In specified head boundaries, the head remains constant. Fluid is simulated as moving in or out of the groundwater at a rate sufficient to maintain the specified head.
The Time-Variant Specified-Head (CHD) package allows the user to specify the heads in cells. The specified heads can vary with time and parameters can be used to specify the specified-head.
The Flow and Head Boundary (FHB) package allows the user to specify heads and flow rates in cells that vary in time in a manner independent of the stress periods.
