Copy of Lab 06 Floods-Szabo
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University of Wisconsin, Madison *
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106
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Geology
Date
Dec 6, 2023
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GEOSCI/ENVIR ST-106: Environmental Geology
Lab 6: Flooding and Flood Data Analysis
Assignment Overview:
Living close to rivers
presents several advantages, in terms of water
supply, recreation, and shipping. However, the
variability in river stages and instances of
flooding can pose risks to property. The USGS
has a wealth of historical data regarding river
flows that is used by planners and insurers to
assess the likelihood of future flooding. In this
lab, you will apply tools such as hydrographs
and flood frequency curves to understand the
Rock River, a tributary of the Mississippi that
flows through Wisconsin and Illinois
Image Credit: Rock River drainage basin from
Wikipedia
IMPORTANT NOTES:
1.
The first half of this lab is based on data from a study produced by the USGS in two large
map presentations. These are provided as PDF files that should be downloaded from Canvas.
Rubric:
Interpreting Historical Hydraulic Data (2
points each)
Developing Peak Flood Recurrence Interval
Analyses (8 points)
1 point - Data presented is accurate and
applies to the question of interest
4 points - Retrieval / plotting of data for flood
frequency analysis
1 point - Analysis is in clear sentences
and uses logical arguments based on
data
6 points - Analysis / interpretation of results
Submission:
To submit the assignment on Canvas, use the following steps:
1.
In Google Docs, generate a PDF: File → Download as → PDF Document
2.
In Google Docs, use Share → Get Shareable Link, and copy the link address
3.
In Canvas, upload your PDF to the assignment, and paste the link address to your
Google Doc in the assignment comments.
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Assignment Questions and Responses
Instructions:
Fill out each red highlighted field (_________)
Part 1: Interpreting Historical Hydraulic Data
The Rock River in Wisconsin flows from Waupun,WI south toward the Illinois border, crossing
closest to Madison near the area of Johnson Creek. A study on this river analyzed flooding with
a particular focus on measurements obtained at two USGS gaging stations - Watertown (to the
north) and Rock River (to the south, closer to the Illinois border). Spend some time viewing and
interpreting the maps presented in the two PDF documents, and then answer the following
questions. You may copy and paste screenshots from portions of the maps if those help to
understand your reasoning.
1. What is the magnitude of the discharge on the Rock River in “cfs” (cubic feet per second)
during the "regional" (100-year) flood at i) Watertown and ii) Afton? Comment, in 3-4 sentences
at most, on what may be causing the different magnitudes in these floods at different locations.
(2 points)
The magnitude of discharge at Watertown is 7130 ft^3/sec, and the magnitude of discharge at
Afton 20200 ft^3/sec. I think these floods could be due to many different things like, flow rate of
the river, depth of river, and the types of turns in the river.
2. On the report maps, find the location of the floodplain cross-section corresponding to
the largest flooded area, and similarly find the location that appears to have the least
flooded area. (Note that the flood plain cross-sections presented use different scales!)
Give the names (use the mile marker) of the locations where the largest and smallest
flooded area occurs, and comment on the features that cause the differences in flooding
at these locations. (2 points)
Watertown
1.
2000*10= 20000- most flooding at mile 226.9
2.
5*400= 2000
3.
10*800= 8000
4.
5*300= 1500
5.
10*400= 4000
6.
5*2750= 13750
7.
5*2400= 12000
Fort Atkinson
1.
10*2750=27500- most flooding at mile 208.1
2.
10*250=2500
3.
10*600=6000
4.
10*700= 7000
5.
15*500= 7500
6.
5*2500=12500
More twists and turns= more erosion= more flooding
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3. Examine the areas shown on the maps that would be inundated by the regional flood. Which
map contains the region that is more impacted by the flooding, in terms of flooding of buildings?
(Note that buildings are represented by dark squares.) What recommendations on land use
might you make as a member of a regional planning commission? (2 points)
Fort Atkinson is more impacted by flooding. For better flood control they could build levees,
because then the water would not overflow and cause flooding. They could also build diversion
channels, but those require large amounts of land. These two could stop water from flooding
into cities.
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https://waterdata.usgs.gov/nwis/dv?referred_module=sw&agency_code=USGS&site_no=05
425500
https://waterdata.usgs.gov/nwis/dv?referred_module=sw&agency_code=USGS&site_no=05
430500
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4. The hydrographs on the previous page represent the most recent 18 months of data
recorded at Afton and Watertown. Write a brief description of a few sentences (1 paragraph
at most) describing your observations of these hydrographs. In commenting on the
hydrographs, describe quantitatively how usual or unusual the peak flow rates seen in these
hydrographs are (i.e., using the recurrence interval concept). Similarly, you may want to
describe what is similar and different about the two hydrographs, and comment on reasons
for any data issues within the plots that you notice. (2 points)
The two towns always flood at the same time. The floods tend to happen two at a time
before going down. A flood happens and then another one happens about a month later and
then the water discharge level goes back down.
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Part 2
:
Developing Peak flood Recurrence Intervals Analyses
The Yahara River has been well-monitored since the late 1970’s and thus has a fairly good
record of peak streamflows relative to other USGS sites (almost 40 years). The peak flow data
measured at this site over this time period can be found here:
Yahara USGS Data
5. In our textbook the recurrence interval is defined as how frequently a flood of a given
severity occurs,
on average
, for a stream. The probability that a flood of a given size occurs
in any one year is the inverse of the recurrence interval. Follow steps i to iii below to create
a flood frequency curve for the Yahara river at Fulton. You may use
this spreadsheet
as a
starting point. (4 points)
i. Determine the ranks (M) of the streamflow discharges (M=1 is highest, M=2 second
highest, etc.), by labeling the discharges in order. Then calculate the recurrence
intervals for each discharge, as R = (N+1)/M, where N is the number of annual peak
streamflow observations that have been recorded. (Hint - You may find that using Data
→ Sort Range… is a useful tool!)
ii. Plot the recurrence intervals for these discharges on a semi-logarithmic plot, which shows
maximum discharge on the y-axis versus recurrence interval on the x axis.
iii. Fit a straight line on the semi-logarithmic plot to represent your flood frequency curve.
Plot the results of your flood frequency curve here.
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6. Create a brief report regarding this stream below. The report should be a few paragraphs
with pictures of your results (flood frequency curves) and any data / analysis that you think is
relevant. (6 points)
In your report, describes the following aspects of your results:
●
How well does your flood frequency curve fit the data? Do you have any concerns?
●
What does your flood frequency curve suggest as a magnitude for the 10-year flood?
100-year flood?
●
Show quantitatively how your results depend on data availability -- for instance, if
you were to remove some years of data, how would your flood frequency curve
change?
●
Based on your flood frequency curve, comment on the hydrograph above, showing
data measured during the past year.
_The flood frequency curve fits the data well because bigger floods happen less often. My graph
suggests that floods with higher discharges happen less frequently. Discharges with about 4000
ft^3/sec happen only about every 40 years whereas floods of about 1000 ft^3/sec happen every
year. The magnitude of a 10 year flood will be about 3000 ft^3/sec and for a 100 year flood the
magnitude will be about 8000 ft^3/sec.
The graph does not change when you remove a few points from the middle, but it changes
when you remove a couple points from the beginning. The graph changes from the lowest
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discharge being below 1000 ft^3/sec to just above 1000 ft^3/sec. But it does not change the
recurrence and the discharge. If you remove points from the end the recurrence and discharge
are still the same as the original graph says a flood with discharge about 2500 ft^3/sec occurs
every 4 years, and when you remove the points at the end the time intervals stay the same.
The hygrograph above suggests that a major flood of almost 3000 ft^3/sec happens every 6
months which aligns with the recurrence and discharge on the graphs that I created through
data.
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