BackgroundThe south of Mexico is the least developed part of the country but its basins generate more than 60% of the country’s available water. Though disturbances to the rivers caused by development are still low, there is concern about the environmental health of the rivers. The calculation of the sediment load with a focus in fine fraction, where nutrients are found, is a priority. However, models for suspended sediment transport in large rivers are difficult to formulate because they carry a large amount of cohesive sediments, those cohesive sediments form aggregates or flocs with primary particles that are less than 65 μm. The hydrodynamic behavior of flocs depends on their size, density and shape, which differs from that of non-cohesive sediments as theirs depends on their interaction with the water column. A classical model to calculate suspended sediment concentration profiles for steady flow conditions is the Rouse equation, which has been extensively validated for non-cohesive suspended sediment. Some authors have demonstrated that when applied in some large rivers in conjunction with non-cohesive settling velocity models it does not perform very well. The difficulty comes from the fact that most of the suspended sediment charge in large rivers is constituted by cohesive sediments.ResultsSuspended sediments from Mexico’s two largest rivers Usumacinta and Grijalva, with a mean flow rate near river mouth of 2020 m3/s and 1150 m3/s respectively, were analyzed in a rotating annular flume (RAF). The shear velocity obtained in the field by ADCP was reproduced in the annular flume, the size and shape of flocs were obtained by means of PTV. Settling velocity was also obtained to calibrate a settling velocity model appropriate for cohesive sediments.ConclusionsThe settling velocity model developed for cohesive sediments in conjunction with the Rouse equation allowed the reproduction of suspended sediment concentration profiles for the rivers Usumacinta and Grijalva. The estimated concentration profiles were compared and validated with the measured concentration profiles in the field. Thus, the model obtained through this research can be used to estimate nutrient delivery to the sea from the largest rivers in Mexico.

中文翻译：

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墨西哥两条河流粘性悬浮泥沙输移模型的实验验证

背景墨西哥南部是该国最不发达的地区，但其流域产生了该国 60% 以上的可用水。尽管开发对河流的干扰仍然很低，但人们对河流的环境健康表示担忧。以发现营养物的细粒为重点来计算沉积物负荷是一个优先事项。然而，大型河流中悬浮泥沙输运的模型难以制定，因为它们携带大量粘性沉积物，这些粘性沉积物形成初级颗粒小于65μm的聚集体或絮体。絮状物的水动力行为取决于它们的大小、密度和形状，这与非粘性沉积物的不同，因为它们取决于它们与水柱的相互作用。计算稳定流条件下悬浮泥沙浓度分布的经典模型是 Rouse 方程，该方程已被广泛验证用于非粘性悬浮泥沙。一些作者已经证明，当与非粘性沉降速度模型一起应用于一些大河流时，它的表现不是很好。难点在于大河中的大部分悬浮泥沙是由粘性沉积物构成。 结果墨西哥最大的两条河流乌苏马辛塔河和格里哈尔瓦河的悬浮泥沙，在河口附近的平均流速分别为2020 m3/s和1150 m3/ s 分别在旋转环形水槽 (RAF) 中进行分析。ADCP在现场获得的剪切速度在环形水槽中再现，絮体的大小和形状通过PTV获得。还获得了沉降速度以校准适用于粘性沉积物的沉降速度模型。结论 结合 Rouse 方程为粘性沉积物开发的沉降速度模型允许再现 Usumacinta 和 Grijalva 河流的悬浮泥沙浓度剖面。将估计的浓度分布与现场测量的浓度分布进行比较和验证。因此，通过这项研究获得的模型可用于估计墨西哥最大河流向海洋输送的养分。结论 结合 Rouse 方程为粘性沉积物开发的沉降速度模型允许再现 Usumacinta 和 Grijalva 河流的悬浮沉积物浓度剖面。将估计的浓度分布与现场测量的浓度分布进行比较和验证。因此，通过这项研究获得的模型可用于估计墨西哥最大河流向海洋输送的养分。结论 结合 Rouse 方程为粘性沉积物开发的沉降速度模型允许再现 Usumacinta 和 Grijalva 河流的悬浮沉积物浓度剖面。将估计的浓度分布与现场测量的浓度分布进行比较和验证。因此，通过这项研究获得的模型可用于估计墨西哥最大河流向海洋输送的养分。