Lookback Tab

UPDATED IN RESSIM 3.5

Selecting Lookback Type

After specifying the operation set for each of your reservoirs, you will need to specify the initial (or starting) conditions for the alternative. This is referred to in ResSim as the Lookback (or warmup) period. You will need to specify what type of data will define each element and parameter during the Lookback period.

To set the Lookback Type for locations in your reservoir network in the Alternative Editor, select the Lookback tab.  (as shown in "Figure: Alternative Editor - Lookback Tab").

Reservoir Lookback

For each location (Reservoir) depending on the parameter (Pool, Controlled Outlet, Uncontrolled Outlet), in the Type column there are different options available from the dropdown list to define the lookback.

Pool

For the Pool parameter lookback elevation and lookback storage should be defined. Lookback options for these parameters are the same (as shown in "Figure: Lookback Elevation/Storage for Pool").

When a lookback option for one of these parameters is defined (elevation or storage) the lookback option for the other one is set to computed automatically to compute the values for storage based on elevation if lookback elevation is defined by the user or to compute the values of elevation based on storage if lookback storage is defined by the user.

There are six options available to define the lookback elevation or storage for Pool:

• Constant
  When you have selected Constant as the lookback type, the value of the lookback is set to the constant value for the lookback time that is set in the simulation time window. Enter the value for the constant in the Value field.
• Time-Series
  When you have selected Time-Series as the lookback type, map the timeseries for the associated lookback variable under Time-Series tab. The value of the lookback is selected from the mapped timeseries for any lookback time that is set in the simulation time window.

• Guide Curve
  When you have selected Guide Curve as the lookback type, the value of the lookback is selected from the defined guide curve for any lookback time that is set in the simulation time window.

• Fn of Release-Start w/ Constant NEW IN RESSIM 3.5
  When you have selected Fn of Release-Start w/ Constant as the lookback type, the first value of the lookback time window is set to constant and the rest is calculated based on the mass balance of net inflow and total release.

• Fn of Release-Start w/ Time Series NEW IN RESSIM 3.5
  When you have selected Fn of Release-Start w/ Time Series as the lookback type, the first value of the lookback time window is selected from the mapped timeseries and the rest is calculated based on the mass balance of net inflow and total release.

• Fn of Release-Start w/ Guide Curve NEW IN RESSIM 3.5
  When you have selected Fn of Release-Start w/ Guide Curve as the lookback type, the first value of the lookback time window is selected from the defined guide curve and the rest is calculated based on the mass balance of net inflow and total release.

Controlled Outlet

There are three options available to define the lookback release for controlled outlet (Figure: Lookback Release for Controlled Outlet).

• Constant
  same as what was described for the pool.
• Time-Series
  same as what was described for the pool.
• Fn of Elevation (Function of Elevation) NEW IN RESSIM 3.5
  When you have selected Fn of Elevation as the lookback type, the lookback reservoir elevation (or storage) along with the known inflows are used to calculate the total lookback release for each timestep of the lookback period. The calculated release is applied to this outlet only. The lookback release for all other outlets will be set to constant zero.

Uncontrolled Outlet

There are two options available to define the lookback spill for uncontrolled outlet (Figure: Lookback Release for Uncontrolled Outlet).

• Constant
  same as what was described for the pool.
• Time-Series
  same as what was described for the pool.

Other Elements

Lookback data can (and sometimes must) be set for other element types as well, including:

Diversions

Options for diversions are the same as for pool outlets.

• Constant
• Time-Series

State Variables

UPDATED IN RESSIM 3.5 State Variables require lookback data to be set in the Alternative Editor. In ResSim versions prior to 3.5, the State Variable Lookback data was optional and was overwritten upon the initialization of the state variables.  Now the state variables are initialized before their Lookback data is set, so the Lookback setting will overrule any settings attempted in the State Variable Initialization tab.

• Constant
• Time-Series

Water Accounts

UPDATED IN RESSIM 3.5 For Alternatives that use Water Account Sets, each water account requires the initial account storage to be set using either a constant or a time-series. Previously, this was not mandatory.

• Constant
• Time-Series