Question

The SPF is usually around ______________________ of the MPF for the basin.

• A. 70%
• B. 80%
• C. 50%
• D. 60%

Hint:

In reservoir design:
- High-risk dams (water storage > 60 million $\text{m}^3$) are designed for the PMF/MPF.
- Intermediate-risk dams are designed for the SPF (which is \(\approx 60\%\) of the PMF).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
In hydrology and water resources engineering, design floods are estimated to size spillways and hydraulic structures safely.
The two primary design floods used are the Standard Project Flood (SPF) and the Probable Maximum Flood (PMF, also called Maximum Probable Flood or MPF).
Detailed Explanation:
Let us clarify the definitions and relationship between these two design floods:
- Probable Maximum Flood (PMF/MPF): The estimate of the boundary physical limit of flood runoff, calculated using the Probable Maximum Precipitation (PMP) under the most severe combination of meteorological and hydrological conditions. It is used for designing high-risk structures like large dams, where failure would cause catastrophic loss of life.
- Standard Project Flood (SPF): The flood estimate resulting from the Standard Project Storm (SPS), which represents the most severe storm recorded in the region of the basin.
It excludes extremely rare, severe meteorological combinations, making it less conservative than the MPF.
- In most standard hydrological practices and design guidelines (including those of the Central Water Commission, India), the Standard Project Flood (SPF) is approximately 60% (ranging between 50% and 60%) of the Probable Maximum Flood (PMF/MPF) for a given river basin.
It is used for hydraulic structures where the risk of failure does not justify the higher cost of designing for the MPF.

Step 2: Final Answer:
The SPF is typically around 60% of the MPF for a basin.