Surface Processes, Part 2

Question 1: Define these parts of a stream: spring, source, headwaters, confluence, run.

Answer 1: Spring: The point at which a stream emerges from an underground course through unconsolidated sediments or through caves. A stream can, especially with caves, flow aboveground for part of its course, and underground for part of its course. Source: The spring from which the stream originates, or other point of origin of a stream. Headwaters: The part of a stream or river proximate to its source. The word is most commonly used in the plural where there is no single point source. Confluence: The point at which the two streams merge. If the two tributaries are of approximately equal size, the confluence may be called a fork. Run: A somewhat smoothly flowing segment of the stream.

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Question 2: What are the typical sources of streams?

Answer 2: Streams typically derive most of their water from precipitation in the form of rain and snow. Most of this water re-enters the atmosphere by evaporation from soil and water bodies, or by the evapotranspiration of plants. Some of the water proceeds to sink into the earth by infiltration and becomes groundwater, much of which eventually enters streams. Some precipitated water is temporarily locked up in snow fields and glaciers, to be released later by evaporation or melting. The rest of the water flows off the land as runoff, the proportion of which varies according to many factors, such as wind, humidity, vegetation, rock types, and relief. This runoff starts as a thin film called sheet wash, combined with a network of tiny rills, together constituting sheet runoff; when this water is concentrated in a channel, a stream has its birth.

Question 3: Define these parts of a stream: thalweg, wetted perimeter, nickpoint, waterfall or cascade and mouth.

Answer 3: Thalweg: The river's longitudinal section, or the line joining the deepest point in the channel at each stage from source to mouth. Wetted perimeter: The line on which the stream's surface meets the channel walls. Nickpoint: The point on a stream's profile where a sudden change in stream gradient occurs. Waterfall or cascade: The fall of water where the stream goes over a sudden drop called a nickpoint; some nickpoints are formed by erosion when water flows over an especially resistant stratum, followed by one less so. The stream expends kinetic energy in trying to eliminate the nickpoint. Mouth: The point at which the stream discharges, possibly via an estuary or delta, into a static body of water such as a lake or ocean.

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