Reservoir Water Quality

Methods in this category are used to select the constituent and approach.

None

No water quality solution is performed. No slots are added.

Layered Salt

The layered salt slots are added (see Layered Salt Slots). The Solve 2 Layer Salt dispatch method is made available.

Layered Temp

All temperature slots are added. The Solve 2 Layer Temperature dispatch method is made available.

Layered Temp and Salt

All temperature and layered salt slots are added (see Layered Salt Slots). This method makes the Solve 2 Layer Temp and Salt dispatch method available.

Layered Temp and DO

All temperature and DO slots are added. This method makes the Solve 2 Layer Temp and DO dispatch method available.

Layered Temp Salt and DO

All temperature and DO slots are added. The layered salt slots are also added (see Layered Salt Slots). This method makes the Solve 2 Layer Temp Salt and DO dispatch method available.

Well Mixed Salt

The well-mixed salt slots are added (see Well-mixed Salt Slots). This method makes the Solve Weight Factor Salt and Solve Pred-Corr Salt sets of dispatch methods available.

Segmented 2 Layer Salt

The segmented salt slots are added (see Segmented 2 Layer Salt Slots). This method makes the Solve Segmented 2 Layer Salt dispatch method available.

Outflow TDG using Tailwater Depth

Models the spill, turbine release and mixed outflow TDG concentration based on the depth of the tailwater.

Note: The method can be used in conjunction with optimization methods. In that case, this method also to compute partial derivatives that are used in subsequent optimization runs. Within Optimization, constraints are generated and the user can write policy to limit the change in deltas. See Opt Outflow TDG Tailwater Depth.

This section describes the mathematical formulation and specifics of the methods used in this approach. It does not outline how to use the approach, however, which is beyond the scope of this document. Contact CADSWES for more information.

Note: TDG concentration is typically reported as the TDG saturation percentage. So a TDG of 115 is 115% of saturation. Some literature uses a decimal, 1.15, some use a percentage 115%. As a result, in RiverWare, all TDG concentrations use the FRACTION unit type. Then the user can choose to see values in either of the two user units: decimal or percent.

This method is available only if one of the “Regulated...” spill methods is selected. It is not available for the None, Monthly Spill, or Unregulated Spill methods

Slots Specific to This Method

Entrained Flow

Type: Series

Units: FLOW

Description: Entrained Flow is the portion of the Turbine Release that has air from the spillways entrained in it. In the tailrace, there are surface deflectors that attempt to move the spill horizontally and keep it from plunging into the tailrace. These deflectors attract water from the turbine release due to the increased velocity. This portion of the turbine release is then entrained with air from the spillways and has the TDG concentration of the spill. This value is nonnegative.

Information: This slot is computed based on the equation .

I/O: Output only.

Links: Not linkable

Inflow TDG Concentration

Type: Series

Units: Fraction

Description: This slot contains the inflow TDG concentration

I/O: Output or required input

Links: Linkable to upstream object’s Outflow TDG Concentration

Outflow TDG Concentration

Type: Series

Units: Fraction

Description: This slot shows the resulting Outflow TDG Concentration. The values can then be compared to the values in the Outflow TDG Concentration Estimate. Once the TDG solution has converged the values in this slot should be equal to the values in the Outflow TDG Concentration Estimate slot at all time steps (within a tolerance)

Spill TDG Concentration

Type: Series

Units: Fraction

Description: This slot shows the resulting Spill TDG Concentration.

Links: Not linkable

Tailwater Bottom Elevation

Type: Scalar

Units: Length

Description: Elevation at the bottom of the tailrace.

Information: The value in this slot is used in the TDGS computation to get the depth of tailwater.

I/O: Required input

Links: Not linkable

TDG c1

Type: Scalar

Units: Fraction

Description: Contains the constant in the TDG equation when Spill is zero.

I/O: Required input

Links: Not linkable

TDG Entrainment b1

Type: Scalar

Units: None

Description: Fraction of Spill that can be entrained. A portion of the Turbine Release up to this amount will have the same TDG concentration as the Spill.

I/O: Required input

TDG Entrainment b3

Type: Scalar

Units: Flow

Description: Constant of Spill that can be entrained. A portion of the Turbine Release up to this amount will have the same TDG concentration as the Spill.

I/O: Required input

TDG Spill b2

Type: Scalar

Units: PerLengthTime

Description: This scalar slot contains the coefficient in the Spill TDG Concentration equation.

Note: This unit type may need to be added.

I/O: Required input

Links: Not linkable

Turbine Release TDG Concentration

Type: Series

Units: Fraction

Description: This slot shows the resulting Turbine TDG Concentration. This is sometimes called the forebay concentration or the reservoir concentration.

Links: Not linkable

Spill and Turbine Release Limit

Type: Scalar

Units: Flow

Description: Lower bound for which spill and turbine release will be treated the same as higher flows. Below this flow limit, the computations will be modified.

I/O: Required input

Method Details

The method is executed by the two water quality dispatch methods.

First, some notation:

TDGS = Spill TDG Concentration

TDGT = Turbine Release TDG Concentration, concentration just above the dam.

TDGO = Outflow TDG Concentration

TDGI = Inflow TDG Concentration (linked to upstream reservoir’s TDGO

Qsm = Spill and Turbine Release Limit (calculations are changed for small flows)

Compute the TDGs:

TW is Tailwater Elevation.

TW0 is the elevation at the bottom of the tailrace, a project constant (scalar length).

is the density of water, a global constant. (internal, 999.7kg/m3)

g is the gravitation constant. (internal, 9.81m/s^2)

patm is the atmospheric pressure. (internal, 101325kg/(m*s)^2)

b2 is a project constant, TDG Entrainment b2, (1 / Length-Time).

Get the TDGT. This is the same as the TDGI which may be linked to an upstream reach that lags the TDG concentration by some number of timesteps.

Compute the Entrained Flow, QE:

QS = Spill

QT = Turbine Release

b1, TDG Entrainment b1, and b3, TDG Entrainment b3, are scalar constants for each project.

The final computation is to compute the TDGO. This is the mixed outflow concentration which could also be called the tailwater concentration.

If QT + QS = 0

c1 is a constant for each reservoir in fraction units.

Else

To provide continuity with the concentration when outflow is zero, the concentration is adjusted when outflow is small.

If c1 >= 0

Else If QS < Qsm

End If

Revised: 01/05/2024