ModelMuse Help

The Lake Properties tab defines the properties of the lake that do not change with time except for the Lake table (if used)

Number of outlets: This specifies the number of outlets from the lake. one outlet tab will be created for each outlet.

Connection directions:

•Horizontal: The lake has connections to cells that are horizontally adjacent to it.

•Vertical: The lake has connections to cells that are vertically adjacent to it.

If a lake has only vertical connections, it, will be treated as being above the lowest layer enclosed or intersected by the object that defines the lake. For example, if the object was only in layer 1 and the lake defined by the object only had vertical connections, the lake would be treated as being above layer 1. If the lake also had horizontal connections, it would be treated as being in layer 1 with horizontal connections to layer 1 and vertical connections to layer 2.

Single-cell lake: The lake is entirely enclosed in a single cell. Such lakes can have horizontal or vertical connections but not both.

Starting stage: This defines the starting stage for the lake. It is measured relative to the same datum as the groundwater heads.

Bottom elevation: This defines the bottom elevation of the lake-cell connection for lakes that have horizontal connections and are are not single-cell lakes.

Top Elevation: This defines the top elevation of the lake-cell connection for lakes that have horizontal connections and are are not single-cell lakes.

Lakebed K: This defines the hydraulic conductivity of the lakebed and helps define the lakebed leakance.

Lakebed thickness: This defines the thickness of the lakebed and helps define the lakebed leakance. If the lakebed thickness is set to zero, it is assumed that the lake is directly connected to the aquifer.

Connection length: This defines the distance between the cell connected to the lake for single-cell lakes. It is not needed for the vertical connections of multi-cell lakes and it is computed automatically by ModelMuse for horizontal connections of multi-cell lakes.

(Note the connection width required by MODFLOW 6 is computed automatically by ModelMuse.)

The Lake Time Properties tab defines the properties of the lake that change with time.

The data that can be specified for the Lake package on the Lake Time Properties tab are the Starting time, Ending time, Status, Stage, Rainfall, Evaporation, Runoff, and Withdrawal.

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

Status: Status can be active, inactive, or constant.

Stage: If the status is constant, Stage is the specified lake stage. Otherwise, stage is ignored.

Rainfall: Rainfall is the rainfall rate onto the lake in units of L/T.

Evaporation: Evaporation is the maximum evaporation rate from the lake in units of L/T.

Runoff: Runoff is the runoff rate into the lake in units of L3/T.

Inflow: Inflow is the inflow rate into the lake in units of L3/T.

Withdrawal: Withdrawal is the withdrawal rate from the lake in units of L3/T.

Density: Density is the density of fluid entering groundwater from the lake. Density is only present if the Buoyancy package is active and Specify Density is selected.

Viscosity: Viscosity is the viscosity of fluid entering groundwater from the lake. Viscosity is only present if the Viscosity package is active and Specify Viscosity is selected.

The Lake Table tab is used to define the relationship between lake stage, volume, surface area, and exchange area. (Exchange area is only used for single-cell lakes.)

A lake table is required for a single-cell lake.

Stage: Stage is the independent variable to which the rest of the data in a row are related.

Volume: This is the lake volume corresponding to Stage.

Surface area: This is the lake surface area corresponding to Stage.

Exchange area: This is the area corresponding to Stage through which the lake exchanges water with the groundwater system. Exchange Area is only used for single-cell lakes.

The GWT tab is used for specifying data for the LKT package in groundwater transport. This tab is only visible if groundwater transport is active.

The left hand side has a list of the chemical species used in the model. For each chemical species, the user specifies the initial concentration and transient data for the species.

STATUS  can be ACTIVE, INACTIVE, or CONSTANT. By default, STATUS is ACTIVE, which means that concentration will be calculated for the lake. If a lake is inactive, then there will be no solute mass fluxes into or out of the lake and the inactive value will be written for the lake concentration. If a lake is constant, then the concentration for the lake will be fixed at the user specified value.

Specified Concentration defines the concentration for the lake. The specified CONCENTRATION is only applied if the lake is a constant concentration lake.

Rainfall Concentration defines the rainfall solute concentration (ML-3) for the lake.

Evaporation Concentration defines the concentration of evaporated water (ML-3) for the lake. If this concentration value is larger than the simulated concentration in the lake, then the evaporated water will be removed at the same concentration as the lake.

Runoff Concentration defines the concentration of runoff (ML-3) entering the lake.

Inflow Concentration defines the concentration of external inflow (ML-3) for the lake. Value must be greater than or equal to zero.

Outlets allow for flow from one lake to another. Outlets are optional.

For outlets, the users define starting time, ending time, rate, invert, width, slope roughness, the outlet lake and the outlet type.

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

Rate is the the extraction rate for the lake outflow. A positive value indicates inflow and a negative value indicates outflow from the lake. Rate only applies to active lakes. A specified rate is only applied if the Outlet type is Specified.

Invert is the invert elevation for the lake outlet. Invert only applies to active lakes. Invert is only applied if the Outlet type is not Specified. The difference between the lake stage and invert elevation is one of the controls of the flow through the outlet if the lake type is Manning or Weir.

Width is the width of the lake outlet. Width only applies to active lakes. Width is only applied if the Outlet type is not Specified. The width is one of the controls of the flow through the outlet if the lake type is Manning or Weir.

Slope is the bed slope for the lake outlet. Slope only applies to active lakes. Slope is only applied if the Outlet type is Manning.

Roughness is the roughness coefficient for the lake outlet. Roughness only applies to active lakes. Roughness is only applied if the Outlet type is Manning.

Outlet lake is the object that defines the lake to which the lake outlet discharges. If no outlet lake is specified, the lake is assumed to discharge to an external boundary. It can also be diverted to the MVR package.

Outlet type defines which of three outlet types applies to the current outlet. The choices are Specified, Manning or Weir.

•Specified: The outlet flow is a value specified by the modeler.

•Manning: The outlet flow is calculated using Manning's equation.

•Weir: The outlet flow is calculated using a sharp weir equation.