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Mountainous soils often contain large amounts of gravels which impact rainfall infiltration, runoff and soil erosion. The flow velocity within gravels is of great importance for research of soil erosion process in rocky mountainous areas. Dye tracer method was commonly used to measure the leading edge velocity. The gravels of about 2 cm in diameter were used to fill to a thickness of about 5cm in a flume of 4m long, 15cm wide and 50cm high. Five sensors were used to measure the electrolyte conductivity change process at 0.3, 0.6, 0.9, 1.2 and 1.5m from the solute injector under three flow rates of 3, 6 and 12L/min and three slope gradients of 4°, 8°and 12°. The peak, mean and leading edge velocities were computed before comparisons were made with those measured by using dye tracer method. The results showed that under different conditions, flow velocity was not significantly affected by discharge rate, but notably affected by slope. With the increase in slope, flow velocity increased from 0.031m/s to 0.070m/s. The peak velocities were 0.81~0.83 times of the leading edge velocity, regardless of the effect of slope and flow rate. Mean velocities were about the same as the peak velocities, which were 0.68~0.78 times of the leading edge velocities and increased with distance increasing. The ratio of mean velocity and leading edge velocity can be also used to calculate the flow velocity within gravels measured by dye tracer method. The method should be useful to understand the hydrodynamics of water flow within gravel layers.