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.

DhruvBadaya · Accepted Answer

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

Sajjad1994 · 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)

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.

Gaurav07 · Answer

Someone please help me with question 3, especially the third part of the 3rd question?

Bunuel · Answer

For each of the following statements, select Yes if the information provided indicates that the statement is true. Otherwise select No.

• A 100-year flood on the Jackson River would directly affect more people than would such a flood on the Porter River.

There is no information in the passage or table that compares the populations or effects of a 100-year flood on these two rivers.

Answer: No.

• In Region X, Evans Creek drains into Jackson River.

The passage and table do not provide information about the drainage connections between specific rivers, such as Evans Creek and Jackson River.

Answer: No.

• The area representing the 1% annual exceedance probability for Deer Creek is 17 sq km.

Tab 1 (Discussion) mentions that the 100-year flood is also considered the 1% annual exceedance probability flood. So, the 6th column, "100-year FB" (sq km), shows the area affected by this flood. Since the table lists Deer Creek’s 100-year floodplain as 17 sq km, the statement is true.

Answer: Yes.

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Gaurav07 · Answer

Thank you Bunuel! This helps a lot.

Goldenfuture · Answer

Bunuel  - Can you help with Q1 and how to do that under 2 mins - considering I spent good time reading the MSR

Bunuel · Answer

The discussion states that a 100 year flood corresponds to a 1% annual exceedance probability, meaning a 1% chance in any given year. That relationship comes directly from the idea of once every N years corresponding to about 1 out of N each year. Using the same logic, a 5 year flood corresponds to 1 out of 5 per year, which is 20% annual exceedance probability.

Legallyblond · Answer

how is 17 sqkm helpinh here? its just that its 100 year old flood and thats why we selected yes for the third one right?

Bunuel · Answer

The 17 sq km is exactly what makes the statement true, because the statement is asking about the area, not just about whether Deer Creek has a 100-year flood. Since the discussion says a 100-year flood is the same as a 1% annual exceedance probability flood, Deer Creek’s 100-year FB value of 17 sq km gives the required area.

ShreyaMittal1609 · Answer

Hi  Bunuel  - I'm confused in determining the overall correlation. I might be missing an important concept here. Your response will be very helpful.
My understanding for correlation is that majority points should move in the same direction (3/5 times in the given question)
E: ACS in proportion to SF
0.9-13
1.2-54
2.0-67
3.1 -8
5.5-3
12.7-16

X: 0.9 → 1.2 → 2.0 and Y: 13 → 54 → 67 → looks positive
But then X increases substantially while Y drops: 2.0 → 3.1 → 5.5, while Y goes 67 → 8 → 3
The final point (12.7, 16) again moves in same direction.

So if the question asks whether these variables have a positive correlation, 3/5 times they moved in the same direction but magnitude is different. How can I determine the overall pattern (I also understand that one or two points can heavily affect the correlation)

egmat · Answer

Hi ShreyaMittal1609,

You're reacting to the elimination of  E  (and the same logic mSKR used to rule out A and B), and your instinct that "one or two points can swing the pattern" is a good one. But let me fix two things, because the way you're testing correlation is actually harder than what this question needs.

Consecutive-pair counting isn't how correlation works

Counting how many  adjacent  pairs move the same direction ( 3/5 , etc.) isn't a valid test. Correlation is about the  overall trend across all points , not whether neighbors happen to rise or fall together. If you sort by ACS and the SF values go  13  →  54  →  67  →  8  →  3  →  16 , there's no consistent climb at all - SF shoots up, then collapses, then bounces. That's simply  not  a positive relationship, and you don't need to quantify it.

On the GMAT you don't compute correlation - you just break the claim

Here's the shortcut. Choice E claims a  general rule : "greater ACS → more prone to snowmelt flooding." A general rule dies to a single clean  counterexample . From the  table ,  Bear Run Creek has the greatest ACS (12.7)  - yet  Jackson River and Evans Creek both have a higher % of snowmelt floods . So the steepest waterway is  not  the most snowmelt-prone. Rule broken → E is out. No pair-counting required.

The same move kills A and B: Bear Run Creek has the highest slope but nearly the smallest drainage area and floodplain boundary.

A tiny stand-in

Claim: "The taller a student, the higher their test score."
Data: the  tallest  student scored the  lowest .

You don't need a correlation coefficient - that one fact already sinks the claim.

That's exactly why the credited answer is  C : it comes straight from the definition (a  5 -year flood =  1/5  =  20% ), no data-pattern judgment needed at all.

Answer: C

	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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	DA (sq km)	ACS (m/km)	SF (%)	100-year FL (m)	100-year FB (sq km)
Jackson River	40,000	1.2	54	10.5	330
Porter River	27,000	0.9	13	12.0	210
Deer Creek	1,300	3.1	8	6.2	17
Miller Creek	660	5.5	3	7.4	6.5
Evans Creek	12	2.0	67	5.7	1.1
Bear Run Creek	2.3	12.7	16	3.3	1.8

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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My Rewards