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Line 61: ==Deck Losses and Pressure Flow== A pressure flow condition can occur when the water level reaches the bridge deck level (as water is forced through a small opening confined by the bridge abutments and the deck), resulting in additional energy losses. As the bridge becomes totally drowned by the water level, the condition will switch back to the normal submerged bridge deck flow condition. To account for this, once water reaches the height of the bridge deck, the TUFLOW BB bridge tests for either the pressure flow condition or drowned flow condition at every timestep by choosing the flow regime that gives the lower flow: :The pressure flow equation is based on the Section 8.3 ~~"All Girders in Contact with Flow (Case II)"~~ of the <u>[https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hds1.pdf Hydraulics of Bridge Waterways (Bradley, 1978)]</u>, with a default deck discharge coefficient of 0.8. This value can be modified using the 1d_nwk HConF_or_WC attribute. Note that the original hydraulic experiment conducted by Liu (1967) used a flume with a pair of bridge abutments and a deck. This means the impact of both abutments and deck are considered in this approach. The entry/exit losses are switched off during the pressure flow calculation to avoid the overestimation of the contraction/expansion losses. :For the drowned flow condition, the BB bridge considers extra energy loss caused by the bridge deck/rails using a deck loss coefficient (default = 0.5) in addition to the entry/exit losses. The deck loss coefficient can be adjusted using the WConF_or_WEx attribute or by specifying the LC (energy loss versus height) table. When pressure flow occurs a flow regime of "P" is reported in the _TSF layer. <br>

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