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Sanh Luong

Academic Year: 2010-2011

The Pros and Cons of Rainwater Catchment in San Diego

Area of Concentration

  • Environment

Key Terms:

water conservation, rainwater catchment, high efficiency appliances, San Diego

Significance/Broader Impact:

    Since 2005, the drought in San Diego has made evident that the issue of water shortage exists and continues to be an issue. More importantly, water consumption is even harder to sustain given San Diego’s semi-arid geographic location. Due to San Diego’s lack of natural water resources, its water supply depends on imported water from the Northern California’s Delta region and Colorado River. Water shortages are caused further by the State of California’s restrictions on San Diego on excess pumping from Northern California’s Delta region and depleting aquifers. The current climate change also produces low rainfall and creates water supply cutbacks from the main distributor of Southern California, the Metropolitan Water District (MWD). Metropolitan Water District is a key player because the San Diego County Water Authority (SDCWA) purchases its water supply from MWD.
    To prevent drastic depletions of water reserves, MWD coordinated with the water agency in San Diego County to implement conservation measures and mandates to reduce excess water consumption. The enforcement policy, “Water Shortage and Drought Responses Plan,” regulates water usage and helps SDCWA to minimize impacts on the region’s economy and the quality of life by responding accordingly to the available water resources.  Through mandated and voluntary water conservation programs, the San Diego County has shown water use reductions by 197,035 acre-feet from 2007 to 2010. Acre-feet is an English standard unit of measurement for volume used by SDCWA to measure water consumption. While consumption decreased, more conservation efforts are needed to alleviate San Diego’s water shortages.
    As an incentive to reduce water consumption, San Diego County Water Authority (SDCWA) created water conservation programs based on MWD’s allocated rebate funding of $6 million dollars for regional residential homes. While the residential rebates are offered for high efficiency laundry washers, high efficiency toilets, rotating lawn nozzles, and weather-based irrigation controllers, this research focuses on rebates only for laundry washers and toilet appliances because these two appliances are the highest water consuming appliances in the home.  Laundry washers will henceforth be referred to as “washers,” due to their large volume capacity, to prevent confusion with the conventional dishwasher. While rainwater catchment (RWC) systems is currently not offered as a rebate product, it is an alternative method to consider for future rebates because it is a viable local water source as imported water becomes difficult and scarce. It is a water source that is readily available during rainy seasons and could be collected quantitatively. Thus, this research focused on evaluating whether RWC would be a beneficial water-saving product compared to high efficiency toilet and washer appliances as a future consideration for rebates.

References

Costanza, R., et. al. (15 MAY 1997). The value of the world’s ecosystem services and natural capital.
Meera, V., & Ahammed, M. M. (2006). Water quality of rooftop rainwater harvesting systems: A review. Journal of Water Supply: Research & Technology-AQUA, 55(4), 257-268.
Li, X., Xie, Z., & Yan, X. (2004). Runoff characteristics of artificial catchment materials for rainwater harvesting in the semiarid regions of china. Agricultural Water Management, 65(3), 211-224.
Karpiscak, M. M., Foster, K. E., & Schmidt, N. (1990). Residential water conservation: Casa del agua. JAWRA Journal of the American Water Resources Association, 26(9), 939-948.
Sturm, M., Zimmermann, M., Schütz, K., Urban, W., & Hartung, H. (2009). Rainwater harvesting as an alternative water resource in rural sites in central northern namibia. Physics and Chemistry of the Earth, Parts A/B/C, 34(13-16), 776-785.
Stapp, William B., et al. (1969). The concept of environmental education.

Links:

SANDAG. San diego of associated governments., 2010, from http://www.sandag.org/
SDCWA. San diego county water authority., 10/2010, from http://www.sdcwa.org/
http://www.sandiego.gov/water/conservation/tips.shtml

Fall SRP Proposal Abstract

This proposal outlines a research strategy to examine rainwater harvesting in San Diego. Current research on rainwater harvesting suggests that it is feasible and sustainable method to acquiring water. The intent of this research is to look at the practicality of rainwater harvesting in San Diego, the demand for the catchment system, and policymaking in the local governments to promote rainwater harvesting.  In addressing these three areas, the study will comply and analyze specifically San Diego’s precipitation trends to determine the impact of rainwater harvesting. The research will contribute to the literature on water conservation, but it will also be shared with local grassroots organizations in hopes that it will promote greater social awareness to conserve water using rainwater catchment systems.

Winter Senior Research Project (SRP) Abstract

Currently, the Southern California Metropolitan Water District and San Diego Water Authority provide rebates for high-efficiency water appliances in single homes in San Diego as an incentive to reduce drought and the city’s dependence on imported water. However, these agencies do not provide rebates for rainwater catchment (RWC) system, a known alternative water-saving method that is practical and widely studied. This research examines the differences between investing in rainwater catchment (RWC) system and high efficiency water appliances for rebates. Its purpose is to address the question of whether rainwater catchment is a feasible investment for future rebates based on the three measures of environmental value, economic value, and social value that were calculated from precipitation records, product costs, benefit-cost ratio, and direct interview with Brook Sarson. The findings indicate that rainwater catchment is not sufficient to meet the high demands of single homes in San Diego. While rainwater catchment’s potential to reduce imported water consumption is not beneficial in terms of the amount of water saved and its benefit-cost ratio, it has high social value towards the water conservation efforts in San Diego.

Study's Major Findings and Contributions

Given Brook Sarson’s efforts in educating citizens about rainwater catchment (RWC), even though RWC systems have lower benefit-cost ratio compared to dual flush toilets, RWC is still a valuable means of alternative non-portable water supply that should not be understated or dismissed.  San Diego County Water Authority and Metropolitan Water District’s water programs are intended to encourage residents to conserve water usage as only proactive and short-term solutions to the region’s water crisis. Brook Sarson’s educational objective is an invaluable social addition and enhancement because her seminars strengthened the significance of water conservation and created self-reliant citizens in a drought crisis. Thus, her seminars echo the message to become more conscious about securing a localized water supply for San Diego in long-term, rather than short-term incentives.

Evidence

  Precipitation data was needed to calculate the volume of rainfall from 1914-2010 and from 2007-2010 to facilitate an understanding of the amount of rainfall available to the city of San Diego over a span of years. Precipitation data from 1914-2010 was collected because it provides a reference amount of rainfall over nearly 100 years in San Diego. Precipitation for the years 2007-2010 were collected because these were the years in which SDCWA implemented the water conservation rebates. The precipitation data was collected from the California Irrigation Management Information System (CIMIS) and Western Regional Climate Center (WRCC), which gave the amount of rain received per month and the rainfall in inches to create average precipitations in both 2007-2010 and the reference years from 1914-2010. Data was acquired from CIMIS’s three weather stations in San Diego County: San Diego II (Lindbergh International Airport), Miramar Airbase, and Otay Lake via the Internet.  The calculated monthly average rainfall for each of the three stations was compiled to generate San Diego’s regional precipitation average from 2007-2010 whereas the reference precipitation average was created solely from the WRCC data recorded at San Diego’s Lindbergh Field Airport since 1914 to 2010.  WRCC data was used as reference because they are significant sample sizes that ensure accurate representation of the annual precipitations pattern that have occurred in San Diego for the last approximately 100 years.
From these two precipitation data, a graph of the amount of rainfall in inches vs. the time in months was then created to show how the precipitation averages from 2007-2010 had deviated from the regional reference average. This ultimately showed that there has been an overall decrease in the amount of rainfall, since there was more rainfall a hundred years ago as compared to current years.
    To analyze RWC’s potential as a supplemental water resource for San Diego’s imported water use, several comparisons were studied. The maximum acre-feet of rainwater was used to study whether rainwater could supplement San Diego’s 2010 imported water use by 100 percent and by 50 percent based on 2007-2010 annual precipitation averages. Another aspect of the study that contributed to environmental value was based on the amount of rainwater 628,652 single homes in San Diego could harvest based on three different rainwater tank sizes if the city invested in rainwater catchment systems. The number of homes was based on the 2000 census published by San Diego’s Regional Planning Agency (SANDAG).  The research studied the amount of water from rainwater each tank size could provide an individual single home compared to the amount of water saved from replacing low efficiency appliances for high efficiency toilet and washers. 
    Economic value, based on monetary amounts, measured the benefit-cost ratio of RWC systems compared to high efficiency toilet and washer appliances. The benefit-cost ratio was determined by dividing the amount of water saved per household per year over the lowest product cost for a high efficiency dual flush toilet and high efficiency Maytag Maxima washer. Then, this benefit-cost ratio was compared to the investment of purchasing three rainwater tanks sizes manufactured by RTS. The study used three selected tanks sizes—600, 1200, and 1500 gallons—to see how much rainwater each tank could collect overall during winter months. The specific sizes were selected because some single homes had limited space and could not fit tanks larger than 1500 gallons. To ensure consistency in data analysis of price versus size for the benefit-cost comparison, all the tanks were from one brand, RTS. For toilets, dual flush are the new efficiency standards that offers a 0.8-gallon per flush for liquid and a 1.6-gallon per flush (gpf) for solids, compared to older 1.6 and 3 gpf models.  High efficiency for washer machines was measured by the amount of water saved per load. Since prices varied by brand and the level of efficiency, price selections for toilet, washer, and rainwater tanks were categorized by the lowest price for each product on various websites, and the lowest priced found was used. 
    The measure of social value looked at how citizens of San Diego can become more educated about effective water conservation practices and rainwater catchment. The research conducted an interview and involved direct participation with local San Diegan – Brooks Sarson, a permaculture specialist and a rainwater catchment advocate. An interview and direct participation at Sarson’s unique water conservation seminar provided an understanding of the importance of grassroots movements as effective grounds for the public to get educated and learn about the importance of water conservation in San Diego.

Spatial Dimension

    Water consumption data for the research was acquired from San Diego County Water Authority (SDCWA), which is made up of 24 municipalities in the San Diego region. Since the consumption data came from SDCWA, the volume of rainfall collected was based on the surface area boundary of the 24 municipalities. In order to acquire the acreage of surface area of the 24 municipalities, Geographic Information System (GIS) was used to measure the dimension of the area with the following equation: (Surface) x (Feet of rain) = volume of rainwater in acre-feet.

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