Comparison between Topographic and Bathymetric LiDAR Terrain Models in Flood Inundation Estimations

Abstract

Remotely sensed LiDAR data has allowed for more accurate flood map generation through hydraulic simulations. Topographic and bathymetric LiDARs are the two types of LiDAR used, of which the former cannot penetrate water bodies while the latter can. Usually, the topographic LiDAR is more available than bathymetric LiDAR, and it is, therefore, a very interesting data source for flood mapping. In this study, we made comparisons between flood inundation maps from several flood scenarios generated by the HEC-RAS 2D model for 11 sites in Norway using both bathymetric and topographic terrain models. The main objective is to investigate the accuracy of the flood inundations generated from the plain topographic LiDAR, the links of the inaccuracies with geomorphic features, and the potential of using corrections for missing underwater geometry in the topographic LiDAR data to improve accuracy. The results show that the difference in inundation between topographic and bathymetric LiDAR models decreases with increasing the flood size, and this trend was found to be correlated with the amount of protection embankments in the reach. In reaches where considerable embankments are constructed, the difference between the inundations increases until the embankments are overtopped and then returns to the general trend. In addition, the magnitude of the inundation error was found to correlate positively with the sinuosity and embankment coverage and negatively with the angle of the bank. Corrections were conducted by modifying the flood discharge based on the flight discharge of the topographic LiDAR or by correcting the topographic LiDAR terrain based on the volume of the flight discharge, where the latter method generally gave better improvements.

Flood Management, Characterization and Vulnerability Analysis Using an Integrated RS-GIS and 2D Hydrodynamic Modelling Approach: The Case of Deg Nullah, Pakistan

“…These flood models can simulate additional flood characteristics such as flood arrival times, flood velocities, flood duration and flood recession times [54]. Moreover, remotely sensed datasets have been extensively used with the HEC-RAS 2D model to simulate, validate and forecast flood events in different regions of the world [16,20,34,36].…”

“…For instance, high flood velocities with a longer flood duration can damage the flood mitigation structures and result in erosion and water pollution, which may cause environmental degradation, economic and life losses [33]. Awadallah et al [34] used the LiDAR datasets in the HEC-RAS 2D model for comparing the flood inundations maps using the bathymetric and topographic terrain models in Norway. Therefore, the use of 2D models becomes indispensable to address the above-mentioned issues.…”

Quantitative Evaluation of Bathymetric LiDAR Sensors and Acquisition Approaches in Lærdal River in Norway

“…The study reach (stretches for 15 km), shown in Figure 1, drains a mountainous catchment of 994 km 2 with an unregulated daily mean discharge of around 31 m 3 /s. The average width of the river ranges between 50 and 70 m linking flat banks of around 2.2 degrees of slope [22]. The longitudinal slope of the river is around 0.43 percent [22].…”

“…Bathymetric LiDAR, on the other hand, is commonly characterized by a laser of 532 nm that penetrates the water and gives bottom detection [16]. The bathymetric LiDAR is the most widespread LiDAR type used in river studies that require high degrees of mapping accuracy such as environmental river studies [17][18][19], sediment transport studies [20,21], and flood modelling [22,23].…”

Effect of flow ramping on stranding potential related to river morphology—Developing hydraulic indices for peaking severity

“…These two factors are considered important for assessing the potential effects of hydropeaking in a river, for example, stranding of fish and invertebrates, and are controlled by the variability of the cross-sectional shape of the river as we move downstream from the outlet of the hydropower plant. In recent years, high-precision laser scans using bathymetric (green) LiDAR (Mandlburger et al, 2015) have become available for several Norwegian rivers (Awadallah et al, 2022), which in combination with efficient 2D hydraulic models makes it possible to describe the dewatering process with a high level of detail over longer river reaches (e.g., Juarez et al, 2019). Combined with topographic LiDAR scans of the adjacent terrain, we can develop digital elevation models (DEMs) covering both the river bathymetry and the areas adjacent to the rivers which provides a full description of the river profile and potential stranding areas.…”