Chapter 2

Question 1

Hydrologic Cycle

Answer 1

The local, regional, and global movement of water in all three phases (gas, liquid,
solid)

Question 2

Watersheds

Answer 2

A land area from which all water drains to a single point, called the watershed outlet, bounded by a ridge

Question 3

Channel Heads

Answer 3

Higher elevation locations where small stream channels start

Question 4

Channels tend to be ____ near their heads and ____ near their outlets

Answer 4

inside narrow, steep valleys
inside broader, flatter areas

Question 5

Floodplain

Answer 5

The land area that is covered in water during a flood

Question 6

Factors that can affect potential flooding

Answer 6

Soil infiltration capacity, soil thickness, slope steepness, amount of water in the soil, and amount of vegetation on the land surface

Question 7

Which types of soil are able to absorb rainwater faster?

Answer 7

Coarse (sandy), as opposed to fine (clayey)

Question 8

Flash Flood

Answer 8

Sudden flooding that typically occurs in the headwater portions of a watershed where slopes are very steep, leading to very rapid surface runoff

Question 9

What typically causes a flash flood?

Answer 9

Intense rainstorms centered over small sub-watersheds, dam failures, sudden breaking of debris jams, or landslides into water bodies

Question 10

Downstream Flood

Answer 10

Floods generally produced by rainstorms of a wide extent and long duration. They occur at lower portions of a watershed, and the runoff from large parts of the watershed may take a long time to arrive, causing the flood to develop relatively slowly. The slope in downstream channels is also flatter, which will also cause the water to move slower

Question 11

Pro and con to downstream floods

Answer 11

Pro: allows for ample warning time
Con: slow to recede, leading to long disruptions and damage

Question 12

Flow Rate or Discharge

Answer 12

The volume of water flowing past a point per unit time (typically cubic meters per second or cubic feet per second)

Question 13

Hydrograph

Answer 13

A plot of flow rate versus time, showing the progress of a flood

Question 14

Flood Frequency

Answer 14

The probability that a flood of at least a certain size will occur in any particular year

Question 15

Recurrence Interval of Floods

Answer 15

The average time (usually years) between floods of a certain size, also the mathematical inverse of frequency

Question 16

Types of damage caused by floods

Answer 16

Damage caused by currents, debris, and sediment
Erosion and deposition of sediment
Pollution of rivers
Hunger and disease

Question 17

Damage caused by currents, debris, and sediment

Answer 17

Floods may leave in their wake tremendous damage to infrastructure (particularly transportation due to damage to bridges). Many people potentially are made homeless by destruction of their residences.

Question 18

Erosion and deposition of sediment

Answer 18

Floods often cause severe erosion, with
the consequence that formerly productive farmland can be degraded. The eroded sediment that is deposited elsewhere can be damaging in many ways.

Question 19

Pollution of rivers

Answer 19

Many pollution-laden structures and facilities (wastewater treatment plants, petroleum storage tanks, etc) are located in floodplains. A serious flood can damage the structures, releasing various types of pollutants into the river system.

Question 20

Hunger and disease

Answer 20

Pathogens are likely to be carried into stream systems by floods. If those streams are used for water supply, disease outbreaks are possible. The damage to farmlands and the general disruptions of major floods can trigger food shortages and famine.

Question 21

Urbanization and Flooding

Answer 21

Urban areas are dominated by pavement and other impervious surfaces that are
unable to absorb waters. The surfaces are also relatively smooth, causing the surface runoff to travel much more quickly than it would on vegetated surfaces. Additionally, many urban areas are drained by storm drains which further accelerate the transport of rainwater to stream, increasing the flood risk. Bridges and other structures built in the vicinity of streams also created the possibility of flooding related to debris jams.

Question 22

Flood damage control methods

Answer 22

Dams, levees, channelization, site improvements, and land use planning

Question 23

Dams

Answer 23

A reservoir space that can temporarily stored flood water, and release it slowly over a long period of time. The same total amount of water eventually flows downstream, but the peak flow is much reduced, hopefully to a level that does not exceed bankfull downstream. Dams are also expensive to construct and difficult to maintain.

Question 24

Possible dam failures

Answer 24

Landslides into the reservoir, erosion of the dam foundation during a flood event, extreme amounts of flood water over-topping the dam, and earthquakes

Question 25

Levees

Answer 25

Common features caused by stream sediment deposited just outside of the stream channel due to periodic flooding of the stream. These levees do increase the size and capacity of the channel and tend to reduce future flooding. Artificial levees can be effective at reducing flooding if used carefully and sparingly. Artificial levees can also create problems because they cause the water to flow at a higher velocity, which can make flooding more severe for downstream neighbors as well as eroding the stream channel. Artificial levees can also lead to breaches or failures with more severe flooding consequences, and are difficult to maintain similarly to dams.

Question 26

Channelization

Answer 26

The process of clearing, straightening, or paving a stream channel. This is intended to increase the flow capacity by decreasing channel roughness. Some problems may arise due to increased flow rates and velocities, worsening flood and erosion issues downstream, and extensive channelization destroys the habitats, ecology, and aesthetics of the stream.

Question 27

Site Improvements

Answer 27

Raising foundation of buildings above the flood hazard, constructing flood walls or mounds, using waterproof construction, installing improved drains and pumps, relocation, and government purchasing/removing of homes damaged by floodwaters

Question 28

Land-use planning

Answer 28

The best strategy for flood damage control. Avoid placing vulnerable structures and facilities in floodplains, made possible by the extensive mapping of floodplains done by FEMA and local governments. This strategy is not always easy, as many structures are already places in floodplains and the progression of urbanization decreases the available safe land to expand to.

Question 29

Ways to overcome the resistance to land-use planning

Answer 29

education and incentives (money or other)