Compare and discuss those stream characteristics that decrease in a downstream direction with those that increase downstream

Please see response attached (which is also presented below), including one supporting study. I hope this helps and best of luck!

RESPONSE:

1. Compare and discuss those stream characteristics that decrease in a downstream direction with those that increase downstream. Also, indicate and discuss whether these changing stream characteristics tend to favor erosion or deposition of sediments.

There are four main characteristics of streams to consider (ranking, gradient, meander and age of the stream) in your discussion of the decrease or increase of the downstream direction. In other words, the streams shape and bottom profile impact the movement downstream, which either favors erosion or deposition of sediment. It is relatively easy to measure how fast the water in a stream is traveling or to measure the discharge of a stream. But what might happen to a stream's velocity if a stream's gradient changes? This happens to real streams as they flow and erode away large amounts of earth materials from their beds and sides.

1. Ranking - Streams in geographic terms are awarded order designations. A stream of the first order is a blue-line stream, which does not have any other blue-line stream feeding into it. A stream of the second order is one, which is formed by the joining of two or more blue-line streams. A third-order stream is one below the confluence of two or more second-order streams; a fourth-order stream is formed by the confluence of at least two third-order streams, and so forth.

2. Gradient - The gradient of a stream is a critical factor in determining its character, and is entirely determined by its base level of erosion. The base level of erosion is the point at which the stream either enters the ocean, a lake or pond, or enters a stretch in which it has a much lower gradient, and may be specifically applied to any particular stretch of a stream. For example, in geologic terms, the stream will erode down through its bed to achieve the base level of erosion and resulting deposition throughout its course. If this base level is low, then the stream will rapidly cut through underlying strata (increase downstream) and have a steep gradient, and if the base level is relatively high, then the stream will form a flood plain and meanders (decrease in downstream direction and result in meanders from erosion and the deposition of bank material).

3. Meander - Meanders are looping changes of direction of a stream caused by the erosion and deposition of bank materials. These may be somewhat sine-wave in form. Typically, over time, the meanders don't disappear but gradually migrate downstream. For example, if some resistant material slows or stops the downstream movement of a meander, a stream may erode through the neck between two legs of a meander to become temporarily straighter, leaving behind an arc-shaped body of water termed an oxbow lake or bayou. A flood may also result in a meander being cut through in this way, and also moves finer sediment further downstream and deposited.

4. Profile - Typically, streams are said to have a particular profile, beginning with steep gradients, no flood plain, and little shifting of channels (increase downstream with high levels of erosion and deposition), eventually evolving into streams with low gradients, wide flood plains, and extensive meanders (decrease downstream with lower levels of erosion and deposition). The initial stage is sometimes termed a "young" stream, and the later state a "mature" or "old" stream. However, a stream may meander for some distance before falling into a "young" stream condition (adapted from http://en.wikipedia.org/wiki/Stream).

Streams also accomplish work in the watershed: they erode the land and move the loosened material down-slope and, eventually, into the sea where it is deposited. This solid material is carried by the stream as bed load, suspended particles, or floating debris. Sediments from erosion increase as one moves down gradient in the watershed due to increased capability of the stream; that is, the increase in volume and velocity of stream water as a result of increasing drainage area, resulting in the stream's ability to maintain greater amounts of sediment and eroded material in suspension. There is usually a decrease in erosion and deposition in deeper, slow moving stream areas in the downstream waters where stream velocity is retarded and sediments settle out. Thus, larger and heavier particles are settling out more readily than the very smallest particles that settle farther downstream. http://www.aecos.com/JOBS/Kawa_stream.html

See attached Kawa Stream Project (1999), which is an interesting study that supports the facts listed above. Kawa Stream like most Hawaiian perennial streams, is characterized by periods of relatively steady, base flow and short periods of high flow (termed freshets) resulting from heavy rains on the watershed. Physical and chemical properties of the water can vary between these two types of flow, as well as between storms of different magnitudes and at different times during storm flow. The study approach requires making water quality measurements at locations, which permit attribution of substances carried in the flow to sources in the watershed.