Lab 10: Rivers and Streams
Part A: Stream Flow Hydrograph (18 points)
(1) Generate a plot showing the precipitation and discharge over the year. You will want precipitation
values to plot with columns, and the stream discharge to plot as line data. This will be what Excel calls a
combo graph, which is the same type of graph that we created in Lab 7 when we made climographs.
Make sure the discharge data are on a secondary vertical axis. Remember to label your axes with units,
include a legend, and give your graph a title. [8 pts.]
Paste your graph into a Word document and get that ready for upload to Canvas. You are going to make
two more graphs that will be added to this file, so don’t upload it yet.
Answer the following questions about this year-long hydrograph:
(2) Based on the data in the hydrograph, describe the general relationship between the daily values of
precipitation and the daily values of river discharge. [3 pts.]
There seems to be a correlation between daily values of precipitation and daily values of river discharge
over the course of the year.
(3) There are two general seasons of the year where there are only very small changes in discharge even
though there are reasonable amounts of precipitation. What are these two general seasons? Explain why
there is not much change in discharge for these precipitation events during these two periods. [4 pts.]
In early winter and late summer there are only very small changes in discharge even though there are
reasonable amounts of precipitation. This is likely because in early winter the precipitation is snow so it
remains on the surface and doesn’t become discharge. In late summer, the soil is likely dry and taking in a
lot of precipitation so there is not a lot of discharge either.
(4) There is also a time of year when there are large changes in discharge even though the amount of
precipitation is relatively small. Again, what time of year does this occur and explain what causes this
relationship. [3 pts.]
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These periods occur after periods of low discharge, so in late winter and early fall. This is because the
snow starts to melt towards the end of the winter and the soil is more saturated by early fall.
Part B: Detailed Hydrograph (9 points)
(1) Generate a detailed hydrograph that only includes the dates above. Make sure that you plot
precipitation in columns and discharge as a line, and that discharge is on a secondary axis. Include a title,
legend, and make sure that the axes are labeled with units. [8 pts.]
Paste this graph into your Word file.
Answer the following questions about this detailed hydrograph:
(2) How long does it take for discharge to reach its peak value after the precipitation has fallen? How is
this water that is making the river rise getting into the river. [3 pts.]
Discharge peaks about a day after precipitation has fallen. The water that is causing the river to rise gets
into the river because the soil is already saturated so it flows across the surface downhill into the river.
(3) What happens in the days following this major rain event? There is still more water in the river than
there was before the rain. How is this water getting into the river? [3 pts.]
In the days following a major rain event, discharge peaks and then gradually declines as more water
enters this river. The leftover groundwater from the rain event continues to flow into the river as the soil
is saturated.
Part C: Flood Recurrence Interval (11 points)
(1) Generate a flood frequency plot of these data. This will need to be an XY scatter plot, and you will
need to use data points only with no connecting lines otherwise the graph will be a mess. Put recurrence
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interval (T) on the horizontal axis using a logarithmic scale, and discharge on the vertical axis with a
linear scale. A logarithmic scale is a scale that spaces orders of magnitude (e.g., 1, 10, 100, 1000 etc.)
evenly on the axis, rather than single units. To convert a regular axis scale to a log-scale, select Format
Axis, select the tab with three vertical columns, and then expand “Axis options”. Check the box next to
Logarithmic Scale. Remember to add labels for both axes with the units. [8 pts.]
Paste this graph into your Word document. It should be ready for upload at this point.
Answer the following questions about your flood recurrence interval data:
(2) The APF event in 2011 was from heavy precipitation caused by Hurricane Irene. What is the
recurrence interval of this event? [2 pt.]
100
(3) Fit a trendline through the data. Experiment with linear, exponential, and logarithmic function, and
see which curve type fits the data the best by maximizing the value for r2. Check the boxes to show r2 and
the equation of the trendline and estimate the approximate discharge values of the 50- , 100-, and 500year floods? [4 pts.]
50-year flood:
52427.7969706
100-year flood:
60170.2509775
500-year flood:
78147.6724594
(4) Major infrastructure projects (e.g., nuclear power plants, dams) are often designed for the 1,000-,
5,000-, or even 10,000-year events, even though most river gauges contain <100 years of data. Experts
will tell you that these statistics are not useless, but there are a few factors that limit our confidence in
these long-term projections. Speculate on two of these factors and explain how they might limit our
confidence. Speculate means that you are thinking about reasonable explanations, but do not feel like you
need to do in-depth research on this topic to produce the correct answers. [4 pts.]
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Because of the changing climate, it will become harder to predict these events as they become more
intense with higher frequency. This will likely cause greater amounts of discharge and therefore higher
flood hazard risk that our infrastructure is not prepared for.
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