The Fundamental Building Blocks –First Order Catchments

Abstract

The role of first order streams in forming larger catchments is examined. In higher rainfall areas these form a “space-filling” network such that no area is far from a first order stream. The existence of these is presented as a battle between the ability of a groundwater outflow to carry away sediment material and the downward movement of sediment material into the channel which tends to bury the stream. The properties of channels and streams and the forest soils upslope of the streams are presented. A comparison is made between small stream and large stream hydraulic properties. The important concept of “minimum continuum levels” or “minimum representative volume” is presented; it is concluded that this is a useful concept but that the minimum level is inconveniently large for most field work applications. The outflow of differing shaped catchment elements – concave, convex, and planar is introduced. Concave catchment elements give sustained spring outflow and are also responsible for the continued headward erosion of streams pushing back into the land. Parallel and convex catchment elements contribute stream variability.