Engineering Objects

Reservoirs

Listed below are all modifications made to Reservoir Objects.

Seepage Calculation Category

A new User Method Category called Seepage Calc has been added to all Reservoirs. The new Category is used to account for seepage through and around the face of a dam. There are two User Methods available for selection in this Category: the default No Seepage and Linear Seepage Calc. The default Method performs no computations and instantiates no slots.

The Linear Seepage Calc method calculates dam seepage based on the Pool Elevation of the Reservoir and a set of coefficients. The coefficients are a seepage base elevation, a linear slope coefficient, and a linear intercept coefficient. All three are input into the Seepage Coefficients table slot. The seepage is computed as:

Seepage = (average Pool Elevation - base elevation) x slope + intercept

Coefficients may be specified which produce a negative seepage; however, since seepage is not permitted to be less than zero, negative seepage values are automatically reset to zero. Seepage is a Reservoir loss in the mass balance, but is not considered part of any Outflows or Spills. Seepage may be linked to another slot if desired. The Inputs and Outputs for this Method are:

Slots with Required Input Data

• Seepage Coefficients (seepageCoeff)

– TableSlot

– LENGTH, AREAperTIME, FLOW

– base elevation, slope, and intercept of the linear equation

Slots with Output Data

• Seepage (seepage)

– SeriesSlot

– FLOW

– flow of water through and around the dam face

Hydrologic Inflow and Loss

A new User Method, Hydrologic Inflow and Loss, has been added to Level Power Reservoirs and Storage Reservoirs. This Method is selected in the Hydrologic Inflow Calculation Category. The Method allows Hydrologic Inflow and Hydrologic Inflow Adjust to be input by the user. If these slots are not linked, any timesteps which do not have input values default to zero. Hydrologic Inflow Net is then computed as the sum of the Hydrologic Inflow and the Hydrologic Inflow Adjust. All of this behavior occurs during the beginning of run, and is identical to the existing Input Hydrologic Inflow User Method.

The Hydrologic Inflow and Loss Method has special behavior when solving for Inflow using one of the following dispatch methods:

• solveMB_givenOutflowStorage

• solveMB_givenOutflowHW

• solveMB_givenEnergyStorage

• solveMB_givenEnergyHW

In these cases, the dispatching slot values may force the computation of a negative Inflow. If the dispatch method calculates a negative Inflow, the Hydrologic Inflow and Loss Method is invoked a second time. When the Method is invoked from a dispatch, it sets the Hydrologic Inflow Adjust to the value of the Inflow (a negative value), sets Inflow to zero, and recalculates the Hydrologic Inflow Net. If Hydrologic Inflow Adjust or Hydrologic Inflow Net are user input at this timestep, the run aborts with an error.

Slots with Optional Input Data

• Hydrologic Inflow (hydrologicInflow)

– SeriesSlot

– FLOW

– additional flow gain to the reservoir

– This value defaults to zero for any timesteps where it is not input.

• Hydrologic Inflow Adjust (hydrologicInflowAdjust)

– SeriesSlot

– FLOW

– adjustment to the additional flow gain to the reservoir

– This value defaults to zero for any timesteps where it is not input. The slot is set to a negative value for any timesteps where a negative Inflow would otherwise result. Under this circumstance, there may not be a user input value at the same timestep.

Slots with Output Data

• Hydrologic Inflow Net(hydrologicInflowNet)

– SeriesSlot

– FLOW

– net additional flow gain to the reservoir

– This slot value is the sum of the Hydrologic Inflow and Hydrologic Inflow Net.

Power Reservoirs

Listed below are all modifications made to Power Reservoir Objects.

Peak Power Calc and Peak Base Power Calc

The Peak Power Calc and Peak Base Power Calc User Methods have two modifications. A warning is no longer posted in the Diagnostics Output Window when the reservoir Pool Elevation is too low to generate power. The low Pool Elevation is not considered a modeling or system error. The Method accurately models this case, and simulation is unaffected.

The second modification concerns the minimum and maximum Operating Head. Previously, these values were set in the Min and Max fields of the Operating Head slot’s Configuration Dialog. This resulted in a warning message every time these criteria were violated. Since violation of the minimum or maximum Operating Head is common and acceptable for these Methods, the values are not the true minimum and maximum for the slot itself. These values are in fact Method parameters, and are now set on the Min and Max Operating Head slot. The new table slot has two rows, the first for minimum Operating Head, and the second for maximum Operating Head.

New Slot with Required Input Data

• Min and Max Operating Head (minMaxOpHead)

– TableSlot

– LENGTH, LENGTH

– the minimum and maximum recommended operating head

Storage Reservoirs

Listed below are all modifications made to Storage Reservoirs.

Cubic Bank Storage Calc

A new User Method, called Cubic Bank Storage Calc, has been added to the Bank Storage Calc Category of Storage Reservoirs. This Method has been developed to duplicate historical reservoir loss calculations for Brantley Reservoir. The calculated Change in Bank Storage is the volume of “net overall loss” including seepage, bank storage, and other unaccounted losses. Empirical coefficients are used to calculate a flow loss according to the following equation:

where y is the Reservoir flow loss, a and b are specific constants, and x is the current reservoir Pool Elevation. A different set of equation constants are used depending on whether the Reservoir Pool Elevation is rising or falling during the current timestep. The coefficients corresponding to rising and falling elevations are specified in the Cubic Bank Storage Rising Coeffs table and the Cubic Bank Storage Falling Coeffs table, respectively. If the Pool Elevation remains constant over the timestep, the coefficients corresponding to the last Pool Elevation change are used. If the Pool Elevation is constant during the first timestep(s) of the simulation, the falling coefficients table is used by default. Finally, the computed flow loss is converted to a volume loss for the timestep.

Slots with Required Input Data

• Cubic Bank Storage Falling Coefficients (cubicFallingCoeffs)

– TableSlot

– FLOW, PER_TIME

– constants for equation when reservoir level is falling

– The first coefficient is the constant term, and the second is the cubic coefficient.

• Cubic Bank Storage Rising Coefficients (cubicRisingCoeffs)

– TableSlot

– FLOW, PER_TIME

– constants for equation when reservoir level is rising

– The first coefficient (column zero) is the constant term, and the second is the cubic coefficient.

Slots with Output Data

• Change in Bank Storage (deltaBankStorage)

– SeriesSlot

– VOLUME

– change in volume of water stored in the reservoir banks

Revised: 08/02/2021