Rainwater harvesting: TTT

Subcatchment element as displayed in the TT menu

Storage element as displayed in the TTT menu

Once the size of cistern has been determined, it can easily be modeled in many open source and proprietary applications. For planning purposes, a RWH system can be integrated into a site plan as a storage element, using the TTT:

1. Create a subcatchment area to harvest rainwater. Maybe this is a one or more building rooftops?

   Select the subcatchment button and draw over the desired catchment area, close the are with a double click.

2. Specify the RWH cistern as the outlet for the subcatchment(s).

   Select the Storage button and place it nearby to the associated catchment.

A roof as a subcatchment (key parameters)

Land Use
Roof (%)	100
Subcatchment
Outlet	Select the name of your RWH cistern storage element (see below)

A rainwater harvesting cistern as a storage element (key parameters)

Stage Storage
Name	Important to have a unique name, to associate with the subcatchment (harvesting area)
Storage type	No removal
Bottom elevation (m)	This will be 0 for installations at ground level, but will often be underground. This is of greater importance when the overflow is coupled to another component within a treatment train
Maximum depth (m)	Height of the RWH cistern
Lined/unlined	Lined
Evaporation factor	0
Curves
The Curves table is designed to accommodate ponds of roughly conical dimensions. Rainwater cistern are usually cuboid or cylindrical in shape, so that the area (m2) will remain the same throughout the depth. The top and bottom dimensions can be placed within the first two rows of the table.

Tank used to store rainwater (typically roof runoff) for later use.

Rainwater harvesting.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

Stormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.

A combination of lot level, conveyance, and end-of-pipe stormwater management practices.

Abiotic transfer of water vapour to the atmosphere.