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How to Calculate Base Flow

Discussing the size of a flowing body of water such as a stream or river presents a challenge as a river's flow fluctuates daily. Precipitation and other climate factors (such as snowpack melt) contribute greatly to the size of a stream or river. Contributions from precipitation are known as overland flow. The same body of water, however, could shrink to a fraction of its size during dry years when it receives no overland flow. Geologists refer to the relatively constant level of water entering a stream from the groundwater as base flow. Calculating base flow allows you to determine the constant, sustainable size of a flowing body of water.

Instructions

- 1
  Download the Base Flow Index (BFI) program from U.S. Department of the Interior website. Run the executable file.
- 2
  Locate the U.S. Geological Survey daily stream flow records from the USGS website. Click on the boxes to select one or more criteria for selecting sites. Click "Submit."
- 3
  Click the button next to "Tab-separated data." Check that the drop-down menu says "Save to file." Click "Submit."
- 4
  Find the tab-separated data file that you downloaded from the USGS website as the input file in the BFI program. Select a location to save an output file. Enter "5" in the "N" field. Enter "0.9" in the "F" field. Press "Run BFI."
- 5
  Open the output file. Scroll down to the bottom of the text file and record the number labeled "Mean Base Flow."

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