Sept 28 lecture (Streams and flooding)

Question 1

T/F

research shows more people are living in floodplains

Answer 1

true

Question 2

hydrosphere=

Answer 2

all water at or near the surface of the earth

Question 3

explain the hydrologic cycle

Question 4

list the 6 aspects of the hydrologic cycle

Answer 4

• evaporation
• condensation
• precipitation
• runoff
• infiltration
• percolation

Question 5

list the approx % of the earth’s water in the following locations:

• oceans
• glacial ice
• ground water
• lakes/ streams
• atmosphere
• soil moisture

Answer 5

• oceans = 97.5%
• glacial ice= 1.81%
• ground water = 0.63%
• lakes/ streams = 0.016%
• atmosphere = 0.001%
• soil moisture = 0.005%

Question 6

stream=

Answer 6

a body of flowing water confined to a channel, regardless of the size

Question 7

The term “river” is generally reserved for the ___(major/ minor) branches of a ___ system

Answer 7

major

stream

Question 8

drainage basin=

Answer 8

the region from which a stream draws its water supply

Question 9

Drainage basins are defined by topographically determined ____, which are often used as ___ ____

Answer 9

divided

political boundaries

Question 10

Why is the size of a stream related to the size of the drainage basin upstream?

Answer 10

It determines how much water can flow into the stream

Question 11

stream discharge=

Answer 11

the volume of water that passes a given point at a given time through a channel of a certain width and depth

Question 12

what is stream discharge measured in

Answer 12

m^3

Question 13

what is the formula used to calculate discharge?

Answer 13

multiply the cross sectional area by the velocity of the flow

cross sectional area= width x depth

velocity= distance/ time

Question 14

Describe laminar flow

Answer 14

straight or gently curved streamlines run parallel to one another without mixing

characteristic of slow moving rivers or along the edges of a fast flowing river

Question 15

describe turbulent flow

Answer 15

the streamlines mix, forming eddies.

Characteristic of fast-flowing rivers

Question 16

Streams work by transporting sediments downhill
The total sediment ___ carried by the stream is its ___, while the stream’s ability to carry a material of a given size is the stream’s ____

Answer 16

load

capacity

competence

Question 17

True/ False

Capacity is closely related to discharge

Answer 17

True

the faster the stream flows, the more water is present; the more (&larger) material can be moved

Question 18

How much of a load is transported ultimately depends on:

give example

Answer 18

the availability of sediment or dissolved ions

ex. a stream flowing over granite won’t pick up much load, but a stream that flows over sand or limestone will

Question 19

stream __ impacts sediment sorting

Answer 19

velocity

Question 20

increased stream velocity ___ (inc/ dec) suspended load and ___ bed load (more bottom shear stress)

Answer 20

increases

increases

Question 21

saltation=

Answer 21

intermittent bouncing of the load in a stream

a transitional state between bed load and suspension

Question 22

___ moving water only carries fine-grained sediments

Answer 22

slow

Question 23

__moving water carries a wider range of grain sizes

Answer 23

fast

Question 24

stream flow velocity fluctuates with the ___

Answer 24

seasons

Question 25

the velocity of a stream is largely dependent on its ___

Answer 25

gradient (steepness of a stream’s channel)

Question 26

a graded stream is said to be at ___.

explain graded streams

Answer 26

equilibrium

there is a balance of erosion and deposition.
A graded stream transports just the amount of sediment it’s capable of (for its velocity and discharge)

Question 27

base level =

Answer 27

the lowest elevation to which a stream can flow

Question 28

the gradient of a stream decreases as it approaches __ __

this appears ___ (concave/ convex) in longitudinal profile

Answer 28

base level

concave (like the bottom of a porabla)

Question 29

what are the 2 major stream types

Answer 29

1. meandering stream

2. braided stream

Question 30

describe a meandering stream

Answer 30

• occur on gentle gradients
• erode unconsolidated sediments/ weak bedrock
• they carry fine sediments
• their path may shift with erosion and deposition

Question 31

what is a point bar

Answer 31

the inside of the corner where deposition occurs (eroded on the outside of the corner)

Question 32

describe a braided stream

Answer 32

• have many channels which variably diverge and merge

- typical of steep gradients and high sediment loads combined with frequent variations in discharge

Question 33

what is an oxbow lake

Answer 33

a U shaped lake that forms when a wide meander of a river is cut off, creating a free-standing body of water

Question 34

a stream hydrograph is a plot of ___ ___ at a point over time

• x-axis:
• y-axis:

Answer 34

stream discharge
time is plotted on x-axis
discharge is plotted in y axis

Question 35

what does a hydrograph record?

Answer 35

fluctuations in discharge or stream height over time