East-West Gateway’s October 2018 Map of the Month depicts stream flowlines by stream order for the East-West Gateway region using data from the National Hydrography Dataset (specifically the NHDPlus High Resolution files). The National Hydrography Dataset is a comprehensive set of digital spatial data that encodes information about naturally occurring and constructed bodies of water, paths through which water flows, and related entities.
Stream order is a classic method for ranking stream segments according to their size and position relative to other streams within the network. Small streams in the headwaters of a watershed are assigned low numeric values and large rivers with many tributaries receive higher values, up to a maximum value of ten. A stream segment without any tributaries is given a value of one and called a “first order stream”. As more tributaries join the first order stream, the stream order value increases, with the increase in value reflecting the stream orders of the various tributaries flowing into the main channel. The St. Louis region has thousands of first order streams. The Mississippi River and Missouri River are both tenth order streams. For more information on the National Hydrography Dataset go to: https://www.usgs.gov/core-science-systems/ngp/national-hydrography/nhdplus-high-resolution