Why is a hydropower project studied in stages of increasing detail?

To spend money on detailed work only for projects that prove worthwhile

Because law requires exactly seven reports

What is the correct order of studies?

Feasibility, reconnaissance, pre-feasibility, desk study

Reconnaissance, desk study, feasibility, pre-feasibility

Pre-feasibility, desk study, feasibility, reconnaissance

Which is investigated at the feasibility stage but not in earlier stages?

Full EIA, subsurface drilling and financial analysis for licensing

How does the accuracy of cost estimates change along the stages?

It improves from about +/-40-50% at reconnaissance to +/-10-15% at feasibility

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Stages of hydropower project study

Short answer

Hydropower studies progress through desk study, reconnaissance, pre-feasibility, feasibility (with EIA), and detailed design. Each stage investigates hydrology, geology, layout, cost, environmental and socio-economic parameters with increasing accuracy to justify investment.

In what stages study of a hydropower project are completed? What parameters do you investigate in each stage? Discuss with hydropower development cycle.

A hydropower project is studied in stages of increasing detail, so that money is spent on detailed work only for projects that prove worthwhile. Together with construction and operation these form the hydropower development cycle.

 Identification / desk study
            |
 Reconnaissance study
            |
 Pre-feasibility study
            |
 Feasibility study  (+ EIA, licences)
            |
 Detailed design & tender
            |
 Construction & commissioning
            |
 Operation & maintenance  --> rehabilitation

1. Desk study / identification

Using maps (1:50 000 topo), existing hydrological records and reports, possible sites are identified and rough power potential $P = 9.81\,QH\eta$ is computed. Several alternatives are listed.

2. Reconnaissance study

A short site visit and study to screen alternatives.

Rough layout: headworks, waterway, powerhouse locations.
Approximate head (altimeter/GPS) and spot flow measurement.
General geology, access, land use, settlements.
Rough cost and power; ranking of sites.

3. Pre-feasibility study

Selects the best scheme and decides whether a full feasibility study is justified.

Topographic survey at larger scale; hydrological analysis (flow duration curve, floods).
Preliminary geology (surface mapping), sediment and seismic data.
Comparison of layouts and capacities; preliminary design and cost estimate.
Initial environmental examination, power market and economic indicators (B/C, IRR).

4. Feasibility study

Detailed enough for financing and licensing decisions.

Detailed topographic surveys; long-term hydrology, design flood, sediment study.
Subsurface investigation: drilling, test pits, seismic refraction, lab tests of construction materials.
Optimisation of installed capacity, firm/secondary energy; final layout.
Design of main structures, construction schedule, detailed cost estimate.
Full EIA, social and resettlement study; power market and transmission; financial and economic analysis (NPV, IRR, B/C, cost per kWh).
In Nepal, the generation licence (DoED) and PPA with NEA are based on this stage.

5. Detailed design and tender

Final engineering drawings, specifications, bill of quantities, tender documents; further investigation where needed.

6. Construction and commissioning

Access roads, river diversion, civil works, electro-mechanical and transmission works; testing and commissioning.

7. Operation and maintenance

Power generation, monitoring of sediment, structures and equipment; later upgrading or rehabilitation, which restarts the cycle.

Stage	Main output	Accuracy of cost
Reconnaissance	Promising sites	±40–50%
Pre-feasibility	Best alternative	±25–30%
Feasibility	Go / no-go, financing	±10–15%
Detailed design	Drawings, tender	±5–10%

✓ Answer checked by Claude Opus 5.5 (high effort)

Stage discharge curve and its application · Hydro Power, chapter 2
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