Tuflow and estry manual Version 3

3.5Model Resolution

3.5.12D Cell Size

The cell sizes of 2D domains need to be sufficiently small to reproduce the hydraulic behaviour. Refer to Section 3.1 above for further discussion.

3.5.21D Network Definition

The adequacy of the 1D domains is primarily dependent on the network representation adopted. In general, the finer the resolution the more accurate the model, but the longer the computing time. For stability reasons, the timestep for computation is normally controlled by the minimum channel length (see Section 3.6.2). The end result may require a compromise between the level of detail and the computational effort.

Prior to Build 2005-05-AN, for 2D/1D models it is highly preferable that the 1D solution does not dictate the timestep as all domains use the same timestep. As of Build 2005-05-AN, different timesteps can be specified for 1D and 2D domains largely removing this constraint.

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. 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. In this way, the model is built up as a series of interconnected channels and nodes with the channels representing the flow resistance characteristics.

For 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. 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 case, a flow path is represented by an “equivalent” channel. 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.

All nodes and channels are labelled with an ID. No two nodes or two channels can have the same ID. Aa node and a channel can have the same ID.