The impacts of Rainwater Catchment as a Supplementary Water Source
in the semiarid San Diego Region
A research proposal submitted to the Urban Studies and Planning Program
University of California at San Diego
Sanh B. Luong
USP 186 Section A02
sbluong@ucsd.edu
January 21, 2011
Abstract:
This proposal outlines a research strategy examining rainwater catchment in San Diego. Low
rainfalls and the decrease of imported water from Northern California in the last several years have
subjected the San Diego region into drought. Rainwater catchment is a supplemental water conservation
method that can help reduce drought and imported water in San Diego. The rainwater catchment is widely
implemented in water scarce region of New Mexico and Arizona, however, rainwater catchment remains
unconventional in San Diego Current research on rainwater harvesting suggests that it is a feasible
method for acquiring water. The intent of this research is to look at economic advantages,
disadvantages, and the social implications of rainwater catchment system in San Diego. The
study will compile San Diego’s precipitation records and data analysis will be conducted to
compare potential rainwater with recorded water usage. The comparison between supplied water
and renewable rainwater will show that is it a viable supplementary water supply for San Diego
to reduce drought. Not only will this research contribute to the literature on water conservation
but it will also be shared with local grassroots organizations in hopes that it’s ideas will promote
social awareness for rainwater catchment systems .
Key terms: Rainwater Harvesting, Water Catchment Systems, Water Conservation, San Diego
Introduction:
This research project will analyze rainwater catchment potential in term of costs,
efficiency, and water saved to an individual homeowner and the potential social effects rainwater
catchment could have on San Diego. The current rainwater catchment initiative is not a common,
nor a sustainable approach for home and infrastructure in San Diego. The region’s conventional
methods of supplying water to homeowners are both costly and energy intensive. San Diego
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needs to have its own self-sustaining water supply; water harvesting can contribute to the overall
needs of the community. At the moment, little is being done by local municipals and water
agencies in the region to promote water catchment of rainwater. Why then should San Diego
residential homeowners invest in a rainwater catchment system? As an incentive, the monetary
value of rainwater collected will pay for the cost of the catchment system over a payback period
of several years. The payback correlates to the amount of money saved from not having to
purchase portable water from local municipal water suppliers. Rainwater would help reduce
residential water demands from municipal water supplies during winter months, thereby
conserving the regional water supply and allowing the reservoir to refill in order to meet the high
water demands during the summer season. This effort would help decrease the drought severity
that typically occurs in San Diego during the summer months.
The current low costs of water discourages the public from seeking out alternate methods
to curb/change their water consumption behaviors. The public does not realize, however, that a
portion of its water consumption can be acquired from collecting and storing rainwater. The
amount of rainwater collected depends on roof surface area and annual precipitation rates. It’s
accumulation can reduce dependence on local water resources during the rainy season. The
stored rainwater can also be used to water crops and landscape, and also has the potential to
power home appliances.
This study will analyze San Diego’s rainfall over the past 5 years, using the Geographic
Information System (GIS) as a tool to create detailed maps and quantitate results to provide
insight into the amount of rainwater a typical home in San Diego can accumulate during the
rainy season based on roof characteristics and how it could supplement the municipal water
supply. Furthermore, this study will look at the effort of Brook Sarson—a San Diegan rainwater
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advocate and founder of H2OME—who demonstrates that rainwater harvesting is simple and can
be easily installed to any residential infrastructure in San Diego. Therefore, the results of this
study are empirically based on quantitative approximation from weather data, aerial imaginary
data, published research on the topic of rainwater catchment, and inputs from rainwater
catchment specialists. The scope of this research is limited by the amount of time given, which
limits the ability to monitor and collect data of an operational rainwater system for a year or
several years.
Conceptual Framework:
The demand for water will increase as San Diego’s population is expected to grow from
the current approximate 3 millions to 4.51 millions by 2050 (SANDAG, 2010). While the costs
of water will increase with its demands, water supplies will decrease. Unfortunately, in San
Diego, and around the world, the rate that depletion of surface fresh water and subterranean
aquifers reservoirs is occurring is faster than the rate at which it can be replenished. Rainwater
harvesting can be a supplementary source of freshwater for the semiarid San Diego region during
the rainy season. Rainwater catchment systems are vital sustainable alternatives for reducing
municipal water use during the winter months. This allows regional water storages to recharge
for peak demands.
In San Diego, the necessary supplies and materials required to construct and assemble a
rainwater system are easily accessible at local hardware stores, like Lowes and Home Depot, or
from specialized rainwater harvesting resellers. However, the lack of sponsorship and incentives
from local authorities limits the potential growth of rainwater catchment in San Diego region. In
addition, the lack of public awareness due to government neglect and cheap water costs continue
to contribute to the lack of rainwater catchment systems in San Diego. Despite the limited local
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government encouragement to adopt rainwater usage there are local grassroots activist like
Brook Sarson who have made it her career to educate, inform, and consult interested member of
the public who wish to incorporate a rainwater catchment system in their home. Brook is
striving to engage other homeowners to see the potential of rainwater harvesting, but in order for
rainwater harvest to have a regional impact it will requires social and political collaboration.
Greater incentives need to be created –along with regulations from local municipals and water
authorities—to promote innovative water conservation implications for San Diego.
In recent years, the continuous population growth in the San Diego region and the
continuous diminishing water supply has caused droughts to occur frequently. Public water
programs that are intended to encourage residents to conserve water usage are only proactive and
short-term solutions to the region’s water crisis. As natural water reservoirs are depleted due to
climate changes, and higher demands for water continue everywhere in California, drought in the
San Diego region will only worsen (SDCWA, 2010). Prolonging the effort to secure a localized
water supply as a long-term sustainable solution will deprive San Diego of socioeconomic
growth, decrease viability to sustain population growth, and cause irreversible damage to natural
habitats throughout the San Diego region.
Around the globe research on rainwater harvesting has been studied and is an ongoing
research topic studied by academics to available address many aspects of how rainwater
catchment system. Rainwater harvesting research studies the benefits and feasibilities of how
rainwater storage can help improve quality of life and compensate shortage of water supply in
both developed and developing countries (Sturm, Zimmermann, Urban, Hartung, 2009). Some of
the ongoing research has examined the cost-benefits of implementing rainwater harvesting, in
addition to using computer and mathematical models to determine the best rainwater harvesting
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location based on topography and weather patterns (Meera, Ahammed, 2006). Research also
exists in the field of forecasting to estimate and determine the amount of expected rain and
storage capacity (Li, Xie, Yan, 2004).
Currently, there are no research publications pertaining to rainwater harvesting which
addresses the water issue nor the rainwater catchment potential for San Diego. Research on
rainwater catchment systems for domestic use in Taiwan and Arizona, however, have been
found. In Taiwan, Chao-Hsien Liaw and Yao-Lung Tsai analyzed the optimization of rooftop
rainwater collection based on a mathematical algorithm that evaluated parameters of roof type
and flow coefficients, and recorded precipitation to determine specific amount of rain water
based on spatial variations. In addition, a study on a residential home called Casa Del Agua in
Arizona provided a new perspective into how efficient water management could promote and
achieve conservation goals without reducing the living quality of the residences (Karpiscak,
Foster, Schmidt, 1990). Unlike the study in Taiwan, which only focused specifically on
optimizing rainwater harvesting, the Casa Del Agua researchers studied the potential
contributions of rainwater catchment in addition to a combination of other water conservation
methods. Both research studies demonstrated that rainwater harvesting was vital for the future; it
should not be regarded as a primitive means of accumulating water, but rather, as a necessary
adaptation towards sustainability for cities and rural villages alike. Each study had a unique
focus with regards to rainwater pertaining to a specific geographic region, weather patterns,
different focus, and methods; but inevitably, all research indicated that rainwater harvesting was
a viable and important practice for modern society.
The algorithm developed by Liaw and Tsai which correlated rooftop surface areas with
rooftop types to determine the potential amount of accumulated rainwater will be use for my
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research to show how much rainwater can be harvested. My algorithm will be more generalized
in mathematical complexity, but still similar to theirs. Rather then combining multiple water
conservation methods to observe the effects water conservation would have on the regional water
supply as was done in Casa Del Agua research, rainwater will be the sole focus of my research.
Given San Diego’s geological location and different social-economic structure, a different
conclusion can and will be drawn regarding the impact of rainwater harvesting (Frasier, Gary,
Lloyd, 1983). The research will further show the cost-benefits of rainwater harvesting and the
correlation between the amount of collected rainwater and money value saved. By
acknowledging the costs, efficiency, and water saved from rainwater harvesting, hopefully the
general public will be encouraged to invest in rainwater catchment systems and continue to help
individuals like Brook Sarson in promoting rainwater catchment as a more effective way to
propel water conservation in the San Diego region.
Research Design and Methods
In order to answer why San Diegans should invest in a rainwater catchment system, the
research will quantitatively show the cost and the efficiency of the rainwater catchment system,
and the amount of water conserved. An essential factor in supporting the feasibility of the
rainwater catchment systems falls in the analysis of precipitation records—from both the
regional and national archived database— of the San Diego region. This research will look at
precipitation records for San Diego between the fall and winter season from the months of
October through March over a time span of 5 years. The months between October and March
are when Southern California receives most of its annual rainfall. Taking the average rainfall of
5 years allows for a more accurate projection of the average rainfall for the next year. Variations
in precipitation, as well as patterns of rainfall distribution can be quantified and analyzed through
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the data obtained. The determined amount of accumulated rainwater over a defined geographic
boundary will be factored into a simplified Liaw and Tsai’s algorithm that incorporates types of
roof surface areas, slope angles, and roof materials for a quantitative estimate of the expected
volume of rainwater for a home located at a given geographical location in San Diego.
Geographic Information System aerial imagery feature will be used to measure roof surface area.
Two separate standardized scales will be created to define the different roof slopes and material
types. The approximate water costs saved by a homeowner and conserved by the region for
drought months will be based upon standardizing the roof characteristics, the volume of
rainwater, and the consumption rate. The monetary value cost and the amount of supplied water
consumed in the San Diego region will be acquired from the regional database provided by
SANDAG and the water authority, Metropolitan Water District (MWD, 2010).
Similar to the calculation of precipitation, variables relating to the roof and the expected
accumulation of rainwater volumes should also add 10%-15% error deviation to the total results.
Accuracy cannot be assured for this research method since direct measurement of rooftop area
and precipitation across a large area is impractical, therefore, the computation can only be
approximate. Geographic Information System will be the primary tool for this research because it
is a versatile software with aerial and analytical capabilities to accurately represent my result on
the costs, the efficiency, and the amount of water conserved in easy visual interpretations.
This research explores my interests in hydrology and water conservation from an
engineering perspective. In addition, it provides insight into reducing dependency on importing
water and diminishing local water supplies by providing a viable and easily renewable
alternative. Numerical computations and quantitative techniques learned from studying
engineering will help me effectively collect data, analyze, and interpret my results. Prior
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experiences with GIS and access to a GIS analyst will help me represent my results and findings
accurately.
The contributions of this research study will help inform San Diego’s residents and
public officials of the effectiveness of rainwater as a sustainable green practice towards water
conservation. Once the public realizes the practicality of rainwater harvesting, hopefully
residents will be influenced to invest in their own rainwater catchment system. As more
residents become active and rainwater harvesting becomes more popular, increased incentives
and public subsidies will become available and encourage the growing San Diego populace to
actively participate in sustaining the viability of the San Diego water supply.
This research is expected to be completed by March 1, 2011. (Appendix 1) The
completed report will consist a detailed research paper, data, results, and GIS maps. Costs will
be minimal since the majority of the resources and data can be obtained from collections
accessible via Internet.
Conclusion
This report is intended for use in acknowledging the benefits of rainwater harvesting and
in persuading residential homeowners to invest in rainwater catchment systems. The contents of
the study will consist of data demonstrating how rainwater harvesting can contribute to the
overall water needs of San Diego during the summer and winter seasons. The monetary benefit
and significance of effective rainwater catchment will be illustrated through detailed graphs, and
maps. Comprehensive charts and data will be provided and produced to show the amount of
water storage based on standardized rooftops and rates of rain. In addition, the prime locations
for harvesting rainwater as well as the expected accumulation rates will be highlighted. A
proposal will also be drafted to provide some suggestions for how the government and
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individuals can transition and adapt rainwater harvesting techniques in San Diego. Furthermore,
the hope is to persuade local government officials [or the local government] in seeing the
importance of water recycling through both reduction and reuse, thereby making rainwater
collection one of the better, more profitable, energy saving methods for San Diego.
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