Calculating river lengths provide interesting information, but it is not always easy to measure
Rivers are essential in shaping landscapes, supporting aquatic life and supplying water to many communities. Extensive research is done in the area of river length measurement. The Nile River is credited as the world’s longest, stretching approximately 4,135 miles across Egypt, North and South Sudan, and Ethiopia. In the United States, the Mississippi is the longest river at 3,870 miles. Measurements are made based on available topographic data and remote sensing imagery.
What to Measure
Prior to measuring river length, the beginning and end of a river need to be determined. Rivers originate from a range of sources, such as glaciers, fountains or lakes, and end by either flowing into the sea or another river. The start of a river is referred to as headwater, while the end of a river is called embouchure. So, calculating river length depends on measuring from the headwater to the embouchure.
Where to Measure
Rivers, especially the larger ones, usually have several contributing headwater streams, and a criterion is followed to decide where to begin measuring. This involves weighing up multiple factors, including which is the longest headwater stream, which has the largest volume of water, and which has the same orientation as the entire river.
Topography is an important geological tool. A topographical map is a two-dimensional figure that represents a three-dimensional surface. Analyzing topographical data is the most common method for measuring river length. Such data is traditionally collected via field surveys, which is often labor intensive. Advanced remote sensing image capture also provides topographic data that can be more accurately interpreted, although pinpointing the beginning of a river remains problematic.
No universal standard exists for measuring the length of a river; the statistics constantly vary. In 2007, Brazilian scientists controversially claimed the Amazon River was close to 100 miles longer than the Nile River. As the source and mouth of a river remain difficult to establish, it is uncertain where measurement should begin or end. Sources of variance arise from questions, such as which tributaries to include or what adjustments to make when a river passes through a lake.