NetMap's Technical Help Guide

Flow Velocity

Stream Flow Velocity
Parameter Description:  Stream flow velocity is predicted using the Manning equation (at bankfull hydrualic geometry).
Data Type: Line (stream layer)
Field Name: FlowVel; Common Name: Flow Velocity
Units:  m/s
NetMap Module/Tool: Fluvial Processes/Hydrualic-Planform Geometry
Model Description:
NetMap contains a tool for predicting flow velocity based on the Manning equation (1889) using bankfull hydraulic geometry (channel width and depth). Velocity is in SI units (m/s (Figure 1)). Hydraulic radius must be calculated and the roughness coefficient (n) is a set function of channel slope (S). n=0.05 when S>0.08; n = 0.03 when S > 0.08 and channel width < 30 m; n = 0.025 when S > 0.08 and channel width > 30 m. The velocity of stream flow may be an important parameter in the context of aquatic habitats. Some species prefer slower water and others prefer high velocity flow (Bisson et al. 1987).
Figure 1. The flow velocity tool in NetMap (Fluvial Processes Tool Module).
Figure 2. An example of predicted bankfull flow velocity.

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