Study On Solute Tracer Method For Runoff Velocity Measurement With Applications To Melt Water Erosion

The overland flow velocity is an important parameter to characterize the dynamic characteristics of slope erosion, is a key determinant of the erosion forces and transport capabilities. The measurement of the overland velocity is important to the mechanism study of soil erosion and the soil erosion prediction mpdel.A method to determinate the optimum measurement distance of the Pulse Boundary Model is proposed from the relationship of velocity and distance, and applied to simulated non-frozen slope and gravel layer. For the velocity measurement of flow along the simulated non-frozen slope using an electrolyte tracer method with a Pulse Boundary Model, the minimum distances for measured velocity with an error limit of5%was2.5m and those for an error limit of10%was2.0m from the injector under the given flow rates (5°,10°,15°) and slope gradients (12,24,36L/min).A series of comparative flume experiments were conducted to study the flow velocity over frozen slopes and simulated ice slope with Pulse Boundary Model method and Dye Tracer method, along both the frozen slopes and non-frozen slope. The results showed that the water flow velocities over frozen slope increased with slope gradients and flow rates. The minimum distances for measured velocity with an error limit of5%was1.7-2.7m and those for an error limit of10%was1.4-2.1m from the injector under the given flow rates and slope gradients. The velocities, over frozen slopes, measured by the Pulse Boundary Model method under the given experimental conditions ranged from0.45m/s to0.98m/s, which were1.43times of those over non-frozen slopes. The velocities, over simulated ice slopes, measured by the Pulse Boundary Model method under the given three flow rates (12,24and48L/min) and three slope gradients (5°,10°and15°), ranged from0.49m/s to1.09m/s. which were5-23%higher of those over frozen slopes, and26-51%higher than those over the non-frozen slopes. The flow velocities over ice slope increased with slope gradients and flow rate, while those over ice slope covered by superglacial moraine increased with slope gradients, but stayed steady generally when the flow rate changed. The velocities, over simulated ice slopes covered by superglacial moraine, measured by the Pulse Boundary Model method under the given four flow rates (3,6,12, and24L/min) and four slope gradients (5°,10°,15°and25°), ranged from0.015m/s to0.217m/s.A series of comparative flume experiments were conducted to measure the shallow water flow velocity, with a computerized electrolyte tracer method and dye tracer method. Centroid velocities, leading edge velocities, peak concentration velocities and velocities estimated by Pulse Boundary Model along the flume were computed for comparison purposes. The correction factor αE by which multiplied the leading egde velocity to obtain the centroid velocity were0.530-0.629, with a mean calue of0.580. The correction factor βE by which multiplied the peak concentration velocity to obtain the centroid velocity were0.819-0.975, with a mean calue of0.884.A series of flume experiments were conducted to measure ephemeral gully water flow velocity with2methods, the electrolyte tracer method. The results showed that the velocity of ephemeral gully water flow increased with flow rate and slope gradient. The velocity measured by the electrolyte tracer method under the given experimental condition ranged from0.55m/s to1.60m/s, as compared with0.71m/s to1.45m/s by the dye tracer method. The velocities measured by the two methods were compared under different slope gradients and flow rates. The velocities measured by the dye tracer tended to be lower than those measured by the electrolyte tracer method. Considering the strong dilution and disturb effects of high rate water flow and strong turbulence on dye tracer, visual detection of dye movement should have caused later detection of the dye movement in water flow. All these indicate that the measured velocity of ephemeral flow seems rational.The study on the melt water runoff velocity is of importance to the study of the machenism of soil erosion under melt water runoff.