The frequency of flooding onto floodplainsthe lands situated adjacent

Question

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.

Sajjad1994 · Accepted Answer

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.

Apt0810 · Answer

A-No,since drainage area decreases but channel slope both Increases and decreases,no positive correlation.

B-No, because when channel slope Increases the area of the 100-year floodplain boundary both Increases and decreases,no positive correlation.

C-100 year flood has 1% annual exceedance probability,so a 5 year flood has more frequency so it's probability of occurrence will also be more ,here 100 year flood =20*5 year flood , meaning 20*1% probability of occurrence=20% annual exceedance probability

D-No it is not sure because the inundation depends on various other cases such as season,climate, absorptive capacity of soil,channel slope.

E-Flooding occurs due to snowmelt runoff season but there is no dependency directly show

2) Snowmelt flooding and drainage area are both shown in Discussion and in the table and only absorptive capacity of soil is only shown in Discussion

3)a)No,since it is not known that how many people live near Jackson or porter river
b)No,Evans creek and Jackson river data is shown independently.
C)Yes, beacuse for Deer creek the flood plain boundary is 17 sq km and 1% annual exceedance probability is in flood plain boundary area

mSKR · Answer

1.  NO : The values of ACS doesn’t change as in proportion to river.

B.  NO:  The values of ACS doesn’t change as in proportion to FB

C:  YES 
A 100-year flood, for example, describes the level of floodwater expected to be equaled or exceeded once every 100 years.
 A 5-year flood, for example, describes the level of floodwater expected to be equaled or exceeded once every 5 years.
If a flood with a 1% chance of being equaled or exceeded in any given year (every 100 year) would be 20 times higher than if the same level needs to be compared every 5 years
Means now we have 20 times more value to compare about the same level

D. NO
 inundated = covered with water
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.

E: NO , The values of ACS doesn’t change as in proportion to SF
0.9-13
1.2-54
2.0-67
3.1 -8
5.5-3
12.7-16

2. Explicitly: clearly defined in Discussion ( means shouldnot be present in table discussion)
NO: In many regions, floods occur primarily during the snowmelt runoff season. + SF snowmelt floods mentioned in Table of Waterway Statistics
YES: such as climate, drainage area, channel slope, and the absorptive capacity of soil. + not defined in Table of Waterway Statistics
NO : such as climate, drainage area, channel slope, and the absorptive capacity of soil.+ discussed in table Table of Waterway Statistics

3. 
Drainage area
J river: 330
P river: 210 
It is true J area is more under flood plain boundary but nothing is mentioned about how people would be affected. It maybe possible that only few people affected along J river

NO

NO: no drains of one river into another river is mentioned

YES: 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)

DhruvBadaya · Answer

Note to self: Read the questions twice and slowly. The first reading should be fast, the second slow.

Arpitamitra · Answer

Question 2, Part 3: Drainage Area - "depends on factors such as climate, drainage area, channel slope, and the absorptive capacity of soil." this is explicitly mentioned in Discussion. Why is answer No for Drainage area then.  Sajjad1994 , please help.

Vishrut16 · Answer

In question 3 we are asked if the info indicate the given statement but that's not a rigid question, once before a question with similar language asked if information support but since info wasn't rigid i marked otherwise and it was incorrect so how do i keep my approach when language is confusing??

If i go by what i learned before q3p1 shall be correct.

If i go by what i learned before q3p1 shall be correct.

riri3026 · Answer

So for q3, if the question asked us to infer- A 100-year flood on the Jackson River would directly affect more people than would such a flood on the Porter River. 
Then our answer would have been yes but since they have asked us to only answer on the basis of the information provided, then its No.

nikitathegreat · Answer

1. Which one of the following can be most logically inferred from the information given?

Option D - The larger a waterway’s drainage area, the more frequently its floodplain becomes inundated.

Can we refer to the column to SF% to understand how frequently its floodplain become inundated? In that scenario. the answer will be yes since higher the drainage area, the more SF% except for 2 values.

karishma   GMATNinja  - Can you please help me with this.

Thanks

asbhd · Answer

KarishmaB   Bunuel  
For Q1 Option B; Don't we find the correlation by tracking the movement of the the two quantities relative to each other. 
If we check ACS & FBM, they move in the same "direction" 3 out of 5 times, and 2 times in opposite direction. So, isnt the "general trend" of a positive correlation?

I think this concept has been used to solve so many tables analysis question on correlations. Could you please clarify

cheshire · Answer

Sure it's technically correlation but it's extremely weak and is closer to no correlation and just randomness than a strong correlation. Had they moved in the same direction 5/5 or even 4/5 times it would be arguable but 3/5 is too inconsistent for this sample size.

	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.

The frequency of flooding onto floodplainsthe lands situated adjacent

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Yes	No
		Snowmelt flooding
		Absorptive capacity of soil
		Drainage area

Yes	No
		A 100-year flood on the Jackson River would directly affect more people than would such a flood on the Porter River.
		In Region X, Evans Creek drains into Jackson River.
		The area representing the 1% annual exceedance probability for Deer Creek is 17 sq km.

GMAT Multi-Source Reasoning (MSR) Questions

The frequency of flooding onto floodplainsthe lands situated adjacent

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