# Inlet formula (Water Overlay)

Inlets are hydraulic structures can pump water in and out of the project area and are connected with a water body outside the project area.

The amount flowing in or out of Inlets is calculated for the cell the Inlet resides on.

*Case 1: Inlet:*

When calculating Inlets, first the capacities are calculated.

If a lower threshold is defined:

If a positive inlet q Q_{t} is defined:

If a capacity Q_{total} is defined:

After calculating the capacities, the actual water inflow is calculated. If any of the terms are undefined, they are not included.

*Case 2 Outlets:*

When calculating outlets, first the capacities are calculated.

If an upper threshold T_{u,t} is defined:

If a negative inlet q Q_{t} is defined:

If a capacity Q_{total} is defined:

After calculating the capacities, the actual water ouflow is calculated. If any of the terms are undefined, they are not included.

Where:

- = The water level on the surface relative to datum, at time t.
- = The LOWER_THRESHOLD of the Inlet at time t.
- = The UPPER_THRESHOLD of the Inlet at time t.
- = The INLET_Q of the Inlet at time t.
- = Computational timestep.
- = The INLET_CAPACITY of the Inlet.

- = The calculated previous amounts of flow.
- = The desired lower water level at the Inlet's location, based on the LOWER_THRESHOLD of the Inlet.
- = The desired upper water level at the outlet's location, based on the outlet's UPPER_THRESHOLD of the Inlet.
- = The amount of water inflow (or outflow when negative) possible based on the INLET_Q of the Inlet and timestep .
- = The total amount of water inflow (or outflow when negative) allowed based on the total capacity of the Inlet.

- = Size of the Inlet/outlet area in m
^{2}, based on the amount of cells and cell size. Current implementation only has one cell. - = The amount of water flow which takes place.

## Related

The following topics are related to this formula.

- Structures
- Inlet
- Models
- Surface model