This tool is used for extracting a watershed from the MAGNET Data Server to serve as either the model domain or a zone feature inside your model. Once the location, watershed level, and genrealization tolerance have been selected (see below), click 'OK' to extract the watershed from the MAGNET Data Center.
Extraction Location
The first step is to zoom to the area of interest and click on the map display (try to click near the center of the watershed, if known ahead of time). The latitude and longitude coordinates shown in the interface will automatically udpate with each click on the map. You can also manually enter the coordinates into the text fields that are provided.Watershed Level
The MAGNET Data Center includes all watershed sizes, or Hydrologic Unit Codes (HUCs), from the US Geological Survey National Hydrography Dataset (USGS NHD). There are six Levels, with the largest watsersheds included in Level 1 (HUC 2-digit); the 2nd largest included in Level 2; and so on. The smallest watersheds are included in Level 6 (HUC 12-digit). More details can be found at following USGS web-page .The default is Level 5 (HUC 10-digit watershed). Nationwide, there are about 20,000 watersheds of this size. Use the drop-down menu next to Watershed Level to change to a different level.
Data Center 2
We are in the process of adding watersheds of different sizes globally (i.e., all areas outside of the United States). Currently, Level 4 is the only size available outside of the US; to utilize one of these watershed, check the box next to DataCenter2. This "overrides" the selection from the Watershed Level drop-down menu.Generalization
Watershed boundaries are often very detailed (many vertices and line segments), but that level of details may not be necessary at your scale of interest. (Using many vertices also causes longer loading times and slower display response.)Therefore, IGW-NET (by default) applies "smoothing" along the watershed edges, where the degree of smoothing is controlled by the Tolerance, or distance scale of smoothing. In other words, details smaller than the Tolderance level are aggregated into a smooth single feature. IGW-NET uses a 500m Tolerance by default.
Change the Tolerance using the text field provided, or uncheck the box next to 'Generalization' to disable the smoothing.