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

Month Toilet Water Needs in Each Building

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

Thank You !