Compound flooding is usually induced by the concurrence of coastal storm surge and heavy precipitation induced river flooding, with the former involving oceanic processes and the latter involving hydrological processes. The simulation of these two types of processes is traditionally handled by two different types of models separately, i.e., hydrological models (e.g., NOAA’s National Water Model (NWM)) and hydrodynamic models. This dichotomy leaves gaps in simulating the interrelated processes in a holistic fashion. In this paper, we present a creek-to-ocean 3D baroclinic model based on SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) that aims to unite traditional hydrologic and hydrodynamic models in a single modeling platform to simulate compound floods, by taking full advantage of the model polymorphism (i.e., a single model grid can seamlessly morph between full 3D, 2DV, 2DH, and quasi-1D modes). Using Hurricane Irene’s impact on Delaware Bay as an example, a seamless 2D-3D model grid is implemented to include the entire US East Coast and Gulf of Mexico with a highly resolved Delaware Bay (down to 20-m resolution). The streamflow from NWM is injected into SCHISM grid at the intersections of NWM’s segments and SCHISM’s land boundary, and the pluvial and fluvial processes are directly handled by SCHISM. We demonstrate the model’s accuracy, stability, and robustness with focus on the compound flooding events. The relative role of different physical processes in such events is examined by a series of sensitivity tests. Our results confirm the occurrence of backwater process into far upstream rivers and creeks and thus demonstrate the need for a dynamic two-way coupling between the hydrodynamic and hydrological models.

中文翻译：

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模拟飓风中的复合洪水事件

复合洪水通常是由沿海风暴潮和大量降水引起的河流洪水共同引起的，前者涉及海洋过程，而后者涉及水文过程。传统上，这两种类型过程的模拟分别由两种不同类型的模型处理，即水文模型（例如，NOAA的国家水模型（NWM））和水动力模型。这种二分法在整体模拟相互关联的过程中留下了空白。在本文中，我们提出了一种基于SCHISM（半隐式跨尺度水科学综合系统模型）的小溪至海洋3D斜压模型，旨在将传统的水文和水动力模型整合到一个建模平台中，以模拟复合洪水。充分利用模型多态性（即 单个模型网格可以在完整的3D，2DV，2DH和准1D模式之间无缝变形。以飓风“艾琳”对特拉华湾的影响为例，实现了无缝的2D-3D模型网格，其中包括整个美国东海岸和墨西哥湾，并具有高度解析的特拉华湾（分辨率低至20 m）。来自NWM的水流在NWM的各个部分和SCHISM的陆地边界的交点处注入SCHISM网格，并且由SCHISM直接处理河流和河流的冲积过程。我们着重于复合驱事件证明了模型的准确性，稳定性和鲁棒性。通过一系列敏感性测试来检验不同物理过程在此类事件中的相对作用。