I am developing several 1D TUFLOW models to simulate existing natural channels and then proposed conditions where a portion of the existing channel becomes replaced with a new box culvert. Both the existing and proposed models have several culverts incorporated into them. In my example, the actual culvert length is 80 feet while the culvert 1d channel segment between cross-sections is 100 feet. The XS lines immediately downstream and upstream of the culverts are slightly beyond the each end of the culvert. In this example, there is a 15’ difference on the left side and a 5’ difference on the right side. The actual culvert lengths were manually entered into the 1d_nwk attribute table; these lengths, however, will not match the channel length between the U/S XS and the D/S XS. Does TUFLOW inherently account for this difference? In other hydraulic modeling programs, you have to specify the distance from the culvert headwall to the adjacent XS – does the same apply for TUFLOW? We want to make sure that TUFLOW is correctly calculating culvert losses based on the true length and that the extra sectional length between the start/end of the culvert and the adjacent XS is being accounted for. If you could provide some insight into how TUFLOW handles this situation and performs calculations that would be appreciated and helpful for us to get a better understanding of the program so we can modify our models if needed. We have several culverts in both the Rag Run and Poorhouse Run models so it is important we clarify this issue. In addition, I am curious as how TUFLOW uses the geographic location of the cross-sections and 1d_network channels. Does TUFLOW use the XS data contained within the CSV files in combination with the specific locations of the XS lines to build the model? Do the channel lengths in the 1d_nwk GIS attribute table have to match the actual length of the stream segment between consecutive cross-section lines? Any help would be greatly appreciated as we are relatively new at using TUFLOW.