Drainage area is an important component of FIBI calculations. The Iowa Department of Natural Resources uses several tools to determine the drainage area of a given site, and the United States Geological Survey (USGS)'s StreamStats web application is one of the most useful.

To use StreamStats to determine a drainage area for a given point, you can work through the following steps:

1. Use the map to zoom into a location, or the search tool to name a town or area. You may even enter the coordinates in a lat, long format, such as 42.53582, -93.78792.
2. Once you have zoomed in sufficiently, you will be able to click a button to select the state or regional study area.
3. Click the "Delineate" button and then click on a blue stream cell to select the point of delineation.
4. Once the delineation is complete, you can click the "Continue" button on the left side.
5. For Drainage Area, click the down arrow next to "Basin Characteristics" to list the parameters, and then check "DRNAREA". Scroll to the bottom of the list and click the "Continue" button.
6. After calculating, you'll see a list of reports to display. If you followed the steps above, there will be a single item, already checked, for Basin Characteristics. Click on the "Continue" button.
7. A modal popup will open, showing a report of the basin and the drainage area in square miles.