Snowmelt
and Streamflow
Part
3: Streamflow Prediction
In this module,
we will determine the streamflow for a river. It will first be
necessary to find out how much snow contributes to the flow, then
the volume of water distributed over the watershed for the river.
Comprehension
Understanding
streamflow, visualizing the method of describing streamflow.
 What type
of function would be appropriate to predict the rate of snowmelt?
 Why is
snowmelt important?
 Why is
it important to predict streamflow or the amount of water in
a river at a given time?
 What are
some factors that might affect streamflow?
 How can
we predict the streamflow for a river?
 How can
we describe streamflow, i.e., what units would be appropriate?
Acquisition
Mathematical Topics
Learn or review
mathematical concepts and skills needed to study snowmelt and
streamflow. See the Menu to the left.
Information
Watershed Area and
Snowmelt
 The area
of the watershed is approximately 335 million square feet.
 Precipitation
is uniform over the entire region.
 Average
temperatures are above freezing from the end of April through
midOctober (See Part 1, Temperature).
 Snow melts
at a uniform rate for two months after temperature exceeds 32
degrees F.
Streamflow
 Stream
flow is the amount of water that flows through the river
measured here in cubic feet per month.
 Base
flow is the minimum amount of water in the river each month,
this amount is constant each month of the year. Base flow comes
from precipitation and for this river is 5 million cubic feet
per month.
 In addition
to base flow, 70% of the precipitation gets to the river bed.
 During
months when temperature is below freezing, the only streamflow
is base flow.
 Each person
uses approximately 30 cubic feet of water each day.
Application
Apply mathematical
tools to analyze snow melt, volume of precipitation, and streamflow
When answering
the following questions refer to the table at the end and record
your answers there. Some answers are already listed; these were
obtained in Part 2, Precipitation. Also, the XXX's indicate that
no data should be entered here. (See Parts 1 and 2, Temperature
and Precipitation.) All figures in all columns except the first
two are in millions.
Watershed Area, Volume
of Precipitation, Snowmelt, and Streamflow
(Write your
answers in millions and enter in the appropriate column in the
Table)
 Compute
the volume of precipitation over the entire watershed for each
month. The unit of measure will be cubic feet of water.
 There is
an average total of 12.70 inches of water from snow each year
(See Part 2, Precipitation.). Compute the total annual volume
of water from snow for the year over the entire watershed.
Again, units will be cubic feet of water.
 Enter the
amount of water from snowmelt in the fifth column in the Table.
 Complete
the remaining columns in the Table. The last column will tell
you the monthly amount of water that can be expected to pass
through the river.
 Make points
from the monthly streamflow figures: the first coordinate should
be the t value for month and the second coordinate the streamflow
for that month. Plot these points on the plot screen, then print
the screen and connect the points with a smooth graph. Does
this look like some of the graphs shown in local newspapers
for local rivers?
 What is
the total annual stream flow for the river?
 How many
people can the river support with its annual flow?
Month 
Precip.
(Inches) 
Precip
(cubic
feet)

Rain
(cubic ft.) 
Snow
Melt (cubic ft.) 
Stream
Flow Contribution (70%)

Base
Flow 
Total
Monthly Stream Flow 
.5
(Jan)

1.98


xxxxxxx

xxxxxxx

xxxxxxx 
5


1.5

2.59


xxxxxxx

xxxxxxx

xxxxxxx 
5


2.5

3.20


xxxxxxx

xxxxxxx

xxxxxxx 
5


3.5

2.89


xxxxxxx

xxxxxxx

xxxxxxx 
5


4.5

2.58





5


5.5

2.27





5


6.5

1.96



xxxxxxx


5


7.5

1.65



xxxxxxx


5


8.5

1.34



xxxxxxx


5


9.5

1.03



xxxxxxx


5


10.5

0.72


xxxxxxx

xxxxxxx

xxxxxxx 
5


11.5

1.33


xxxxxxx

xxxxxxx

xxxxxxx 
5


Reflection
 Do you
think that the graph for steamflow is reasonable?
 Do you
think that the assumptions regarding snowmelt are valid each
year
 What effect
would a sudden heat spell (above 50°) early in the season have
on the watershed? What if it were followed by a second cold
spell which brought more snow?
 Do you
think that your model should be used for prediction of streamflow
for this river next year?
 Reconsider
your answer to #7 above. Could the river support that many people
each month? What would your strategy be to use the water so
as to effectively support this many people?