Fluvial Geomorphology Question Sheet
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Cosumnes River College *
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Course
392
Subject
Geography
Date
Feb 20, 2024
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15
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Lab 15: Fluvial Geomorphology
Part A. Streamflow and Carrying Capacity
Refer to Figure 15.1.
1. What is the minimum speed of water that will erode clay particles?
The minimum speed
of water required to erode clay particles can vary based on several factors such as the type of
clay, its composition, environmental conditions, and the presence of other sediments in the
water.Generally, clay particles are cohesive and tend to stick together, requiring higher
velocities of water flow to erode them compared to sand or silt particles. In most cases, a
minimum velocity of around 0.3 meters per second (1 foot per second) might start the erosion
process for some types of clay particles. However, this is a very approximate estimation and
the actual erosion threshold can be higher or lower depending on the specific characteristics
of the clay and the situation.
2. What is the minimum speed of water that will erode sand particles?
Sand particles are
generally easier to erode compared to clay particles due to their larger size and less
cohesive nature. However, the minimum speed of water required to erode sand
particles can still vary based on factors such as the type of sand, grain size, shape,
and other environmental conditions.In general, sand particles can start to be
transported by water at relatively low velocities. A minimum water speed of around
0.15-0.3 meters per second (0.5-1 foot per second) can begin the process of erosion
for sand particles. Again, this is a rough estimate and the actual erosion threshold
may differ depending on specific conditions.
3. Why do you think the speeds to erode clay and sand particles are different?
The
difference in erosive thresholds between clay and sand particles primarily stems
from their distinct physical properties. Clay particles are smaller, more cohesive, and
tend to stick together due to their electrostatic forces and molecular structure,
requiring higher water speeds to break their bonds and initiate erosion. Conversely,
sand particles are larger, less cohesive, and have a granular structure, making them
more easily dislodged and transported by water at lower velocities. The cohesive
nature of clay particles results in a stronger resistance to detachment, necessitating
greater energy from water flow to overcome these cohesive forces compared to the
relatively looser and more readily movable sand particles.
4. You are exploring a creek bed and come upon a rock which has been transported
downstream. The rock is the size of a bowling ball (8½ inches; 215 millimeters). How fast
must the water have been moving to transport that rock?
Determining the exact
speed of water needed to transport a rock of bowling ball size (8½ inches or 215
millimeters) downstream involves various factors such as the shape and weight
of the rock, as well as the specific characteristics of the creek's flow. Generally,
larger rocks require faster-moving water to transport them. However, it's crucial
to note that the precise speed cannot be determined without additional details
about the rock's weight, shape, the flow dynamics of the creek, and the presence
of other sediments.As a reference point, rocks of similar size and weight might
typically require water speeds exceeding several feet per second (often more
than 3-4 feet per second or approximately 1-1.2 meters per second) to be
transported downstream in a creek. This is a rough estimation and the actual
speed could be influenced by numerous variables within the creek's environment
5. You are studying a river that is flowing at 1 meter/second. What size materials would
you expect to see...
a
. ...
eroding?
Higher velocities in rivers can erode various sizes of particles
depending on their resistance to erosion. For instance, at 1 meter per second,
the river might be capable of eroding smaller sediments like silt, sand, and
potentially finer gravel. Clay particles might also start to erode under these
conditions, albeit more slowly due to their cohesive nature.
b
. ...
being transported?
With a velocity of 1 meter per second, the river can
transport materials that are smaller and lighter than what it can erode. It can
transport smaller particles like sand, silt, and clay along with smaller gravel
particles downstream. Heavier materials like larger gravel, cobbles, and
boulders would likely remain stationary or be transported only during higher
flow events when the water velocity increases significantly.
c
. ...
being deposited on the riverbed?
The deposition of materials depends on the
river's energy and its ability to carry particles. At 1 meter per second, finer
materials like silt and clay particles might settle and deposit on the riverbed.
However, coarser materials like sand and larger gravel would likely remain in
suspension or be transported further downstream before settling. Larger
materials such as cobbles and boulders would generally require much slower
water velocities to be deposited onto the riverbed.
1
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Lab 11: Fluvial Geomorphology
Hydrographs and Storm Events
Refer to Figure 15.2.
6. What is the approximate lag time for the urbanized area?
The approximate lag time for
an urbanized area can vary significantly based on multiple factors including the
extent of urban development, the nature of the terrain, the efficiency of drainage
systems, and the intensity of precipitation events. Generally, in urbanized regions
where impervious surfaces like roads, sidewalks, and buildings dominate the
landscape, the lag time—referring to the delay between peak rainfall and peak
discharge—tends to be shorter compared to more natural or rural areas. This
shortened lag time is due to rapid runoff from impermeable surfaces directly into
storm drains, streams, or rivers, bypassing the slower infiltration process that occurs
in natural landscapes. In some cases, this reduced lag time in urban areas might
lead to quicker and higher peak flows during storm events, potentially increasing the
risk of flash floods and placing greater stress on drainage systems.
7. What is the approximate lag time for the rural area?
In rural areas characterized by
more natural landscapes with greater permeability due to vegetation, soil, and fewer
impervious surfaces, the approximate lag time between peak rainfall and peak
discharge tends to be longer compared to urbanized regions. In these rural settings,
precipitation takes more time to infiltrate into the soil, flow over the land, and
eventually make its way into streams or rivers. The lag time can vary but typically
ranges from hours to days, allowing for a more gradual and delayed response to
heavy rainfall events. The presence of vegetation, natural depressions, and more
porous surfaces in rural areas contributes to increased infiltration and water
retention, resulting in a slower movement of water toward waterways
8. Use Your Critical Thinking Skills: Why is there a difference between the lag time for an
urbanized area and a rural area? Explain your response in one to two sentences.
The
difference in lag time between urbanized and rural areas primarily arises due to
their contrasting land cover and surface characteristics. Urban areas consist
largely of impervious surfaces like concrete and asphalt, which rapidly generate
runoff, leading to a shorter lag time. In contrast, rural areas possess more
permeable surfaces, such as soil and vegetation, allowing for slower infiltration
and storage of water, thereby resulting in a longer lag time as water takes more
time to reach the waterways.
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9. Use Your Critical Thinking Skills: What if the storm event dropped snow, rather than
rain? What would the hydrograph look like? Explain your response in one to two
sentences.
If the storm event deposited snow instead of rain, the resulting
hydrograph would likely show a delayed and more gradual response. Snow
accumulation acts as a temporary storage of water, and the gradual melting
of snow over time would result in a slower increase in discharge, leading to a
more extended peak and a longer duration of elevated flow in the
hydrograph.
10. Use Your Critical Thinking Skills: What if the storm event was a warmer, more tropical
storm dropping a larger quantity of warm rain on a pre-existing snow pack? What would the
hydrograph potentially look like? Explain your response in one to two sentences.
a warmer,
more tropical storm depositing a larger quantity of warm rain onto a pre-existing
snowpack would likely accelerate the melting of the snowpack. This situation could
result in a rapid increase in discharge, causing a sudden and pronounced peak in the
hydrograph due to the combined effect of snowmelt and the additional warm rainfall
contributing to the streamflow.
2
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Lab 11: Fluvial Geomorphology
Part B. Stream Profiles
Longitudinal Profiles
c
12. In what part of the river would you expect to see the greatest amount of erosion taking
place? Explain your response in one sentence.
The greatest amount of erosion is
expected to take place in the head region of the river. The head region of the
river has highest slope, as a result would have the highest water velocity.
13. Where would you expect to see deposition of sediment? Explain your response in one
sentence.
The deposition of sediment is expected to occur in the mouth region
of the river. The mouth region of the river has the lowest slope, as a result
would have the least water velocity.
14. What happens to transported materials in a river, once the river reaches the mouth
(flowing into a lake or ocean) and the movement stops? What type of feature is created?
Explain your response in two to three sentences. Hint: consider what feature is found at
the mouth of most major rivers throughout the world.
When the river reaches a lake
or ocean, the most common feature formed would be a Delta. The materials
being transported by the river get deposited as the velocity of water flow reduces.
1
Figure by Scott Crosier is licensed under
CC BY-NC-SA 4.0
3
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Lab 11: Fluvial Geomorphology
Vertical Profiles
Area of Active Channel x Velocity = Stream Discharge
Now you try! Assume you and some classmates have surveyed a stream and found the active
channel to be 7.6 meters squared. The average flow rate is 0.75 meters per second. Note: 1
cubic meter has the volume of 1,000 liters.
15. How many cubic meters of water are passing that location per second?
We have to find how many cubic meters of water are passing that location per second means t=1s
So,Water passing that location per second = 7.6m2 x 0.75 m/s x 1s
=
5.7m3
16. How much water is passing that location per minute? Show your calculation.
Now we have to find how much of water passing that location per minute means t = 1 minute =
60 s (As 1 minute= 60 seconds) So, Water passing that location per minute = 7.6m2 x 0.75m/s x
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60 s
=
342 m3
17. Use Your Critical Thinking Skills: Now you’re the city planner! The Federal Emergency
Management Agency (FEMA) has designated a region near your community as a 100-year
floodplain. This designation suggests that the region, statistically, has a 1% of a flood of a given
magnitude in any given year (Hint: A 100-year floodplain can be interpreted as a 1 in 100
chance).
a. As a city planner, what do you believe is an appropriate use of that land? What is not? Explain
your response in three to four sentences.
As a city planner, an appropriate use of land within a
designated 100-year floodplain involves careful consideration and implementation of regulations
that prioritize resilient and flood-resistant development. Areas within the floodplain can be
utilized for purposes that are compatible with occasional flooding, such as parks, green spaces,
recreational areas, or stormwater management facilities. However, constructing critical
infrastructure, residential or commercial buildings in these zones could pose significant risks
during flooding events, leading to property damage, safety hazards, and potential loss of life.
Therefore, avoiding or minimizing permanent development in high-risk flood zones is crucial to
safeguarding both property and public safety, while utilizing the land for purposes that can
coexist with occasional flooding is more advisable.
b. A land owner proposed building a house in the floodplain. Do you approve the building
permits? What extra requirements might you require for the building? Explain your response in
two to three sentences.
Regarding the proposed house in the floodplain, granting building
permits would necessitate stringent measures to mitigate flood risks. Extra requirements might
include elevating the structure above the base flood elevation level, implementing flood-resistant
construction techniques, installing flood vents or breakaway walls, and ensuring access to
reliable flood warning systems. These measures aim to enhance the building's resilience against
flooding and minimize potential harm to occupants and property in the event of a flood.
c. What criteria do you use in these decisions? List at least three criteria.
Criteria used in decision-making for development in flood-prone areas:Risk assessment based on
flood hazard maps, historical data, and hydrological analyses to understand the extent and
probability of flooding.Adherence to local building codes, zoning regulations, and land use
policies that specifically address construction in flood-prone areas.Implementation of resilient
design practices, including elevation, flood-proofing, and mitigation measures, to reduce
potential flood damage and ensure public safety and welfare.
4
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Lab 11: Fluvial Geomorphology
Part C. Rivers Shaping the Landscape
Meandering Streams
Figure 15.6: The Velocity of a Stream depends on whether the Channel is Straight or Curved.
2
Refer to the
river channel labeled B in Figure 15.6.
18. On which side of the river would you anticipate more erosion? On the outside of the
turn (right side in diagram example B) or the inside (on the left side in diagram example
B)?
In a meandering river channel like the one labeled B in Figure 15.6, more erosion is
typically anticipated on the outside of the turn, which is the right side in the diagram
example B. This occurs because the higher velocity of water on the outside of the bend
leads to greater erosive force against the riverbank. The water flow on the outer curve
has more energy due to centrifugal force, causing increased erosion, undercutting of the
bank, and eventual sediment deposition on the inner side of the bend. As a result, the
outer bank experiences more erosion and contributes to the widening and meandering of
the river channel over time.
19. On which side of the river shown on example B would you anticipate more deposition?
In the river channel labeled B in Figure 15.6, more deposition is typically anticipated on
the inside of the turn, which is the left side in diagram example B. Slower water flow on
the inner curve of the bend results in reduced erosive force, allowing sediments carried
by the river to settle and deposit due to the decreased energy of the water. As a result,
the inner bank experiences deposition, contributing to the accumulation of sediment
and the formation of point bars or gentle slopes on the inner side of meandering river
bends.
20. Apply What You Learned: If this were to occur over a great deal of time, what change
would you anticipate for the path of the river? Explain your response in one to two
sentences.
Over an extended period, the continual erosion on the outside of the
river bends and deposition on the inside would likely lead to a gradual shift or
migration of the river's path towards the direction of the outer bends. This
process, known as lateral migration, contributes to the widening of the river
channel and the formation of new meanders, altering the course of the river
over time
21. On the river channel labeled B in Figure 15.6, label the cut bank and the point bar. Also,
label the cut bank and point bar on the bird’s-eye view of the river shown on the
left-side of Figure 15.6.
2
Figure
by Steven Earle is licensed by
CC BY 4.0
5
|
Lab 11: Fluvial Geomorphology
Oxbow Lakes
Virtual Field Trip to a Meandering River
22. Using Google Maps or Google Earth, navigate to the following coordinate along the
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Sacramento River in Butte County, California:
39.67, -121.97
. Turn on the satellite view.
Zoom out to an extent where you can see several of the bends in the river.
23. In the box provided below (Figure 15.9), sketch the pathway of the Sacramento River
where the river is flowing in from the upper right (Northeast) corner, making a
significant turn on the left (West) side, and eventually flowing out the bottom (South) of
the box.
Figure 15.9: Blank Map.
3
24. In your sketch above (Figure 15.9), label the cut banks and point bars.
3
Figure by Scott Crosier is licensed under
CC BY-NC-SA 4.0
6
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Lab 11: Fluvial Geomorphology
25. Do you see any signs that suggest there is or was an oxbow lake present? Sketch where
you suspect and label it on Figure 15.9.
26. Based on what you have learned regarding the migration patterns of rivers, where might
you anticipate a future oxbow lake? Outline with a dotted line and label the area on
Figure 15.9.
Waterfalls
27. Refer to Figure 15.10. Based on what you know about the erosional processes in
waterfalls, would you anticipate that the waterfall moves upstream or downstream?
Explain your response in one to two sentences.
Waterfalls typically move upstream over time due to the erosive action of the
falling water wearing away the rock at the base of the waterfall. As the
underlying rock erodes and weakens, the waterfall gradually retreats or
moves upstream, creating a gorge or canyon as the process continues.
Deltas
Virtual Field Trip to Three Deltas
The Nile River: 30.81, 31.09
.
28. Based on the color of the region, what do you suspect in the main land use of the
region?
I suspect the region is mainly used for agriculture.
29. What is the overall shape of the area?
has a triangular or fan-shaped form where the
river divides and spreads out into multiple distributaries as it empties into the
Mediterranean Sea.
30. Zoom further out. What is the land cover for most of the surrounding regions?
There are desert regions surrounding these areas, as Egypt has a significant
portion of its land covered by desert landscapes such as the Eastern Desert
and the Western Desert.It is also a fertile floodplains due to the Nile's annual
inundation, supporting agriculture and settlements along its banks
7
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Lab 11: Fluvial Geomorphology
The Mississippi: 29.53, -90.78
.
31. What is the overall land use for this region?
The overall land use for the region around
the coordinates (29.53, -90.78) along the Mississippi River includes a mix of agricultural
land, wetlands, urban areas, and industrial zones. There are extensive agricultural fields,
particularly in the river's floodplain, along with marshes and wetlands, especially closer to
the Mississippi River delta. Urban development and industrial facilities are also present in
certain areas.
32. What patterns do you see which are similar or different from what you saw in Egypt at
the River Nile?
Similar to the Nile River region in Egypt, the land around the
Mississippi River displays a mix of agricultural use, particularly in floodplain areas,
and urban development. However, the Mississippi River delta has extensive wetlands
and marshes, which are critical ecosystems that differ significantly from the arid
landscapes bordering the Nile River in Egypt. Additionally, the Mississippi River
delta's vulnerability to erosion and subsidence contributes to unique environmental
challenges compared to the Nile River's floodplain.
33. Use Your Critical Thinking Skills: The Gulf of Mexico is prone to hurricanes and
significant storm surges. These are extremely high waves that result from the strong
winds in a hurricane. What influence would the Mississippi River delta have on the storm
surges? Why might they be important to Gulf Coast cities such as New Orleans? Your
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response should be two to three sentences in length.
The Mississippi River delta can
mitigate storm surges to some extent by acting as a natural buffer, dispersing and
reducing the intensity of storm surges before they reach inland areas. The wetlands and
marshes in the delta help absorb and slow down the surge, providing a degree of
protection to Gulf Coast cities such as New Orleans. Preserving these coastal wetlands is
crucial as they serve as a natural defense against storm surges, helping to reduce the
impact of hurricanes on coastal communities by acting as a barrier and dissipating some
of the storm's energy.
California!: 38.05, -121.58
.
34. As you zoom out, what land use seems to dominate this region?
the Sacramento-San
Joaquin River Delta region is dominated by a combination of agricultural land use,
wetlands, and waterways.
35. What patterns do you find in common with the other deltas that you have virtually
visited?
Common patterns observed in various river deltas, including the
Sacramento-San Joaquin River Delta, often involve the presence of
extensive wetlands, marshes, and a network of waterways created by river
branches and distributaries. These deltas often serve as crucial
ecosystems, providing habitats for diverse wildlife and supporting
agricultural activities.
36. To see the full extent of the delta, zoom out to an extent where you see Antioch on the
west side of the display and Stockton on the East. In one sentence, describe the patterns
of many of the waterways in this region.
In the region between Antioch on the west
side and Stockton on the east side, the patterns of many waterways appear to
form a complex network of interconnected channels, sloughs, and rivers within
the Sacramento-San Joaquin River Delta.
8
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Lab 11: Fluvial Geomorphology
While you are here, navigate just slightly to the South, to the following coordinate:
37.83,
-121.56
. This is the beginning of the California Aqueduct!
37. Using the navigation tools in Google Maps or Google Earth, follow the Aqueduct as far
as you can. How far were you able to follow the aqueduct flow?
The California
Aqueduct, a part of the California State Water Project, conveys water across
the state to various regions, including agricultural areas and urban centers in
Southern California. It traverses through a mix of landscapes, including
agricultural lands, valleys, and potentially some semi-arid or arid regions.
38. What types of landscapes does the California Aqueduct flow through?
Regarding the
comparison of the Nile, Mississippi, and California deltas: Similarities among these
deltas include their ecological significance as important habitats for wildlife,
particularly birds and marine life, and their roles in supporting agriculture.
Additionally, they all face challenges related to land subsidence, erosion, and
environmental conservation efforts due to human activities.
39. Compare and contrast the Nile, Mississippi, and California deltas. What are the
similarities and differences among the deltas? Explain your response in two to three
sentences.
Differences lie in their geographical locations, climate conditions,
and the surrounding landscapes. The Nile Delta is situated in a more arid
region, while the Mississippi and California Deltas experience varying
degrees of wetland ecosystems but differ in terms of scale, vegetation, and
the surrounding land use patterns. The Mississippi Delta is larger and
characterized by extensive wetlands, while the California Delta, part of the
Sacramento-San Joaquin River Delta, has a mix of wetlands, agricultural
lands, and a complex network of waterways.
Part D. Wrap-Up
This is a new lab manual that your professor is working on developing. Below are some
reflective questions that I would like to hear from you. Your critical critique would really be
appreciated!
40. What is the most important idea that you learned in this lab? In two to three sentences,
explain the concept and why it is important to know.
In studying river deltas and
waterways, one crucial concept is the interplay between erosion and deposition
in shaping landforms. Understanding how rivers erode their banks on the outside
of bends (cut banks) while depositing sediments on the inner curves (point bars)
elucidates the dynamic nature of river channels. This knowledge is fundamental
for managing river systems, predicting changes in river courses, and
implementing effective measures to mitigate flooding or protect sensitive
ecosystems within these dynamic environments.
41. What was the most challenging part of this lab? Explain why it was challenging. If
nothing challenged you in the lab, write about what you think challenged your
classmates.
The most challenging part for me in the lab was drawing the map
because I am on a pc soi had to draw with a mouse on docs.
42. Review the learning objectives on page 1 of this lab. How would you rate your
understanding or ability for each learning objective? Write one sentence that addresses
each learning objective?
I would rate it a 8 because I understood it pretty well but did
get stuck a little bit trying to come up with explanations for the shapes of the deltas
around certain areas and a couple other questions.
9
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Lab 11: Fluvial Geomorphology
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