Details of Final Design

Catchment System Design

Catchment Basin

The catchment basin (roof) was seperated into 5 areas. These areas helped determine the correct size of gutters that would be needed.

Available Flow

The available flow was based off of precipitation trends of wet and dry seasons throughout the year. A wet season is when the average precipitation is over 2.5 inches in a month and a dry season is when the average precipitation is less than 2.5 inches in a month. Below shows the average precipitation for each month in the area surrounding the project site.

Demand

The table below shows how much water is available based off of the precipitation data for the dry and wet seasons throughout a given year.

The table below shows how much water is needed for the client to water his garden and to flush the toilets. The dry seasn requires 835 gallons per month but only 205 gallons per month can be collected during the dry season months. Storage of excess water during the wet season is needed to be stored for the dry season months so that our client is able to use this system on a regular basis.

Filtration

To filter the water, a mesh basket filtration system will be used. This system will be located outside of the cistern, and will be installed at a depth of 21-41 inches. The basket mesh is 0.35 millimeters. Once the cistern is full, the excess water will flow to the storm drain located out front of the client's property.

Cistern Design

The team decided to go with a pre-cast concrete cistern. Equation 1 was used to figure out how much water would be needed for the client to be able to continuously use this system which is 2,700 gallons. This equation only works with the assumption that the client does not use this system for the first two months after construction. The team chose to get a 3,000 gallon tank to allow for 12 inches of freeboard. The water in the cistern will be disinfected bi-weekly with 3 inch chlorine tablets. The foundation for the cistern will be a 6 inch aggregate base which will be supplied by the cistern manufacturer.

Pump Selection

Below shows the pump that was chosen, and the operating points for this pump.

Pressure Tank Specifications

The pressure tank will be located in the client's utility closet and will run at a pressure of 30-50 psi. The pressure tank will be the distribution source for both of the toilets and the irrigation for the vegetable garden.