The exchange flow between preferential flow paths and matrix in soils: from pore to continuum scale with tensors

当试图定量描述结构性土壤中的水和溶质运动时，优先流动仍然是一个巨大的挑战。经验模型基于现象学方法，考虑大孔网络和多孔基质的流动域，并作为域之间交换的关键组成部分。然而，如果对宏观孔隙内的流动以及优先流动路径与土壤基质之间的流动交换没有足够的物理上的孔隙尺度理解，就无法解释优先流动的许多方面。问题包括使用连续假设的大孔系统和流动的高度非均质孔隙具有空间可变的局部性质。目标是为具有明确优先流的新型数字土壤物理模型创建基础，其中与土壤基质的交换通量由孔隙尺度物理通知，并考虑非标量和非对角项土壤的空间非均质润湿性和张拉流动特性。流动交换系数将根据孔隙尺度模拟显式计算。采用Navier-Stokes方程研究了大孔隙中非蠕变流动效应发生的条件。最后，将开发更多基于物理的土壤水文连续体模型，这些模型基于孔隙尺度模拟的结果，用于推导大孔隙中提升尺度的孔隙尺度流动和与多孔基质的流动相互作用的“函数”。为了进行比较，将使用基于richards的模型和单个裂缝模型。该项目将分析现有的优先流动观测和突破性数据，并打算改进荧光染料示踪技术，用于定量流动交换，以测试孔隙尺度模型。该合作项目将孔隙和连续尺度建模与实验验证相结合。来自RAS （Moscow）和ZALF （m<s:1> ncheberg）的两个小组在荧光示踪剂实验、双连续体模型评估以及孔隙尺度与多域方法的比较方面进行了合作。可用的土壤数据、优先流观测和染色成像将被使用；开发了额外的铀示踪技术。Kirill Gerke博士的小组将进行随机重建的孔隙尺度分析，以计算张拉特性，孔隙尺度流动模拟，并为升级导出函数。Horst H. Gerke博士（ZALF）的团队专注于实验和追踪以及传统的双连续体建模。德国和俄罗斯的研究小组最终将重新解释以前的研究，以获得基于孔隙尺度信息的优惠和交换流的改进知识。改进的模型可以帮助解释非饱和土中的优先流动为孔隙尺度效应，并通过转移和比较到更大的尺度模型中进行放大。

Preferential flow still poses a great challenge when trying to quantitatively describe water and solute movement in structured soils. Empirical models are based on phenomenological approaches that consider flow domains for the macropore network and the porous matrix and as a key component the exchange between domains. However, many aspects of preferential flow cannot be explained without a physically adequate pore-scale understanding of both, the flow within macropores and the flow exchange between preferential flow paths and the soil matrix. Problems include the use of the continuum-assumption for the macropore system and flow in highly heterogeneous pores with spatially variable local properties. The objective is to create a foundation for novel class of digital soil physics models with explicit preferential flow where exchange fluxes with soil matrix are informed by pore-scale physics with accounting for spatially heterogeneous wettability and tensorial flow properties of soils for non-scalar and off-diagonal terms. Flow exchange coefficients will be explicitly calculated based on the pore-scale simulations. Conditions for the occurrence of non-creeping flow effects in larger macropores will be studied by using Navier-Stokes equations. Finally, more physically-based soil hydrological continuum models will be developed, which are based on results of pore-scale simulations used to derive "functions" for upscaling pore-scale flow in macropores and flow-interaction with porous matrix. For comparison, Richards-based models and individual fracture models will be used. This project will analyze available preferential flow observations and breakthrough data and intends to improve fluorescence dye tracing techniques for quantification of the flow exchange for testing the pore scale modelling. The collaborative project combines pore and continuum scale modeling with experimental validation. The two groups from RAS (Moscow) and ZALF (Müncheberg) collaborate with respect to fluorescence tracer experiments, dual-continuum model evaluation, and comparison of pore-scale with multi-domain approaches. Available soil data, preferential flow observations, and staining imaging will be used; additional Uranine tracer techniques developed. The group of Dr. Kirill Gerke will carry out pore-scale analyses for a stochastic reconstruction to compute tensorial properties, pore-scale flow simulations, and to derived functions for upscaling. The group of Dr. Horst H. Gerke (ZALF) focusses on experimental and tracing and conventional dual-continuum modeling. Both German and Russian groups will finally re-interpret previous studies to obtain improved knowledge on preferential and exchange flow based on pore-scale information. The improved modelling may help explaining preferential flow in unsaturated soils as a pore-scale effect and upscaled by transferring and comparison into larger scale models.