ERSC / GEOG 2P XXXXXXXXXXFall 2021 Drainage basins, stream networking and stream ordering Introduction: Landscapes developed dominantly as a result of fluvial erosion are composed of drainage basins...

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ERSC / GEOG 2P05 Fall 2021 Drainage basins, stream networking and stream ordering Introduction: Landscapes developed dominantly as a result of fluvial erosion are composed of drainage basins and drainage networks. The development of a landscape is thus equal to the sum total of the development of each drainage basin. The major processes at work being fluvial erosion, sediment transport and deposition exhibited in the form, of the stream network or pattern developed within each basin. It has been shown that in any location or situation a definable relationship exists between streams of differing size and power within any one stream network system. In drainage basin analysis a system is seen as an open system, one in which inputs and outputs can be measured and in which ultimately a balance or equilibrium is achieved between rates of import and export of debris (sediment) and energy. This state is referred to as steady state. Since the evolution of a drainage basin and is stream network is time dependent, the condition of steady state is also time dependent/ However, the influences active upon the development of a drainage basin are multifold. The influence of already existing regolith, of underlying lithology, of climate and covering vegetation all play a causal role leading to responses of fluvial processes that result in differing networks and drainage basins across the Earth’s surface. Stream Ordering: As stated by Doornkamp & King (1964) and Ritter et al., (2011), the problem of defining a drainage basin lies in locating the boundary of the basin on the ground, or on the map. Critical to any analysis of drainage basin characteristics is the concept of stream ordering (Fig. 1). Figure 1: Stream ordering systems of Horton (1945), Strahler (1952b) as used in this lab, and Shreve (1967.) A system of stream channel ordering was suggested as early as 1914 by Grvelius but the work of Horton (1932, 1945) marked the beginning of widespread stream ordering system development. Variations in the method used are shown in Fig. 1. The system used in the lab will be the Strahler system (center of Figure 1). Please watch the video provided which explains in further detail. Objectives: 1. To carry out a partial drainage basis analysis 2. To examine the validity of the Law of Stream Numbers 3. To examine the validity of the Law of Mean Stream Lengths Procedure: 1. Plot a map of stream orders using the Strahler system for the network provided. (9 marks) 2. Using your data in Excel, plot on a graph the quantity (frequency) of each stream order. (5 marks) 3. Using your data, plot on a graph the mean stream length versus stream order in excel. (5 marks) 4. Discussion (6 marks) a. Does the graph from Question 2 validate the Law of Stream Numbers? If so, how? b. Does the graph from Question 3 validate the Law of Mean Stream Lengths? If so how? SteamOrderingSystem 100 m