MAW: Multi-Aquifer Well Package Pane

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The MAW: Multi-Aquifer Well package pane is on the MODFLOW Features tab of the Object Properties dialog box.

The MAW: Multi-Aquifer Well package pane can only be selected if the object being edited is a point object on the top view of the model with zero Z formulas.

MODFLOW 6 does not allow a single multi-aquifer well to define more than one well screen in a single cell.

There are three tabs on the pane: Well definition, Well screens, and Transient.

hmtoggle_plus1Well definition

The Well definition tab is used to define data that apply to the entire well.

Radius —radius for the multi-aquifer well.

Bottom —bottom elevation of the multi-aquifer well.

Starting head (strt)—starting head for the multi-aquifer well.

Conductance Equation (condeqn) defines the conductance equation that is used to calculate the saturated conductance for the multi-aquifer well. Possible multi-aquifer well condeqn strings include:

•SPECIFIED– to indicate the multi-aquifer well saturated conductance will be specified.

•THEIM– to indicate the multi-aquifer well saturated conductance will be calculated using the Theim equation.

•SKIN– to indicate that the multi-aquifer well saturated conductance will be calculated using the screen top and bottom, screen hydraulic conductivity, and skin radius.

•CUMULATIVE– to indicate that the multi-aquifer well saturated conductance will be calculated using a combination of the Theim equation and the screen top and bottom, screen hydraulic conductivity, and skin radius.

•MEAN– to indicate the multi-aquifer well saturated conductance will be calculated using using the aquifer and screen top and bottom, aquifer and screen hydraulic conductivity, and well and skin radius.
hmtoggle_plus1Well screens

The Well screens tab is where well screens are defined. The elevations of the well screens determine which cells are part of the well.

Screen top: (scrn_top) defines the top elevation of the screen for the multi-aquifer well connection. scrn top can be any value if the Conductance equation is SPECIFIED or THEIM. If the specified scrn top is greater than the top of the cell it is set equal to the top of the cell.

Screen bottom: (scrn_bot) defines the bottom elevation of the screen for the multi-aquifer well connection. scrn bot can be any value if the Conductance equation is SPECIFIED or THEIM. If the specified scrn bot is less than the bottom of the cell it is set equal to the bottom of the cell.

Skin K: (hk_skin) defines the skin (filter pack) hydraulic conductivity (if the Conductance equation for the multiaquifer well is SKIN, CUMULATIVE, or MEAN) or conductance (if the Conductance equation for the multi-aquifer well is SPECIFIED) for each cell connected to the multi-aquifer well. hk skin can be any value if the Conductance equation is THEIM.

Skin radius: (radius_skin) defines the skin radius (filter pack radius) for the multi-aquifer well. radius skin can be any value if the Conductance equation is SPECIFIED or THEIM. Otherwise, radius_skin must be greater than radius for the multi-aquifer well.
hmtoggle_plus1Transient

The Transient tab is used to define the data for the stress periods for the well.

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

Status: option to define well status. status can be ACTIVE, INACTIVE, or CONSTANT. By default, status is ACTIVE.

Flow rate: (rate) is the volumetric pumping rate for the multi-aquifer well. A positive value indicates recharge and a negative value indicates discharge (pumping). rate only applies to active (IBOUND> 0) multi-aquifer wells. By default, the rate for each multi-aquifer well is zero.

Specified Head: (well_head) is the head in the multi-aquifer well. well_head is only applied to constant head (STATUS is CONSTANT) and inactive (STATUS is INACTIVE) multi-aquifer wells.

Flowing well (FW): FLOWING WELL—keyword to indicate the well is a flowing well. The flowing well option can be used to simulate flowing wells when the simulated well head exceeds the specified drainage elevation.

FW elevation: (fwelev) elevation used to determine whether or not the well is flowing.

FW conductance: (fwcond) conductance used to calculate the discharge of a free flowing well. Flow occurs when the head in the well is above the well top elevation (fwelev).

FW reduction length: (fwrlen) length used to reduce the conductance of the flowing well. When the head in the well drops below the well top plus the reduction length, then the conductance is reduced. This reduction length can be used to improve the stability of simulations with flowing wells so that there is not an abrupt change in flowing well rates.

Rate limitation:  Choices are none, Scaling and Shutoff.

•none

•Scaling activates rate scaling. If rate scaling is specified, both pump elevation and scaling length must be specified. rate scaling cannot be used with Use head limit.

•Shutoff activates well shut off capability. Subsequent values define the minimum and maximum pumping rate that a well must exceed to shutoff or reactivate a well, respectively, during a stress period. shut off is only applied to discharging wells (rate< 0) and if head limit is specified (not set to ‘off’). If head limit is specified, shut off can be deactivated by specifying a minimum value equal to zero. The shut off option is based on the shut off functionality available in the MNW2 (Konikow and others, 2009) package for MODFLOW-2005. The shut off option has been included to facilitate backward compatibility with previous versions of MODFLOW but use of the rate scaling option instead of the shut off option is recommended. By default, shut off is not used.

Pump elevation: pump elevation is the elevation of the multi-aquifer well pump (pump elevation). pump elevation cannot be less than the bottom elevation (bottom) of the multi-aquifer well. By default, pump elevation is set equal to the bottom of the lowest cell connected to a MAW well.

Scaling length: (scaling_length) is the height above the pump elevation below which the pumping rate is reduced. The default value for scaling length is the well radius.

Min flow rate:( minrate) is the minimum rate that a well must exceed to shutoff a well during a stress period. The well will shut down during a time step if the flow rate to the well from the aquifer is less than minrate. If a well is shut down during a time step, reactivation of the well cannot occur until the next time step to reduce oscillations. minrate must be less than maxrate.

Max flow rate: (maxrate) is the maximum rate that a well must exceed to reactivate a well during a stress period. The well will reactivate during a timestep if the well was shutdown during the previous time step and the flow rate to the well from the aquifer exceeds maxrate. Reactivation of the well cannot occur until the next time step if a well is shutdown to reduce oscillations. maxrate must be greater than minrate.

Use head limit: Activates (or deactivates) the Limiting head.

Limiting head: (head limit) is the limiting water level (head) in the well, which is the minimum of the well RATE or the well inflow rate from the aquifer. HEAD_LIMIT can be applied to extraction wells (RATE < 0) or injection wells (RATE > 0). The HEAD_LIMIT option is based on the HEAD_LIMIT functionality available in the MNW2 (Konikow and others, 2009) package for MODFLOW-2005. The HEAD_LIMIT option has been included to facilitate backward compatibility with previous versions of MODFLOW but use of the RATE_SCALING option instead of the HEAD_LIMIT option is recommended. By default, HEAD_LIMIT is ‘OFF’. See Shutdown theta and Shutdown kappa on MAW: Multi-Aquifer Well Package Pane

See also: MAW: Multi-Aquifer Well Package Pane on the MODFLOW Packages and Programs dialog box.