California; Potential Rainfall Harvesting at California State University, Northridge

1. Potential Rainfall Harvesting at CSUN
Why Rainfall Harvesting? Snap Shot of Water Usage At Selected CSUN Lawns
CSUN’s Water Day in October 2009 inspired us to work on a project (Shown As Green In the Map to the Left)
to help solve our water crisis. We learned that in June 2008 Gover-
nor Arnold Schwarzenegger declared California in a statewide
drought (CA.gov). Water is becoming increasingly expensive to trans-
port from distant locations such as the Colorado River (TreePeople).
Southern California is facing higher water restrictions because of the
diminishing freshwater supplies coming from the Sacramento-San
Joaquin Delta (PBS). We consume approximately 20 percent of our
state’s electricity for water-related energy use (EPA). With expected
population increases in the Los Angeles area, the need for water is
growing.
In our efforts to become self-sustaining and lessen our dependence
on Northern California water supply, we turned to rainwater harvest-
Method (Cont.)
ing as one solution to increase our CSUN water sustainability efforts. We divided the result with 100 to get HCF. Next, we selected only the buildings that
Rainwater harvesting is the process of capturing and storing rain- could capture more than 1,000 HCF: Redwood Hall, Jacaranda Hall, Cypress Hall, B3
water using systems such as cisterns (large containers) for irrigation Potential Buildings
or household use (Florida Rainwater Harvesting). At CSUN rainwater Parking, B5 Parking, and G3 Parking. We created a new layer to distinguish these po-
CSUN Buildings tential buildings from others and then labeled the buildings. The total amount of rain-
can be used to irrigate CSUN fields, to lower our water supply cost
and to reduce urban runoff that pollutes our rivers, bays and oceans. Lawns water we could capture, based on these calculations, is 8,163.22 HCF.
NOW, let’s talk about the cost of water.
Cistern Samples Method Currently, the cost of water is about
First, we used the clip tool to limit our analysis to only the buildings in the south- $1.53/HCF. However, this price does not
ern part of the campus. We chose the southern part of campus because all the po- stay constant but increases between 5-
tential buildings located there have the largest rooftop catchment areas. Secondly, 8% each year (LADWP). To simplify this,
we calculated how much rainfall each building can capture. we assumed that the rate would increase
7% each year. Over a forty-year period,
We started by calculating how much rainfall we usually get in a year. We found the
the price of water per HCF would in-
median of total annual rainfall from 1996-2005 to be 14.05 inches using Microsoft
crease from $1.53 to $12.46!
Excel. We used the median instead of the mean because the range between the
highest and the lowest annual net rainfall is very distant. Then, we used the me- Even though we may be only saving ap-
Source: BAE, North Carolina State University Source: www.harvestH2O.com
dian annual rainfall in formula seen below to find the possible amount of rain we proximately $12,500 the first year, in the
could capture for each building by using the field calculator in the attribute table. long term, we will save at least $102,000 each year solely from rainwater harvesting.
Rainwater Collection and Irrigation System The formula was provided by Dr. Elizabeth Dougherty, the Director of Wholly H2O This does not include other costs involving
(www.whollyh2o.org). transporting and capturing water from
elsewhere to Los Angeles.
*Rain Captured in Cubic Foot =
Thus, the formula we inputted in the field calculator was: Conclusion
([Shape_Area] *14.05 *80) /1000
After our research, we concluded that
starting a rainfall harvesting system at
At this point, we had the amount CSUN would be a valuable asset to create a
of rainfall each building could sustainable campus. The fact that we
get in cubic. We changed the unit receive a decent amount of annual rainfall
into hundred cubic feet to stan- and have many rooftops promises us an
dardize the unit accordingly to effective rainfall harvesting system. However, the cost of water needs to increase for the
the price the campus pays for community to value rainwater. Future research is required to understand how we can
Source: Purucker Engineering water, which is $1.53 per HCF. effectively and efficiently implement a rainwater harvesting system at CSUN.
(Now, you may wonder why we
Data
have to bother capturing rainfall Presented By
CSUN aerial map in raster .IMG format from Nathaniel Wilson,
when the water is so cheap. We Sheela Bhongir and Areeya Tivasuradej
CSUN Campus Architect
will address this later.) Geography 306
Precipitation data from 1996 to 2005 in Excel spreadsheet from
Tim Boyle and Dr. Gong-Yuh Lin, Geography Department Instructor: Dr. Shawna Dark
*The rough rule of thumb for calculating rainfall runoff volume on a catchment surface : You can collect 80 cubic foot (600 CSUN Geography Department
Existing CSUN building polygon (vector) from Dr. Shawna Dark gallon) of water per inch of rain falling on 1,000 square feet of catchment surface.