When building a ground water model, it is important to ensure that consistent units are used when entering model parameters. To simplify the management of model units, define the units for length, time, mass, force and concentration in the Units dialog. A units label is placed next to each of the input fields in all the model dialogs in GMS where the units are known. For example, the units for hydraulic conductivity are length / time. If the length units are defined as "m" (meters) and the time units are defined as "d" (days) in the Units dialog, then the units string next to the hydraulic conductivity input field would be "m/d".
Length units are specified in the Display Projection dialog which is accessed by clicking on the button to the right.
Concentration units can be defined separately, and potentially inconsistently with, mass and length units. This allows for more flexibility but can also lead to confusion so use care when selecting concentration units.
The Units dialog is accessed by using the Units... command in the Edit menu.
Generally speaking, GMS does not convert quantities from one system of units to another. GMS only displays the chosen units to help in checking consistancy. However, in a few places, GMS will use the currently defined units in it's calculations. These include:
- in the FEMWATER Fluid Properties dialog,
- in the Curve Generator dialog,
- when calculating the stream stage constant when saving MODFLOW, and
- in the Measure tool.
GMS – Groundwater Modeling System
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