First Advisor

Bill Fish

Date of Award

Spring 2014

Document Type


Degree Name

Master of Science (M.S.) in Civil & Environmental Engineering


Civil and Environmental Engineering




Water harvesting -- Oregon -- Portland, Storage tanks -- Design, Precipitation (Meteorology) -- Oregon -- Portland -- History, Water-supply -- Oregon -- Portland, Water -- Storage




Rainwater harvesting can ease the water availability problems for many parts of the world where water is not easily available. It is also a solution for minimizing stormwater runoff and better managing sewers by preventing combined sewers to overflow. The goal of this project is to calculate the reliability of rainwater harvesting systems and provide optimum size of the storage tank using historical records for Portland specific rain pattern. A simple water balance approach for historical data is used to calculate the reliability by which rainwater harvesting system can be used as a means of irrigating gardens in Portland. The size of the storage units needs to be adequate with the area of the roof and the desired water use rate. The maximum storage required to attain 100% reliability is more than 20m3 for lower end of irrigation demand and more than 100m3 for upper end of the irrigation demand for specific catchment area. The reliability with which Portland backyard gardens can be irrigated is approximately 20%- 50%, with lower end of range representing 1m3 storage and the upper end of range representing 5m3 of storage tank. Roof top runoff inputs to the combined sewer system are reduced by approximately 15% and potable water saved is 38% with storage tank volume of 5m3. A cost benefit analysis suggest that for a tank of 5m3 it takes 15 years to recover the investment done for installing rainwater harvesting system.


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A research project report submitted in partial fulfillment of the requirement for the degree of Master of Science in Civil and Environmental Engineering.

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