--- title: "Cross drainage structures and types" subject: "Transportation Engineering I" chapter: 4 key: "semester_6/transportation_engineering_i:cross-drain-types" source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/cross-drain-types site: BCT Engineering --- # Cross drainage structures and types Transportation Engineering I · Chapter 4: Highway Drainage - Asked in: 2080 Chaitra, 5 marks; 2078 Baisakh, 8 marks; 2074 Bhadra, 8 marks (asked 3 times) - Video: [Types of cross drainage structure](https://www.youtube.com/watch?v=Mh2Fv0f4rbs) — PSC Civil - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/cross-drain-types - Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-4 ## Question Define cross-drainage structure. Explain its types / the application of various types of highway cross drainage with neat sketches. ## Short answer Cross-drainage structures carry water across the road. Types: pipe culvert (small discharge, low fill), box culvert (moderate-large discharge, weak foundation), slab culvert (up to 6m span, firm foundation), arch culvert (hill roads, stone available), causeway/drift (wide shallow streams), minor bridge (span >6m), aqueduct/siphon (canal crossings). Selection depends on discharge, foundation, embankment height, materials, cost. ## Answer #### Cross-drainage structure A **cross-drainage structure** is a structure built across or under the road to carry water from one side of the road to the other. It lets streams, gullies and the drainage collected from the road pass the alignment without damaging the road. #### Types and application The main types, in increasing order of discharge and span, are listed below (IRC/NRS 2070). | Type | Use | |---|---| | Pipe culvert | Small discharge, flat or low-fill roads, minor streams | | Box culvert | Moderate to large discharge, weak foundation, high fill | | Slab culvert | Small to medium span (up to about 6 m), firm foundation | | Arch culvert (masonry) | Hill roads, stone available, high fill, good foundation | | Causeway / drift (Irish bridge) | Wide, shallow streams with short flood duration | | Minor bridge | Span above about 6 m, higher discharge | | Aqueduct / siphon | Canal crossing the road | #### 1. Pipe culvert Concrete (Hume) or steel pipes laid under the embankment in one or more barrels. Minimum diameter 600 mm (900 mm preferred for ease of cleaning), minimum cover about 0.6 to 1.0 m. It is cheap and quick to build, but its capacity is limited and it may choke with debris. ```text ====== road level ====== ====== fill (cover) ==== ___________ ( pipe ) -> flow ----------- inlet headwall outlet apron ``` #### 2. Box culvert RCC rectangular section, single or multiple cells. The top slab acts together with the walls and the base slab, so the load is spread over the soil. It suits soft ground and large flows and needs little cover. ```text ====== road ====== | _____________ | | | | | | <- 2 cells | |______|______| | |_________________| base slab ``` #### 3. Slab culvert RCC slab deck on masonry or concrete abutments with wing walls. The waterway is open, so it is easy to clean. It is used where the bed is firm and the stream needs a clear span of up to 6 m. ```text ____deck slab_______ | | |abutment abutment| |_____waterway_______| ``` #### 4. Arch culvert Masonry or concrete arch, which acts mainly in compression and so uses stone effectively, but needs strong abutments and a good foundation. #### 5. Causeway (drift) and Irish bridge The road is carried across the stream at bed level, with or without small pipes (vented). The road is submerged during floods. It is used for broad streams that rise only for short periods and where a bridge is too costly. Protection works (aprons and cut-off walls) are needed. ```text road ----\__________/---- road (dip) vents == low-water flow flood level ~~~~~~~~~~~~~ ``` #### 6. Minor bridge Used when a culvert cannot pass the discharge; the length is above 6 m and up to about 60 m (IRC). It is designed for the HFL with adequate free board (soffit clearance) as per IRC/NRS bridge standards. #### 7. Aqueduct and siphon An aqueduct carries a canal across a drainage channel or road; an inverted siphon carries drainage water under a canal or a road in a pipe running full. **Selection** depends on discharge, stream slope, nature of the bed and foundation, height of embankment, availability of materials, and cost. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A cross-drainage structure is one that: A. Runs along the road edge B. Carries water from one side of the road to the other C. Lowers the water table D. Reduces camber Answer: B. It is built across or under the road so streams and gullies pass the alignment. (Key point: Definition) 2. Which is true of a pipe culvert? A. Used for large discharge B. Cheap and quick but limited capacity and may choke C. Needs no cover D. Used for spans above 6 m Answer: B. Pipe culverts suit small discharge, with minimum diameter 600 mm and cover 0.6-1.0 m. (Key point: Pipe culvert) 3. When is a box culvert preferred? A. Rock foundation with firm banks B. Weak foundation, high fill, moderate to large discharge C. Very wide shallow streams D. Canal crossing Answer: B. The rigid RCC box spreads load over the base, suiting soft ground and large flows. (Key point: Box culvert) 4. Where is a causeway or drift used? A. Wide shallow streams with short flood duration, where a bridge is too costly B. Spans above 30 m C. Canal crossings D. Streams with permanent deep flow Answer: A. The road is at bed level and gets submerged briefly during floods. (Key point: Causeway) ## Related in Transportation Engineering I - [Hill road drainage structures](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ahill-drainage-structures) — Transportation Engineering I, chapter 5, asked 4× - [Requirements of highway drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Arequirements-highway-drainage) — Transportation Engineering I, chapter 4, asked 6× - [Define highway drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Adefine-highway-drainage) — Transportation Engineering I, chapter 4, asked 5× - [Importance of highway drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Adrainage-importance) — Transportation Engineering I, chapter 4, asked 4× - [Cross-sectional elements of a highway](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Across-section-elements) — Transportation Engineering I, chapter 3, asked 2× - [Classification of highway drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Aclassify-highway-drainage) — Transportation Engineering I, chapter 4 ## Related in other subjects - [Types of cross drainage works with sketches](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acd-works-types-definition-sketches) — Irrigation and Drainage Engineering, chapter 8, asked 9× - [Drop structures: need and types with sketches](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Adrop-structures-types-sketch) — Irrigation and Drainage Engineering, chapter 7, asked 6× - [Cross drainage works favourable in hilly areas](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acd-works-hilly-areas) — Irrigation and Drainage Engineering, chapter 8 - [Cross drainage: Q 25, uplift on roof of barrel](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acd-q25-uplift-roof-barrel-800) — Irrigation and Drainage Engineering, chapter 8, asked 2×