NetMap's Technical Help Guide

Rosgen

 
Channel Classification (Rosgen)
 
Parameter Description: The Dave Rosgen Stream Classification system, implemented within a GIS
 
Data Type: Line (stream layer)
 
Arc Field Name: Rosgen; Common name: Rosgen Classification
 
Units: Categories
 
NetMap Module/Tool: Fluvial Processes/Channel Classification-Rosgen
 
Model Description:
Rosgen stream classification system (Rosgen 1996) requires information on: 1) entrenchment ratio (valley width/channel width), 2) channel width to depth ratio, 3) sinuosity, 4) channel gradient and 5) substrate size (gravel, cobbles etc.). NetMap’s tools contain all of the necessary parameters (1-5) to create a Rosgen stream classification (Figure 4). Although NetMap contains a tool for calculating sinuosity, the results are likely too approximate (based on DEMs) to inform the Rosgen classification system. Thus sinuosity is excluded from NetMap’s Rosgen classification. Measuring channel sinuosity is best conducted in the field.
 
NetMap can be used to create two levels of Rosgen stream classification. Level 1 requires the attributes of entrenchment ratio, width to depth ratio, and gradient to create Rosgen divisions A, B, C, and E  Divisions F and G pertain to damaged and recovering channels and these can only be defined in the field. Categories D and DA pertain to braided channels and NetMap does not contain a braided channel attribute (at present) but channel gradient could be used as a surrogate (e.g., less than 0.001). The user may elect to add substrate type (D50, median grain size) to create classification subdivisions such as A1, A2, B1, B2 and so forth. NetMap contains a tool for estimating the relationship between shear stress and substrate size (D50); this tool is located in the Module Fluvial Morphology/Hydraulic/Planform Geometry.
 
Please refer to Rosgen source materials about the classification system for additional information (Rosgen 1996); and see http://www.bae.ncsu.edu/programs/extension/wqg/srp/ppts/classification.pdf.  Rosgen stream classification, like all stream classification systems, is best implemented  in the field at the reach or small tributary scale.
 
NetMap’s classification tools is best used for screening for different channel types at large watershed to landscape scales.
 
Figure 1. The Rosgen classification tool in NetMap. A user may elect to add substrate size to the classification, if the parameter is not already available, the substrate tool is used. A classification is conducted (3) and different map color codes can be generated (4).
 
Figure 2. Output from NetMap’s Rosgen stream classification system provides an approximation of different channel types across watersheds.
 
Technical Background
Channel morphology (i.e., pool-riffle, step pool, cascade etc.) is largely a function of channel size, gradient, and valley confinement (Kellerhals et al. 1976, Bisson et al. 1982, Rosgen 1994, Montgomery and Buffington 1997). These attributes can all be estimated with digital elevation data (drainage area correlates well with channel size), so that an initial estimate of channel types within a basin, and the proportion of each, can be obtained solely through analysis of the DEM. Other aspects of channels can be incorporated into stream classification such as tributary confluence effects (Benda et al. 2004a, Bigelow et al. 2007) and natural disturbance regimes (Benda et al. 1998)
 

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