Abstract Modeling preferential flow in soils is still a challenge for the scientific community working on water resources. Indeed, it is an issue to determine the functional parameters of models dedicated to water flow, that are currently obtained by fitting processes, whereas their relationships with soil structure remain poorly known. Improved models are expected from a better understanding of the links between functional and structural parameters, which can be achieved thanks to recent developments in imaging methods such as X-ray Computed Tomography (CT). The paper seeks to improve a dual-porosity model, coupling matrix flow (by Richards equation) and preferential flow (by a Kinematic Dispersive Wave), by substituting some model parameters, usually obtained by inversion of experimental data, by those assessed from CT images of the soil structure. Thus, two versions of the model are compared, the “classical” and the “advanced” one including parameters determined using the 3D images of the sample structures. To compare model versions with real situations, infiltration experiments were conducted in lab on two different soils at two initial water contents. An X-ray medical scanner allowing acquisitions of large soil volumes (≈ 1700 cm3) with a voxel size of 400 µm was used to image the sample structures. Then, we derived two geometrical parameters from the macroporosity network: the percolating macroporosity and a characteristic dimension of this macropore network, the mean inter-macropore distance. The sensitivity analysis conducted on the classical version of the model showed that the kinematic coefficient and the dimensional parameter of the porous medium are the two main contributors to the cumulated drainage whatever the initial condition. Although experimental data are better simulated by the classical version of the model, drainage dynamics is also well simulated by the advanced version. However, differences between the model versions that are small for both soils at field capacity become significant for the dried state (mean initial matric potential of −3.5 m). This emphasizes the crucial effect of the sink-source term and in particular the complex effect of the dimensional parameter that it contains. Indeed, difficulties to simulate properly water exchange between porosity domains are encountered for both versions of the model. We conclude that empirical parameters that were up to now fitted from experiments could be deduced from geometrical indicators computed from CT images and that owning to these first results the applied methodology is promising to achieve a better understanding and modeling of preferential flow processes and to improve model predictability.

中文翻译：

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从 CT 图像中获得的结构数据能否替代优先流动模型的参数？

摘要 模拟土壤中的优先流仍然是水资源科学界面临的挑战。事实上，确定目前通过拟合过程获得的专用于水流的模型的功能参数是一个问题，而它们与土壤结构的关系仍然知之甚少。更好地理解功能和结构参数之间的联系有望改进模型，这要归功于 X 射线计算机断层扫描 (CT) 等成像方法的最新发展。本文试图通过代入一些模型参数来改进双孔隙模型，耦合矩阵流（由理查兹方程）和优先流（由运动色散波），由那些根据土壤结构的 CT 图像评估的人。因此，模型的两个版本进行了比较，“经典”和“高级”版本包括使用样本结构的 3D 图像确定的参数。为了将模型版本与实际情况进行比较，在实验室中对两种不同土壤、两种初始含水量进行了渗透实验。使用 X 射线医学扫描仪可以采集体素大小为 400 µm 的大土壤体积 (≈ 1700 cm3)，用于对样品结构进行成像。然后，我们从大孔隙网络推导出两个几何参数：渗透大孔隙率和该大孔隙网络的特征维度，即平均大孔隙间距离。对该模型的经典版本进行的敏感性分析表明，无论初始条件如何，多孔介质的运动学系数和尺寸参数都是累积排水的两个主要贡献因素。虽然模型的经典版本可以更好地模拟实验数据，但高级版本也可以很好地模拟排水动力学。然而，两种土壤在田间持水量下的模型版本之间的差异在干燥状态下变得显着（平均初始基质电位为 -3.5 m）。这强调了汇源项的关键影响，特别是它包含的维度参数的复杂影响。事实上，两种版本的模型都遇到了正确模拟孔隙度域之间的水交换的困难。