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 is defined:

Q_lth = max( 0 , T_l,t - w_t )

If a positive Inlet q 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 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

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

If an upper threshold T_u is defined:

Q_uth = min( 0 , T_u - w_t )

If a negative Inlet q 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 at time t, relative to datum.
• T_l,t = The LOWER_THRESHOLD attribute of the inlet at time t.
• T_u,t = The UPPER_THRESHOLD attribute of the inlet at time t.
• q_t = INLET_Q attribute at time t.
• Δt = Computational timestep.
• Q_total = The INLET_CAPACITY attribute of the inlet.
• Q_0..n = The calculated previous amounts of flow.
• Q_lth = The amount of water inflow desired based on the inlet's LOWER_THRESHOLD attribute.
• Q_uth = The amount of water outflow desired based on the outlet's UPPER_THRESHOLD attribute.
• Q_t = The amount of water inflow (or outflow when negative) possible based on the INLET_Q attribute and timestep Δt.
• Q_c = The amount of water outflow possible based on the total capacity of the outlet.
• 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.

See also

• Inlet