--- title: "Economic analysis of canal lining" subject: "Irrigation and Drainage Engineering" chapter: 4 key: "semester_6/irrigation_and_drainage_engineering:canal-lining-economic-analysis" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-lining-economic-analysis site: BCT Engineering --- # Economic analysis of canal lining Irrigation and Drainage Engineering · Chapter 4: Design of Canals - Asked in: 2075 Bhadra, 5 marks; 2065 Kartik (old course), 8 marks (asked 2 times) - Video: [Economic Analysis of Canal Lining As per IS 10430 2000](https://www.youtube.com/watch?v=0iokXsb7vJE) — Irrigation 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-lining-economic-analysis - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-4 ## Question Describe the economic analysis of canal lining (how will you justify the economics of canal lining for an existing canal) during design of irrigation canal. ## Short answer Lining is justified if annual benefits exceed annual cost. Annual cost = initial cost×(interest+depreciation) + extra maintenance. Benefits: water saved (70‑80% seepage reduction) valued by extra irrigated area, reduced maintenance, prevention of waterlogging, and smaller cross‑section. Compute B/C ≥ 1. ## Answer Lining an existing canal is justified when the yearly benefit exceeds the yearly cost of the lining. The analysis compares cost and benefit on an annual basis. #### Annual cost of lining $$ C = (\text{Initial cost of lining})\times(i + \text{depreciation}) + \text{Extra maintenance} $$ - Initial cost: lining cost per metre $\times$ length (materials, labour, subgrade preparation, joints). - Interest at the annual rate $i$, and depreciation (sinking fund) over the life of the lining (say 30-40 years for concrete). #### Annual benefits 1. **Saving of water by reduced seepage** – seepage loss before lining minus seepage loss after lining (often 70-80% is saved). The value of the saved water is its irrigation worth, i.e. the extra crop it can produce on additional area. 2. **Increased command area** from the saved water. 3. **Reduction in the cost of maintenance**, silt clearance and weed control. 4. **Saving in land** and structures: the higher velocity allows a smaller cross-section, with less excavation and embankment. 5. **Prevention of waterlogging**, and the cost of drainage avoided. 6. **Fewer breaches** and easier operation (higher permissible velocity, more reliable supply). #### Procedure 1. Estimate the unlined seepage loss $= $ (seepage rate, m³/s per million m² of wetted area) $\times P\,L$, using the Punjab or Davis-Wilson formulas; estimate the lined loss in the same way. 2. Water saved $=$ the difference, converted to hectares of extra irrigation using the duty $D$ (ha per m³/s). 3. Annual benefit $=$ (extra area $\times$ net return per ha) $+$ maintenance savings $+$ other savings. 4. Compute the annual cost of lining (above). 5. Benefit-cost ratio: $$ \text{B/C} = \frac{\text{Annual benefit}}{\text{Annual cost}} \ge 1 $$ The lining is economical if $B/C > 1$. The **break-even cost** of lining per square metre is the cost at which $B/C = 1$. The type of lining (concrete, brick, soil-cement, plastic membrane) is chosen as the cheapest one that gives an acceptable benefit. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. When is lining of an existing canal justified? A. When annual benefit exceeds annual cost, B/C > 1 B. When initial cost is smallest C. When seepage is zero D. When B/C < 1 Answer: A. Lining is economical if the benefit-cost ratio exceeds 1. (Key point: Criterion) 2. Annual cost of lining includes A. Initial cost only B. Initial cost x (interest + depreciation) plus extra maintenance C. Seepage loss only D. Initial cost divided by canal length Answer: B. Capital is charged with interest and depreciation over the lining life. (Key point: Annual cost) 3. Which is the main benefit evaluated? A. Increased seepage B. Reduced canal velocity C. Water saved by reduced seepage, converted to extra irrigated area via duty D. Greater excavation Answer: C. Saved water irrigates additional land, valued by net return per hectare. (Key point: Main benefit) 4. What is the break-even cost of lining? A. The cost at which B/C = 0 B. The cost with no maintenance savings C. The cost at which seepage equals duty D. The cost per square metre at which B/C = 1 Answer: D. Above that cost, lining is not economical. 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