Tuflow and estry manual Version 3

3.13.2.1Storage (NA) Tables

Using an elevation versus surface area table (NA table – NA stands for Nodal surface Area). This provides the opportunity to accurately define the storage of the floodplain including any backwater areas that do not act as flowpaths.

NA tables are entered using ESTRY’s original fixed field formats as detailed in Section E.4 or by accessing a table in a comma or space delimited text file linked to a 1d_ta layer (see Section 3.13.3).

3.13.2.2Using Channel Widths

The storage is calculated from one or more of the channels connected to the node. This approach does not require any specification of a NA table and is therefore the easiest. It is suited to nodes where the storage is accurately defined using the channel widths. For example, nodes connecting channels that model the in-bank flowpaths of a river. It may not be a suited to, for example, floodplain areas where the storage may differ significantly from that calculated using the widths of the floodplain channels.

The channel storage approach is invoked using the Use_Chan_Storage_at_Node attribute described in Table 4 .10. If the attribute is set to “T” (true), the storage from the channel is assigned to both of the nodes the channel is connected to. The storage is split equally to the two nodes. For each node the surface area at different elevations is calculated as the product of the channel width by half the channel length.

If the Use_Chan_Storage_at_Node attribute is set to “F” (false), the storage of that channel is not used in calculating the storage at the two nodes.

Care should be taken using this option for G or S channels that have very steep slopes – check that the resulting NA table in the .eof file is satisfactory.