Bhambra_Kanika_A4
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School
University of Waterloo *
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Course
238
Subject
Geography
Date
Dec 6, 2023
Type
Pages
2
Uploaded by DeaconBarracuda1640
Assignment #4 - Water Balance Concepts and Calculations
You are studying a watershed 4 km
2
in area and have collected the following data over
the period of one year. You can assume this watershed is of very general shape and
topography.
a)
Assuming that the watershed is at
steady state
over the year, the water balance
equation can be written as P = E
ET
+ Q. Calculate the total
evapotranspiration
for the
year (you can also assume that E = E
V
+ E
T
)?
Provide your answer in mm/day
. (8
marks)
Total Evapotranspiration (E
T
)
= Σ(P - Q) over the 12 months
= (63.7 - 0.01) + (80.4 - 0) + (36.8 - 0.14) + (32.4 - 0.21) + (62.7 - 0.11) + (36.8 - 0.04) +
(20.4 - 0.03) + (51.9 - 0.04) + (73.6 - 0.06) + (80.4 - 0.11) + (61.7 - 0.1) + (42.4 - 0.07) =
642.28 mm
Average evapotranspiration/day = E
T
/ number of days in a year
= 642.28mm/365 days
= 1.759 ≈
1.76 mm/day
b)
The estimated average evapotranspiration for the month of July is 0.053 cm/day,
what is the
change in storage
of the watershed for July? Be sure to
indicate
if it is an
increase or decrease in storage.
Provide your answer in cubic metres (m
3
)
. (5
marks)
ΔS = P - E
T
- Q
= 20.4 - (0.053 cm/day * 31 days) - (0.03 m
3
/s * 31 days)
= 20.4 - 1.643 cm/day - 0.93 m
3
/s
= 20.4 - 1.643x10
-6
m
3
/day - 0.93 m
3
/s
= 19.469 ≈
19.47 m
3
(positive value indicates increase in storage)
c)
Assuming that the change in storage in July is entirely from a small
lake
within
your watershed, and the
area
of the lake is 0.0645 km
²
, what is the change in the
lake
level
(i.e. depth) in July, and indicate whether the lake level decreased or increased?
Provide your answer in metres (m)
. (2 marks)
0.0645 km
2
= 64, 500 m
2
Change in lake level (ΔL) = (change in storage/area of lake)*1000
ΔL = (19.47 m
3
/64, 500 m
2
)
= 0.00030186 ≈
3.02x10
-4
m
Positive value indicates increase in lake level in the month of July.
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