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:

$Q_{c}=Q_{total}-\sum _{0..t-1}Q_{i}$

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

$\Delta w={\frac {max(0,min(Q_{lth},Q_{t},Q_{c}))}{A}}$

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:

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

If a capacity Q_total is defined:

$Q_{c}=-Q_{total}-\sum _{0..t-1}Q_{i}$

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

$\Delta w={\frac {min(0,max(Q_{uth},Q_{t},Q_{c}))}{A}}$

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.
• $\Delta t$ = 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

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