The North Fork Shenandoah River, Virginia

 

In PHABSIM, the channel cross-section is described as a series of x and y coordinates, called verticals. The x-coordinate is the horizontal distance of a sample point along the transect, occuring at a regular interval (every 3ft, 4ft, 5ft, etc). The x-coordinate distance is also referred to as the station. The y-coordinate is the channel bed elevation at each specified station.

A survey of the bed elevation (channel profile) was conducted at each transect relative to the transect pins. 30 to 40 measurements (X,Y;vertical) were taken at each transect, and considered an adequate range to describe the channel morphology.

With our transects and verticals established, each study site is represented by a grid of equally spaced stream cells.

At any given discharge (flow), each cell along a transect will have a unique combination of hydraulic and habitat characteristics (depth, velocity, water surface elevation, substrate, and cover). PHABSIM will model how these characteristics vary in response to changes in flow.

 

 

Illustrations created by W. Scott Chappell & Adrienne Weimer