Question 1

Which of the following statements is NOT true regarding artificial levees?

Accepted Answer

Artificial levees are not used to help keep the channel straight so water flows faster. Their primary purpose is to raise the height a stream must reach before overflowing its banks. However, artificial levees can create the potential for catastrophic flood in areas downstream and can make flooding worse in areas upstream. They can be made of concrete or earthen materials.

Question 2

What best describes the headwaters of a drainage basin?

Accepted Answer

The headwaters of a drainage basin are the collection of small channels in the upper part of a basin that merge into larger streams. These small channels are typically the starting point of a river system and are where the water initially enters the watershed.

Question 3

Which of the following is NOT part of the hydrologic cycle?

Accepted Answer

Sequestration is not part of the hydrologic cycle. The hydrologic cycle involves evaporation, transpiration, infiltration, and overland flow. Sequestration refers to the long-term storage of carbon dioxide or other substances, and is not directly related to the movement of water through the environment.

Question 4

Which of the following terms is used to describe the volume of water flowing past a specific point in a stream over a given time period?

Accepted Answer

Discharge refers to the volume of water flowing past a specific point in a stream over a given time period, commonly measured in cubic meters per second or cubic feet per second. Flux refers to the flow of any substance (not just water) through a surface or boundary, and is usually measured in mass or volume per unit time. Square volume and specific capacity are not commonly used terms in the field of hydrology. Overland flow refers to the movement of water over the ground surface as opposed to through a stream channel.

Question 5

What best explains why stream valleys become wider over time?

Accepted Answer

Meandering streams erode their banks through lateral erosion and undercutting, leading to mass wasting events that contribute to the widening of stream valleys over time.

Question 6

Streams located near the mouth of a river are quite different compared to those near the headwaters. What best characterizes streams near the mouth?

Accepted Answer

Streams near the mouth of a river have low velocity because the gradient is reduced and the channel is wider. However, they have high discharge because the stream has already collected water from many tributaries. Meandering channels are also characteristic of streams near the mouth because the water has less energy and easily bends around obstacles.

Question 7

Which of the following statements best describes losing streams?

Accepted Answer

Losing streams are common in arid regions where the water from the stream is lost to the groundwater system due to the permeable materials in the streambed, leading to a decrease in the stream's flow.

Question 8

Some rivers naturally carry more water than others. Which of the following best explains why the Amazon River in South America carries 12 times more water than the Mississippi?

Accepted Answer

The Amazon's drainage basin lies mostly within a tropical rainforest which receives much more rainfall than the Mississippi's drainage basin.

Question 9

How do hydrologists measure the severity of floods?

Accepted Answer

Hydrologists measure the severity of floods by the height (stage) above which a stream overflows its banks, as it indicates the extent to which water levels exceed normal conditions and cause flooding.

Question 10

What best describes the basic role of streams in the Earth system?

Accepted Answer

Streams primarily function to drain water from the landscape and transport sediment. This process shapes the Earth's surface by eroding, transporting, and depositing sediment.

Question 11

Which of the following natural factors affect the degree or severity of flooding?

Accepted Answer

Rainfall volume is one of the main factors affecting the degree or severity of flooding, as well as the infiltration capacity of the ground. When the volume of rainfall exceeds the ground's capacity to absorb or hold the water, flooding can occur. Other factors, such as the size of raindrops or wind speed, may contribute to the intensity of a storm but do not have as direct an impact on flooding as rainfall volume and infiltration capacity. The slope of the land can also affect the severity of flooding, as steeper slopes may allow water to flow more quickly and intensely, exacerbating the impact of heavy rainfall.

Question 12

What best explains why groundwater baseflow is important to maintaining a healthy stream ecosystem in humid climates?

Accepted Answer

Groundwater baseflow is crucial for maintaining a steady flow of water in streams during dry periods, which helps to sustain aquatic life and maintain a healthy ecosystem.

Question 13

What best characterizes downstream flooding?

Accepted Answer

Downstream flooding is characterized by a large volume of water that rises and falls slowly, often resulting from prolonged rainfall or snowmelt in upstream areas. This type of flooding gives more warning time compared to flash floods, which rise and fall rapidly.

Question 14

In addition to cutting laterally, streams can also cut downward in their channels to form deep valleys and canyons. What best explains how streams can cut downward through solid rock?

Accepted Answer

Transported sediment causes abrasion of bedrock, which is a primary mechanism by which streams cut downward through solid rock. The sediment acts like sandpaper, grinding and wearing away the rock beneath the flowing water.

Question 15

Why is hydraulic sorting of sediment important in environmental geology?

Accepted Answer

Hydraulic sorting of sediment produces relatively pure deposits of sand and clay, which can have implications for environmental geology. For example, certain types of clay can act as natural barriers to contaminants, while sand can be used for filtering and erosion control. Identifying and understanding the characteristics of sediment deposits can be important in managing environmental hazards and resources.

Question 16

What best explains how hydrologists determine the frequency of flooding?

Accepted Answer

Hydrologists determine the frequency of flooding by calculating recurrence intervals from historical discharge records. This involves analyzing past floods to determine how frequently certain levels of flooding occur, and using that data to make predictions about future floods.

Question 17

What best describes a drainage basin?

Accepted Answer

A drainage basin, also known as a watershed or catchment, refers to the land area that collects water for a given network of streams. It is typically defined by high points or ridges of land that separate water flowing to different rivers, basins, or seas.

Question 18

Which of the following are effective ways of reducing the effects of flooding?

Accepted Answer

All the options listed (B, C, D, E) are recognized methods for reducing the effects of flooding. Channelization can improve drainage and reduce flood risk in certain areas. Wetlands act as natural sponges, absorbing and slowly releasing flood waters. Artificial levees protect land from floodwaters by acting as barriers. Erosion controls can prevent the loss of land that might otherwise contribute to increased flooding.

Question 19

Which of the following best explains why urbanization has led to larger and more frequent floods?

Accepted Answer

Urbanization leads to larger and more frequent floods primarily because impermeable surfaces like roads and buildings prevent water from being absorbed into the ground, increasing surface runoff.

Question 20

Which of the following statements is NOT true with respect to dams and reservoirs?

Accepted Answer

While dams can be used for electricity generation, they are also commonly used for flood control.

Quiz 8: Streams and Flooding