The cell sizes of 2D domains need to be sufficiently small to reproduce the hydraulic behavior. A node and a channel cannot have the same ID. No two nodes or two channels can have the same ID.
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Experience has indicated that in most cases an adequate calibration can be achieved by deriving a single channel equivalent to a number of series or parallel channels using the steady state Manning's relation for deriving the equivalent channel characteristics.Īll nodes and channels are labeled with an ID. In this case, a flow path is represented by an “equivalent” channel. In practice this requirement cannot always be met, particularly where a fine resolution of detail is not required in a portion of the study area. In this way, the model is built up as a series of interconnected channels and nodes with the channels representing the flow resistance characteristics.įor compatibility with the mathematical assumptions, the channels would ideally have more or less uniform cross-sections with constant bottom slope and a minimum of longitudinal curvature. Following this step the flow paths are linked at junctions, or nodes, and each node is considered as a storage element, which accepts the flow from the adjoining channels. The first step in setting up a model is to define the flow patterns and to use each identified flow path as the basis for a channel of the network. The end result may require a compromise between the level of detail and the computational effort.ĭifferent timesteps can be specified for 1D and 2D domains largely removing this constraint. For stability reasons, the timestep for computation is normally controlled by the minimum channel length.
In general, the finer the resolution the more accurate the model, but the longer the computing time. The adequacy of the 1D domains is primarily dependent on the network representation adopted. Alternatively, a 1D network may be imported or dynamically linked to an external database. Surveys of key hydraulic controls such as levees / embankments (3D breaklines), culverts, bridges, etc.ġD link-node networks are developed in XPSWMM with the graphic toolset. Peak levels should be attached as attributes to the calibration points. ocean water levels, catchment inflows, rainfall, evaporation, etc).Ĭalibration data locations as points in a GIS layer. If bed resistance varies over the model, geo-corrected aerial photography or other GIS layer from which material (land-use) zones are digitized for setting Manning’s n values.īoundary conditions (e.g. The vertical accuracy is dependent on the typical depths of inundation in key areas. However, for large scale models ± 0.2m is preferred, whilst for fine-scale urban models < ± 0.1m is recommended. The vertical accuracy depends on the modeling objectives and budget constraints.
The minimum data requirements for setting up a 2D/1D hydraulic model are:Ī DTM with sufficient resolution and accuracy to depict the topography of all flowpaths and storage areas in the 2D domain(s). General Considerations for building a 2D Model Data Requirements
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