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 - Discussion on Floodplains and Flood Frequency
| Information from Dataset | Analysis |
|---|---|
| ""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."" |
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| ""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."" |
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| ""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"" |
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| ""Hydrologists commonly map the boundaries of 100-year floods to advise public officials on flood risk management and containment strategies."" |
|
Summary:
- This educational text explains how flood frequency is determined by various factors including climate, drainage area, channel slope, and soil absorption
- Defines the concept of a 100-year flood as a 1% annual probability event used for risk management planning
Understanding Source B: Table - Waterway Statistics for Region X
| Information from Dataset | Analysis |
|---|---|
| ""Channel slope is the difference in elevation between two points on a waterway divided by the horizontal distance between them."" |
|
| ""Drainage area is the total surface area, upstream from the mouth of that waterway, from which water will drain to that point."" |
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Table Analysis:
- The table shows 6 waterways with varying characteristics:
- Jackson River has largest drainage area (40,000 sq km)
- Bear Run Creek has smallest drainage area (2.3 sq km)
- Channel slopes range from 0.9 to 12.7 m/km
- Snowmelt floods percentage varies widely (3% to 67%)
- 100-year flood levels range from 3.3m to 12.0m
- Floodplain boundary areas range from 1.1 to 330 sq km
- Key pattern: Larger drainage areas generally correspond to larger floodplain boundaries (Jackson River with largest drainage area has largest floodplain boundary at 330 sq km)
- Connection to Source A: Source A's theoretical factors (drainage area, channel slope) are all measured here with specific values for each waterway
- Regional variation: Source A mentioned snowmelt as a flood cause ""in many regions"" - Source B shows this varies dramatically even within one region (3% to 67%)
Summary:
- The table provides comprehensive hydrological data for six waterways in Region X
- Demonstrates how Source A's theoretical flood factors manifest with dramatic variation in real measurements
- Shows range from tiny creeks to large rivers
Overall Summary
- Framework integration: Source A provides the theoretical framework explaining that flood frequency depends on climate, drainage area, channel slope, and soil absorption, while Source B applies these concepts with actual measurements from Region X waterways
- Data variation: The data reveals huge variations within a single region: drainage areas range from 2.3 to 40,000 sq km, snowmelt's role in flooding varies from 3% to 67%, and 100-year flood boundaries span from 1.1 to 330 sq km
- Validation: The same statistical event (100-year flood) manifests very differently across waterways depending on their physical characteristics, validating Source A's multi-factor approach to understanding flood risk
Question Analysis
Understanding the Question
- Main task: Determine which statement can be logically concluded from the waterway data and flood information provided
- Key constraints:
- Must be logically inferred from the given information
- Only one statement should be most logically supported
- Must consider both Source A (flood concepts) and Source B (waterway data)
- Answer type needed: Logical inference evaluation
Connecting to Our Analysis
- The analysis shows relationships between drainage area, channel slope, snowmelt flooding percentages, and floodplain sizes across six waterways
- Need to evaluate each statement against these relationships and Source A's flood probability concepts
- Can answer from analysis: Yes - the analysis contains all necessary relationships and data patterns
Evaluating Key Relationships
Mathematical foundation: Source A establishes that 100-year floods have 1% annual exceedance probability
Statement Evaluations
Statement 1 Analysis
""The drainage area and channel slope of a waterway are positively correlated.""
- Claim: Drainage area and channel slope increase together
- Data shows: Jackson River (40,000 sq km) has 1.2 m/km slope; Bear Run Creek (2.3 sq km) has 12.7 m/km slope
- Reality: Larger drainage areas correspond to lower slopes
- Result: INCORRECT - data shows inverse relationship
Statement 2 Analysis
""The channel slope of a waterway is positively correlated with the area of the 100-year floodplain boundary.""
- Evidence from data: Negative correlation between slope and floodplain size (12.7 → 1.8 vs 1.2 → 330)
- Result: NOT SUPPORTED - data shows inverse relationship
Statement 3 Analysis
""A 5-year flood has a 20% annual exceedance probability.""
- Claim: A 5-year flood has 20% annual probability
- Mathematical calculation: 1/5 years = 0.20 = 20% probability
- Established principle: 100-year flood = 1/100 = 1% probability
- Logic: Follows the same mathematical principle as Source A
- Result: CORRECT - logically follows from established principle
Statement 4 Analysis
""The larger a waterway's drainage area, the more frequently its floodplain becomes inundated.""
- Problem: No frequency data available to evaluate
- Result: NOT SUPPORTED - insufficient data to determine relationship
Statement 5 Analysis
""The greater the average channel slope of a waterway, the more prone the waterway is to snowmelt flooding.""
- Claim: Steeper slopes lead to more snowmelt flooding
- Data shows: Bear Run Creek (12.7 m/km slope) has 16% snowmelt; Evans Creek (2.0 m/km slope) has 67% snowmelt
- Reality: No clear pattern between slope and snowmelt percentage
- Result: INCORRECT - no positive correlation exists
Complete Statement Review
- Statement 1: Negative correlation between drainage area and slope (40,000 → 1.2 vs 2.3 → 12.7)
- Statement 2: Negative correlation between slope and floodplain size (12.7 → 1.8 vs 1.2 → 330)
- Statement 3: Mathematically consistent with Source A's probability framework
- Statement 4: No frequency data available to evaluate
- Statement 5: No correlation between slope and snowmelt percentage in data
Answer
""A 5-year flood has a 20% annual exceedance probability.""
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.