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Hi, We are modelling a fully submerged trunk drainage culvert with flood depth to invert > 7 m due to regional tailwater. There is hydraulic grade across the structure due to local upstream flows. Intitial water levels in both the 1d and 2d domain are set based on the regional tailwater. We have checked the time series results and the .eof file. At the beginning of the event, the water level in the culvert starts at the IWL/fixed tailwater condition, but then drops below by approx. 100 mm throughout the storm. Flow regime is 'F' (submerged entrance and exit, full pipe flow, downstream controlled), which is what we expect. We do not understand how the head in the 1d domain can drop below the tailwater conditions. We think the head drop at the outlet could related to the nodal area, as the automatically created nodal area table in the .eof stops just short of our fixed tailwater level. Is there a quick way extend the automatically created nodal area table of a 1d_nwk culvert, or do we need to take an alternate approach via an NA table and 1d table link? Regards, Francis