Gillian Murphy

I have attached a sketch of the cross-section of an example bridge and my suggested representation using a link channel. In this case the floodplain is large and you would not expect a large headloss once water levels exceed the bridge deck, therefore I don't believe using a parallel weir is justified. Instead I would create a link channel with the level-width data of the floodplain and bridge deck and link this to the main channel immediately upstream and downstream of the structure.

Any comments on this set up would be welcome. I am primarily concerned about the discretisation along the channel, making sure the link channel is connected to prevent any double counting with the cross-sections.

I am undertaking some flood modelling of a large river catchment and have a query about representing flow which bypasses structures.

I understand the general approach is to use a weir in parallel to the structure (with the same chainage). However for cases such as at a weir, there is no specific change in elevation across the floodplain area. Therefore I feel that using a weir to represent out of bank flow in this instance would result in a greater head loss than is realistic.

Does anyone use a link channel to represent flow around structures, connected to the main river immediately up and downstream of the structure? Are there any limitations with this approach?

Thanks in advance for views / suggestions.