By
Zhuo Li1, Robert W. Peters1, and Matthew Winslett2
1Department
of Civil, Construction, and Environmental Engineering
2Facilities Management Department
University of Alabama at Birmingham
Alabama Water Resources Conference 2013
Orange Beach, AL
September 5-6, 2013
Overview
 Significance of Water Conservation at UAB
 Site Description
 Estimation of Irrigation Water Needs
 Design of Rainwater Harvesting System
 Sensitivity Analysis
 Results and Discussion
 Conclusions
Significance of Water Conservation
at UAB
 Water Consumption at UAB (Winslett, 2011):
 2008-2009: 697,920 ccf (522,080,416 gallons)
 2009-2010: 659,271 ccf (493,168,956 gallons)
 Corresponding water and sewer costs at UAB:
 2008-2009: $7,025,011
 2009-2010: $6,907,892
 An underground storage tank (UST) was installed in 2010
at the University Boulevard Office Building (UBOB).
Study Investigation
 Study investigation at Texas A&M University (TAMU)
 For purpose of controlling storm runoff volume and
landscape irrigation, Saour (2009) performed a feasibility
study of implementing rainwater harvesting system (RHS).



Uses an equation from TAMU to estimate water supply and demand
Performed payback period with two scenarios of 20 and 14 years
The results showed little effect on control of stormwater runoff
volume
 This study is similar to the project at UAB but the project at
UAB is not concerned about reduction of stormwater runoff.
Site Description
 The Campus Green is
bordered by Blazer Hall, the
Dining Commons, the
Campus Recreation Center,
and Heritage Hall.
 Overall, the permeable and
impermeable area are
approximately 52% and
48%, respectively.
Source: Google Map, 2013
Estimation of Irrigation Water Needs
 Effective precipitation
 The mean value (inches) of last five-year precipitation data is used for
estimation purpose:
Mean Precipitation Value from Year 2008-2012
7
Precipitation, (inches)
6
5
4
3
2
1
0
Month
Source: Birmingham Weather Forecast Office, 2011
Estimation of Irrigation Water Needs
 Effective precipitation was estimated by Natural Resource Conservation
Service (NRCS) curve number method (SCS,1986)
 Assuming antecedent moisture condition (AMC) II.
 Hydrologic soil type B (SCS, 1982)
 It was assumed that the measured value was used to calculate the runoff
without considering estimation errors.
Area
Land Type
Square Feet
Acres
Street and Roads (Paved Area)
220,000±11,000
5.1±0.25
Open Space (Grass and Trees)
469,000±24,000
10.8±0.55
Roof Area
207,000±10,000
4.8±0.23
Total
896,000±45,000
20.7±1.03
Estimation of Irrigation Water Needs
 Evapotranspiration
 The Blaney-Criddle formula (Blaney and Criddle, 1950) was used, and minimum
crop factor of 0.6 was selected for turf .
Mean Temperature from Year 2008-2012
Temperature, (°C)
30
25
20
15
10
5
0
Month
Source: Birmingham Weather Forecast Office, National Weather Service, 2011
Estimation of Irrigation Water Needs
 Irrigation water needs= ETcrop – Pe (Brouwer and Heibloem, 1986).
 A well designed and operated irrigation can have efficiency ranges from
80% to 90 % (University of California Extension System, 2000).
Estimated Irrigation Water Needs, (gallons)
Irrigation Water Needs, (gallons)
1,000,000
800,000
600,000
400,000
200,000
0
-200,000
-400,000
Month
Note: negative value indicates no additional water needs for irrigation beside rainwater
Design of RHS at UAB
 The UAB Campus Recreation
Center pumps the
groundwater in order to
avoid being flooded.
 The quantity of pumped
groundwater is
approximately 1.0 million
gallons per year.
 Assuming in each month,
equal quantities of
groundwater are pumped,
hence 85,000 gallons per
month.
Design of RHS at UAB
 Irrigation scheme
 Most installers usually assume an efficiency of 75% to 90% (The Texas Manual
on Rainwater Harvesting, 2005). Assuming 90% efficiency:
Month
Irrigation Water
Need, (gallons)
Collectable
Rainwater,
(gallons)
Groundwater,
(gallons)
January
February
March
April
May
June
July
August
September
October
November
December
30,000
173046
30,000
439,619
93,172
819,852
296,129
594,586
30,000
598,105
233,124
30,000
569,382
496,473
706,713
488,373
889,563
396,947
531,192
662,736
444,396
521,548
487,601
535,050
85,000
85,000
85,000
85,000
85,000
85,000
85,000
85,000
85,000
85,000
85,000
85,000
Total
3,367,633
6,729,974
1,020,000
Design of RHS at UAB
 Tank size determination
 Refers to UST at UBOB and situation in this project, the tank size was
determined to be 60,000 gallons, which are two 30,000 gallon tanks.
 Commercial water costs $3.21/CCF (Birmingham Water Works Board, 2013).
 Total water cost saving ~$ 13,284
Draco, Inc. Underground Water Tanks with Purpose of Landscape Irrigation
Size of Tanks (gal)
Diameters of Tank (ft)
Price of polyethylene Tank, ($)
10,000
10
15,750
20,000
10
26,537
30,000
12
37,908
40,000
12
53,005
50,000
12
62,080
Source: www.darcoinc.com/ (Darco Inc., 2013)
Tank Size Determination (Cont’d)
Accessories and other cost
30000 gallon polyethylene tanks
2 HP Pump
60 GPM Filter
Misc. such as landscaping, locating drains, connecting sprinklers, etc.
Dig tank hole and backfill
Concrete tank support
Gravel around tank
Piping to tank
Electrical/controls
Subtotal Costs
Overhead 10%
Engineering 15%
Contingency 15%
Total
Source: UAB Facilities Management Department, 2012
Cost, ($)
37,908
585
70
8,500
8,000
4,000
25,000
12,000
10,000
106,063
10,606
15,909
15,909
148,488
Tank Size Determination (Cont’d)
 If use one 60,000 gallon tank:
UST Cost
 The payback period = Water charge per year =
$148,488+$ 37,908
$12,715
= 14.6 years
 Double costs if use two 30,000 gallon tanks
 If only use a 30,000 gallon tank :
UST Cost
 The payback period = Water charge per year =
$148,488
$ 12,458
= 11.9 years
$163,584
$ 12,544
= 13 years
 If only use a 40,000 gallon tank:
UST Cost
 The payback period = Water charge per year =
 The optimize tank size can be 30,000 gallons.
 The UAB Facilities Management Department performed a
preliminary study that suggests using a 30,000 gallon tank.
 Smaller tank can make a little better payback but less of capacity
for efficient irrigation which is not preferable.
Design of RHS at UAB
Sensitivity Analysis
 A sensitivity analysis was performed in order to explore
the impact on tank size, payback period.
 The study investigated changes of±5%,±10% and
± 25%
 If the water supply can fully meet the demand, the tank
size will be reduced. Otherwise, it will remain the same.
 Three scenarios were studied:
 Change of precipitation
 Change of ET
 ET and precipitation increase or decrease at same time
Results and Discussion
 Sensitivity analysis shows no impact on tank size and overall





payback period.
With a decrease in precipitation or an increase in
evapotranspiration, the payback period will be shorter.
Overall, the designed rainwater harvesting can meet
approximately 86% of the total irrigation water requirement.
The ongoing research project on recovery of condensed water
at UAB indicates good water quality that can be supplemented
for irrigation.
To reduce the payback period, concrete water storage tanks or
other cheap material-made tanks can be alternatives to
decrease the capital investment.
The UST has a potential problem (algae formation) that can be
controlled by disinfection and maintenance but leads to higher
cost.
Conclusion
 The study provides a general estimation involving a feasibility
study of implementing a RHS at the UAB Campus Green.
 The estimation may be not highly accurate in some details but
generally it is reasonable providing results similar to the study
at TAMU and UAB Facilities Management Department.
 Based on the financial aspect, the payback period is a little
long, ~12 years, indicating that rainwater harvesting is not
economically viable for large scale implementation for
irrigation purposes.
 However, in an effort to make the campus “greener”, the RHS
may be a viable approach.
Acknowledgements
 Sincere gratitude to Dr. Robert W. Peters for his valuable
time.
 Thanks offered to Mr. Matt Winslett for his strong support
by providing data need for this investigation.
 Thanks and appreciation to the Facilities Management
Department of UAB funding this study.
 Thank you for your time.
 Questions?
Mean Daily Percentage (p) of Annual Daytime Hours for
Different Latitudes
The latitude of Birmingham is 33°31' 14" N, rounded to 33°.
Latitude
South North
Jul
Jan
Aug
Feb
Sep
Mar
Oct
Apr
Nov
May
Dec
Jun
Jan
Jul
Feb
Aug
Mar
Sep
Apr
Oct
May
Nov
Jun
Dec
60
55
50
45
40
35
30
25
20
15
10
5
0
0.15
0.2
0.26
0.32
0.38
0.41
0.4
0.34
0.28
0.22
0.17
0.13
0.17
0.21
0.26
0.32
0.36
0.39
0.38
0.33
0.28
0.23
0.18
0.16
0.19
0.23
0.27
0.31
0.34
0.36
0.35
0.32
0.28
0.24
0.2
0.18
0.2
0.23
0.27
0.3
0.34
0.35
0.34
0.32
0.28
0.24
0.21
0.2
0.22
0.24
0.27
0.3
0.32
0.34
0.33
0.31
0.28
0.25
0.22
0.21
0.23
0.25
0.27
0.29
0.31
0.32
0.32
0.3
0.28
0.25
0.23
0.22
0.24
0.25
0.27
0.29
0.31
0.32
0.31
0.3
0.28
0.26
0.24
0.23
0.24
0.26
0.27
0.29
0.3
0.31
0.31
0.29
0.28
0.26
0.25
0.24
0.25
0.26
0.27
0.28
0.29
0.3
0.3
0.29
0.28
0.26
0.25
0.25
0.26
0.26
0.27
0.28
0.29
0.29
0.29
0.28
0.28
0.27
0.26
0.25
0.26
0.27
0.27
0.28
0.28
0.29
0.29
0.28
0.28
0.27
0.26
0.26
0.27
0.27
0.27
0.28
0.28
0.28
0.28
0.28
0.28
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
0.27
Adapted from: Brouwer and Heibloem, 1986
Warm Season Turf
 The grass type is warm season turf, which is suitable for
growing during the warm climate season.
 A minimum proper crop factor of 0.6 was selected for
calculation in order to conserve water.
Source: The University of Arizona Cooperative Extension, 2000
Source：SCS, 1986
Land Use
Area,
acres
CN
Product,
Area×CN
Street and Roads
(paved Area)
Open Space (grass
and trees)
Total
5.1
98
494.9
10.8
61
657.2
15.9
1152.1
Steps of Calculating Effective Runoff
 Thus, the composite CN was computed as:
𝐶𝑁 = 1152.1 ÷ 15.9 = 72.5
 The maximum possible retention for this area at AMC-II is:
𝑆 = 1000 ÷ 72.5 − 10 = 3.79 𝑖𝑛𝑐ℎ𝑒𝑠
 The initial abstractions were estimated to be:
𝐼𝑎 = 0.2𝑆 = 0.2 × 3.8𝑖𝑛𝑐ℎ𝑒𝑠 = 0.76 𝑖𝑛𝑐ℎ𝑒𝑠
 Because P>𝐼𝑎 , the depth of runoff (effective precipitation)
was estimated as:
4.92 − 0.2 3.8 2
𝑃𝑒 =
= 2.14 𝑖𝑛𝑐ℎ𝑒𝑠
4.92 + 0.8 3.8