The first step is to define the map projection for your specific project based of preservation and precision issues. As an example, Texas has some common map projections that are regularly used by many state agencies. For detailed information you can take a look at the following website:

Texas Natural Resources Information System (TNRIS): http://www.tnris.state.tx.us/digitaldata/projections.htm

Once you have all the digital base maps from the previous phase and after defining the geographic reference or map projection system best suited for your project you can create the geodatabase (using the ArcCatalog application of the ArcGIS Desktop software) for your project and start importing one by one the basic features classes that represent your hydrological system.

There are two Arc Hydro database designs that you can apply to your project. The simplified version (a.k.a. Framework) and the Full version. The application of one or the other pretty much depends on the amount of information that your have gathered for your project. Thus, if you only have available the basic digital maps for your project the Framework is a good preliminary choice that you may upgrade later on. But if you have an abundant number of layer available that comply with the Arc Hydro data model design you might be in good shape to apply the full version of the model. The simplified structure of the model is shown below for quick reference. Please refer to the Arc Hydro book for details on both versions of the model. Arc Hydro GIS for Water Resources, David R. Maidment, Editor, ESRI Press, 2002

Thus, to conform with Arc Hydro it is important that you take look at the data base design to identify what feature datasets you need to create for your project and what features classes go into each of those feature datasets. Again, to conform with the Arc Hydro Data Model your layers should have a standard name. This standard nomenclature will make the process of model generation much easier.

The basic layers to be loaded are: HydroEdge, Watershed, Waterbody, and MonitoringPoint.

It is important that you start importing the Shapefiles or Coverages into the Geodatabase starting with the one that has the biggest spatial extent. This is because the spatial extent of a feature dataset cannot be changed once it is assigned, thus the spatial extent must be large enough to contain ALL the thematic feature classes that will be inside a given feature dataset. From the above basic five layers, Watershed will probably have the biggest spatial extent.

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