Create → Channel Geometry Grids → With HS Order Grid

This dialog allows you to create grids for several key channel properties by parameterizing them in terms of a Horton-Strahler order grid. The channel cross-section is modeled as a trapezoid, with bottom width, w, bank angle, a, and a Manning roughness parameter, n. The cross-section is triangular when w = 0, and is rectangular when θ = 0. For overland flow, (w >> d) and R → d. Here, R is hydraulic radius and d is the flow depth.

The lowest orders here correspond to grid cells on hillslopes and by default, the transition from overland flow on hillslopes to channelized flow is set to occur at a Horton-Strahler order of 4. None of the default settings are expected to be valid in general.

The bed width grid is special in the sense that for hillslope pixels it is used to model overland flow. The value for hillslope pixels is therefore determined by the grid spacing and you should set the Order 1 width to the DEM grid spacing.

A Manning's N value of 0.3 is often used for hillslopes, while for channels, N is typically between 0.01 and 0.05, with 0.03 being a typical middle-range value. N varies with the bed material and may be modeled by Strickler's formula: N = D50^(1/6) / 21.2, where D50 is median grain size in meters.

Bank angles should never be set to 90 degrees and should be set to 0 on hillslopes. If channel bed width is taken proportional to the square root of discharge, then it should roughly double with a unit increase in order. Note that best results will be obtained if measured vs. estimated values are used for each order.