HW2_CEE350_SP23(1)
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School
University of Illinois, Urbana Champaign *
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Course
350
Subject
Industrial Engineering
Date
Dec 6, 2023
Type
Pages
4
Uploaded by UltraExploration8833
CEE 350
SP 2023
Homework #2
Due: Tue, Apr 4
1.
(
30 points
) Stormwater control is an important consideration in urban areas where there
are large impervious areas. Green roofs are being promoted as an effective method to reduce
stormwater runoff, since rain will infiltrate into the soil layer and be stored there for later
removal by drainage or evapotranspiration. A typical cross-section of a green roof is shown in
Fig. 1.
Fig. 1. Illustration of green roof.
In this problem, we will evaluate the performance of the green roof for design storms. We will
make the following assumptions:
The green roof covers approximately 280 m
2
(about 3,000 ft
2
)
Thickness of the vegetation layer is 6 inches (152.4 mm)
Soil type= loamy sand (see Text Table 9.12 for soil properties; use porosity = 0.44,
and wetting front suction head = 61 mm)
initial moisture content,
θ
i
=0.12
We assume that any ponded water will immediately run off into the roof gutters (i.e., H=0, see
Fig 9.23). We also assume that the draining layer is at atmospheric pressure so that any water
that infiltrates to the bottom of the vegetation layer is at atmospheric pressure and can freely
flow away and on to the rest of the roof.
(1) (
4 points
) What is the maximum amount of rain that can infiltrate before there is any runoff
onto the roof?
(2) (
20 points
) Use the Green-Ampt method to compute and plot the infiltration rate,
cumulative infiltration, depth of the wetting front, and runoff for TWO storms with different
rainfall intensity: (a) 60-minute storm with rainfall rate = 5.2 cm/hr; (b) 60-minute storm with
rainfall rate = 4.0 cm/hr.
(3) (
2 points
) Compare your results with the total volume of runoff for a conventional roof
where all the rain is runoff. Discuss the performance for the two different design storms.
(4) (
4 points
) Explain qualitatively (you do NOT need to do any calculations) what would
happen if the thickness of the vegetation layer was reduced.
2.
(
30 points
) Daily weather data collected from a weather station for the months of July
and October are provided in the Excel spreadsheet uploaded to the ZJU Blackboard. You will
see that the reported data include total solar radiation (Rs), air temperature (in
o
F - degree
Fahrenheit), relative humidity, and wind speed (in MPH – mile per hour). Actual vapor pressure
(column P) are also included, which were calculated using equation 13.44 in the text with the
measured air temperature and relative humidity.
The latitude, longitude and elevation (meters) of the weather station are: 40.0840, 88.2404,
219, respectively. The wind is measured at 10 m height, temperature at 2 m height. The Julian
Day table for non-leap years is at:
http://uop.whoi.edu/UOPinstruments/frodo/aer/julian-day-
table.html
(1) (
20 points
) Use these data and the Penman-Monteith method to calculate the daily ET for
standard short grass. Ignore the soil heat flux (G=0). Plot the daily ET during the months of
July and October.
(2) (
5 points
) Discuss briefly the variation throughout the month and how the two months
compare.
(3) (
5 points
) Note that you will also find a calculated daily ET (inches/day) in the weather
station data (column M). This is computed by a modified version of the Penman equation and
is the potential ET. How do your values compare with those ET values?
Hint:
Be careful with units.
PI
111
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in
conventional
roof
is
much
larger
than
the
green
roof
when
there
is
first
storm
will be
runoff
and
the
vegetation
lager
will be
saturated
When
second
storm
it
will
not
saturated
4
the
runoff
will
be
larger
pz.ly
my
October
2
variation
is
large
month
to
month
evaporation
varies
greatly
My's
evaporation
October
3
estimated
values
exceed
the
value
determined
using
the
modified
Penman
Equation