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Slope Calculator
Plugin ID: 5259
Calculate river reach slope from a DEM using Average Slope or Equal Area Slope.
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Slope Calculator computes the slope of each river reach feature (line or multiline) from an underlying DEM raster, supporting two methods:
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<b>1. Average Slope (Mean Gradient)</b> — The absolute elevation difference between reach endpoints divided by the total reach length. The simplest and most commonly used slope measure.
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<b>2. Equal Area Slope</b> — 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).
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Both methods produce dimensionless slope values (m/m), 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.
