Water Science and the Environment HWRS 201 Dr. Marek Zreda
[email protected] 621-4072 Harshbarger 230 A watershed Characterizing watersheds (stream networks) Hydrologists want to understand how the physical characteristics of watersheds influence the water balance within them. If possible, we want to characterize watersheds by simple indicators because frequently we don’t have detailed information about them. We’ve already discussed three ways of characterizing watersheds: 1. Discharge at a point (e.g., feet3/sec, km3/year) 2. Drainage basin area 3. Stream length But none of these quantify the shape and connectedness of the streams in the network. The fourth way does that: 4. Strahler ordering Sketch of a stream network Note that confluences are always higher in elevation than the main stem descending from them. All streams flow downhill (due to gravity) Sub-basins and self-similarity All large watersheds are composed of sub- basins, which are watersheds within watersheds. The Rio Grande is a good example. It comprises 7 major sub-basins, which are themselves composed of sub-sub-basins, etc. Each sub-basin is like a miniature of its parent basin. For this reason, we say watersheds are self-similar and that they scale. Elements and properties of stream networks The concept of self-similarity has a particularly nice representation in the concept of stream networks. Stream networks are composed of stream segments, which are sections of the network between confluences. A confluence is a place where 2 streams come together and form a new stream that continues on downhill. The 2 upper streams are tributaries of the new stream.