pyValleyWidth

• An importable package: valley classification, swath widths, an optional variable rim, smoothing along the stream network, the normalized steepness index k_sn, and river-profile figures.
• valley_width_example.ipynb, an end-to-end run on the Big Tujunga DEM shipped with TopoToolbox. It routes flow, can mask to the largest catchment, measures width two ways, and draws maps, k_sn, longitudinal and chi–elevation profiles, and threshold or excess topography. The notebook is the user guide, including notes on stream area, the HAND threshold, swath spacing, smoothing, and saturated transects.
• The method figure at the top of this page.

Width comes from height above the channel network, a valley polygon, and cross-stream swaths. A profile perpendicular to the channel can overestimate width on a tight bend, so the workflow can resample and smooth widths along the network with a moving window. A variable-rim mode is also available: each transect is clipped to the local divides, and the rim is picked from a sweep of how width changes with the height threshold.

1. Terrain and streams. Flow routing and stream extraction with pytopotoolbox. An optional mask keeps the largest connected catchment, so later steps use one basin.
2. Valley mask, two choices inside dem2widths. A constant HAND threshold treats every cell below a fixed height above the nearest stream as valley, and returns widths and that height field. The variable-rim mode clips each transect to the local drainage divides, sweeps the HAND threshold upward, and takes the last qualifying peak in dW/dT between a noise floor (min_dwdt) and a divide-scale ceiling (max_dwdt). Those per-transect thresholds are lifted onto the stream nodes, smoothed with a rolling median, and passed to the same flood fill. That mode also returns a valley depth. plot_transect_diagnostic draws one transect (map, HAND profile, and the dW/dT sweep) so the two thresholds can be chosen by eye.
3. Widths from swaths. Cross-stream profiles on the valley raster, with an optional filter when a transect is too short to be trusted.
4. Widths on the network. Raw widths at the sample points, then a gap-filled, vertex-averaged, Gaussian-smoothed field (smooth_valley_width_on_stream_network).
5. Add-ons in the example notebook. k_sn from a slope–area fit with fixed concavity, longitudinal and chi–elevation profiles with the trunk highlighted, a trunk profile that pairs width with valley-top height in the variable-rim mode, and threshold or excess topography at a chosen slope (35° in the example).

• dem2widths runs routing, drops short streams, builds the valley mask, measures swaths, and returns drainage area and gradient at the width samples.
• valleyclass_elev, swath_width, and peak_valley_width build the mask and find the rim in the variable-threshold mode.
• plot_transect_diagnostic is the three-panel check at one map point.
• stream_utils drops short streams and builds the swath geometry.
• valley_width_stream flattens stream coordinates, smooths width on the network, and orders samples along the trunk.
• ksn_analysis handles the slope–area fit, k_sn, smoothing, and filling empty values along streams.
• river_profile_plots draws the longitudinal profile, the chi–elevation profile, the paired k_sn and valley-width panels, and the threshold and excess-topography figures.