River Slope Calculator
Plugin ID: 5262
Calculate river reach slope from a DEM using Average Slope or Equal Area Slope. Output unit selectable: m/m or %.
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River Slope Calculator computes the slope of each river reach feature (line or multiline) from an underlying DEM raster, supporting two methods:
1. Average Slope (Mean Gradient) — The absolute elevation difference between reach endpoints divided by the total reach length. The simplest and most commonly used slope measure.
2. Equal Area Slope — The slope of a line through the outlet that creates equal areas above and below the longitudinal elevation profile. Adopted in Australian Rainfall and Runoff (ARR, 1987) for the Bransby Williams time-of-concentration formula. Reference: Ladson (2017), NZ Ministry of Works (1980).
Both methods compute slope internally as dimensionless values (m/m). A new Output unit option lets you choose between m/m (dimensionless) and % (percent) — the result is multiplied by 100 when percent is selected. Slope values are added as new fields on a copy of the input reach layer. DEM elevation is sampled at a user-defined interval along each reach using trapezoidal integration for the Equal Area Slope.
