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The frequency of flooding onto floodplains—the lands situated adjacent to rivers and other waterways—depends on factors such as climate, drainage area, channel slope, and the absorptive capacity of soil. In rainy regions, the floodplain may be inundated frequently, and in arid regions the floodplain may remain dry for years. In many regions, floods occur primarily during the snowmelt runoff season.
Floods are often described in terms of their statistical frequency. A 100-year flood, for example, describes the level of floodwater expected to be equaled or exceeded once every 100 years. Such a flood is also considered the 1% annual exceedance probability flood (i.e., a flood with a 1% chance of being equaled or exceeded in any given year). Hydrologists commonly map the boundaries of 100-year floods to advise public officials on flood risk management and containment strategies.
Which one of the following can be most logically inferred from the information given?
The drainage area and channel slope of a waterway are positively correlated.
The channel slope of a waterway is positively correlated with the area of the 100-year floodplain boundary.
A 5-year flood has a 20% annual exceedance probability.
The larger a waterway's drainage area, the more frequently its floodplain becomes inundated.
The greater the average channel slope of a waterway, the more prone the waterway is to snowmelt flooding.
| Information from Dataset | Analysis |
|---|---|
| "The frequency of flooding onto floodplains...depends on factors such as climate, drainage area, channel slope, and the absorptive capacity of soil" |
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| "In rainy regions, the floodplain may be inundated frequently, and in arid regions the floodplain may remain dry for years" |
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| "floods occur primarily during the snowmelt runoff season" |
|
| "A 100-year flood...describes the level of floodwater expected to be equaled or exceeded once every 100 years" |
|
| "Such a flood is also considered the 1% annual exceedance probability flood" |
|
| "Hydrologists commonly map the boundaries of 100-year floods to advise public officials" |
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Summary: This source explains the key factors that control flooding (climate, drainage area, channel slope, soil absorption) and introduces the important concept of 100-year floods that hydrologists use as a standard planning measure.
Table Analysis:
Summary: This table demonstrates Source A's principles with real data from Region X, showing extreme variations in all flood-controlling factors across six waterways and confirming that 100-year flood mapping is indeed standard practice.
The question asks which statement logically follows from the information provided in the sources. This requires:
The answer type needed is a logical inference based on data patterns and theoretical explanations.
The analysis contains data relationships, correlation patterns, and theoretical explanations that can be used to evaluate each inference. The linkages between Source A's flood probability explanation and Source B's data patterns are particularly relevant. The analysis contains all necessary information to evaluate each statement independently.
The evaluation process involves assessing each statement against the data patterns and theoretical framework provided in the sources. Key data points include drainage areas, channel slopes, floodplain boundaries, and probability patterns for flood events.
Statement: "The drainage area and channel slope of a waterway are positively correlated."
Statement: "The channel slope of a waterway is positively correlated with the area of the 100-year floodplain boundary."
Statement: "A 5-year flood has a 20% annual exceedance probability."
Statement: "The larger a waterway's drainage area, the more frequently its floodplain becomes inundated."
Statement: "The greater the average channel slope of a waterway, the more prone the waterway is to snowmelt flooding."
Additional verification confirms that:
Only Statement 3 follows logically from the established probability pattern and can be mathematically derived from the given information.
"A 5-year flood has a 20% annual exceedance probability."
This statement is the only one that can be logically inferred from the sources through direct mathematical calculation using the probability pattern established for flood events.
The drainage area and channel slope of a waterway are positively correlated.
The channel slope of a waterway is positively correlated with the area of the 100-year floodplain boundary.
A 5-year flood has a 20% annual exceedance probability.
The larger a waterway's drainage area, the more frequently its floodplain becomes inundated.
The greater the average channel slope of a waterway, the more prone the waterway is to snowmelt flooding.