Influence of Topographic Resolution and Accuracy on Hydraulic Channel Flow Simulations: Case Study of the Versilia River (Italy)

Abstract

The Versilia plain, a well-known and populated tourist area in northwestern Tuscany, is historically subject to floods. The last hydrogeological disaster of 1996 resulted in 13 deaths and in loss worth hundreds of millions of euros. A valid management of the hydraulic and flooding risks of this territory is therefore mandatory. A 7.5 km-long stretch of the Versilia River was simulated in one-dimension using river cross-sections with the FLO-2D Basic model. Simulations of the channel flow and of its maximum flow rate under different input conditions highlight the key role of topography: uncertainties in the topography introduce much larger errors than the uncertainties in roughness. The best digital elevation model (DEM) available for the area, a 1-m light detection and ranging (LiDAR) DEM dating back to 2008–2010, does not reveal all the hydraulic structures (e.g., the 40 cm thick embankment walls), lowering the maximum flow rate to only 150 m3/s, much lower than the expected value of 400 m3/s. In order to improve the already existing input topography, three different possibilities were considered: (1) to add the embankment walls to the LiDAR data with a targeted Differential GPS (DGPS) survey, (2) to acquire the cross section profiles necessary for simulation with a targeted DGPS survey, and (3) to achieve a very high resolution topography using structure from motion techniques (SfM) from images acquired using an unmanned aerial vehicle (UAV). The simulations based on all these options deliver maximum flow rates in agreement with estimated values. Resampling of the 10 cm cell size SfM-DSM allowed us to investigate the influence of topographic resolution on hydraulic channel flow, demonstrating that a change in the resolution from 30 to 50 cm alone introduced a 10% loss in the maximum flow rate. UAV-SfM-derived DEMs are low cost, relatively fast, very accurate, and they allow for the monitoring of the channel morphology variations in real time and to keep the hydraulic models updated, thus providing an excellent tool for managing hydraulic and flooding risks.

Development of damage curves for buildings near La Rochelle during Storm Xynthia based on insurance claims and hydrodynamic simulations

“…Regarding the first point, there is a trend that indicates that better topography/bathymetry data gives hydrodynamic variables that correlate better with the damage ratio. The explanation of this is basically because higher resolution data brings generally more accurate results of the real flood conditions (Luppichini et al, 2019 andEttritcha et al, 2018). Damage curves developed with a better representation of the topography (IGN + structures) improve the accuracy indicators (Table 2), though scatter in the data itself (Figures A1, A2 or A3) is large for all topographies.…”

“…We use two types of topography datasets: a global dataset for the bathymetry/topography (GEBCO 2019, which is based on SRTM 15+ v2 over land), and a higher resolution bathymetry (MNT -HOMONIM project) and topography (IGN institute). Luppichini et al (2019) and Ettritcha et al (2018) found that the quality of bathymetry and topography data has a large effect on estimation of the hazard, and Brussee et al (2021) similarly found topography data quality affects resulting damage estimates. In order to investigate the effect of the quality of topographic and bathymetric data on the resulting damage 75 functions, three scenarios are considered in our work (Table 1).…”

A New Beach Topography-Based Method for Shoreline Identification

“…The model with the least number of GCPs is model 4, which is the smallest in terms of coverage area. The number of GCPs of these models is a limiting number that takes into account the study performed by [30]. The DEM resolution is of 2.79 cm/pix for model 1; 2.56 cm/pix for model 2; 2.72 cm/pix for model 3, and 2.67 cm/pix for model 4.…”

Camera Calibration Using Multiple Unordered Coplanar Chessboards

“…Indeed, a significant number of applications of SfM/UAV photogrammetry with pre-calibrated cameras have relied on available chessboard-based calibration software (recent examples include Cucchiaro et al, 2018;Erenoğlu & Erenoğlu, 2018;Halik & Smaczýnski, 2018;Menge & Lohsträter, 2018;Probst et al, 2018;Ventura et al, 2018;Wierzbicki, 2018;Burnett et al, 2019;Javadnejad et al, 2019;Kölling et al, 2019;Luppichini et al, 2019;Mahmood et al, 2019;Musci et al, 2019;Yurtseven, 2019), often without particular considerations, e.g. concerning focusing distance and frame coverage.…”