Cell Stress Overlays The term Cell Stress in Graphic Groundwater refers to four of the original MODFLOW stresses, which may (but do not need to) be included in the model. These stresses are set for a particular cell or group of cells, not for every cell in the model. In addition, unlike Property or Area Stress overlays, a Cell Stress overlay can have more than one stress per cell. For example, a model could have more than one well in a single cell. The Cell Stress overlays implemented in Graphic Groundwater include: Drain General Head Boundary River Well Cell Stresses have one or more properties that must be set for a cell that contains that stress. MODFLOW documentation describes the theory on how the Cell Stresses are implemented. Here the nature of the input for each one is summarized: Drain Conductance: The conductance of the drain and sediment in the immediate vicinity of the drain in units of square length per time. Conductance must be positive. Elevation: The elevation of the drain in units of length relative to the model datum. General Head Conductance: The conductance controlling the flow into or out of a cell from some external stress in units of square length per time. Conductance must be positive. External Head: The head in the external source or sink in units of length. River Stage: The elevation of the water in the stream channel in units of length relative to the model datum. Bed Conductance: The conductance of the stream bed layer in units of square length per time. Conductance must be a positive value. Bed Bottom Elevation: The elevation of the base of the stream bed layer in units of length relative to the model datum. Well Discharge: Volumetric flow rate in units of cubic length per time. A positive value indicates injection, a negative value indicates withdrawal. The Cell Stress Overlay window has a distinctly different look and feel to it when compared to the Area Stress and Property Overlay windows. The interface was developed in order to allow more than one stress to be entered into a cell if desired. The window includes one or more text boxes for entering and displaying property values for a particular stress, Stress, Slice, Period, and Other drop down lists, and Add Stress, Delete Stress, Clear Stress, Set Stress, and Discharge Face, and Finished buttons. You must first add a stress. A stress is defined as one or more cells that share the same slice (consult Chapter 4 for more information about model slices), period, discharge face, and stress properties. For example, a well stress would be one or more cells operating in the same slice, for the same stress period, with the same discharge and discharge face. Add a stress by clicking on the Add Stress button. The Stress drop down list changes to show the number of the new stress. Select one or more cells where this stress is operating. The Discharge Face button displays the Discharge Face pop-up window which contains option buttons for setting how discharge is handled for this stress in MODPATH. Click on the appropriate option button, choose the period and layer, enter the value or values in the text boxes, then click on the Set Stress button. Graphic Groundwater indicates the change by displaying a green inner border and the number of the stress in the selected cells. You can change the discharge face, any property value, the period, or the slice, but you must click on the Set Stress button for the change to take effect. You do not have to select the cells, just make the changes in the text boxes, drop down lists, and option buttons. You can add cells to a stress by selecting one or more cells and then clicking the Set Stress button. The cells set earlier still remain in that stress. To remove a particular cell or cells from a stress, first select the cell or cells, then click on the Clear Stress button. A click on the Delete Stress button removes the stress and renumbers all remaining stresses. Clearing all the cells in the stress will also delete the stress. Graphic Groundwater displays all cells for a particular stress in the grid. For example, with the River Cell Stress overlay, Graphic Groundwater shows all river cells. Choosing a stress in the Stress drop down list highlights all the cells in that stress and changes the Discharge Face option, the Period and Slice drop down lists, and the text boxes to the values for that stress. If one or more stresses share one or more cells with the stress highlighted in the Model window, the Other drop down list is activated and displays the number of the other stress or stresses in that group of cells. Graphic Groundwater only displays the number of the first stress set for that cell. If a cell has more than one stress, another green border is displayed, nested inside the original green border. You navigate between the different stresses with either the Stress drop down list or Other drop down list (if enabled). In addition, selecting a stress cell will cause the Stress drop down list to display the stress number and changes the Discharge Face option, the Period and Slice drop down lists, and the values in the text boxes to those for that particular stress.