Accounting for Missing Bathymetric Data in Dtm for Large-Scale 1d Hydraulic Modeling (PAP014753)
Flood risk management in mega cities
Elevations for channels or lakes bottom are not usually represented in most digital terrain models (DTM) for many reasons. Typically, where there is a channel or water body wider than the pixel size, the DTM gives a flat elevation of normal flow water surface or an interpolated surface derived from nearby points, e.g., the bank or levee top elevation. However, the missing bathymetric geometric area has to be considered in order to develop accurate flood maps. This aspect becomes even more important for estuaries or regulated rivers, where the geometric area below normal flow water surface is significant. To solve this problem, most existing methods add simple hypothetical shapes to the cross sections or deduct a certain amount of discharge based on geomorphological regressions. In this paper, a new method based on a 1D hydraulic approach is proposed for large-scale flood hazard modeling. In the approach, a formula with one free parameter is derived to estimate the discharge flowing below the DTM surface. The parameter can be readily estimated or calibrated at cross sectional level from observations at gauges before extending to a wider area. The parameter can be related to remotely measurable channel characteristics. This approach has been applied in a regional flood hazard study for the Weser river basin in Germany. Our results and maps show that the approach is able to reduce the bias of the DTM data effectively and improve the accuracy of the model outputs.