Finding the Ideal Size of a First Flush Diverter of a Rainwater Catchment System

by Jacob Marchand

Submitted : Spring 2019

A first flush diverter is a frequently used tool in rainwater catchment systems. It works by having the first portion of the rainwater put into it, and then allowing the rest of the rainwater to go into the main collection tank. It does this because the first portion of rainwater contains most of the pollutants. Sizing the first flush is a problem that has been tackled before and is the problem approached by this project. This project does this by using an equation for turbidity to see how long it takes for rainwater to wash an acceptable amount of pollutants off roofs. The volume of water that will be collected during this time is then calculated using the equation for the volume of a cylinder using integrals. The height needed for the first flush diverter is then found using a known radius and the equation mentioned previously. This method is applied to four different houses in the community of Mirmar in the Dominican Republic.

The conclusion of this project is that the amount of water that would be wasted using the first flush diverter makes other methods of rainwater catchment more appealing.

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