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Rainwater Harvesting using 3D roofs in Rainwater Harvesting using 3D roofs in Corpus Christi, TexasCorpus Christi, Texas
By Tongren Zhu Dec. 20th,2012
Rainwater Harvesting
DefinitionDefinitionRainwater harvesting is the accumulation and storage of rainwater for reuse before it reaches the aquifer.
UsesIncluding water for garden, water for livestock, water for irrigation, cleaning of bathrooms as in first flush, etc.
BenefitProvide sufficient water supply, serve as a valuable stormwater management tool.
Corpus Christi
Fifth largest US port, with an unemployment of 6.6% and annual GDP growth of 3.1%
With a population of 305,215 according to 2010 census, 10% increase since 2000
Growing needs for water, but declining supply from reservoir
Growing Demands & Declining Supply
0
50000
100000
150000
200000
250000
300000
350000
1900 1920 1940 1960 1980 2000 2020
Population of Corpus Christi
Year
Po
pu
lati
on
Lake Corpus Christi Reservior
http://www.nueces-ra.org/CP/CITY/day.phphttp://corpuschristi.usgulf.info/Level.asp
Additional Source of Water Needed!!!
Project Area
237 buildings in total
All commercial buildings in downtown
With field value of roof areaXY, facade area, reletive height, roof slope etc.
Will look into potential of rainwater for toilet use
Calculation of Toilet Water Needs
Lavatory Faucet: 5.7L(1.5 gallon) per minute
Assume 10 hours in the office per dayFor male, use toilet 1 time, use urinal 4 times, 21.2L/(cap-day)For female, use toilet 5 times,30L/(cap-day)
For one capita, 25.6L/day. We use 30L/day here.
Urinal: 3.8L(1 gallon) per flush
Toilet: 6L(1.6 gallon) per flush
30L/(Cap-d)
Calculation for water Needs
Parameters set: 4.5m/floor, 25m2/cap
Water Needs in Building=30L/(cap-day)×Capita
For Some special buildings, area are remeasured.
/cap25m
ight/4.5RelativeHea0.9RoofAre
/cap25m
StoryaXY0.9RoofAre
/cap25m
OfficeAreaBuildingin Capita
222
Rainwater Captured
• Precipitation Data
• Rainwater Captured
=Precipitation× Roof AreaXY×0.850.00
1.00
2.00
3.00
4.00
5.00
6.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Monthly Precipitation Data(inches)
Month
Pre
cip
ita
tio
n(i
nc
hes
)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Median 0.99 1.36 0.78 1.39 2.70 2.43 1.04 2.64 4.00 2.60 1.34 0.90
Average 1.54 1.85 1.36 2.03 3.12 3.16 1.80 3.28 5.21 3.50 1.57 1.59
Month Balance Calculation
End of Month=End of Previous Month+Rainwater Captured this month-Water Used this month
In the case of ObjectID=1 building:
To ensure water supply, the lowest End of Month Storage value(-1.021m3)×Safety Factor(1.5) should be considered the smallest tank volume which is filled in the beginning. Here, we choose 1.5m3.
If tank volume larger than this value, rainwater captured can be put into other use in addition to toilet flush.
0.000
5.000
10.000
15.000
20.000
25.000
Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Water in Tank at End of Month
Volu
me(m
³)
Month Balance Calculation
End of Month=End of Previous Month+Rainwater Captured this month-Water Used this month
In the case of ObjectID=15 building:
To ensure water supply, the lowest End of Month Storage value(-2128.5m3) ×1.5 should be considered the smallest tank volume which is filled in the beginning. This value is wierd!!!
So for tall buildings with comparatively small roof area, rainwater cannot be the only source for toilet flush water. Other source is water is still needed and rainwater harvest system under such case acts more like a demonstration project.
Feasibility • Usually, a tank volume of 50m3(13,000gallon) is considered as the threshhold for feasibility.• For buildings occupy large area(>500m2), a tank volume of 100m3(26,000gallon) is conside
red as the threshhold for feasibility.• For buildings occupy a very large area(>1000m2), a tank volume of 150m3(39,000gallon) is
considered as the threshhold for feasibility.
For those lacking feasibility now, more specific work is needed when checking rainwater harvesting potential.
Conclusion
• Corpus Christi is enjoying steady population and economy growth which may lead to more water consumption
• Reserviors for Corpus Christi is declining, meaning new source of water is needed
• For buildings with large roof areas and fewer stories, rainwater harvested has great potantial.
• For skyscrapers, rainwater might work for some specific use, or be used above a certain floor which needs more detailed consideration under given project.
Reference & Acknowledge
The Texas Manual on Rainwater Harvesting, Texas Water Development Board, Third Edition,2005,Autin, Texas
Nueces River Authority website http://www.nueces-ra.org/CP/CITY/day.php
USEPA WaterSense website http://www.epa.gov/WaterSense/index.html
City of Corpus Christi website http://www.cctexas.com/
ArcGIS online basemap
CyberCity3D
Dr. Maidment, Dr. Tarboton and Dr. Kilic
All GIS in Water Resources classmates