> For the complete documentation index, see [llms.txt](https://eflow.gitbook.io/ffc-readme/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://eflow.gitbook.io/ffc-readme/functional-flow-calculator/metrics/all-year/average-annual-flow.md).

# Average Annual Flow

## Definition

The arithmetic mean of daily flow is calculated individually for each water year. This metric is in units of cfs.

## Steps

1. Convert raw date and flow data columns into a flow matrix based on water year. Each column starts with the beginning of the water year (i.e. 10/1) and ends with the end of the water year (i.e.9/30).
2. Calculate the average annual flow for each water year:

   ```python
   average_annual_flows.append(np.nanmean(flow_matrix[:, index]))
   ```


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