Look at the graph of the river stage - its depth relative to an arbitrary starting point, or datum . The USGS, among its excellent Web pages, has access to both real-time data like you saw for the Gallatin River and historic data from its Water Resources page for the entire country. The data from which this graph was generated were downloaded from the USGS Historical Data page for Bridger Creek and were processed in Microsoft Excel for graphing. This graph may help you to explain the stream discharge behavior from June to August and at low flow. Flood Hydrology Discharge which exceeds the channel capacity is termed flood discharge.
Floods do much of the work of shaping river channels and valleys through erosion and deposition.
They also are among the most dangerous of natural events, resulting in tens of deaths and hundreds of millions of dollars in damage or more each year. What we will do is to download those data, import them into Microsoft Excel, and analyze them. Build a spreadsheet containing the historic annual peak discharges from the Gallatin River. Select your data. Scroll down the page to locate the table of discharge records.