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A Subgrid Approach for Modeling Microtopography Effects on Overland Flow

机译：建模微地形对陆流影响的子网格方法

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摘要

Microtopography, or heterogeneities in the elevation across scales much smaller than the domain of interest, plays a critical role in surface water retention, surface/subsurface interactions, and runoff. Resolving microtopographic influences on flow requires high-resolution simulations that are computationally demanding even when considering the surface system in isolation and even more so when surface flow is one component in integrated simulations that couple surface flow with unsaturated subsurface flow. There is thus significant motivation for models that allow the effects of subgrid microtopography to be better represented. Subgrid models modify coarsened models to capture the microtopography-induced nonlinear effects on hydrologic processes. We present a subgrid model that alters the water storage and flow terms in the diffusion wave equation for surface flow. Stochastically generated microtopography with strongly contrasting spatial structure, high-resolution digital elevation maps from a polygonal tundra site on the North Slope of Alaska and a hummocky microtopography from a field site in Northern Minnesota are used to assess the accuracy and applicability of the subgrid model to disparate landscapes. Approaches for determining subgrid model parameters are tested and simulation results using the subgrid model are compared to benchmark fine-scale simulations and to coarse simulations that ignore microtopography. Our findings confirm that a properly parameterized subgrid model greatly improves the coarse-scale representation of hydrographs and total water content in the system. Using the polygonal tundra example, we propose and test a strategy for moving to application-relevant spatial scales by combining microtopography classification and a few fine-scale simulations on small subdomains.
机译：微观形貌或跨尺度的高程异质性远小于所关注的区域，在地表水滞留，地表/地下相互作用和径流中起关键作用。解决微观地形对流量的影响需要高分辨率的模拟，即使在单独考虑地表系统的情况下，对计算的要求也很高，因此，当表面流是将表面流与不饱和地下流耦合在一起的综合模拟中的一个组成部分时，就更是如此。因此，存在着极大的动机来建立模型，以更好地表现亚网格微形貌的影响。子网格模型修改了粗化模型，以捕获微观地形引起的对水文过程的非线性影响。我们提出了一个子网格模型，该模型改变了表面流扩散波方程中的储水量和流量项。随机生成的微观形貌具有强烈的空间结构对比，使用阿拉斯加北坡多边形苔原地带的高分辨率数字高程图和明尼苏达州北部野外场所的丘陵形微地貌，来评估亚网格模型的准确性和适用性不同的景观。测试了确定子网格模型参数的方法，并将使用该子网格模型的仿真结果与基准细规模仿真和忽略微形貌的粗略仿真进行了比较。我们的发现证实，正确设置参数的子网格模型可以大大改善水文图的粗略表示和系统中的总含水量。以多边形苔原为例，我们提出并测试了一种策略，该方法通过将微地形学分类和一些在小子域上的精细模拟相结合，来转移到与应用程序相关的空间尺度。

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