---
title: "Studies in reconnaissance, pre-feasibility, feasibility"
subject: "Hydropower Engineering"
chapter: 2
key: "semester_7/hydropower_engineering:recon-prefeas-feas-studies"
source: https://www.bctengineer.com/q/semester_7/hydropower_engineering/recon-prefeas-feas-studies
site: BCT Engineering
---

# Studies in reconnaissance, pre-feasibility, feasibility

Hydropower Engineering · Chapter 2: Planning of Hydropower Projects

- Asked in: 2073 Shrawan, 7 marks; 2072 Chaitra, 8 marks; 2070 Ashad, 4 marks (asked 3 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/hydropower_engineering/recon-prefeas-feas-studies
- Whole chapter: https://www.bctengineer.com/md/semester_7/hydropower_engineering/chapter-2

## Question

Highlight the major studies and investigations carried out during reconnaissance, pre-feasibility and feasibility studies (list the minimum checklist for these studies).

## Short answer

Reconnaissance: desk study, site visit, regional hydrology, rough layout, environmental screening. Pre-feasibility: moderate surveys, site hydrology, geophysics, alternative layouts, scoping. Feasibility: detailed surveys, long-term hydrology with floods/sediment, drilling, optimized design, complete IEE/EIA and financial analysis.

## Answer

Hydropower studies are done in stages so that money is spent in steps and weak projects are dropped early. Each stage gives more detail and less uncertainty (cost accuracy about ±30-40% at reconnaissance, ±20-25% at pre-feasibility, ±10-15% at feasibility).

#### 1. Reconnaissance study
Purpose: to identify possible sites and find if the project is worth further study.
- Desk study: topographic maps (1:25,000/1:50,000), satellite images, geological maps.
- Rapid site visit: access, river and valley shape, rough geology.
- Hydrology: use of nearby station data and regional methods (e.g. WECS-DHM method, MIP) to get mean flow.
- Rough layout, installed capacity, energy and rough cost estimate.
- Quick check of environment and social issues; ranking of sites.

#### 2. Pre-feasibility study
Purpose: to compare layout options and choose the best one.
- Topographic survey of the headworks and powerhouse areas (1:2,000-1:5,000), river cross-sections.
- Hydrology: at least 1 year of gauging if possible; flow duration curve, floods (design flood 100 yr), sediment.
- Geology: surface mapping, geophysical survey (seismic refraction/resistivity), a few drill holes.
- Alternative layouts and capacities; selection of the best.
- Cost estimate (±20-25%), preliminary economic analysis (B/C, IRR), preliminary environment study (scoping).
- Access road and transmission line options.

#### 3. Feasibility study
Purpose: to prove the technical, economic and environmental viability so that the investor and lender can decide.
- Detailed topographic survey (1:500-1:1000 for structures).
- Hydrology: long term flow series, FDC, 100-year and 1000-year flood, GLOF, sediment load.
- Geology: detailed mapping, drilling at all structures, tunnel and test adits, construction material survey and laboratory tests.
- Optimisation of capacity; layout design of headworks, desander, canal/tunnel, forebay, penstock and powerhouse; selection of turbines and equipment.
- Bill of quantities and cost estimate (±10-15%), construction schedule and plan.
- Financial and economic analysis (NPV, B/C, IRR, sensitivity).
- Complete IEE/EIA, resettlement plan, and risk assessment.

#### Minimum checklist
| Item | Recon | Pre-FS | FS |
|---|---|---|---|
| Maps and survey | Existing maps | Moderate survey | Detailed survey |
| Hydrology | Regional | Site gauging, floods | Long series, floods, sediment |
| Geology | Desk and visit | Mapping, geophysics | Drilling, tests |
| Layout | Single | Alternatives | Final optimised |
| Cost | Rough | ±20-25% | ±10-15% |
| Environment | Screening | Scoping | IEE/EIA |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What cost accuracy goes with reconnaissance, pre-feasibility and feasibility?
   A. ±30-40%, ±20-25%, ±10-15%
   B. All ±5%
   C. ±10-15%, ±20-25%, ±30-40%
   D. ±50%, ±40%, ±30%
   Answer: A. Accuracy improves as studies get detailed. (Key point: Cost accuracy)

2. What is the purpose of the reconnaissance study?
   A. Financial closure
   B. Prepare tender
   C. Identify possible sites and decide if worth further study
   D. Final design
   Answer: C. It screens and ranks sites. (Key point: Reconnaissance purpose)

3. What is the main aim of pre-feasibility?
   A. Construction
   B. Only desk study
   C. Operation
   D. Compare layout options and choose the best
   Answer: D. Alternatives are compared. (Key point: Pre-feasibility)

4. What geology work is done at feasibility stage?
   A. Only surface mapping
   B. Desk study only
   C. None
   D. Drilling at all structures, adits and lab tests
   Answer: D. Detailed drilling and tests are needed. (Key point: Feasibility geology)

## 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
- [Pre-feasibility vs feasibility; site investigations](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aprefeasibility-vs-feasibility-investigations) — Hydropower Engineering, chapter 2
- [Development phases; pre-feasibility factors](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Adev-phases-prefeasibility-factors) — Hydropower Engineering, chapter 2

## 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