--- title: "Pre-feasibility vs feasibility; site investigations" subject: "Hydropower Engineering" chapter: 2 key: "semester_7/hydropower_engineering:prefeasibility-vs-feasibility-investigations" source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/prefeasibility-vs-feasibility-investigations site: BCT Engineering --- # Pre-feasibility vs feasibility; site investigations Hydropower Engineering · Chapter 2: Planning of Hydropower Projects - Asked in: 2071 Chaitra, 8 marks - Video: [#5 PRE-FEASIBILITY & FEASIBILITY STUDY IN HINDI | PROJECT MANAGEMENT](https://www.youtube.com/watch?v=N5F37nvcBbs) — Sonu Singh - PPT wale - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/prefeasibility-vs-feasibility-investigations - Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-2 ## Question Differentiate between pre-feasibility and feasibility studies of a hydropower project, explaining the site specific hydrological and topographical investigations. ## Short answer Pre-feasibility selects the best alternative with moderate survey, short hydrology, mapping, geophysics, few boreholes, cost accuracy ±20-25%, and scoping. Feasibility confirms viability with detailed surveys, long hydrology, floods, sediment, drilling, design optimisation, cost accuracy ±10-15%, and IEE/EIA. Hydrological: gauge, flow measurement, FDC, floods, sediment. Topographical: detailed mapping, cross-sections, alignment survey. ## Answer Pre-feasibility selects the best option and decides if detailed study is worthwhile; feasibility confirms the selected option in full detail so that the investment decision can be made. | Point | Pre-feasibility | Feasibility | |---|---|---| | Aim | Compare alternatives, select best | Confirm viability of selected project | | Survey | Moderate (1:5,000 to 1:2,000) | Detailed (1:1,000 to 1:500) | | Hydrology | Short gauging, regional methods | Long series, floods, sediment | | Geology | Mapping, geophysics, few holes | Drilling at all structures, tests | | Design | Conceptual | Preliminary design, optimisation | | Cost accuracy | ±20-25% | ±10-15% | | Environment | Scoping | IEE/EIA | | Output | Choice of layout, go/no-go | Bankable report | #### Site-specific hydrological investigations - Collect all available rainfall and runoff records (DHM) and the catchment characteristics. - Install a staff gauge or automatic gauge at the headworks; measure discharge by current meter or salt dilution regularly; develop the rating curve. - Derive the mean monthly flow, flow duration curve and low flow using correlation with a nearby gauged basin or the WECS/MIP method. - Estimate floods (return periods 2-1000 years), by frequency analysis or empirical methods, and check for GLOF/snow melt. - Measure suspended sediment concentration; estimate the sediment load and the particle size. - Record the high flood marks and the tail water level at the powerhouse. #### Topographical investigations - Topographic mapping with contours at the headworks, along the waterway and at the powerhouse. - River cross-sections and longitudinal profile (for the stage-discharge and head). - Reservoir area-capacity curve if the pond/reservoir exists. - Alignment survey of the canal/tunnel, penstock, access road and transmission line. - Benchmark control (GPS/total station), and the location of boreholes and test pits. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main difference in aim between pre-feasibility and feasibility studies? A. Pre-feasibility compares alternatives and selects the best; feasibility confirms the selected project in detail B. Pre-feasibility confirms viability; feasibility compares alternatives C. Both aim at tender documents D. Pre-feasibility is done after construction Answer: A. Pre-feasibility chooses the option; feasibility confirms its viability for the investment decision. (Key point: Aim difference) 2. Which survey scales fit pre-feasibility and feasibility respectively? A. 1:500 and 1:5,000 B. 1:5,000-1:2,000 and 1:1,000-1:500 C. 1:50,000 and 1:25,000 D. Both 1:100,000 Answer: B. Moderate survey at pre-feasibility becomes detailed survey at feasibility. (Key point: Survey scales) 3. What is done at the headworks gauge to get discharge records? A. Only water level is recorded and discharge ignored B. Discharge is guessed from rainfall C. Discharge is measured regularly by current meter or salt dilution to develop a rating curve D. The gauge is removed after one day Answer: C. Regular discharge measurements are related to stage to form a rating curve. (Key point: Rating curve) 4. How are mean monthly flows and low flows derived at an ungauged site? A. By correlation with a nearby gauged basin or WECS/MIP method B. By using the average of the sea level C. By measuring only floods D. By assuming constant flow Answer: A. Short records are extended by correlation with a gauged basin or regional methods. (Key point: Ungauged flow estimation) 5. Why are river cross-sections and a longitudinal profile surveyed? A. To decide the generator colour B. For the stage-discharge relation and head C. To design the turbine blade D. Only for the access road Answer: B. They give the stage-discharge relation and the available head along the river. (Key point: Topographic investigations) ## Related in Hydropower Engineering - [Pre-feasibility site-specific investigations](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aprefeasibility-site-investigations) — Hydropower Engineering, chapter 2 - [Studies in reconnaissance, pre-feasibility, feasibility](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Arecon-prefeas-feas-studies) — Hydropower Engineering, chapter 2, asked 3× ## Related in other subjects - [Pre-feasibility versus feasibility studies](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aprefeasibility-vs-feasibility) — Hydro Power, chapter 3