I have developed the flood model and in order to calibrate the model i have used observed water level from mean sea level with time at one gauge station. Before run the model i set that location elevation in the grid node as 0 (mean sea level elevation). After simulated the model, when i check the water level for particular location in graph window it showed different elevation for ground elevation (in my case it showed as 6.5 m- see attached figure) and water level are shown from that elevation. Could you explain me why does it happen and how to calibrate model when the water level data available with time. Thanks in advance