Design of Underground Storage Tanks Involving Water Collection for Water Reuse of Irrigation Purpose: A Case Study for

1. Design of Underground Storage Tanks Involving Water Collection for Water Reuse of Irrigation Purpose: A Case Study for the Campus Green Area of UAB By ZhuoLi1, 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

2. 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

3. 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).

4. 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.

5. 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

6. Estimation of Irrigation Water Needs • Effective precipitation • The mean value (inches) of last five-year precipitation data is used for estimation purpose: Source: Birmingham Weather Forecast Office, 2011

7. 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.

8. Estimation of Irrigation Water Needs • Evapotranspiration • The Blaney-Criddleformula (Blaney and Criddle, 1950) was used, and minimum crop factor of 0.6 was selected for turf . Source: Birmingham Weather Forecast Office, National Weather Service, 2011

9. 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). Note: negative value indicates no additional water needs for irrigation beside rainwater

10. 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.

11. 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:

12. 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 Source: www.darcoinc.com/(Darco Inc., 2013)

13. Tank Size Determination (Cont’d) Source: UAB Facilities Management Department, 2012

14. Tank Size Determination (Cont’d) • If use one 60,000 gallon tank: • T • Double costs if use two 30,000 gallon tanks • If only use a 30,000 gallon tank : • T • If only use a 40,000 gallon tank: • T • 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.

15. Design of RHS at UAB

16. 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

17. 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.

18. 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.

19. Acknowledgements • Sincere gratitude to Dr. Robert W. Peters for his valuable time. • Thanks offered to Mr. Matt Winslettfor his strong support by providing data need for this investigation. • Thanks and appreciation to the Facilities Management Department of UAB funding this study.

20. Thank you for your time. • Questions?

23. Mean Daily Percentage (p) of Annual Daytime Hours for Different Latitudes The latitude of Birmingham is 33°31' 14" N, rounded to 33°. Adapted from: Brouwer and Heibloem, 1986

24. 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

25. Source：SCS, 1986

27. Steps of Calculating Effective Runoff • Thus, the composite CN was computed as: • The maximum possible retention for this area at AMC-II is: • The initial abstractions were estimated to be: • Because P>the depth of runoff (effective precipitation) was estimated as: