Deck 9: Rivers and Flooding

Question 1

The portion of rainfall that flows off the land and directly into a river is called

A)watershed
B)flood magnitude
C)recurrence interval
D)runoff

Answer 1

D

Question 2

Why is flood hazard mapping considered an important step in floodplain management?

A)Flood hazard mapping guides appropriate development in the floodplain.
B)Flood hazard mapping mandates that the floodplain should not be developed.
C)Flood hazard mapping shows those parts of the urban environment that are impervious.
D)Flood hazard mapping is a first step toward channel restoration.

Answer 2

A

Question 3

The base level of a stream is typically sea level.

Answer 3

True

Question 4

What type of river channel is characterized by multiple channels and gravel bars?

A)meandering
B)riffling
C)pooling
D)braided

Question 5

What is river base level?

A)the lowest level to which a river may erode
B)the river discharge that is maintained year round
C)the elevation of the stream bed
D)the smallest amount of sediment a stream can transport

Question 6

The bed load is the dominant portion of the total load for most rivers.

Question 7

The Ventura Beach RV Resort was flooded because

A)it was constructed in an unrecognized distributary channel that became active
B)intense rainfall struck the resort
C)urbanization had increased impervious cover by a large degree
D)it sits adjacent the ocean, which produced anomalously high waves

Question 8

A faster-moving stream has greater competence than a slow-moving stream.

Question 9

The total load of sediment that a river carries in a given period of time is called

A)competency
B)bed load
C)base level
D)capacity

Question 10

The degree of urbanization consists of

A)percentage of impervious cover and the percentage of area served by storm sewers
B)the number of buildings taller than two stories
C)the degree to which streams are impacted by paving of streets
D)the proportion by which infiltration capacity of soils is changed

Question 11

If a stream channel is of constant width and depth, how must increased discharge be accommodated?

A)greater sediment transport
B)flooding
C)increased velocity
D)steeper channel slope

Question 12

Which type of flood is typically caused by intense rainfall of short duration?

A)downstream flood
B)stage flood
C)overbank flood
D)upstream flood

Question 13

How do point bars and cut banks differ from one another in a stream system?

A)Cut banks are sites of erosion, while point bars are sites of deposition.
B)Cut banks typically host riffles, while point bars are characterized by pools.
C)Point bars are characteristic of meandering streams, while cut banks are characteristic of braided streams.
D)They are both areas of deposition, but the cut bank typically receives a greater volume of sediment.

Question 14

The suspended load of most rivers consists mostly of

A)gravel
B)sand
C)silt and clay
D)dissolved substances

Question 15

For the same amount of discharge, a narrow, shallow channel will have a higher water velocity than will a wide, deep channel.

Question 16

Why did extensive flooding occur upstream of St. Louis during the 1993 Mississippi River flood?

A)Widespread urbanization in the upper portion of the basin increased runoff to a great degree.
B)Floodwalls protecting St. Louis caused a bottleneck in the river's flow.
C)The St. Louis floodwall failed, flooding St. Louis and the area upstream.
D)An intense thunderstorm dropped several inches of rain on the area in only a few hours.

Question 17

Why might logging of a drainage basin change the slope of the river?

A)The base level of the stream is altered by the increased sediment load.
B)The stream must steepen to accommodate the increased runoff.
C)Increased sediment load causes the river to steepen its gradient to transport more sediment.
D)Decreased erosion shuts off sediment supply, causing the river to erode.

Question 18

In what way can structural control of floods actually increase flood damage?

A)by decreasing impervious cover in the urban environment
B)by increasing runoff in the upper portions of drainage basins
C)by encouraging development on the floodplain
D)by making the water transmitting capacity of the stream less efficient

Question 19

What is the best description of the "10-year flood"?

A)a flood that can occur only once every 10 years
B)a flood that has a 10% chance of occurring each year
C)a flood that occurred within the last 10 years
D)a flood that lasts for approximately 10 years

Question 20

The floodplain is usually considered as a distinct system with respect to the river system.

Question 21

Structural flood controls often increase overall flood hazard.

Question 22

Urbanization generally increases the lag time between the peak of rainfall and the peak of the resulting flood.

Question 23

Streams generally maintain a(n) ________ between the sediment transported and the sediment delivered to the stream.

Question 24

Protection of banks by planting trees and other vegetation is a form of ________.

Question 25

________ are shallow portions of a meandering stream, in which the water is typically fast-moving at low flows.

Question 26

A(n) ________ pond is used to hold back water during a storm and release it more slowly into the stream system

Question 27

The objective of ________ is to maximize beneficial use of the floodplain while minimizing flood damage and the cost of flood protection.

Question 28

The total load of a river is dominated by the ________ load.

Question 29

Flood hazard mapping and floodplain regulation are modern means of reducing flood damages.

Question 30

The lag time between peak rainfall and peak stream discharge is typically increased by urbanization.

Question 31

Braided channels are typically characterized by fine-grained bed load.

Question 32

________ changes many characteristics of floods in smaller streams.

Question 33

A braided stream usually has just one channel.

Question 34

The continuity equation pertains to the accommodation of ________ by a stream channel.

Question 35

The 100-year flood is the flood that occurred exactly 100 years ago.

Question 36

The ________ is the period of time in which a flood of given magnitude is expected.

Question 37

Downstream floods typically cover larger areas than do upstream floods.

Question 38

Following Hurricane Floyd in 1999, residents in one part of the state of ________ were relocated from a badly impacted floodplain.

Question 39

The region drained by a single river or river system is the ________.

Question 40

The principal objective of channelization is to control floods.

Question 41

A(n) ________ stream system is one in which multiple small channels are dispersed across a sand or gravel channel.

Question 42

________ consists of straightening, deepening, widening, clearing, or lining existing stream channels.