LAK: Lake Package Pane

The LAK: Lake package pane is on the MODFLOW Features tab of the Object Properties dialog box.

The data that can be specified for the Lake package are the Starting time, Ending time, Minimum stage, Maximum stage, Precipitation, Evaporation, Overland runoff, Withdrawal, Lake ID, Initial stage, Center Lake, and Sill.

The user can also define lake gages in the Gage package on this pane.

Starting time and Ending time are explained in the help for the MODFLOW Features tab.

Minimum stage is the minimum stage allowed for each lake in steady-state solution. The values of Minimum stage are only used for steady-state stress periods but must be defined for all stress periods.

Maximum stage is the maximum stage allowed for each lake in steady-state solution. The values of Maximum stage are only used for steady-state stress periods but must be defined for all stress periods.

Precipitation is the rate of precipitation per unit area at the surface of a lake (L/t).

Evaporation is the rate of evaporation per unit area from the surface of a lake (L/t).

Overland runoff is overland runoff from an adjacent watershed entering the lake. If Overland runoff > 0, it is specified directly as a volumetric rate, or flux (L3 /T). If Overland runoff < 0, its absolute value is used as a dimensionless multiplier applied to the product of the lake precipitation rate per unit area (Precipitation) and the surface area of the lake at its full stage (occupying all layer 1 lake cells).

When Overland runoff is entered as a dimensionless multiplier (Overland runoff < 0), it is considered to be the product of two proportionality factors. The first is the ratio of the area of the basin contributing runoff to the surface area of the lake when it is at full stage. The second is the fraction of the current rainfall rate that becomes runoff to the lake. This procedure provides a means for the automated computation of runoff rate from a watershed to a lake as a function of varying rainfall rate. For example, if the basin area is 10 times greater than the surface area of the lake, and 20 percent of the precipitation on the basin becomes overland runoff directly into the lake, then set Overland runoff = -2.0.

Withdrawal is the volumetric rate, or flux (L3 /t), of water removal from a lake by means other than rainfall, evaporation, surface outflow, or groundwater seepage. A negative value indicates augmentation. Normally, this would be used to specify the rate of artificial withdrawal from a lake for human water use, or if negative, artificial augmentation of a lake volume for esthetic or recreational purposes.

Lake ID is a positive integer that uniquely defines a particular lake (or sub-lake). If necessary, ModelMuse will renumber lakes during export of the MODFLOW input files to ensure that the lake numbers conform to other requirements imposed by MODFLOW.

Initial stage is the stage in the lake at the beginning of the first stress period.

If the current object specifies a sublake, Center Lake identifies another lake with which the current lake will merge if the head in the lake exceeds Sill.

Sill.is the sill elevation that determines whether the center lake is connected with a given sublake. If the head in the lake is higher than the sill elevation, the sublake is considered to be connected to the center lake.

The Gage output determines the OUTTYPE in the Gage package for the current lake. If any of the checkboxes is checked, a gage will be defined for the lake. For each gage that is defined, a separate output file will be created containing data for that gage in every time step. The files will have the extension .lakg[i]. Unlike other packages, the Gage package is not activated through the MODFLOW Packages and Programs dialog box. Instead, if any gages are defined, the Gage package is activated.

Total lake conductance is the sum of conductances of each seepage interface for each lake. The changes in stage, volume, and concentration are listed both as incremental change since the previous time increment and as cumulative change since the start of the simulation.

If TABLEINPUT has been specified for the Lake package, the user must also specify the bathymetry for each lake on the Bathymetry tab. This can be done either with an external file or by specifying values of lake stage, volume, and area in the table. Each lake bathymetry input file must contain exactly 151 lines with values of lake stage and the corresponding lake volume, and area in each line. Seepage between lakes and groundwater is calculated on cell-by-cell basis using the area of cells inundated by the lake, and not the lake surface area specified with the external lake bathymetry file.

If the user selects a bathymetry file directly, the path of the bathymetry file will be stored in the ModelMuse file relative to the location where the ModelMuse file is stored.

If PEST is activated, A Calibration tab will be visible on the Lake Package Pane.

Two types of observations can be defined: Direct Observations on the top and Comparison Observations on the bottom. Direct observations come directly from an output file whereas with Comparison Observations, the observation value is the difference between two direct observation values.

Direct Observations

Observation Name (OBSNME) is the name of the direct or comparison observation.

Observation type is the type of data to be extracted from the output file for direct observations.

Observation Group (OBGNME} is the name of the observation group to which the observation is assigned. Observation group names are specified in the Pest Properties dialog box. Observation group names can be be assigned later in the Pest Properties dialog box if a suitable observation group has not yet been defined.

Observation Time is the time at which the observation was made.

Observation Value (OBSVAL) is the measured value to which the simulated value should be compared.

Observation Weight (WEIGHT) is the weight assigned to the observation.

Comment is an optional comment about the observation.

Comparison Observations

Observation Name (OBSNME) is the name of the comparison observation.

Observation Group (OBGNME) is the name of the PEST observation group to which the observation is assigned. Observation group names are specified in the Pest Properties dialog box. Observation group names can be be assigned later in the Pest Properties dialog box if a suitable observation group has not yet been defined.

First Observation (OBSNME1) is the name of the first observation that will be compared.

Second Observation (OBSNME2) is the name of the second observation that will be compared.

Observation Value (OBSVAL) (OBSVAL1 - OBSVAL2) is the observed difference in value between the first and second observations. It is computed as value of the first observation minus the value of the second observation.

Observation Weight (WEIGHT) is the weight assigned to the comparison observation.

Comment is an optional comment about the observation.