1. Rainwater Harvesting using 3D roofs in Corpus Christi, Texas
By Tongren Zhu Dec. 20th,2012

2. Rainwater Harvesting Definition Uses Benefit
Rainwater harvesting is the accumulation and storage of rainwater for reuse before it reaches the aquifer.
Uses
Including water for garden, water for livestock, water for irrigation, cleaning of bathrooms as in first flush, etc.
Benefit
Provide sufficient water supply, serve as a valuable stormwater management tool.

3. 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

4. Growing Demands & Declining Supply
Lake Corpus Christi Reservior
Additional Source of Water Needed！！！

5. 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

6. Calculation of Toilet Water Needs
Toilet: 6L(1.6 gallon) per flush
Urinal: 3.8L(1 gallon) per flush
Lavatory Faucet: 5.7L(1.5 gallon) per minute
30L/(Cap-d)
Assume 10 hours in the office per day
For 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.

7. 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.

8. Month Toilet Water Needs in Each Building

9. Rainwater Captured Precipitation Data Rainwater Captured
=Precipitation× Roof AreaXY×0.85
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
2.03
3.12
3.16
1.80
3.28
5.21
3.50
1.57
1.59

10. 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.

11. 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( m3) ×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.

12. 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 considered 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.

13. 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.

14. Reference & Acknowledge
The Texas Manual on Rainwater Harvesting, Texas Water Development Board, Third Edition,2005,Autin, Texas
Nueces River Authority website
USEPA WaterSense website
City of Corpus Christi website
ArcGIS online basemap
CyberCity3D
Dr. Maidment, Dr. Tarboton and Dr. Kilic
All GIS in Water Resources classmates

15. Thank You !