Mapping Table:Mapping Table File
The Mapping Table file has been designed for easy assignment of most of the parameters needed to model different processes in GSSHA. The Mapping Table consists of a short series of data tables, linked to a small number of integer-based index maps. The data tables are associated with different processes that can be simulated in GSSHA that require parameter values in every cell in the watershed, i.e. overland flow, infiltration, etc. From these inputs, GSSHA is able to internally create over two-dozen floating-point GRASS ASCII maps, which would otherwise have to be created by the user and specified with project cards. Consolidating the parameters into a series of tables and index maps reduces model construction time, organizes information, makes calibration easier, and allows easy parameter assignment for project alternatives and future scenarios. By using index maps as the patterns for assigning parameters, many different input parameters for a single cell can be assigned by changing the number in the index map.
Parameter values in the Mapping Table file are linked to the index maps through the identification numbers (IDs) used in the index maps. Data in the tables are arranged according to ID. The index maps contain the spatial distribution of the IDs over the watershed. To build the required input GRASS maps, GSSHA reads in the specified index maps, and replaces the index map ID values with the data corresponding to the ID from the appropriate table. This information is stored internally as an input floating-point map. Most watersheds can be simplified into a small set of parameters and a few index maps, but even large and complex watershed models can be quickly constructed using the Mapping Table file. The program WMS V6.1 and later releases, is designed to work with the Mapping Table file and parameters are assigned with the Mapping Table file when using WMS V6.1. When using WMS 6.1 and higher, WMS will place the MAPPING_TABLE card in the project file when one or more processes requiring distributed parameter values are chosen to be modeled. The MAPPING_TABLE project card, followed by the name of the Mapping Table file, informs GSSHA to obtain parameters needed for process simulations from the Mapping Table file, and that detailed ASCII maps or uniform values of parameters will not be used.
The following is a description of the overall structure of the Mapping Table file, followed by a detailed description of the structure of the index maps, the structure and organization of the various tables in the Mapping Table file, and a description of how to link the index maps to the tables in the Mapping Table file. Finally, a summary of the different sections of the Mapping Table file is given, as well an example of the Mapping Table file.
- 12 Mapping Table