脉冲边界模型测量冻土坡面径流流速与距离优选

Optimum Measurement Distance of Water Flow Velocity over Frozen Slopes with Pulse Boundary Model Method

在室内不同坡度和流量条件下,用电解质脉冲边界模型以及染色剂示踪法进行冻土坡面和未冻土壤坡面径流流速测量的对比研究。采用长3.8 m、宽0.2 m和深0.08 m的试验土槽,用新疆阿克苏温宿县科其喀尔冰川流域草甸土,装土容重为1.0 g/cm^3、厚度5 cm,将土样饱和后冻结,制备用于试验的冻土坡面。为提高试验效率,采用在砂纸上粘贴土壤颗粒的方法模拟未冻土壤坡面。在坡度5°、10°和15°,流量12、24和48 L/min条件下,采用电解质脉冲边界模型方法和染色剂示踪方法测量冻土和未冻土壤坡面径流流速,并确定电解质脉冲边界模型方法的最优测量距离。结果表明：电解质脉冲边界模型测量流速随着测量距离增加呈指数增加,并逐渐趋于恒定。通过流速随沟长的变化关系,计算得到冻土坡面条件下,电解质脉冲边界模型测量流速与实际流速相差5%和10%,所需测量距离分别为1.7～2.7 m以及1.4～2.1 m。电解质脉冲边界模型法测得的冻土坡面径流流速随坡度、流量增大而增大,为0.45～0.98 m/s,是未冻土壤坡面径流流速的1.43倍。冻土坡面染色剂示踪法测得的流速较电解质脉冲边界模型测得的流速大3%～20%;未冻土壤坡面染色剂示踪法测得的流速较电解质脉冲边界模型测得的流速大6%～35%。

The water flow velocity over hillslope is an important hydraulic parameter. A series of comparative flume experiments were conducted to study the flow velocity with pulse boundary model method and dye tracer method, along both the frozen slopes and non-frozen slopes. The flume used in the experiments was 3.8 m long, 0.2 m wide, and 0.08 m high, with soil taken from Koxkar Glacier basin in Akesu, Xinjiang Automous Region. The experimental soil was packed evenly into the flume to a bulk density of 1.0 g/cm3 and a thickness of 5 cm. The packed soil was saturated before frozen prior to each experiment. The experiments involved three flow rates （12, 24 and 48 L/min） and three slope gradients （5°, 10° and 15°）. The velocities measured by pulse boundary model method increased exponentially with distance from the solution injection location, before becoming steady. The distances for measuring flow velocity with pulse boundary model method on the frozen slope were calculated from the relationship of velocity and distance. The calculated results showed that the minimum distances for measured velocity with an error less than 5% were 1.7 -2.7 m and those for an error less than 10% were 1.4 -2.1 m 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 from O. 45 m/s to 0.98 m/s, increased with slope gradients and flow rates, which were 1.43 times of those over non-frozen slopes. The velocities over frozen slopes, as measured by the dye tracer method were 3% -20% higher than those measured by the pulse boundary model method under different slope gradients and flow rates. Those over non-frozen slopes measured by the dye tracer method were 6% -35% higher than those measured by the pulse boundary model method. The result is useful and important to understand the hydraulic dynamic process of frozen soil erosion.