Low Flow Requirement
The Low Flow Requirement category is used to configure the Control Point to have a required low flow rate. In addition to computing the low flow requirement, these methods add slots that can be referenced by RPL logic (the MeetLowFlowRequirement function) to determine the reservoir releases required to meet the low flow rates.
NoneThis is the default method. There are no slots or calculations associated with it.
Low Flow Periodic LookupThis method is used to specify the low flow requirement as a function of date/season using a periodic slot.
Slots Specific to This Method
Low Flow Requirement
Type: Periodic Slot
Units: flow
Description: The low flow requirement as a function of date/season
Information: The low flow requirement is computed at the beginning of each timestep using the current date to look up the value from this slot.
I/O: Required input
Links: Not linkable
Computed Low Flow Requirement
Type: Series Slot
Units: flow
Description: The computed low flow requirement
Information: This slot is computed given the current date and the Low Flow Requirement slot.
I/O: Output only
Links: Not linkable
Low Flow Deficiency
Type: Series Slot
Units: flow
Description: The portion of the low flow requirement that has not been met.
I/O: Output only
Links: Not linkable
Low Flow Reservoirs
Type: List Slot
Units: none
Description: A list of the reservoirs that are used to meet the low flow requirement
Information: These reservoirs must all be upstream of the control point.
I/O: Required input
Links: Not linkable
Method Details
The Low Flow Periodic Lookup method executes at the beginning of the run. Each timestep in the run is used to look up a value in the Low Flow Requirement slot. The resulting value will be set in the Computed Low Flow Requirement slot. The Low Flow Deficiency slot is computed each time the object dispatches. It is computed as the low flow requirement minus the total control point flow. The Low Flow Reservoirs slot is used by a RPL function (MeetLowFlowRequirement) to determine the reservoir releases necessary to meet the low flow requirement.
Reservoir Level LookupThe Reservoir Level Lookup method is used to compute the low flow requirement as a function of the date/season and the operating level of a specified reservoir.
Slots Specific to This Method
Level vs Low Flow Requirement
Type: Periodic Slot
Units: flow
Description: The low flow requirement as a function of reservoir level and date/season
Information: Each column corresponds to a reservoir’s operating level. For each operating level, the requirements are specified for each date range in the periodic slot.
I/O: Required input
Links: Not linkable
Low Flow Requirement Reservoir
Type: List Slot
Units: none
Description: The reservoir used to compute the low flow requirement
Information: The previous timestep operating level of this reservoir is used to look up the low flow requirement in the Level vs Low Flow Requirement slot.
I/O: Required input
Links: Not linkable
Computed Low Flow Requirement
Type: Series Slot
Units: flow
Description: The computed low flow requirement
Information: This slot is computed from the Level vs Low Flow Requirement slot.
I/O: Output only
Links: Not linkable
Low Flow Deficiency
Type: Series Slot
Units: flow
Description: The portion of the low flow requirement that has not been met.
I/O: Output only
Links: Not linkable
Low Flow Reservoirs
Type: List Slot
Units: none
Description: A list of the reservoirs that are used to meet the low flow requirement
Information: These reservoirs must all be upstream of the control point.
I/O: Required input
Links: Not linkable
Forecast Period
Type: TableSlot
Units: NONE
Description: The forecast period is a number of timesteps, including the current simulation timestep, that is used in the algorithms for calculating forecasted hydrology, regulation discharge and flood releases. This can be propagated from a computational subbasin of which the control point is a member.
Information:
I/O: Required input
Links: Not linkable
Method Details
Note: If the specified reservoir is disabled and is set to Pass Inflows, no low-flow requirement can be computed. See Low-flow Requirements Based on Disabled Reservoirs in USACE‑SWD Modeling Techniques for details.
The Reservoir Level Lookup method will execute on the Control Point object at the beginning of each timestep. For each timestep (t) in the forecast period, the Low Flow Requirement Reservoir’s previous timestep’s (current timestep‑1) operating level and the forecast timestep’s date (t) will be used to lookup a value in the Level vs Low Flow Requirement slot. The resulting value will be set in the Computed Low Flow Requirement slot. This is an estimated requirement that is used through the forecast period. It is reset at the beginning of the next timestep. Whenever the Control Point object dispatches, it will compute the Low Flow Deficiency based on the flow through the control point. The Low Flow Reservoirs slot will be used by the RPL predefined function to determine the low flow releases. The RPL function will order the reservoirs specified in the Low Flow Reservoirs slot in descending order beginning with the most full (highest level) reservoir. Each reservoir makes a release until the requirement is met or the reservoir reaches its maximum low flow delivery rate.
Revised: 08/02/2021