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 $T_{l,t}$ is defined:

$Q_{lth}=max(0,T_{l,t}-w_{t})$

If a positive inlet q Q_t is defined:

$Q_{t}=\Delta t\cdot Q_{t}$

If a capacity Q_total is defined:

Q_c = Q_total- ΣQ_0..t-1

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

Δw = max( 0 , min( Q_lth , Q_t , Q_c ) ) / A

Case 2 Outlets:
When calculating outlets, first the capacities are calculated.

If an upper threshold T_u,t is defined:

Q_uth = min( 0 , T_u,t - w_t )

If a negative inlet q Q_t is defined:

Q_t = Δt * Q_t

If a capacity Q_total is defined:

Q_c = -Q_total - ΣQ_0..t-1

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

Δw = min( 0 , max( Q_uth , Q_t , Q_c) ) / A

Where:

• w_t = The water level on the surface relative to datum, at time t.
• T_l,t = The LOWER_THRESHOLD of the inlet at time t.
• T_u,t = The UPPER_THRESHOLD of the inlet at time t.
• q_t = The INLET_Q of the inlet at time t.
• Δt = Computational timestep.
• Q_total = The INLET_CAPACITY of the inlet.

• Q_0..n = The calculated previous amounts of flow.
• Q_lth = The desired lower water level at the inlet's location, based on the LOWER_THRESHOLD of the inlet.
• Q_uth = The desired upper water level at the outlet's location, based on the outlet's UPPER_THRESHOLD of the inlet.
• Q_t = The amount of water inflow (or outflow when negative) possible based on the INLET_Q of the inlet and timestep Δt.
• Q_c = The total amount of water inflow (or outflow when negative) allowed based on the total capacity of the inlet.

• A = Size of the inlet/outlet area in m², based on the amount of cells and cell size. Current implementation only has one cell.
• Δw = The amount of water flow which takes place.

Related

The following topics are related to this formula.

Structures

Inlet

Models

Surface model