**Percentage Risk of Dam Failure during Construction**

To calculate the percentage risk that the dam may fail before the completion of the construction, we need to consider the design flood return period and the construction period.

**Design Flood Return Period:**

The dam is designed for a 50-year flood. This means that the dam is designed to withstand a flood event that has a 2% chance of occurring in any given year. The design flood return period indicates the level of flood the dam is expected to withstand without failure.

**Construction Period:**

The construction period is given as 8 years. During this time, the dam is being built and may not have reached its full capacity or strength. The risk of failure is higher during the construction phase compared to when the dam is completed.

**Calculating the Risk:**

To calculate the percentage risk of dam failure during construction, we need to consider the probability of a flood event occurring during the construction period. Since the dam is designed for a 50-year flood, we can assume that the probability of a flood event occurring in any given year is 2%.

The probability of a flood event occurring during the construction period can be calculated using the formula:

P = 1 - (1 - p)^n

Where P is the probability of a flood event occurring during the construction period, p is the probability of a flood event occurring in any given year, and n is the number of years in the construction period.

Substituting the values:

P = 1 - (1 - 0.02)^8

P ≈ 0.1450

Therefore, the percentage risk of dam failure during construction is approximately 14.50%.

**Conclusion:**

The percentage risk that the dam may fail before the completion of the construction is approximately 14.50%. This means that there is a 14.50% chance of a flood event occurring during the 8-year construction period, which could potentially lead to dam failure. It is important to consider this risk during the planning and construction phases to ensure appropriate mitigation measures are in place to minimize the potential consequences of a flood event.