Learn about the key components that impact the cost of rainwater irrigation systems compared to conventional irrigation. Discover insights for the LEED Green Associate Exam.
Table of Contents
Question
In a large site that has a short, intense rainy season and a long, dry season, what component of a collected rainwater irrigation system is most likely to make it cost prohibitive over a conventional system?
A. Irrigation piping systems
B. Irrigation control systems
C. Rainwater storage cisterns
D. Landscaping plant selection
Answer
C. Rainwater storage cisterns
Explanation
Rainwater storage cisterns are components of a collected rainwater irrigation system that are most likely to make it cost prohibitive over a conventional system in a large site that has a short, intense rainy season and a long, dry season.
A collected rainwater irrigation system is a system that collects, stores, and distributes rainwater for irrigation purposes. Rainwater storage cisterns are containers that store the collected rainwater until it is needed for irrigation.
In a large site that has a short, intense rainy season and a long, dry season, the rainwater storage cisterns would need to be very large and durable to capture and store enough rainwater for the dry season. This would increase the initial cost and maintenance cost of the system compared to a conventional system that uses potable water or groundwater for irrigation.
In a large site with a short, intense rainy season followed by a long, dry season, rainwater storage cisterns are the component most likely to make a collected rainwater irrigation system cost prohibitive compared to a conventional irrigation system.
Here’s why:
Rainwater must be collected and stored during the brief rainy season to provide irrigation water for the rest of the year. The long dry season necessitates very large storage cisterns to capture enough rainwater to irrigate the landscape for many months.
Cistern capacity needs to be sized based on the area of the landscape, the water requirements of the plants, and the length of the dry season. On a large site, the cisterns may need to hold millions of gallons of water to irrigate for extended periods. Large-scale water storage tanks are expensive to construct and can make rainwater irrigation cost-prohibitive.
In contrast, the other irrigation system components like piping, control systems, and plant selection, while important, do not have as significant an impact on cost between rainwater and conventional irrigation. These components are necessary for both types of irrigation systems.
Landscaping plant selection can help reduce irrigation demands, but with a long dry season, most plants will require some supplemental irrigation. So plant choice alone cannot eliminate the need for large, costly rainwater storage on sites without consistent, year-round rainfall.
In summary, rainwater storage cisterns are the component most likely to make collected rainwater irrigation systems cost-prohibitive compared to conventional irrigation for large sites with short, intense rainy seasons and long dry seasons. The need to store very large volumes of water for irrigation over extended dry periods often makes rainwater collection economically unfeasible in these climates.
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