The frequency of flooding onto floodplains—the lands situated adjacent to rivers and other waterways—depends on factors such as climate, drainage...
GMAT Multi Source Reasoning : (MSR) Questions
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?
OWNING THE DATASET
Understanding Source A: Text Source - Discussion on Floodplains and 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" |
|
| "In rainy regions, the floodplain may be inundated frequently, and in arid regions the floodplain may remain dry for years" |
|
| "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" |
|
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.
Understanding Source B: Table - Waterway Statistics for Region X
Table Analysis:
- What the table shows: Measurements of six waterways in Region X including drainage area, channel slope, snowmelt flood percentage, and 100-year flood data
- Key patterns observed:
- Drainage areas range enormously: from 2.3 sq km (Bear Run Creek) to 40,000 sq km (Jackson River)
- Channel slopes vary inversely with size: smaller waterways have steeper slopes
- Snowmelt contribution ranges from 3% (Miller Creek) to 67% (Evans Creek)
- 100-year flood levels range from 3.3m to 12.0m
- Floodplain boundaries generally correlate with drainage area size
- Inference: Wide variations exist across all measured factors, confirming the complexity of flood prediction
- Linkage to Source A: The table provides actual measurements for the exact factors (drainage area, channel slope) that Source A identified as key flood determinants
- Linkage to Source A: The snowmelt percentages quantify Source A's statement about snowmelt being a primary flood cause - showing it varies from minor (3%) to dominant (67%)
- Linkage to Source A: All six waterways have 100-year flood measurements, confirming Source A's statement that this is standard hydrological practice
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.
Overall Summary
- The sources work together to provide both theoretical understanding and practical application of flood science
- Source A explains that drainage area, channel slope, climate, and soil absorption control flooding frequency
- Source B provides concrete measurements showing these factors vary dramatically across Region X waterways
- The data confirms that snowmelt's importance as a flood cause ranges from minimal to dominant depending on the waterway
- 100-year flood mapping - the 1% annual probability standard - is actively used for all waterways regardless of size
Question Analysis
The question asks which statement logically follows from the information provided in the sources. This requires:
- Logical inference from given data
- Support from provided information
- Selection of single best answer
The answer type needed is a logical inference based on data patterns and theoretical explanations.
Connecting to Our Analysis
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.
Extracting Relevant Findings
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.
Individual Statement Evaluations
Statement 1 Evaluation
Statement: "The drainage area and channel slope of a waterway are positively correlated."
- Evidence: Jackson River (40,000 sq km drainage area) has 1.2 m/km slope
- Evidence: Bear Run Creek (2.3 sq km drainage area) has 12.7 m/km slope
- Analysis: Shows negative correlation between drainage area and channel slope
- Pattern: As drainage area increases, channel slope decreases
- Conclusion: Incorrect - The data shows negative correlation, not positive correlation
Statement 2 Evaluation
Statement: "The channel slope of a waterway is positively correlated with the area of the 100-year floodplain boundary."
- Evidence: Bear Run Creek (12.7 m/km slope) has 1.8 sq km floodplain boundary
- Evidence: Jackson River (1.2 m/km slope) has 330 sq km floodplain boundary
- Counter-evidence: Evans Creek (2.0 m/km slope, 1.1 sq km boundary) breaks any potential correlation
- Analysis: Mixed results with no clear positive correlation pattern
- Conclusion: Incorrect - No positive correlation evident in the data
Statement 3 Evaluation
Statement: "A 5-year flood has a 20% annual exceedance probability."
- Source reference: Source A states '100-year flood...1% annual exceedance probability flood'
- Mathematical pattern: X-year flood = \(\mathrm{\frac{1}{X}}\) annual probability
- Calculation: \(\mathrm{\frac{1}{5} = 20\%}\) for 5-year flood
- Logic: Direct mathematical inference from established probability pattern
- Conclusion: Correct - Logical extension of the probability pattern explained in Source A
Statement 4 Evaluation
Statement: "The larger a waterway's drainage area, the more frequently its floodplain becomes inundated."
- Analysis: Sources don't provide flood frequency data for different drainage areas
- Available data: Only factors affecting frequency, not actual frequency measurements
- Conclusion: Cannot be determined - Insufficient data to support this inference
Statement 5 Evaluation
Statement: "The greater the average channel slope of a waterway, the more prone the waterway is to snowmelt flooding."
- Evidence: Evans Creek (2.0 m/km slope, 67% snowmelt)
- Evidence: Miller Creek (5.5 m/km slope, 3% snowmelt)
- Analysis: No correlation between channel slope and snowmelt percentage
- Conclusion: Incorrect - Data shows no positive correlation between slope and snowmelt flooding
Systematic Checking
Additional verification confirms that:
- Statement 1 shows negative correlation rather than positive
- Statement 2 lacks consistent correlation pattern
- Statement 3 follows directly from the mathematical relationship established in Source A
- Statement 4 cannot be evaluated due to insufficient data
- Statement 5 contradicts the available snowmelt data
Only Statement 3 follows logically from the established probability pattern and can be mathematically derived from the given information.
Final Answer
"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.