The model QUAL2K represents a river as a series of reaches. These represent stretches of river that have constant hydraulic characteristics (e.g., slope, bottom width, etc.). The reaches are numbered in ascending order starting from the headwater of the river’s main stem. Finally, any model reach can be further divided into a series of equally-spaced elements.
In summary, the nomenclature used to describe the way in which Q2K organizes river topology is as follows
- Reach:a length of river with constant hydraulic characteristics.
- Element: the model’s fundamental computational unit which consists of an equal length subdivision of a reach.
- Segment: a collection of reaches representing a branch of the system. These consist of the main stem as well as each tributary.
- Headwater: the upper boundary of a model segment.
Tomado de Chapra et al., 2007