Rain-on-grid simulations for the modeling of 2D unsteady flows in response to precipitation input are implemented in Hydrologic Engineering Center's River Analysis System (HEC-RAS) software by means of a finite volume method and a sparse parallel linear solver running on a unique processor. Obviously, this may fail due to memory shortage when the discretization yields too large linear systems. Such simulations are good candidates for the design of partition and domain decomposition methods for the modeling of very large catchments by means of hydrological sub-units. Thinking in load-balanced computations, the proposed area-balanced partition method is based on the flow accumulation information. Implemented in HEC-RAS, the domain decomposition method comprises 2D–1D models combining 2D sub-unit meshes to 1D channels for extracting outflow data from upstream units and passing the information to downstream units. The workflow is automated using the HEC-RAS Controller. As a case study, we consider the French Saar catchment (1,747 km²). The new partition methods demonstrate a better equilibrium for sub-basin areas and the computational load for the sub-problems. The total computational time is substantially reduced. Domain decomposition is required for carrying rain-on-grid simulations over the Saar watershed (2,800,000 elements). The resulting discharge and flood maps show very good agreements with available data.

在水文工程中心的河流分析系统 (HEC-RAS) 软件中，通过有限体积法和运行在唯一处理器。显然，当离散化产生太大的线性系统时，这可能会由于内存不足而失败。此类模拟是设计分区和域分解方法的良好候选者，用于通过水文子单元对超大流域进行建模。考虑到负载均衡计算，所提出的区域均衡分区方法是基于流量累积信息的。在 HEC-RAS 中实施，域分解方法包括将 2D 子单元网格与 1D 通道相结合的 2D-1D 模型，用于从上游单元提取流出数据并将信息传递给下游单元。该工作流程使用 HEC-RAS 控制器实现自动化。作为一个案例研究，我们考虑法国萨尔流域（1,747 公里² )。新的划分方法对子流域区域和子问题的计算负载表现出更好的平衡。总计算时间大大减少。在萨尔流域（2,800,000 个元素）上进行网格降雨模拟需要域分解。由此产生的流量和洪水地图显示与可用数据非常吻合。