有黏性和无黏性沙坡面流的挟沙力比较

Comparison on flow transport capacity of overland flow between cohesive and non-cohesive sand

水流挟沙力是土壤侵蚀过程模型的重要参数。利用黑龙江省嫩江县的黑土(中值粒径d黑土为0. 01 mm)作为有黏性沙的代表进行了坡面流挟沙力试验,将有黏性沙水流挟沙力与前期完成的没有粒径分级的的无黏性沙(该试验用沙从北京市永定河获取,中值粒径为0. 28 mm)水流挟沙力进行比较,并利用前期完成的粒径分级的无黏性沙关于中值粒径的方程式进行验证。试验共设计了5个坡度(3°、6°、9°、12°和15°)和6个流量(0. 25、0. 50、0. 75、1. 00、1. 50和2. 00×10-3m3/s),共30组试验,在长5. 0 m,宽0. 4 m的水槽上进行。研究结果表明:1)有黏性沙和无黏性沙坡面流挟沙力均随着流速、水流剪切力和水流功率的增加而增加; 2)在相同水动力条件下有黏性沙的水流挟沙力大于无黏性沙的水流挟沙力; 3)有黏性沙的水流挟沙力与流速、水流剪切力和水流功率的关系可以用幂函数较好地表达,用流速模拟有黏性沙的水流挟沙力效果最好,用水流剪切力和水流功率模拟无黏性沙的水流挟沙力效果最好; 4)有黏性和无黏性沙的坡面流挟沙力存在差异,用无黏性沙作为试验材料得到的关于中值粒径的水流挟沙力方程式不适用于有黏性沙的水流挟沙力计算。本研究为坡面土壤侵蚀过程的深入理解和模拟提供了基础知识。

[ Background ] Flow transport capacity refers to the maximum flux of sediment that can be transported under specific hydrodynamic conditions, and is an important parameter of soil erosion process model. Domestic and foreign scholars have carried out research works on the flow transport capacity of overland flow;however, the experimental materials are relatively simple, and the soil is not fully considered in the object of the overland flow and the experimental object is concentrated in the non-cohesive sand. Therefore, it is necessary to compare the flow transport capacity of overland flow between cohesive and non-cohesive sand.[ Methods ] The cohesive sand (sampled from black soil of Nenjiang county in Heilongjiang province and the median particle size of 0.28 mm) was used as experimental material. The experiment was designed with 5 slope degrees (3°,6°,9°,12°,and 15°) and 6 flow rates(0.25, 0.50, 0.75, 1.00, 1.50, and 2.00×10 -3 m 3 /s), totally 30 experiments. The experiments were carried out in a flume with 5.0 m long and 0.4 m wide. Dyeing method was to measure the flow rate. The hydraulic parameters and the flow transport capacity of cohesive sand were processed using SPSS software and Origin software, and graphed to obtain the relationship between the flow transport capacity of the cohesive sand and the different hydraulic parameters. The measured results were compared with the ones calculated by equations previously from non-cohesive sand in our laboratory.[ Results ] 1) Flow transport capacity of both the cohesive sand and the non-cohesive sand increased with the increase of the flow velocity, shear stress and stream power. 2) Under the same hydrodynamic conditions, the flow transport capacity of the cohesive sand was greater than that of non-cohesive sand. 3) The relationship between the flow transport capacity of the cohesive sand and the flow velocity, shear stress and stream power was expressed as a power function, and the coefficients of determination were 0.91, 0.72 and 0.80, respectively. The flow velocity was the best hydraulic parameter for calculating the flow transport capacity of cohesive sand. The shear stress and stream power provided the higher accuracy for calculating the flow transport capacity of the non-cohesive sand. The coefficients of determination were 0.98 and 0.98. 4) The measured critical flow velocity of cohesive sand was 0.245 m/s,<0.309 m/s calculated by the equation from the non-cohesive sand previously. The coefficient of determination and Nash-Sutcliffe efficiency coefficient of cohesive sand were 0.72 and 0.78 respectively, while the shear stress equation of non-cohesive sand was used to calculate the flow transport capacity of the cohesive sand. The coefficient of determination and Nash-Sutcliffe efficiency coefficient of cohesive sand were 0.80 and 0.43 respectively, while the stream power equation of non-cohesive sand was used to calculate the flow transport capacity of the cohesive sand. The coefficient of determination of cohesive sand was 0.20 while the relationship between the flow transport capacity of the cohesive sand and the unit stream power was fitted by a power function.[ Conclusions ] There are differences in flow transport capacity of a slope between cohesive and non-cohesive sand, he flow transport capacity equation obtained from non-cohesive sand is not suitable for cohesive sand.