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packages are identified by first using the word `program'. Many of these packages have been <br />integrated within a GUI that documents the workflow and allows editing of control files prior to <br />running the individual packages. This complex process is best understood by summarizing the <br />individual steps on workflow diagrams. Figure 1 shows an overall flowchart that delineates the <br />steps in this process. A reference number is associated with each of the major blocks to facilitate <br />discussion in this TM Figure 2 shows the modeling process in a sequential manner, focusing on <br />groundwater tasks. The surface water component of the data centered modeling process is <br />relatively well developed and is implemented by the surface water or consumptive use <br />consultants, and will not be considered in detail in the Task 50 analysis. The following sections <br />address the source of data and the pre- and post-processing steps for major data elements used in <br />the groundwater model. <br />2.2 Conceptual Model Development <br />A conceptual model is a concise description of the hydrologic characteristics of the region under <br />consideration. Box 1 on Figure 1 identifies the basic elements included in a conceptual model. <br />This portion of the modeling process identifies the aquifers that are present and their physical <br />configuration, hydraulic properties of aquifers and aquitards, sources of recharge and discharge, <br />and external boundary conditions. The conceptual model framework, aquifer properties and <br />external inflow and outflow boundaries are defined using GMS. Elements of the conceptual <br />model, including irrigated lands, wells, canals, streams and diversions are maintained in the GIS <br />repository. Data such as streamflow measurements, diversion records, water level records, <br />pumping, and hydrogeologic data that are collected at structures or other point locations are <br />maintained in HydroBase. <br />The layers used in the groundwater model are defined by the elevations of their tops and <br />bottoms. These are defined with existing GMS capabilities using data from boring logs and land <br />surface elevations. A database containing elevations of tops and bottoms of units is developed <br />and exported to a format suitable for use in GMS. Surfaces describing each layer boundary are <br />then developed by creating a TIN (Triangulated Irregular Network) within GMS. These TINS <br />are used to create 3-dimensional solids, and cross-sections. These solids are used to help identify <br />anomalous data points that are then corrected or removed from the database. After quality <br />control checking is done, the 3-dimensional solids are refined to eliminate overlap, and exported <br />to the defined finite difference grid. Hydraulic characteristics, including vertical and horizontal <br />hydraulic conductivity and storage characteristics are initially assigned using zones for each <br />layer that are based on field tests and hydrogeologic analysis. This information is maintained <br />within GMS map layers, which are similar to typical GIS polygon coverages. Internal GMS <br />tools are then used to assign properties to individual grid cells in the model. Boundary inflows <br />are defined as line features at boundaries within GMS map layers, with boundary type and <br />parameters linked. Since the basic coverages, including layer elevations, aquifer extent, <br />boundary conditions, and hydraulic properties, are maintained independent of the model grid, <br />changes in the computational grid may be completed rapidly using internal GMS tools. <br />