--- title: "Canal components, borrow pit and spoil bank" subject: "Irrigation and Drainage Engineering" chapter: 3 key: "semester_6/irrigation_and_drainage_engineering:canal-components-borrow-spoil" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-components-borrow-spoil site: BCT Engineering --- # Canal components, borrow pit and spoil bank Irrigation and Drainage Engineering · Chapter 3: Canal Irrigation System - Asked in: 2078 Chaitra, 5 marks - Video: [Berm |Counter Berm|Spoil Bank|Bank|Borrowpit|ServiceRoad|Canal Component|| Irrigation Engineering](https://www.youtube.com/watch?v=XvHbao4LPnc) — PRER FOR CIVIL ENGINEERING - 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/canal-components-borrow-spoil - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-3 ## Question Explain with appropriate sketch the components of the canals and requirement of borrow pit and spoil bank in canal section. ## Short answer Canal components include bed, banks, berm, and service road. When excavation is less than fill, borrow pits supply earth; when surplus, spoil banks store excess. They are placed safely away from the canal to avoid instability and seepage. ## Answer #### Components of a canal section ```text spoil bank bank bank borrow pit __ ____ ____ ___ ____/ \____ GL ____/ \__ FSL __/ \___/ \____ berm \______/ berm bed ``` - **Bed and side slopes:** the bottom and the inclined sides of the channel. - **Full supply level (FSL) and free board:** the water level and the safety height above it. - **Banks:** earth embankments on one or both sides; the top of the wider bank carries the service road. - **Berm:** a horizontal strip between the canal and the toe of the bank; it gives stability, protects the bank from erosion and leaves room for silting. - **Dowel (dowla):** a small bank on the outer side of the road for safety and protection. - **Borrow pit:** a pit from which earth is taken to build the banks when the excavation of the canal is not enough (canal mainly in filling). - **Spoil bank:** a heap of surplus excavated soil placed in layers along the canal when the excavated earth is more than that needed for the banks (canal in deep cutting). #### Requirement of borrow pit and spoil bank - If the canal depth is **less than the balancing depth**, the excavation is less than the filling needed, and earth must be taken from **borrow pits**. They are preferably dug within the canal section (in the bed), where they later fill with silt. If they are outside, they should be shallow, continuous strips at least about 5 m from the toe of the bank, so that they do not cause seepage problems or breaches. - If the depth is **greater than the balancing depth**, there is surplus earth, which is dumped as a **spoil bank** at a safe distance from the canal edge so that it does not slide back or block drainage. - Both are located so as to avoid damage to land, with the least possible lead and cost. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. When is a borrow pit required? A. When canal depth is less than balancing depth, so excavation is short of the fill B. When depth exceeds balancing depth C. When the canal is lined D. When banks are absent Answer: A. Insufficient excavated earth must be supplied from borrow pits. (Key point: Borrow pit) 2. What is a spoil bank? A. Earth taken for the banks B. Surplus excavated earth dumped away from the canal when depth exceeds balancing depth C. The service road D. Bank of the river Answer: B. Deep cutting gives surplus soil, placed at a safe distance. (Key point: Spoil bank) 3. Where should borrow pits be placed? A. Inside the canal section B. Right at the toe of the bank C. Outside the berm at a distance from the toe, as shallow strips D. On top of the bank Answer: C. This avoids seepage and breaches. (Key point: Location of borrow pits) 4. What is the berm's function in the section? A. Carrying the road B. Storing spoil C. Raising FSL D. Stability, protection from erosion and room for silting Answer: D. It lies between canal and bank toe. 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