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Development of User Interface in ArcGIS for Watershed Management
2. DEM Data Acquisition
A 7.5 USGS (United States Geological Survey, 1990) DEM of scale1:50,000 representing the Cowansvile and St-Espirit regions of Quebec, Canada were obtained from the Walter Hitschfeld Geographic Information Center Library, McGill University, Montreal, Canada for generating the output using the developed interface. The data of digitized stream drainage network from topographical survey maps was also acquired to validate the output from the interface. The geographic location of both east and west DEMs of Cowansvile covered longitude -73° 00 to 72° 30 and latitude 45° 00 to 45° 15. The DEM covering the St-Espirit watershed were within longitude 74° 00 to 73° 30 and latitude 45° 45 to 46° 00north latitude. The location of St-Espirit watershed is within -73° 41 32 and -73° 36 00west longitude to 45° 55 00and 46° 0000north latitude (Romero et al., 2002). As per USGS standards (USGS, 1990) the 7.5 DEM data have a grid spacing of 30 X 30m and the contour interval of 10m. The DEM has a square grid array and is thus computationally efficient. The DEM is under UTM (Universal Transverse Mercator) projection based on North American datum of 1983 (NAD 83), which is widely used in the North American regions. The projection is for the UTM datum and grid zone 18N.  Fig. 1. System Architecture of Interface WMET (Ver 2.0) 3. Theoretical Considerations The WSDT interface [4] processes the DEM to demarcate watersheds and generate stream networks from DEM. On the other hand, threshold condition provides the number of cells constituting one small watershed. This is an engineering decision based on the hydrologic characteristics that the scenario presents and is a function of the cell size and the selected drainage area. This concept used in WSDT interface is : 
Where TN is Threshold number and, DA is drainage area in area unit and C is size of the cells in are unit. The threshold number has to be an integer (INT), because it is a function of the number of cells upstream and number of cells cannot be a fraction. For theoretical concepts about morphological parameters used in the analysis and further details, Ritter et al. (2002) and Sarangi et al. (2001) can be referred. 3.1 Concepts used in the Watershed Morphology Estimation Tool (WMET) Interface The schematic diagram of the Watershed Morphology Estimation Tool (WMET) interface structure is shown in Fig. 2. The basic objective of this tool is to estimate useful geomorphological parameters of watersheds as discussed in the theoretical consideration section of this article. The geomorphological parameters directly or indirectly reflect almost the entire watershed based causative factors affecting runoff and sediment loss. The land morphology of the watershed needs to be investigated and quantified in form of geomorphological parameters for studying the watershed hydrologic responses. Thus, the estimation of these parameters assumes importance in watershed management. The manual estimation of these parameters (Tables 1 & 2) from topological maps and databases are cumbersome and time consuming. Moreover, this interface overcomes all these limitations and is useful for analysis within a GIS environment.  Fig. 2. The activated WMET interface with the command buttons. |