- 2071 Chaitra · 8 marks
Pre-feasibility vs feasibility; site 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.
Differentiate between pre-feasibility and feasibility studies of a hydropower project, explaining the site specific hydrological and topographical investigations.
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.
✓ Answer checked by Claude Opus 5.5 (high effort)
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