---
title: "Flow duration curve and planning parameters"
subject: "Hydro Power"
chapter: 3
key: "semester_6/hydro_power:fdc-planning-parameters"
source: https://www.bctengineer.com/q/semester_6/hydro_power/fdc-planning-parameters
site: BCT Engineering
---

# Flow duration curve and planning parameters

Hydro Power · Chapter 3: Planning of Hydropower Projects

- Asked in: 2071 Bhadra, 2+6 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/hydro_power/fdc-planning-parameters
- Whole chapter: https://www.bctengineer.com/md/semester_6/hydro_power/chapter-3

## Question

What is the flow duration curve? Describe in brief the parameters influencing planning of hydropower projects.

## Short answer

A flow duration curve graphs river flow versus exceedance probability. Key planning parameters include hydrology (flow, floods), topography (head), geology (foundation, seismic risk), sediment load, power market demand, grid access, and environmental and economic factors.

## Answer

#### Flow duration curve
A **flow duration curve (FDC)** is a graph of river discharge against the percentage of time that discharge is equalled or exceeded. It is drawn by arranging the recorded flows in descending order and plotting each against $P = \frac{m}{N+1}\times 100\%$. It is used to find firm flow, design discharge (e.g. Q40, Q65) and annual energy.

#### Parameters influencing planning of hydropower projects
1. **Hydrology:** the amount and variation of river flow (FDC, mean monthly flows, floods, low flows) decides firm power, installed capacity, and spillway size. Long, reliable records are needed.
2. **Topography (head):** power depends on $Q \times H$. Steep rivers with a short distance between intake and powerhouse give high head cheaply. Valley shape decides dam type, reservoir area and layout.
3. **Geology:** the foundation of the dam, tunnel route and powerhouse must be strong and stable. Faults, weak rock, landslides and seismic zones raise cost and risk (very important in the young Himalaya).
4. **Sediment:** Himalayan rivers carry heavy sediment, which needs desanders and causes turbine wear and reservoir filling.
5. **Power market and demand:** size and type of plant (base load or peaking, run-of-river or storage) must match the load curve, demand growth and possibility of export.
6. **Access and transmission:** distance to roads and to the grid; long transmission lines add cost and losses.
7. **Environmental and social factors:** land acquisition, resettlement, environmental flow, fish, effect on downstream users; an EIA/IEE is required.
8. **Economic and financial factors:** project cost, interest rate, energy tariff, benefit–cost ratio, IRR and payback period.
9. **Legal and institutional aspects:** licences, water rights, government policy and royalty.
10. **Construction materials and logistics:** availability of sand, aggregate and cement near the site.
11. **Multipurpose use:** irrigation, flood control, water supply and navigation needs can change the reservoir operation.

## Check yourself

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

1. What is the FDC used to find?
   A. Dam foundation strength
   B. Firm flow, design discharge (e.g. Q40, Q65) and annual energy
   C. Sediment grain size
   D. Tariff rates
   Answer: B. The FDC gives firm flow, design discharge and energy. (Key point: FDC uses)

2. Which planning decisions does hydrology control?
   A. Firm power, installed capacity and spillway size
   B. Only access roads
   C. Only the resettlement plan
   D. Only the tariff
   Answer: A. Flow variation and floods decide firm power, capacity and spillway size. (Key point: Role of hydrology)

3. Why are geology and sediment important in Himalayan projects?
   A. They only affect tariff
   B. They have no effect on cost
   C. Weak rock, faults and seismicity raise cost and risk, and heavy sediment needs desanders and wears turbines
   D. They fix the head
   Answer: C. Geology governs stability and cost; sediment causes turbine wear and reservoir filling. (Key point: Geology and sediment)

## Related in Hydro Power

- [Flow and power duration curves](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Aflow-power-duration-curves) — Hydro Power, chapter 3
- [Power duration curve and primary/secondary energy](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Apower-duration-curve-energy) — Hydro Power, chapter 3
- [Stages of hydropower project study](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Ahydropower-study-stages) — Hydro Power, chapter 3, asked 3×
- [Power market, hydrology and geology in planning](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Apower-market-hydrology-geology) — Hydro Power, chapter 3
- [Stage discharge curve and its application](https://www.bctengineer.com/question.md?key=semester_6%2Fhydro_power%3Astage-discharge-curve) — Hydro Power, chapter 2

## Related in other subjects

- [Flow duration curve and power at mean flow](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aror-capacity-fdc-flow-table-79) — Hydropower Engineering, chapter 3
- [Flow duration curve; firm and secondary energy](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Afdc-firm-secondary-energy-69) — Hydropower Engineering, chapter 3
- [Load duration curve; diesel plant; ROR flow duration](https://www.bctengineer.com/question.md?key=semester_7%2Fhydropower_engineering%3Aload-duration-diesel-import-fdc) — Hydropower Engineering, chapter 3
- [Flow duration curve and its applicability](https://www.bctengineer.com/question.md?key=semester_8%2Fpower_plant_design%3Aflow-duration-curve) — Power Plant Design, chapter 3, asked 3×