Area Stress Overlays The term Area Stress in Graphic Groundwater refers to two of the original MODFLOW stresses, which may (but do not need to) be included in the model: Evapotranspiration Recharge These stresses have one or more properties that must be set for every active head cell for every stress period in which the stress is active. MODFLOW documentation describes the theory on how recharge and evapotranspiration are implemented. Here the nature of the input for each one is summarized: Evapotranspiration Surface: The elevation in units of length relative to the model datum where evapotranspiration achieves its maximum value. Maximum Rate: The maximum rate of evapotranspiration in units of length per time. A positive value indicates removal of water from the cell, a negative value indicates addition of water. Extinction Depth: The depth in units of length relative to the evapotranspiration surface where the evapotranspiration ceases. Layer: The layer where evapotranspiration occurs. This overlay is only relevant if you have selected the Specified Layer option in the Evapotranspiration window. Recharge Rate: Recharge rate in units of length per time. A positive value indicates addition of water to the cell, a negative value means loss of water. Layer: The layer where recharge occurs. This overlay is only relevant if you have selected the Specified Layer option in the Recharge window. The Area Stress Overlay window includes one or more text boxes depending on the Area Stress overlay, an option button or buttons immediately adjacent to the text box or boxes, the Period drop down list, and Set Node, Clear Node, Interpolate, Set, Set All, and Finished buttons. Clicking on the option buttons refreshes the screen, displaying values for the property adjacent to the option button. For example, with the recharge Overlay window, if you click on the option button adjacent to the Rate text box, all of the grid cells will display the current values of recharge rate. If you click on the option button adjacent to the Layer text box, all of the grid cells will display the current value for recharge layer. A disabled text box or option button indicates either homogeneous conditions, or that the stress is not active for the current period. Choose a period, select a cell or a group of cells, enter a value in the text box, then click the Set button. The values in the selected cells change. If the scale is large enough (see the View menu) and the Cell Values box is checked (see the View Preferences window), the value will appear within the cell. A dot is displayed in the cell if it is too small to display the entire number. Values can be changed simply by repeating the process. Clicking on the Set All button will set the value of every property in the selected cells, instead of just the property currently visible in the grid. Graphic Groundwater includes features to allow you to interpolate Area Stress values in the grid. A node is a cell that has a fixed value in the interpolation algorithm. You set a node or nodes by selecting a cell or group of cells and then clicking the Set Node button. A node cell is indicated by a blue circle circumscribed in the cell or cells. If you then select a group of cells (this can be a discontinuous block of cells) that includes one or more nodes, then click the Interpolate button, Graphic Groundwater will interpolate values in all the selected cells, based on the node values, by applying an inverse distance algorithm. This feature is particularly useful in setting values that trend across a grid. A selected node is cleared with the Clear Node button. Consult the section on Property Overlays for more information on the interpolation algorithm.