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

在定量描述结构性土壤中水和溶质运动时，优先流仍然是一个很大的挑战。经验模型是基于现象学的方法，考虑流域的大孔网络和多孔基质和作为一个关键组成部分的域之间的交换。然而，许多方面的优先流不能解释没有物理上足够的孔隙尺度的理解，大孔隙内的流动和优先流动路径和土壤基质之间的流量交换。问题包括使用的连续假设的大孔隙系统和流动的高度非均匀孔隙空间可变的局部属性。其目的是创建一个基础，一类新的数字土壤物理模型与明确的优先流交换通量与土壤基质的孔隙尺度物理学与会计空间异质性的润湿性和张量流特性的土壤的非标量和非对角项。流量交换系数将明确计算的基础上孔隙尺度模拟。将使用Navier-Stokes方程研究在较大的大孔隙中发生非蠕动流效应的条件。最后，更多的物理为基础的土壤水文连续模型将开发，这是基于孔隙尺度模拟的结果，用于获得“功能”的放大孔尺度流在大孔隙和流动与多孔基质的相互作用。为了进行比较，将使用Richards模型和个体裂缝模型。该项目将分析现有的优先流动观测和突破数据，并打算改进荧光染料示踪技术，以量化流动交换，测试孔隙尺度建模。该合作项目结合了孔隙和连续体尺度建模与实验验证。来自RAS（莫斯科）和ZALF（慕尼黑）的两个小组在荧光示踪剂实验、双连续模型评估以及孔隙尺度与多域方法的比较方面进行合作。将使用现有的土壤数据、优先流观测和染色成像;开发额外的铀示踪技术。Kirill Gerke博士的小组将进行随机重建的孔隙尺度分析，以计算张量特性，孔隙尺度流动模拟以及用于放大的衍生函数。Horst H. Gerke（ZALF）专注于实验和跟踪以及传统的双连续建模。德国和俄罗斯的研究小组最终将重新解释以前的研究，以获得更好的知识，优惠和交换流量的基础上孔隙规模的信息。改进后的模型可能有助于解释优先流在非饱和土壤中作为一个孔隙尺度效应和升级的转移和比较到更大的规模模型。

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.