Official Explanation
1. Which one of the following can be most logically inferred from the information given?
Explanation
According to the table, Bear Run Creek has the least drainage area (2.3 square kilometers) and the greatest average channel slope (12.7 meters per kilometer), so drainage area and average channel slope are not positively correlated (ruling out A). Likewise, Bear Run Creek has the greatest average channel slope (12.7 meters per kilometer) but the second-to-least 100-year floodplain boundary area (1.8 square kilometers), so average channel slope and 100-year floodplain boundary are not positively correlated (ruling out B). Although the passage indicates that drainage area is a factor in the frequency of flooding onto floodplains, it does not suggest that a larger drainage area leads to more frequent flooding (ruling out D). Again, Bear Run Creek has the greatest average channel slope (12.7 meters per kilometer), but there are two other waterways in the table (Jackson River and Evans Creek) with a greater percentage of their floods that are snowmelt floods, showing that average channel slope and likelihood of snowmelt flooding are not positively correlated (ruling out E). The passage indicates that a 100-year flood level is expected to be equaled or exceeded once every 100 years. It follows logically that a 5-year flood is expected to be equaled or exceeded once every 5 years, making its annual exceedance probability 20% (C).
The correct answer is A 5-year flood has a 20% annual exceedance probability.
2. For each of the following, select Yes if it is explicitly mentioned in the passage (Discussion) but not in the table. Otherwise select No.
The question asks for information explicitly mentioned in the Discussion but not the table.
RO1
Snowmelt floods is a column heading in the table, so it does not meet the question’s criterion.
The correct answer is No.
RO2
Absorptive capacity of soil does not appear in the table, but the Discussion lists it as a factor that affects the frequency of flooding onto floodplains.
The correct answer is Yes.
RO3
Drainage area is a column heading in the table, so it does not meet the question’s criterion.
The correct answer is No.
3. For each of the following statements, select Yes if the information provided indicates that the statement is true. Otherwise select No.
RO1
Neither the Discussion nor the table provides information about the number of people affected by flooding, so there is no basis for determining the truth of this statement.
The correct answer is No.
RO2
Neither the Discussion nor the table provides information about the location of the rivers in Region X, so there is no basis for determining whether Evans Creek drains into Jackson River.
The correct answer is No.
RO3
According to the passage, a 100-year flood … is also considered a 1% annual exceedance probability flood. The table indicates that the area of the floodplain boundary of a 100-year flood for Deer Creek is 17 square kilometers.
The correct answer is Yes.