainage structures. Enlist the different types of cross drainage structures. Which type of cross drainage structure is favorable in hilly areas of Nepal? ## Short answer Cross-drainage structures carry canal and drain across each other. Types: aqueduct, siphon aqueduct, super-passage, canal siphon, level crossing, inlet-outlet. In Nepal's hills, an aqueduct is most favorable because it safely passes sudden high-velocity floods with debris under the canal, needs no floor on rocky beds, and avoids silting or choking of barrels. ## Answer #### Definition (1 mark) A **cross-drainage structure** is a structure built where an irrigation canal crosses a natural drain or stream, to carry the canal and the drainage water across each other without mixing or damage. #### Types (2 marks) 1. Aqueduct (canal over drain, drain flows freely). 2. Siphon aqueduct (canal over drain, drain flows under pressure). 3. Super-passage (drain over canal, canal flows below with a free surface). 4. Canal siphon (drain over canal, canal under pressure). 5. Level crossing (canal and drain at the same level, with regulators). 6. Inlet and outlet (drain enters or leaves the canal). #### Type favourable in the hills of Nepal (1 mark) The **aqueduct** (a canal flume or trough carried over the drain) is the most favourable. In the hills, canals run along the hillside and cross many small, steep, deeply cut streams (khola) whose beds are well below the canal bed. An aqueduct: - Passes sudden, high-velocity floods with boulders and debris freely under the structure. - Needs no floor or cut-off in the drain bed, which is often rocky. - Avoids the silting and choking of barrels that troubles siphon types. - Is simple and cheap in stone masonry or RCC, and keeps the canal supply safe from floods. Where a small gully or landslide channel crosses above a canal that is cut into the hillside, a super-passage (or a covered canal section) is used instead. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a cross-drainage structure? A. A structure built where a canal crosses a natural drain, to pass canal and drainage across each other B. A structure for measuring canal discharge C. A weir across a river D. A structure for raising canal water level Answer: A. It lets the canal and the natural drain cross safely without mixing or damage. (Key point: Definition) 2. Which is NOT one of the listed types of cross-drainage structure? A. Siphon aqueduct B. Level crossing C. Canal escape weir D. Super-passage Answer: C. The types are aqueduct, siphon aqueduct, super-passage, canal siphon, level crossing and inlet/outlet. (Key point: Types) 3. Which type is most favourable in the hills of Nepal? A. Canal siphon B. Aqueduct C. Siphon aqueduct D. Level crossing Answer: B. Hill canals run high above deeply cut khola beds, so a flume over the stream passes floods freely. (Key point: Type for hills) 4. Why is an aqueduct better than siphon types for steep hill streams? A. It passes boulders and debris freely and avoids choking and silting of barrels B. It needs heavy floors and cut-offs C. It works only for tiny flows D. It requires the canal to be below the stream Answer: A. Free flow under the structure avoids the silting and blockage problems of pressure barrels. 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