The 2011 Tohoku earthquake damaged many small earthen dams in Japan, causing flood damage and human casualties. Since then, the necessity for developing accurate inundation hazard maps for areas at risk has been highlighted. We constructed a numerical model using two-dimensional shallow-water equations with the finite element method to simulate such flood flows and tested this approach by simulating the 2011 breach of the Aotashin-ike dam and subsequent flow into the downslope Ohya-ike dam. In addition, we investigated the effect of different inflow hydrographs at a collapsed dam’s breaching point on simulated flood flow comparing three different peak timings. While the spatial extent of the simulated inundation area was not affected, the timing of flood arrival and the simulated water depth in the drainage channel were moderately affected by the inflow hydrograph; the maximum water level in the drainage channel increased with a peak timing delay. The methodology presented here can determine further efforts to better define inundation risk for Japan’s small earthen dams and provides practical procedures to account for downstream topographic features such as spillways and drainage channels.

中文翻译：

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小型土坝溃坝后洪水流量的数值模拟：以2011年东北地震为例

2011年的东北地震损坏了日本的许多小型土坝，造成洪水灾害和人员伤亡。从那时起，针对高风险区域开发准确的淹没危害图的必要性就得到了强调。我们使用二维浅水方程式和有限元方法构建了一个数值模型，以模拟这样的洪水流，并通过模拟2011年Aotashin-ike大坝的溃决以及随后流入下坡Ohya-ike大坝的方法对该方法进行了测试。此外，我们比较了三个不同的高峰时间，研究了倒塌水坝破坏点处不同流入水位图对模拟洪水的影响。虽然模拟淹没区域的空间范围不受影响，入流水文图对洪水到达的时间和排水渠的模拟水深有适度的影响。排水通道中的最大水位以峰值定时延迟增加。此处介绍的方法可以确定进一步的工作，以更好地确定日本小型土坝的淹没风险，并提供实用的程序来说明下游地形特征，例如溢洪道和排水渠。